Background Information: Hypothesis: -fresh juices have more vitamin C than long-life juice that is ‘not from concentrate’ is best in terms of vitamin content -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 products -the amount of vitamin C content in given fruits is: So the amount of vitamin C and its percentage in fruit juice must go with the given ratio which means that guava and apple juice should have the highest and lowest concentration respectively.
Controlled: Materials Required: 6 test tubes, 50 cm3 burette, 10cm3 pipette, 1cm3 pipette, 3 small beakers, DCPIP solution, 0. 1% ascorbic acid, distilled water, 4 varieties of fruit juice, for example, mango, grape, apple, guava etc. Preparation Take a properly washed beaker and make 0. 1% solution of vitamin C or ascorbic acid with 0. 1 g of vitamin C in 100 cm3; this is 10 mg cm-3 or one may also use a readily prepared 0. 1%ascorbic acid. Take a 0. 1% solution of DCPIP. Take 6 test tubes and label them as A, B, C, D, E and F. Now slowly pipette out 1cm3 of DCPIP solution into each test tube using a 1 cm3 pipette. Take 5cm3 of the 0. 1%ascorbic acid using a 10cm3 pipette. Using a graduated pipette or a burette, add 0. 1% ascorbic acid drop by drop to the DCPIP solution. Shake the tube gently after adding each drop. Add the acid solution until the blue colour of the final drop does not disappear. Record the exact amount of ascorbic acid that was added. Similarly, in test tube B add the same volume of distilled water and gently shake the test tube to observe the change in colour. Investigation
Dilute all the juices, that is, mango juice in C, grape juice in D, apple juice in E and guava juice in F before testing because fruit juices have a strong colour that will interfere with determining the endpoint. Now keep adding mango juice drop by drop with the help of a 50 cm3 burette in test tube C containing DCPIP solution and gently shake the test tube until the DCPIP solution is decolourised. Repeat the same for other 3 fruit juices, that is grape, apple and guava. Uncertainties and errors.
Uncertainty or error while preparing ascorbic acid = Uncertainty of solid vitamin C + uncertainty of water = 0. 01+ 0. 1 = 0. 101.
Uncertainty while making the mixture of DCPIP and vitamin C = uncertainty of DCPIP(1cm3 pipette) + uncertainty of ascorbic acid (10cm3 pipette) = 0. 01 + 0. 101 = 0. 111
Uncertainty while making the mixture of DCPIP and fruit juices = Uncertainty of DCPIP(pipette) + uncertainty of fruit juices(burette) = 0. 01 + 0. 1 = 0. 11
Data Volume of ascorbic acid added to decolourise DCPIP = 2. 25(+ 0. 1) cm3. Calculating the concentration of ascorbic acid.
Concentration of ascorbic acid in fruit juice (%) = Volume of ascorbic acid added to DCPIP x 0. Volume of fruit juice added to DCPIP Uncertainty = uncertainty in the volume of ascorbic acid + uncertainty in the volume of fruit juice = 0. 111 + 0. 11 = 0. 221.
Concentration of ascorbic acid in mango juice = 2. 25 x 0. 1 = 0. 02% 11.
Concentration of ascorbic acid in grape juice = 2. 25 x 0. 1 = 0. 01% 16
Concentration of ascorbic acid in apple juice = 2. 25 x 0. 1 = 0. 006% 36. Concentration of ascorbic acid in guava juice = 2. 25 x 0. 1 = 0. 04% 5 .