Chemistry 3.1: Practical Investigations in Chemistry
In collaboration with the Canterbury Science Teachers' Association, the University of Canterbury has re-developed a number of practical chemistry investigations. They are intended for use by students carrying out NCEA Chemistry 3.1: Extended practical investigation into variations in the amount of a substance.
Ethanol analysis of aqueous solutions
Determining the concentration of ethanol in solution using dichromate redox chemistry. Applicable to alcoholic beverages.
Chloride ion analysis
- Titration (Mohr)
Determining the concentration of chloride ions by precipitation titration with silver nitrate under neutral/weakly basic conditions. Applicable to water samples.
- Gravimetric analysis
Determining the concentration of chloride ions in solution by collecting the precipitate formed with silver nitrate. Applicable to seawater or solutions with high chloride ion concentrations.
- Titration (Volhard)
Determining the concentration of chloride ions by precipitation titration with silver nitrate under acidic conditions. Applied to a cheese sample.
Vitamin C (ascorbic acid) analysis
- Titration (with Iodine)
Determining the concentration of Vitamin C in solution by redox titration with iodine. Applicable to Vitamin C tablets, fruits, vegetables and juices.
- Titration (with Iodate)
Determining the concentration of Vitamin C in solution by redox titration with potassium iodate. Applicable to Vitamin C tablets, fruits, vegetables and juices.
Calcium and magnesium ion analysis
- Complexometric titration - calcium
Determining the concentration of calcium ions by complexometric titration with EDTA. Applicable to samples containing dissolved calcium or solid calcium carbonate.
- Complexometric titration - calcium and magnesium
Determining the total concentration of calcium and magnesium ions by complexometric titration with EDTA. Applicable to samples containing dissolved calcium/magnesium or solid calcium/magnesium carbonates.
Iodate in Iodised Salt analysis
- Titration (pdf 84kb)
Determining the amount of iodate (IO3-) in iodised salt by first producing iodine, then titrating this with thiosulfate.
Determination of Iron by Thiocyanate Colorimetry
In this analysis the iron present in an iron tablet or food sample is extracted to form ferric (Fe3+) ions. Thiocyanate ions (SCN-) are added that react with Fe3+ ions to form a blood-red coloured complex of iron thiocyanate [FeSCN]2+. By comparing the intensity of the solution with known standard solutions, the concentration in the initial sample can be determined.
Method for use with a colorimeter (pdf 103kb)
Method for use if you don't have access to a colorimeter (pdf 108kb)
- Redox reaction and colorimetry - fertiliser (pdf 44kb)
In this method manganese is oxidised to a coloured permanganate solution by reacting it with an excess of potassium periodate in acid. The amount of permanganate is determined by comparison of the purple colour with known standards.
- Permanganate colorimetry - steel samples
Most kinds of steel contain a small amount of manganese (~1%). It can be detected by oxidising it to the permanganate ion, which has an intensely purple colour. The amount of permanganate is determined by comparison of the purple colour with known standards.
Method for use with a colorimeter (pdf 415kb)
Method for use if you don't have access to a colorimeter (pdf 419kb)
Phosphate in Soil Analysis
- Complexation reaction and colorimetry (pdf 63kb)
This method uses a complexation reaction to produce a coloured complex of molybdate and phosphorus. The colour of the complex is dependant on the initial phosphate concentration in the sample.