Suggested investigations

Topic	Suggestions	Advice
Enzyme kinetics	Catalase (yeast/potato) 2H₂O₂ —> 2H₂O + O₂ Polyphenoloxidase (banana) on 1,2-di-hydroxybenzene substrate Urease on CO(NH₂)₂ + H₂O —> CO₂ + 2NH₃ Lipase on glyceryl triethanoate substrate Amylase on starch substrate	Three variables from: concentration (enzyme and substrate); temperature; pH; inhibition; compared with inorganic catalysts. These experiments are easy to do, especially catalase, but are lengthy and difficult to maintain over several weeks. Check the solutions, each day, by running a standard experiment.
Clock reactions	Iodine (hydrogen peroxide) H₂O₂ + 2I^- + 2H⁺ —> I₂ + 2H₂O Iodine (peroxodisulphate) S₂0₈^- + 2I^- —> 2S0₄^2- + I₂ Bromine (bromate(v)) 5Br^- + BrO₃^- + 6H⁺ —> 3Br₂ + 3H₂O Halogenoalkane (CH₃)₃CX + OH^- —> (CH₃)₃COH + X^-	Three variables eg concentrations of each reactant, and temperature. Analysis section to include order, rate equation and activation energy. Top investigations discuss mechanisms and try to find a catalyst and its activation energy. Again, always check your solutions, each day, by running a standard experiment. Easy experiments to do and repeat.
Aspirin	Preparation Titration (acid-base) Colorimeter Back titration pH titration	Analysis should find the percentage of salicylic acid in the sample. Compare the different methods. Melting points and thin layer chromatography are poor choices for the time spent.
Bleach	lodine/thiosulphate titration Volume of oxygen Thermometric titration	A popular choice but rarely done well. Need sodium chlorate(I)(aq) of known concentration. Compare methods and then try commercial bleaches.
Vitamin C	Iodine DCPIP N-bromosuccinimide	Difficult titrations to do well. Need a standard solution of vitamin C. Compare methods and then try fruit juices.
Electrode potentials	Concentration Temperature pH Complexing	Quick experiments but not always easy to reproduce data. You must use clean degreased electrodes, and use a new salt bridge for each experiment.
[Cu²⁺]	Thiosulphate titration Colorimeter EDTA titration lon-exchange Gravimetric	Recommend three methods to compare, using a known concentration (analar copper sulphate crystals). Then try an unknown concentration. With its variety of methods this should become more popular.
Ester hydrolysis	Concentration Temperature Ester Catalyst	Either rate of attainment of equilibrium or equilibrium constants can be studied. Need to be organised and have several experiments on the go because some of these are lengthy.
Kinetics	Propanone / I₂ Manganate(VII) / C₂O₄^2- Thiosulphate / H⁺	Need at least three variables. Analysis section to include order, rate equation and activation energy.
Wine ethanol	Back titration (Cr₂O₇^2-) Colorimeter (Cr₂O₇^2-) Weighing	Need a pure sample of ethanol to test and compare the methods. A white and a red wine could then be attempted.
Paracetamol	Extraction Redox titration Colorimeter	A pure sample can easily be extracted from the tablets using propanone. The titration uses Ce(IV) with ferroin indicator. Compare the methods and then analyse a tablet.

NOTE: There is significant emphasis in the assessment descriptors on planning and evaluating, and on the evidence collected being accurate and reliable. It is vital, therefore, for students to review critically each set of data as soon as it has been collected to decide whether further experiments are required. Students should concentrate on the quality, rather than the quantity, of the evidence gathered. Any aspect of chemistry can be investigated, but will only be classified as a "good" investigation if it has enough scope and produces enough data.