3.1 Questions and Answers - Chemteach - University of Canterbury - New Zealand

3.1 Questions and Answers Archive

  1. 1. Investigations on galvanic or secondary cells.
  2. Using projects by students doing transitional or NCEA level 2 for 3.1
  3. Acceptable amount of teacher assistance
  4. Aspirin investigations
  5. Why does the method have to be in their own words?
  6. Using Palm pilots
  7. Quality and quantity of data
  8. Range for calcium carbonate content of eggshells exemplar
  9. Can students use the same method with a different purpose?
  10. Assessment issues
  11. Assessment issues
  12. Cost of resources
  13. Acidity in wine
  14. Back titrations in 3.1
  15. EDTA titrations
  16. Ethics of using alcohol
  17. Ethics of dissolving coins\
  18. Recovering silver from exposed film in a gravimetric analysis
  19. Concentration of permanganate required for iron analysis
  20. Timeframe for loss of Vitamin C over time
  21. Sourcing Hydroxy Napthol blue indicator
  22. % Calcium in eggshells
  23. When moderated I was told that not a big enough range was used
  24. Standard solutions (gravimetry and colorimetry)
  25. Standard solutions
  26. Standardising phosphate solutions
  27. Mailing group for Chemistry teachers
  28. Classroom hours for 3.1
  29. Resource book of investigations to use for 3.1
  30. Effectiveness of calmagite as an indicator for Ca/Mg ions
  31. Sourcing Pasteur pipettes
  32. Just up files for 2004 on TKI site
  33. Change in standard to "collect data related to a possible trend"
  34. Aspirin content and looking at trends
  35. Including conversions in the calculation
  36. Number of titrations to obtain excellence
  37. Bizarre observation when doing the direct iodate titration for Vitamin C
  38. Determination of Chloride method
  39. Sodium thiosulfate as a primary standard
  40. Calculation errors in AS 3.1 Extended Investigations
  41. Titre errors in AS 3.1 Extended Investigations
  42. Reliability of a method for excellence
  43. “Trend” requirement of 3.1
  44. Do experiments measuring the oxygen content from source to sea meet 3.1 requirements?
  45. “Trend” requirement of 3.1
  46. “Trend” requirement of 3.1 with respect to Ca or Al
  47. Follow up comment on “Trend” requirement of 3.1 with respect to Ca or Al
  48. “Trend” requirement of 3.1
  49. "Trend requirements and enzyme kinetics
  50. Use of an incorrect molar mass for thiosulfate
  51. Moderation of the Extended Investigation
  52. A few questions about 3.1
  53. Students lost log book

Q1. I have some Year 12 students working on 3.1. One of them interested in electrical engineering wants to do some work on galvanic cells or secondary cells. The idea is to run an investigation that compares EMF from galvanic cells for different concentrations of electrolytes or as alternative compare discharge rates in secondary cells with concentration of sulfuric acid.

Do you feel that these would comply with criteria for AS 3.1 investigations?

A. It would do if the student uses a quantitative technique to actually measure the concentrations of the electrolyte used - rather than just diluting a stock solution by various amounts. e.g. if sulfuric acid was used they could do a simple acid-base titration to determine the concentration in each case.

This would then meet the requirement that variations in amounts or concentrations of a chemical are measured. Alternatively if the student didn't want to do this they could always consider it as a level 3 Science Investigation. Back to top.

Q2. Can projects done under the Transitional 6 th Cert be used in 3.1 next year ? I can't see a problem.

A. I presume you mean projects done this year by Year 12 (who may be doing transitional or NCEA level 2). There is no problem with collecting the evidence this year and submitting the results of this next year when the Level 3 standards have been registered. Certainly that is what we are doing here at St Cuths. When and how the evidence is obtained is irrelevant – what matters is does the evidence meet the requirements of the Ach Std. Back to top.

Q3. What amount of teacher assistance can be tolerated during the investigation? There is nothing in the standard to give a teacher help with this (direction vs supervision vs guidance in science investigations). The group thinks this should be added to the standard. Clarification of this would also be helpful for those students considering using the investigation for their Silver Crest award. The task mentions using a consultant, but not what the limits of assistance the consultants may provide - a statement in the standard would clarify this.

A. Will certainly consider this when the standard is reviewed. My personal feeling is that a teacher can't be proactive with advice/suggestions (particularly with decisions about the nature of the investigation itself) but should be able to discuss possible strategies to deal with practical issues arising during the investigation without actually telling them the “answer”. Back to top.

Q4. Please remind me why the aspirin investigation would not be suitable, yet the acetic acid in vinegar would.

A. It just doesn't work well with anything other than aspirin so it is too difficult to source a suitable range of products to compare. Many students think other painkillers will work but they contain and ibuprofen etc which are not carboxylic acids. Back to top.

Q5. Why does the method have to be in their own words (Merit on your Assessment Schedule Template)? This is not in the Activity schedule, nor the standard!

A. It provides clear evidence to the assessor as to how well the student understands the chemical concepts behind the particular analytical technique used. Evidence for this could alternatively be obtained through interview but then the issue is having to record this conversation to provide evidence for moderation purposes. Back to top.

Q6. Discussing the logbook, we also considered advances in technology, and thought that students using Palm pilots etc would obviously be able to word process their logbooks as they go. Same sorts of Authenticity checking required as for hand written logbooks.

A. True. Teachers could possibly devise some sort of code that could be inserted electronically by the teacher or could ask for electronic copies to be e-mailed to them at each checkpoint Back to top.

Q7. Quality and quantity of data. At our Western Bay of Plenty training day a lot of discussion centred around what is an appropriate range for the independent variable. Page 78 suggests 4 is the minimum for Merit, with at least 3 determinations (titration) for each. The generic task uses 5 variations in both examples, setting as it were a de facto standard of 5 as the minimum range.

Would you define a limited range of variables as anything less than 4, or is 5 the expected.

Also, teachers have queried the Orange/Kiwifruit example (student 12). If the student had used 5 oranges, and five kiwifruit and averaged the results, would this have been sufficient (all other things being done correctly) to move up to Merit, or even Excellence? Would they have had to do 3 titrations for each orange/kiwifruit? What about using 5 oranges/Kiwifruit, pulping them together and then just doing 3 titrations on the resulting juice? How can we help teachers draw the necessary line?

I would appreciate some feedback on this.

Because there are so many possible variations for these investigations it is impossible to have fixed “rules' about the requirements for quantity and quality of data. e.g. endpoint determinations of Ca using EDTA are less precise than Vit C titrations with thiosulfate but even within EDTA titrations, endpoints for aluminium are more demanding than for calcium. Certainly with respect to the accuracy of any of the techniques covered in the other stand alone achievement standards, the quality of data should be consistent with the specific requirements of each standard .

With respect to quantity of data some awareness of the relative time spent on each sample determination has to be taken into account when comparing different methods e.g. alcohol back titrations and ashing of foods to extract iron are much more time consuming than Vit C titrations.

Once teachers have undertaken these investigations for a year or two they will develop a ‘feel” for this aspect of the standard requirements and it is difficult to explain this realistically to teachers who have not yet seriously undertaken these type of investigations. Back to top.

Q8. In the “calcium carbonate content of egg shells” exemplar on the TKI web-site (which is an Excellence exemplar) only two types of eggs are used. (is this the range?). Three eggs of each type are tested (these are quoted as the “appropriate range” on the exemplar) and 3 titrations are done for each egg (the repeats).

Does this exemplar still illustrate Excellence?

A. This exemplar was put up quite early on and certainly now I wouldn't consider it to be excellence but it does illustrate a useful point that relates to the rest of your query below. The overall grade should be a holistic judgement and the check list approach is there for convenience and to provide some guidance but is not expected to be cut and dried. For many investigations, the overall grade is limited by the quality and depth of the interpretation and discussion rather than the quality and quantity of data collected. In the case of the egg shells exemplar referred to in your query, it is difficult to imagine how a student can draw any reasonable or significant inferences from an investigation which only compares two types of eggs – no matter how accurately, carefully or extensively she has carried out the practical determinations. Back to top.

Q9. I had a query yesterday about the individual purpose for this investigation. Some schools have several classes of Y13, do all students need a different purpose, or can those in different classes do the same thing?

A. There is definitely no problem with students using the same method (whether they are in the same class or not) but hopefully they would not have exactly the same exact purpose, same range and same samples, ie. if it was to determine amounts of Ca in milk then presumably they could select at least some milks that were different. Back to top.

Q10. We have just had the second of our workshops on 3.1, I think it went OK. Most people seemed to find it worthwhile although there are some who don't like us going over things that are already written down for them!!

However, there was some difficulty with the level of achievement for this standard especially from the exemplars available for marking. For student no. 9 most people only wanted to give Achievement because of the limited range of data and the inapproriate graphs of titration data. It was especially felt from people involved in Science workshops that this was insufficient for Merit.
I agree that only having 3 data points is marginal and is more indicative of an achievement than a merit. The inappropriate graphs were treated a sneutral rather than negative but overall a weak merit would certainly be more justified than a strong merit. Personally I feel that holistically some aspects of the discussion partly made up for the weakness in quantity of data but could accept a final decision of strong achievement.

A. Once teachers have done this standard for a year or two the expected standard should become clearer (as has happened with the Science investigations) and after all this is what the moderation process is all about. Back to top.

Q11. Then for student no 10 there was some difficulty assigning an Excellence grade because of the wrong order in her method (6 and 7) coupled with some confusion as to the thiosulfate ion concentration (she writes about a 1 in 10 dilution of 1 mol L-1 but uses 0.01 in her calculation), she doesn't use units correctly, doesn't provide a graph for comparison of data, and there is no comment on the reliability of her technique and not a good discussion on accuracy of data. We wanted to give this a good Merit although could see the potential for Excellence perhaps on resubmission but not as it stands.

On further reflection this is probably fair enough - certainly at the time of assessment I thought the lack of a comparative graph was a significant omission and agree that the discussion on accuracy and reliability is marginal but gave it the benefit of the doubt based on existing guild of knowledge i.e very few students are able to offer much that is sensible in this area so until we are able to upskill them appropriately I don't think our expectation should be too high or unrealistic. I think the wrong order and dilution comments are just carelessness but I assume that the assessor would be better placed to able to make a clear decision about this. I certainly take your point that a little reworking would remedy many of these deficiencies so perhaps the judgement should be strong merit with potential for excellence if a few areas are reworked. Back to top.

Q12. A query about cost of resources. I have recently purchased your CD ROM containing Year 12 and 13 Chemisry notes and help with the Year 13 extended practical.

In the practical determining Mg and Ca content in milk etc, hydroxy napthol blue indicator is mentioned. I went to order some $239 for 100g. No way our school can afford that, particularly as it states making solutions of 10g/100ml distilled water.

Do you have a source you purchase from cheaper and if so would you mind letting me know?

A. We purchased 100g from Biolab Scientific for $135 late last year. The ordering code was SIGH2516/100g but the price may have since changed although with the stronger NZ dollar I would have thought this unlikely.

Obviously this is still expensive but a cheaper 50g bottle is also available and it does go a long way. Other alternatives to reduce the cost are to share the purchase with some neighbouring schools, to see if you can get a small quantity gratis from a dairy company or tertiary institute or to use the alternative method using Erio T indicator (which being more common is more likely to already be available or be cheaper). Back to top.

Q13. One of the possible topics for the extended practical investigation is"Acidity in Wine".  On the surface this presents as a relevant and interesting subject. However, assuming that a student decides to investigate the levels of total acid in white wine it seems this would probably have to be with respect to one other variable. eg. would they be expected to measure the acid levels across a range of varieties of say 4 or 5 white wines from 2003? Or to compare the acid levels for a number of North and South Island Chardonnays from the same year?

In view of the fact that winemakers may often add extra acid if they judge that a wine is too low in acidity, the significance of the students results needs to be treated cautiously.

We thought it would also be useful for a student to measure and compare the pH levels of the same wines. As the pH range would probably be about 1 this could only be done with narrow range papers or a pH meter.

A. Yes you are quite right in assuming that the extended investigation has to measure the concentration of a particular unknown with respect to some other variable. The choice of variable depends on the purpose of the investigation.

If the investigation was to see if the type of grape used had an affect on total acidity then the student should measure acid levels of some wines from  the same vintage and same geographical area or "terroir" (perhaps even the same producer although this may not be possible) but using different grape types.

If the investigation was to see if the climate had an impact on total acidity then wines of the same type/brand could be selected from different vintages and collated back to the weather from each particular year. Alternatively wines of the same style could be chosen from different regions which would presumably have different weather patterns although other characteristics such as soil type would also have an influence.

Of course, total acidity is also hugely influenced by other aspects of the wine making process itself which are beyond the control of the investigation and any discussion ensuing from the results should take this into account. Details of the specific wine making process are usually obtainable from individual wine makers e.g via the tasting notes should also acknowledge the very important impact that the particular processing.

There are a wide range of possible other scenarios that could be investigated just for total acidity and when you add in the possibility of investigations involving alcohol or sulfur dioxide then the possibilities with wine are endless.

On the negative side of course is the cost of obtaining the samples and the need to obtain permission for the student to access/store the wine samples etc.

I have had a number of students over the years carry out successful investigations along these lines. Back to top.

Q14. Back titrations in 3.1. We have started doing AS3.1 and have found that in the Vit c titration, dilution of the juice doesn't seem to affect the titre values. Are we doing something wrong as this doesn't make sense?

Can you help, I remember on the course that it worked well using your method.

A. As this is a back titration you may effectively be getting a null result (because little or no Vit C is present in the sample). Therefore diluting the sample would not affect the titre value as effectivley it is close to a blank reading anyway.

To check you need to do a titration with just water as the sample.

This blank titration value (which might be 20 or 30 mL depending on how much iodine is generated  initially) is the highest value that you can expect for any sample. If a sample titration equals this blank value or is only 1 or 2 ml less than it, it means that your sample does not contain enough Vit c and either it needs to be less dilute or a bigger volume needs to be added.

Under these circumstances diluting the original sample will produce virtually no diffreence to the titre as it is close to the blank ("zero") value already. Back to top.

Q15. We had real problems obtaining the indicators described in your guide so we contacted Bay Milk at Edgecumbe for alternatives. They provided us with the procedure they used to calculate Ca conc in milk products (see attachment). It is an EDTA back titration similar to yours but uses Patton Reeders Reagent as the indicator and worked very successfully. Unfortunately they wouldn't supply the reagent to us so we bought the raw indicator (very expensive) directly from Merk and our technician prepared the reagent from the indicator. If any other schools would like to buy any, we are willing to supply the indicator for $15 / 5g . In our experience of about 8 students using it this year, we used less than 1g of reagent. Contact d.ballard@tbc.school.nz if interested.

A. Thanks for the feedback. I had come across mention of that indicator in some earlier research but as we didn't have any, we bought the hydroxy napthol blue which was recommended. Sometimes too, these are just different names for the same material but not in this particular case from memory. Note: The Outreach Programme at the University of Canterbury has some that they can send out to schools. Back to top.

Q16. As an extended practical investigation, a student has nominated to analyse the quantity of alcohol in vodka. Another is interested in analysing the strength of beers. As most of my students are not yet of legal age are we crossing any moral boundaries for bringing alcohol into school for the purposes of an experiment?

A. We ask for a letter of consent signed by the parents/guardian giving permission for the students to bring the alcohol and we then keep the alcohol on the premises. In an ideal (but somewhat naaive) world the students shouldn't be able to access the source of alcohol without adult involvement anyway. Surplus opened stock is usually discarded at the end of the investigation.

I guess permission should also be obtained from your Principal or Board. We fortunately have never had any instances of abuse of this system but I'm sure it could happen. Back to top.

Q17. This is just a quick question. For the exemplar "copper in a dime", is it actually legal to dissolve a 10c coin in acid? I could be wrong but destroying the Queen's image and/or destroying legal tender sounds illegal. Perhaps we should all use the copper sulfate alternative?

A. Probably it is illegal technically although I would find it difficult to imagine anybody being prosecuted for this. However, plenty of other alternative sources of copper exist such impure copper sulfate, various garden fungicide sprays or samples of brass or bronze or other copper containing alloys - actually "Goldilocks scourers work really well as they have the advantage of being in a finely divided form so dissolution is quick. Back to top.

Q18. I have a student who wants to recover silver from exposed film as her extended study for 3.1 (gravimetric analysis.) Do you have a suitable method including appropriate concentrations of reagents and equations to complete calculations. I am a bit stumped.

A. I don't know how the silver can be extracted initially from the photographic film. A solvent would be required to dissolve the film emulsion itself and then depending on what form the silver is then in elemental or some sort of complex ion?) it needs to be converted into silver ions.

Then the procedure (for a solution of about 200mL containing about 0.1g of silver and about 1% nitric acid) is:

  • Heat to about 70oC and add 0.2 molL-1 HCL until no further ppt occurs.
  • Allow the ppt to settle and cool in a dark place for several hours or overnight.
  • Transfer to a weighed sintered glass crucible, wash with 0.1 moll -1 nitric acid.
  • Dry the ppt at 100oC and then 140oC.
  • Cool in a dessicator and reweigh. Back to top.

Q19. J ust a check, I have a student who is analysing iron tablets for his investigation, Do you know if the permanganate required to titrate against is 0.1mol/L or 0.01 mol/L?

A. I think one of the original NCEA redox titration tasks for C3.2 included some possible values/conditions for this experiment but I can't find it at the moment. Anyway, as part of the investigation, it is the student's responsibility to carry out some initial rough trials to determine the appropriate set of values that will give titre values within the desirable 10 – 20 ml range. I would be working on the basis of using 0.01 molL-1 permanganate as this is certainly strong enough to detect the colour change at end point and is obviously cheaper etc. So trials should be done with this and the iron tablet diluted appropriately. The factors that will affect the final titre values include brand and size of tablet, volume of solution each tablet is made up in, any dilution factors and the volume taken for each titration. Back to top.

Q20. Do you know what time frame would be best for a student to do a Vitamin C investigation involving investigating loss of Vitamin C from a juice over time.

A. Depends whether it is being heated or not. With heating it would be minutes. Just left at room temperature it is more likely to be days although I do know that vegetables such as sweet corn lose about half their Vit C within hours of being picked. Back to top.

Q21. I am a science technician and have been given your email address from our head of chemistry in regards to sourcing Hydroxy Napthol blue indicator, any ideas as to where we can purchase this and costs? can't seem to find it in any of our suppliers catalogues, any help with this would be greatly appreciated.

A. We purchased 100g from Biolab Ltd in Auckland (0800 933966) for $135 late last year. The ordering code was SIGH2516/100g but the price may have since changed although with the stronger NZ dollar I would have thought this unlikely. Obviously this is still expensive but a cheaper 50g bottle is also available and it does go a long way. Back to top.

Q22. Last year my class did 3.1 practical investigation and due to the fact that 5/7 of my students this year have not done L2 chem I want to do it again. We used different types of eggs (brown v white, size 6 v size 7, sick chicks eggs v healthy cicks eggs) to see how much calcium was in the shells. the kids came up with very low % (40%) of Ca. We dissolved it in 0.1% HCl - just like the exemplar on the net. Then titrated it with 0.1 NaOH. Have you any suggestions why the % was so low? Acid not strong enough? Shell not left long enough to react? Have I missed some obvious step!!!!

A. Can you tell me what the 40% Ca is measured as. E.g. if it is mass % of total shell mass then assuming the shell is made of CaCO3 the expected mass of Ca would only be 40% by mass. However, I suspect you mean that you are only finding 40% of what you would expect to be present in the shell? Back to top.

Q23. When moderated I was told not a big enough range was used, ie 2 types of egg not enough. We used 3 samples of each egg (brown and white)and then 3 samples from each of those eggs. How can you compare brown eggs and white eggs with something else???

A. Re the moderation relating to range. A variation between only two types makes meaningful discussion of the results challenging. To extend the range to look for patterns etc perhaps you could use brown eggs/white eggs from a range of different suppliers/brands. If all the brown (or white) eggs were consistently higher regardless of brand then you could draw a useful/valid conclusion. With only one type used, any variation could be the result of some other factor such as organic vs standard or free range vs battery or just be a consequence of the diet supplied by one specific manufacturer. Back to top.

Q24. If students want to do a gravimetric analysis (like fat in milk) or colorimetric (like phosphate in water), that puts the student in the difficult position of not having a solution to standardise, and in the gravimetric case the most difficult solution to make is an 88% potassium chloride solution (not hard). What can they do? It seems silly to make and standardise any old random solution if it has no bearing on their investigation just to show how they did it. In the colorimetric case, their phosphate solutions seem to be a primary standard anyway!

A. Can you clarify what you mean by “puts the student in the difficult position of not having a solution to standardise”?

In general, gravimetric analyses are often problematical because there is limited “chemistry” involved but colorimetric methods are fine provided the student is not using a precalibrated automatic spectrophotometer. For colorimetric work the preparation of a calibration curve using prepared standards of the unknown is perfectly adequate. Back to top.

Q25. Follow up Question. I assumed from the moderation report that came out that students had to make and standardise a solution as part of their investigation, but if it is okay to make the solutions required to prepare the calibration curve then that is even better.

A. The purpose of preparing a standard solution of known concentration is so that the students can determine how reliable/accurate their method is, so to meet the discussion requirements of merit and excellence in particular this would still be required. Back to top.

Q26. In the case of our boys wanting to do the colorimetric analysis of phosphate in water, do you know of a solution they can use to standardise their ‘standard' phosphate solution? We have had a look in all our books and have been unable to find anything.

A. You would need to use at least a reagent grade of any soluble phosphate containing chemical you already have or can access.

Common examples that are readily available include potassium hydrogen phosphate and potassium dihydrogen phosphate ( we have both of these) and I'm sure there are others. If you don't have any already, try approaching a tertiary institute or local industry (dairy factory?) to see if they will give you a small sample. As last resort, you may need to buy the smallest sample available from your chemical supplier – I don't think they are expensive and are certainly common enough to be held in stock. Back to top.

Q27. Another teacher mentioned a mailing group for chemistry teachers. Would I be able to join this please?Also I am interested in purchasing a copy of the resource you made for level 3 chemistry practical investigations. Is it email, CD or hard copy?

A. Have added you to the existing e-mail database of about 420 NZ Chem teachers. Let me know if you want me to send you the 4 newsletters sent to date this year. Otherwise you will just start receiving future issues. Next one probably in about 2 weeks time.

All the McTogi resources are word documents on CD and the one off cost entitles the institution to lifetime photocopy rights of the resource – including the opportunity to modify each resource such as student notes to meet you particular needs e.g. order of teaching, emphasis, NCEA coverage etc. Back to top.

Q28. How many classroom hours have you given students for 3.1?  Do you spread the time out over several weeks or give them a set block of time? 

A. We introduce the investigation in small blocks of 5-10 minutes scattered during lessons at least a month before the actual working time. During these sessions they receive the student info sheets and get to look at our booklet of quantitative techniques to see what is involved in each type of experiment. They are also expected to have done some initial background research once they select an idea for investigation. About 2 weeks before they start the investigation they have to hand in a resource sheet which states what their aim is, what method they will use, what chemicals/solutions they will require (including identification of which need to be known accurately as they will be responsible for preparing these – other solution may be provided in bulk or can be prepared by appropriate dilution of existing stock solutions). They are also required to give an indication of their expected range. This enables the technician to ensure we have the appropriate chemicals in sufficient quantity.

We then allocate a 3 week continuous block of time during which they carry out the actual practical work. Over this time period we open the labs for the last two weekends (4 days in total) when the students can come in for part or all day to work on their investigations. This is particularly important for students who miss some classes through illness or sports or other commitments but we also find most of the students elect to come in anyway as they really enjoy it.

Students are expected to request help with calculations where necessary during their 3 week class time but all write ups are done in their own time. Back to top.

Q29. You referred to a booklet of experiments provided to the students which is a great idea.  We purchased the McTogi resource with Y12 and Y13 notes plus the extended practical investigations which has 5 investigations in detail.  Was there another resource which could be purchased with a lot more experiments (about 50) or is my memory playing tricks?

A. We do use a resource booklet which we have prepared that gives the basic recipes for about 20+ quantitative techniques. But because we don't have the level of detail and teacher support material for all of this yet, it is not available as a McTogi resource. We intend to release a supplement with this material in at some stage but not until we find the time to get it into the quality form that we would be happy with. Our aim is to do this next year while we are transitioning our investigations from our Year 12 to Year 13 course which means next year none of our students will be doing 3.1 (as this years Yr 12 has already done it). Back to top.

Q30. I recall hearing from someone about the effectiveness of calmagite as an indicator for Ca/Mg ions. Do you have a recipe to make the indicator up from the powder,

A. A 0.05% aqueous solution is made up from the calmagite powder Back to top.

Q31. When I participated in the Chemistry Scholarship course at your school a couple of weeks ago I spotted your long disposable plastic Pasteur pipettes. I would like to buy them for our school, but I do not see them in the catalogues of our suppliers. Where did you buy them?

A. BER262 Transfer pipette extra long 9in 6ml From Biolab @ $57.45 / 400pces Back to top.

Q32. Can you help me- I am trying to get into Just - Up files for 2004 on tki website. But I can't access this, only 2003 or 2005. The file I need is the exemplar for chem AS 3.1 with the annoted examples of A M and E.

A. The page is still there but the link doesn't seem to be working so try http://www.tki.org.nz/e/community/ncea/justup/archive-2004.php

Back to top.

Q33. After setting up our Y13 classes for projects I have now noticed the change to the standard regarding a possible trend.  Correct me if I am wrong but if a student is wishing to measure concentration of glucose in a range of drinks they now cannot do this.  Instead they must modify a variable to produce a possible trend eg temperature to quote the standard.  In effect this puts further limitations on what they can do to fit the standard ie consumer analysis is limited to temperature effects, storage time, how long you leave the lid off etc. 

A. Yes, the standard has changed to “collect data related to a possible trend”. The word “possible” is used because it is not always known when starting an investigation whether any trend (or indeed any variation at all) actually exists. e.g students could discover that exposure to light does not actually change the amount of Ca present in milk at all, and they shouldn't be penalised for getting a “null” result, although hopefully where possible teachers would provide some guidance on this when students are deciding on their investigative aim.

The link to a “trend” was introduced because the moderation process determined that many of the investigations being done were merely measuring the amount of "something" in a range of a particular product and these were really experiments rather than investigations. The change was designed to stop students doing things like simply measuring vitamin C in a range of juices, etc. although these are still good “experiments”. ie. the change has been made to ensure that it is an “investigation” as opposed to an experiment.

In my own experience, investigations of the consumer product type were often limited to Achievement anyway because they usually provided limited opportunities for discussion and interpretation of results.

Avoiding these types of investigations also has the advantage that the students don't have to purchase lots of samples of "whatever" as they only need one for the first run through and, for excellence, a second bottle to repeat for reliability of method.

So, in summary, the key change is that the purpose of the investigation must be related to a possible trend. So aims of “measuring the alcohol content of 5 different wines or the Vit C content of 6 commercial juices or the Ca content of 5 different milks would be unacceptable,  whereas the effect of  temperature or light, storage time, storage method, etc would all provide investigations with a valid purpose that could lead to the identification of a possible trend.

However, it is still possible to carry out a consumer product type investigation provided there is a valid purpose relating to a possible trend. Examples of valid investigations could include:

  • to determine whether the alcohol (or SO2) content of a series of different, but related wines is affected by vintage, or geographical location or wine type or storage medium (bottle vs cask) etc.
  • Vit C content from oranges taken from different trees of either different varieties or different locations would also have a valid purpose.
  • Calcium content of different milks could be measured to determine if there is a relationship between their calcium and fat contents. Back to top.

Q34. I wonder if you can help me with the following. I have a student who is keen to study the various amount of aspirin in tablets. If she is able to get a range do you think that it is is a too simple one that could not meet excellence criteria.

A. If you look at the changes in the standard for this year you will note that simply looking at the aspirin content in different brands no longer meets the requirements of an investigation.

The only way she could validly look at something like this would be to investigate the effect of some variable like storage time on the amount of aspirin still actually present in the tablet.  I am guessing that the time span necessary to detect any observable difference in the quantities present would be at least months which is impractical given the limited time constraints of most schools in practice. However, the student could get around this by obtaining tablets of the same brand but with significantly different expiry dates. As a control they would need to determine that the quantity present in different packets with the same expiry date did not vary significantly.

Finally, I should note that we have had difficulties with obtaining consistent data from some brands of aspirin in the past –possibly because of the nature of the fillers in the tablet and it is not a determination that we would recommend to our students.

If the student investigation does proceed I would appreciate any feedback on how it went in practice. Back to top.

Q35. I have just been updating the marking schedule for AS3.1 and noticed the standard only says determine the composition of the unknown. This could easily be read as the straight mol/L calculation and not include the g/L calculation for merit and above. Is it fair to require both calculations if the standard does not require it? I notice the exemplar for the iron II does include both calculations.

A. Explanatory note 4 (see below) of the standard specifies the requirement to include one conversion in the calculation as part of the overall standard. Determination of the composition of the sample will involve one mathematical conversion between the concentration of the solution analysed and the composition of the sample, eg:

  • concentration of the sample before dilution
  • concentration in grams per litre (g L–1) or % (w/v)
  • % composition (or purity) of a solid Back to top.

Q36. Is a titration performed with 5 variable changes (ie 5 different temperatures) with each titration of the same repeated to obtain concordant titres enough to obtain excellence (assuming rest of report is up to this standard.  I have concerns that the student must repeat the whole experiment again which is expecting too much in the 12 hours allotted. 

A. At least one of the investigations (ie one temp only) has to be repeated in its entirety as a check on the reliability/accuracy of the method (and possibly source material composition) to allow excellence to be obtained.

If the procedure simply uses a single sample from which successive aliquots are taken for concordant titrations, this does not meet this requirement. Back to top.

Q37. A number of our students have made a bizarre observation when doing the direct iodate titration for Vitamin C (see attached). When they increase the temperature of their Vit C sample, the iodate titre increases. The first time it happened, I just went "there, there, do it again"... but it kept cropping up. I wondered about a competing reaction, but couldn't think what it might be. Do you have any idea? They accessed this method from the Canterbury University website, via a link from Anne Wignell's Continuing Chemistry CD. ( http://www.outreach.canterbury.ac.nz/chemistry/index.shtml )

A. I think the essential problem is that iodine is a non-selective oxidising agent for Vit C. i.e it will also oxidize other reducants present in the mixture as well. As there are lots of organic molecules present in fruit juice (or similar) that are capable of being oxidized (e.g reducing sugars) the titre represents the sum of all oxidisable material present – not just the Vit C. Hence, Vit C titrations using Vit C usually indicate higher levels of Vit C than are actually present – we typically get values twice the stated value on commercial drinks (although some of this may be because the manufacturer states a minimum value to allow for the expected degradation of Vit C over the shelf life of the product).

I have come across the heating effect with my own students previously and my best bet is that heating cause some of the organic molecules present in the sample to be hydrolysed (or in some way broken down ) into simpler molecules that the iodine is able to oxidize – hence producing increasing titre values when a direct iodine titration is used (or a reducing titre value if the back titration method is used).

Other readers out there may be able to suggest other possible reasons.

Unfortunately I have not come across any simple, cheap alternative to iodine titrations for Vit C but again someone else may have a suggestion. In the past I have used N-bromosuccinimide which is reasonably Vit C specific, but I never found the endpoint to be satisfactory and I think its use is banned now anyway. Back to top.

Q38. We are just starting 3.1 this year and have a query about the chloride determination method.  It says to standardise the silver nitrate with magnesium chloride but according to The Textbook of Quantitative Inorganic Analysis by Vogel,  silver nitrate is a primary standard.  If so, then it seems a little odd to have to standardise it against something that has waters of crystallisation.  And if a standardisation is required, do we have to drive the waters off the magnesium chloride or is there a better alternative?

A. A freshly made solution of AgNO3 is OK for a while – particularly if stored in dark bottles.

However, because of the cost of the solid AgNO3 we (and most schools probably) don't allow access to the solid for students because of wastage/spillage. Instead we make up some stock solution for them and it is their responsibility to ascertain its conc at the time of use – hence the MgCl2 determination. If you only have one or two students doing it and they are reliable and careful then they could make up their own standards from the solid and avoid the issue. Back to top.

Q39. I have just finished 3.1 and am working through the marking. I used your lab manual as the guideline, giving the students that selection of possible procedures. I now am looking at the moderation report we recieved last year and find that the comment for 1 student's report was that "It is not good practice to use sodium thoisulphate as a primary standard". Unfortunately, almost all investigations I have directed students into this year have done just that! Can it or can it not be used as a reliable std?

A. Sodium thiosulfate in the form Na2S2O3.5H2O is readily available in a state of high purity but because there is always some uncertainty as to the exact water content because of the slight efflorescent nature of the salt, it is not usually considered to be a primary standard (but only a handful of substances are). However, it is stable in solution and therefore is certainly an excellent secondary standard which can have its exact concentration determined by titration with potassium iodate (a primary standard). However, in practice I have always found that the variation between the calculated concentration and that determined by the standardisation process to be less than the error expected by any titration procedure itself so am somewhat surprised that moderation is not accepting it as a nominal primary standard for our purposes. Back to top.

Q40. just a quick note to see what your marking would give the following candidate in my Level 3 Chem class for his 3.1 investigation. The Student was carrying out the alcohol investigation, "percentage increase in ethanol as a brew progresses from day 1 until finished brewing"

He has submitted his report and made the following significant error, (I believe is significant) He has in his calculations used the titre value of dichromate by equation ratio to be the amount of alcohol present.  His equations are correct and balanced, but his omission is not subtracting the amount of dichromate used from the initial dichromate present and then used this value to calculate the amount of alcohol that reacted with the dichromate.  He has then gone onto give concentrations of alcohols in mol L-1 that when converted to percentages are ridiculous, day 1 giving around 9%, and day 7 giving around 23%.  He did not do the conversions from Mol L-1 to % that I did when marking it, so his 1.87 Mol L-1 on day 1 and his 5 mol L-1 on day 5 probably seemed okay to him but incorrect. The rest of the write up is okay for an achieved, in terms of discussion etc, but I think that this error gives his final award to a not achieved.  Am I being too harsh?  Is this error allowed as a mistake for achieved?  What is the expectation in terms of calculations?

A. In general if the chemistry involved in the analysis is not understood and consequently leads to results that are not sensible, and not recognised as such, then an N award is appropriate. Part of the requirement is an understanding of related chemistry, and if this is sufficiently poor it seems that this does not equate to level 3. In this case the student obviously has no concept of how a back titration works and has not recognized the lack of sensible results (and presumably has therefore done no background research/reading on the fermentation process) and therefore I think an N award is fair. Back to top.

Q41. We ran the Level 3 redox internal using potassium permanganate and iron (II), so a pale pink endpoint.  As expected, most of the titre results were deviated to either side of one of the teacher's titre values, but there was a group of students (about six out of 70, and one teacher) who's titres were too high.  When graphing the titres from the 70 students, these six were skewed beyond the trend of values.

So two questions:

1. Do you think they added too much permanganate because they were unable to see the pale pink endpoint soon enough, i.e. were colourblind.

2. How would you determine fairness in determining whether any students titre was accurate to the teacher's, seeing as one teacher was also judging the endpoint late?

Do you take the lower of the two teacher values, which rewards low titre values but penalises larger ones (and those "colourblind" students)?

Do you take the higher of the two teacher values, which has the opposite effect?

Do you compare student titres to the average of the two teachers?

Do you compare each student to whichever teacher is closest, to maximise their grade?

First question – why are you expecting a pale pink colour at the endpoint? At the concentrations used for these titrations there is no way the eye will pick up any colour of the resulting manganous ion so the end point is effectively colourless . I suspect this is the cause of the variation in titre values as different people are making judgements as to what “pale pink” is.

Q. Once all the Fe2+ is oxidised, and one excess drip of MnO4 goes in, the colour is pale pink, of pale purple ish. You scared me. Pale pink because of MnO4, as opposed to pale pink of the Mn2+ which I agree at these concentrations is colourless

A. Sorry – wasn't thinking- titration can be done other way around with Fe2+ in burette to avoid the problem with trying to read the burette through the purple permanganate colour. The other way round (as done by you obviously) we describe the resulting colour as pale purple to reinforce where the colour comes from.

How big were the variations and do you have A or B grade burettes and pipettes and if they are B grade have you ever calibrated them?

Were the 6 students all in the same class or were they randomly distributed throughout different classes.

Q. From memory they are +/- 0.01mL but that might be wrong.  I would presume A grade.  The students came from three classes randomly, so it wasn't a solution issue.

No I have never calibrated, by which I assume you mean weighed the liquid that came out of them??

A. Correct re calibration method – we label our assessment glassware with nos and students record what pieces they used so that if there is an anomaly we can go back and check the specific equipment.

Because we use a different stock solution for each class we base our judgement on the average of the results obtained by the teacher supervising that class. In your case I would simply average all teacher results (assuming all solutions were the same) and base the judgements on that with the appropriate accuracy allowances for E, M, A etc. Unless you suspect there is a particular issue/problem (ie because all of the 6 students are normally very accurate/precise) then I would just assume they couldn't do the expt very well. The two most common sources of large systematic errors are in pipetting technique (ie they could have been blowing out the residual solution from the pipette which results in titres beng too large) or in reading a burette backwards (ie reading 39.62 mL as 40.28 mL etc) Back to top.

Q42. A student has analysed the variation of time on the concentration of hypochlorite.  She used 3 different bleach bottles which were diluted independently and analysed by repeat titration each week for a period of 8 weeks.  How does this fit into reliability of the method for excellence? What is your opinion.

A. I would have assumed this was fine in terms of analyzing reliability/reproducibility of results. Back to top.

Q43. I've been thinking about AS 3.1, the extended practical investigation, and the possibilities opened up by the “trend” requirement in version 2 of the AS.

My first thoughts were of investigating the possible reduction in the Vitamin C content of fruit juice after exposure to the air at room temperature for a few days(?) or after heating for a few minutes at 30, 40, 50 … deg. C.  And the same sort of thing with opened wine bottles and hypochlorite bleach. 

But then I thought about some of the problems I've had myself organising redox titrations, and I wondered if some more purely “chemical” investigations would be acceptable.

What about, for example, tracking the oxidation of Fe(II) solutions or (synthetic) vitamin C solutions on storage (some possibilities include also investigating the effect of temperature or pH or other (complex-forming) ions on the rate of oxidation); the deterioration of permanganate solutions over time; determining the solubility of oxygen in water at different temperatures.  The scope for such investigations is very wide.

On a slightly different note do you think that simply determining the change in total acidity of wine after exposure to air for several days (or weeks?) would be a valid investigation for level 3?  And I just thought of an excellent method (I think) for determining CO2 in soft drinks by adding excess barium hydroxide to ppt BaCO3, followed by decanting and back titration with HCl.  But is this a valid investigation or is it too simple?

A. Problem in some of your cases is that the variations observed in say 2 weeks time period can be quite small and may be of a similar magnitude to the margin of error which makes meaningful analysis of results difficult. Otherwise all suggestions are fine- what would the trend in CO2 in soft drinks involve –amount remaining after leaving cap off?

I have done CO2 previously by expelling CO2 (heating works well as gas solubility reduces hugely with temp) into known excess base and then back titrating with standardized acid. Back to top.

Q44. of my students are interested in following the path of a small stream in Auckland from source to sea measuring the oxygen content and seeing if any variations relate to surroundings. This would cover the new requirements?

A. No problem with that. Back to top.

Q45. We're carrying out the Level 3 Investigation but need clarification on the “Carry out an extended practical investigation involving quantitative analysis”.  I think that it's a shame that the requirement have moved away from eg, testing the vitamin C content of a range of orange juices to those that involve a trend such as the change in vitamin C content with increasing temperature.  It seems to really restrict the students and maybe even take away the fun.  What do you think? We're using the Investigation book that both Jan and yourself have written, it's excellent – thanks!  However, as the requirements have changed we're finding it difficult to assist our students with recommendations involving trends.  Can you recommend a few to us?

A. Apparently the investigation requirements were modified because moderation revealed that too many schools were just doing a series of standard expts rather than an actual investigation and I would have to agree with it I principle although I have reservations about it eliminating some rate type investigations and also to some extent the consumer testing type investigation which students enjoyed and found non-threatening. Note however, that I guess it is still possible to do these as a level 3 Science investigation.

With Vit C, temperature and sunlight are obvious possibilities but for something like Ca it is hard to imagine anything altering the amount of Ca present and null results aren't very satisfying for either student or teachers. With alcohol it is still valid to compare alcohol (or SO2) in wines of different years or grape type or manufacturer or region etc. Back to top.

Q46. To NZQA moderation. Am I correct in thinking that it is now unlikely that a Ca investigation will meet the requirements of the extended investigation as I can't think of any factor that would actually affect the Ca content and null effects are fairly pointless usually. Personally I think the elimination of EDTA type titrations would be a shame but I can't think of any variation that could be usefully investigated wrt Ca or Al et al.

A. Even though the content of Mg or Ca may not change, students don't seem to realise this. The student is still determining an amount (or concentration) of a species (with respect to another factor) and looking for a possible trend. So, no problems with these EDTA titrations, they fit the standard. Back to top.

Follow up Q47. But what possible trend could there be - ie sunlight and temp have no effect on Ca content so that would be a pointless and frustrating exercise even if the students are unaware of this before they start. Is it acceptable to determine the Ca content of  arrange of milks with a view to seeing if there is a relationship (trend) between say the fat content and the Ca content (or even between the price and Ca content). This where I think teachers still need some guidance/clarification?

Q48. Can you confirm the following thoughts please.

  1. Straightforward Acid-base titrations are not up to the mark for 3.1
  2. Specific methods like iodide in salt are not going to be that useful in view of the need to look at trends in the amount of substance.
  3. Gravimetric and colorimetric procedures are OK according to the AS . E.g. Colorimetric analysis of manganese in steel. Once again it is specific and trends may be a problem but would a project to find the effect on properties of differing % of manganese in steel fit 3.1 criteria? Assuming you could find steels with differing % of Mn.
  4. Does "precipitation" as an analytical technique as referred to in the standard mean precipitation titrations or does it include gravimetric analyses?

A. 1. Correct. 2. Could potentially still be used 3. Could possibly look at impact of Mn on some physical property? 4. I assume it means both.

The following is a “series of discussions” relating to the consequences of the changed emphasis in the revised 3.1 standard away from “consumer testing” towards a measurable “trend”. I still feel it is an area that we need further clarification on and in particular an increase in the number of analytical techniques that are suitable for use in a secondary school lab with its limited resources.

Incidentally, I am looking at the possibility of running a 1 day workshop on this in conjunction with tertiary educators at the ChemEd007 conference next year. I also know that The university of Canterbury Outreach program is also doing some work in this area  e.g. they currently have a PhD student looking at the issues surrounding Vit C titrations. Back to top.

Q49. Is it possible to do an experiment on enzyme kinetics and if so can they still get an Excellence?

The things we were looking at were similar to the following http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/EnzymeKinetics.html

The rate at which apples go brown and how changing the concentration of an inhibitor can slow that down?

A. Provided they are measuring the changing concentration quantitatively with a spectrophotometer (or colorimeter) and not just by eye, and it meets the other criteria for the standard I can't personally see a problem myself. In fact I think explorations of rate mechanisms etc is a huge and interesting area that may well be worth more exploration via the Extended Investigation mechanism.

The only potential concern I have is that though the concentration of the ‘browning' can be quantitatively measured by spectrophotometer it can't be converted into an absolute concentration as we would normally do with say Fe3+ or Cu2+ by using a calibration curve. In the context of a rate investigation this doesn't matter but perhaps it could be a problem wrt meeting the requirements of 3.1.

[A further comment from NZQA moderation follows:]

The only issue with the apple browning is that if the colour is quantitatively measured using a spectrophotometer, and a calibration curve is not obtained using standards to convert to concentration, then this is not really different from using a 'kit' of some kind to do the measurement of a quantity/concentration. In that case it would not meet the requirements of the standard. Use of a 'kit' avoids much of the 'processing' and it is the work involved with the calibration curve that would parallel this processing. If a calibration curve were determined and used for concentration then it definitely met the standard, but if not then it was not meeting the intention of the standard.

There are some good 'rate context' investigations but it seems they may be difficult to fit against the standard as it currently exists.

[My response to this was]

A typical rate investigation such as the browning issue or similar would typically involve: 1. A determination of optimum wavelength for absorption to read at i.e obtaining a plot of absorption vs wavelength for a specific sample 2. For each variable such as temp or pH or amount of enzyme etc to determine the rate would require at least 10 measurements of absorption against time to allow a suitable graph to be drawn 3. At least one value of the variable would need to have this replicated sufficient times to ensure concordancy or to allow estimation of uncertainty limits etc. I would have thought this would have been reasonably equivalent to the amount of work required to use a calibration curve to determine absolute values.

If the rate investigation involved the reaction or production of a known specific chemical it would obviously be possible to obtain a calibration curve and determine absolute values.

However, with a complex change such as browning more than one chemical may be involved and even if only one chemical was involved it would not be possible to obtain or isolate the chemical in a pure form so standard solutions as required for a calibration curve is not going to be possible. It seems to be a shame to knock these investigations out as a possibility as an example as clearly they are really good examples of real investigations. I would add than when we originally prepared the standard it was intended that rate investigations could be included.

[Further response from NZQA moderation]

The expectation is that the amount (or concentration) of substance is determined. Although the standard simply states a possible trend in the amount of substance, given that this is a chemistry standard, we do expect calculation to determine amount/concentration to be included.

Otherwise it seems that it would be acceptable (which it is not) to use a testing kit of same kind as this would be considered comparable.

So in summary:

Unless there is an absolute quantitative determination of the amount of substance being investigated, then it will not qualify as an extended investigation. This means some rate investigations could work but the browning one won't as it is not possible to determine an absolute concentration of the “chemical responsible for browning”. The only consolation is that this will be reconsidered during the next review of the 3.1 standard. Back to top.

Q50. I've just been marking some AS3.1 reports, and have come across an unusual problem.

Some students analysed for alcohol in wine by using the method described in your handbook, i.e., (1) oxidation with excess acidified dichromate, (2) reaction with KI to generate I2 and, finally, (3) titration with thiosulfate.

They all obtained great results BUT the problem is that they all used an incorrect molar mass for thiosulfate (158 rather than 248).

They argue that they shouldn't be penalised for this because:

  1. It's only 1 error in 10-15 hours practical work.
  2. They got results close to what they'd expect, so how could they spot that something was wrong?
  3. The method doesn't require them to do a blank titre or make up a standard alcohol soln, so ... as (3).

So. What do you think?

A. Sorry about the delay but wanted to check this one out through "the system" a bit more widely before responding. My response would be that assuming the outcome/purpose of the investigation was to investigate some change in alcohol level (as opposed to an absolute value to compare against the “given' values) then the investigation would still be valid as a comparative exercise and I would award anything up to Merit(depending on everything else meeting this standard).

Alternatively, if the rest of the investigation and report was at excellence standard (and almost invariably this relates to the quality and depth of the discussion of results and final conclusion) I would return the investigation and tell the student there was a mathematical error in their calculation and ask them to check it. If they found the error and corrected it I would be tempted to award up to Excellence (subject to everything else being up to that standard). Back to top.

Q51. Have just received back moderation report for this standard.  The moderator's judgement for two of the exemplars of student work I submitted were Achieved (cf my grades of Merit).  The only comment s/he makes is that the student needs to test at least 5 values of the independent variable to have a sufficient range for Merit.  Both students had 4 values for their independent variable.  I had based my comments to students (re number of values required for independent variable) on the assessment notes in the Practical Investigation resource from McTogi which suggests that 4-6 values for the independent variable constitutes a suitable range.  I can find no reference in the standard itself or the 2004 moderator's report to a minimum of 5 being a suitable range for merit, and would assume I am not the only person to be caught out by this.  Do you know when or where the minimum of 5 was decided on, if indeed it was?

A. The guideline for range given to moderators is: for achievement 3 values of independent variable and for merit 5 values of independent variable. However, this is not "set in concrete" as the nature of the investigation must be considered. i.e. - it does relate to the difficulty / complexity of the analysis.

Although in the moderation process, numbers such as these may tend to be used rather rigidly, it has proven to be the best way to establish guidelines.

For most investigations the guidelines seem to be appropriate but there may be others where a larger, or smaller, range is appropriate. In such situations, remember that you can always send in material for an appeal if you so choose. Back to top.

Q52. Just have a few more questions about 3.1

* If the students have titration values less than 10mLs we have marked them down to a Merit as they haven't modified the method to increase the accuracy (minimise the error)  of their results.  Does this sound ok?

* Also with the chloride ion titration, magnesium chloride is used as the primary standard.  And in the calcium titration Magnesium sulphate was used as the standard.  We thought that primary standards were not supposed to have waters of crystallisation.  Our magnesium chloride was so hygroscopic that we got our students to use sodium chloride instead (but that has issues with having potassium and other impurities in it).

Can we please get a list of suitable and widely accepted primary standards that the students can use?  One of our Chemistry teachers was told as a student that silver nitrate was one of the most accurate primary standards but that doesn't seem to be a widely accepted theory.

* also it may be useful to have access to moderation reports to see what was/is accepted at each grade boundary.  Is there some way that could be collated and made readily available?

A. If they haven't modified the "starting recipe" at all and get titres less than 10 mL then fair enough - however in extreme conditions wheer they may have already diluted their standard solution significantly (to the point where its accuracy may start to become an issue or the amount of sample they are using is as large as is practicable I w personally would accept titre values under these circumstances, even down to about 5 mL.

It is more a question of have they attempted to address the issue, rather than sticking to a predetermined limit. I would also be concerned with results where titre values were significantly greater than 25 mL if no attempt had been made to vary the starting parameters.

I agree with your comment about the hydrated salts - we often dehydrate them and keep the samples in a dessicator for this reason. I will see if I can find some info on which reagents can be usefully considered to be primary standards and circulate this through the newsletter.

Re your request about the grade boundary issues wrt moderation, I agree that this is an excellent idea but is unlikely to happen although the National Moderator may take this on board when they read this (in the next e-mail). However, I do sympathise with them because of the wide variation in the nature and type of extended investigations carried out and the need to retain some flexibility for moderators to allow moderators to apply common sense and use a holistic approach to specific cases.

I also suspect that the moderation process may have some much bigger issues to deal with regarding what teachers/sdtudents consider to be an extended investigation. Personally, I do not believe that just doing more of a standard type of experiment where essentially all students do the same prescribed expt meets the requirements or expectations of an extended investigation as originally envisaged. Perhaps some guidelines along these lines in the annual National Moderator's report would also be useful. Back to top.

Q53. I am just about to mark 3.1 and one of my students has lost his logbook!  He claims a friend of his, at another school, contacted someone at NCEA and they said that the logbook didn't need to be handed in to achieve the standard.  I have copied, from the NCEA site, details where the logbook is mentioned and I guess, if he has all his data processing in his report, then that would be OK to achieve the standard?  Have you had any other enquiries re this.

A. Haven't come across it at all before so don't know how the moderation process would handle it. I guess the key phrase is "log book must be kept during the investigation".  The main purpose of the logbook is to check authenticity and to be able to check back on the raw data when there is a potential issue in the processing part of the report. As you say if all the processed data is in the report and if you feel comfortable about the authenticity aspect (ie the work was largely done during supervised periods) then I think it it should be OK - one of those professional judgement things. However, if an issue arises with the processed data that would require reference to the raw data then I guess they can't receive the benefit of the doubt. Perhaps someone involved in moderation might like to comment if the issue has arisen before. Back to top.

  • Department of Chemistry
    chemistry@canterbury.ac.nz
    Phone +64 3 364 2413
  • Chemteach
    University of Canterbury
    Private Bag 4800, Christchurch
    New Zealand
  • Follow us
    FacebookYoutubetwitterLinked In