Core practical:

Measure the vitamin C content of a sample of fruit juice by measuring the volume of the sample required to decolourise a solution of DCPIP. Calibrate the results by comparison with a known concentration of vitamin C.

Preparationa Make up a 1% solution of vitamin C with 1 g of vitamin C in 100 cm3; this is 10 mg cm3.b Make up a 1% solution of DCPIP.Investigationc Pipette 2 cm3 of vitamin C solution into a test tube.d Using a graduated pipette or a burette, add 1% DCPIP drop by drop to the vitamin C solution. Shake the tube gently after adding each drop. Add DCPIP solution until the blue colour of the final drop does not disappear.e Record the exact amount of DCPIP solution that was added.f Repeat the procedure and calculate an average result.g Repeat with the fruit juices to be tested. If more than 5 cm3 of DCPIP are completely decolourised, dilute the fruit juice and repeat the test. If the fruit juice has a strong colour that will interfere with determining the end point, dilute the juice before testing.h Calculate the amount of vitamin C in the standard solution in mg cm3. Calculate how much vitamin C there is in each of the fruit juices in mg cm3.

Hypotheses to test could include fresh juices have more vitamin C than long-life juice not from concentrate is best in terms of vitamin content fruit squashes have less vitamin C than fruit juices if heat destroys vitamin C, then heat-treated long-life juices will have lower concentrations if heat destroys vitamin C, then boiled fruit juice will have lower concentrations than unboiled manufacturers generally provide reliable information about their productsvitamin C degrades in vitamin tablets, and old tablets will have less than fresh ones