In this section
Management Issues for 3.1
Experience suggests a minimum allocation of 2 to 3 weeks of class time be dedicated to the carrying out of the required practical work. This time allocation does not include preparatory time for identifying a purpose, some initial research and a limited amount of trialing. Time also needs to be allocated for processing and interpreting the data although teacher help with calculations usually occurs while the practical work is occurring to ensure the investigation is delivering useful data.
To ensure sufficient time is available to meet the needs of the more dedicated or enthusiastic students, a laboratory can be made available outside of class time subject to the availability of teacher supervision. Another possibility is to offer “open weekends” where students can spend an entire day working in the laboratory without interruptions. Without the distraction of setting up and clearing up every hour many students can achieve as much worthwhile data in a single day as they can in two weeks of ordinary class time – particularly once they have overcome initial teething problems and made any required modifications to their method. Many students have also commented that they have found this investigation and the casual camaraderie evident on such open days one of their most rewarding and enjoyable experiences in chemistry.
Although the extended investigation is a Level 3 Achievement Standard it is quite feasible to offer it as part of a Year 12 chemistry course. This would require structuring the course so that the internally assessed standards, which are based on practical abilities, are covered in the first half of the year.
Once gravimetric analysis (including the use of stoichiometric relationships in quantitative analysis), acid-base titrations (including the concept of concentration) and the principles of oxidation-reduction have been mastered students have the pre-requisites required to undertake the extended investigation.
Advantages of assess ing the extended investigation in Year 12 include
It allows students in Year 13 to focus on the requirements of the externally assessed standards – particularly for students requiring minimum entry requirements for restricted courses or aiming for success in the Scholarship standards.
The experience of hands on chemistry that is more realistic than much of the illustrative, cookery book type exercises they usually experience may encourages students to continue on with chemistry in Year 13.
A small amount of time may be allocated in Year 13 to allow further work (either practical based or in the processing and interpretation of existing data) towards a reassessment opportunity.
Disadvantages of assessing the extended investigation in Year 12 include
A 24 credit chemistry course is not available in Year 13 unless there is some other reallocation of standards such as moving a small Level 2 standard to Year 13 – both to readjust the credits available at each level and to free`up the time required for the extended investigation at year 12.
A small reduction in credits may also help with the workloads of students in year 13 who are focussing on the scholarship standard.
Carrying out the extended investigations at Year 12 where the number of chemistry students is larger places a greater demand on the limited resources available.
Because of the requirements to carry out a large number of experiments on an individual basis, this achievement standard places extremely high demands on available resources such as chemicals, equipment and technician/teacher time.
Chemicals: The cost of chemicals required to make up large quantities of required solutions and other reagents can be very expensive but students can be encouraged to use weaker concentrations and compensating by the use of smaller or more dilute samples (at the expense of some loss in accuracy of their final data). Schools may also choose to limit particular analytical procedures where the reagents required are particularly expensive.
It is expected that students will provide their own samples for the investigation and they obviously need to be aware of the cost of this in situations where they are sampling commercially produced products.
If their investigation involves the determination of alcohol present in commercial alcoholic beverages an appropriate permission/agreement form would need to be signed by a parent.
Schools will almost certainly need to order extra stocks of common reagents to meet the demands of these investigations, but the actual requirements will not be known until after students actually decide on their particular investigation and purpose statements. For this reason it is recommended that the initial preparation, decision making and some limited trialing takes place up to a term before the actual practical work commences. This allows time for stock requirements to be determined, collated and pre-ordered.
Equipment: Simple titration procedures (including acid-base, redox, compleximetric and precipitation) allow a large range of analytical techniques to be carried out such as determinations of Vit C; Ca, Mg or Al; alcohol; SO2; OCl-/ Cl2; dissolved O2/BOD; Cl-/salt; Cu2+; I-; ammonia; tannin and “vinegar”.
The most common requirements are burettes, pipettes and balances. The latter two are readily shared but it is impractical for each student requiring a burette not to have it available at all times during each period. In larger schools this requirement can often be met by sharing equipment between rooms and/or having different classes scheduled to carry out the investigation at slightly different times of the year. Smaller schools may need to share resources with another local school. All schools should be budgeting to aim to build up their stocks of the required equipment over a period of time.
Similarly there are gravimetric methods suitable for the determination of species such as phosphate and sulfate. If a colorimeter or spectrophotometer is available the number of suitable investigations increases even further – such as the determination of iron, glucose, alcohol, lead and copper.
While these instruments are expensive to buy, it is possible to build DIY devices for less than $50. It is also possible to obtain older, but still working machines that are being replaced by tertiary institutes or local businesses. These are usually available at little or no cost other then the time, effort and determination to track down possible sources.
A good case can also be argued by HODs for provision of such items from the capital expenditure budget on the basis of the need to meet the requirements of NCEA.
One item that is likely to be in short supply is sufficient quantities of stock bottles – for students to collect and store samples as well as the storage of their stock solutions. Cleaned 1L (and 2L) plastic milk containers meet this requirement adequately at no cost but collection of these needs to be organised early in the year.
Technician time: Where possible, it is useful to have a technician (or teacher) pre-prepare a number of stock solutions that will be required by the students in their investigations. Where necessary these can be diluted by the students as and where necessary. However, this provision should only apply to reagents where the concentration only needs to be approximate (e.g. common acids, buffers, indicators, and reagents added in excess). All reagents where the concentration needs to be known exactly must be either prepared (or standardised) by the students themselves.