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Unit 3 PPA 3 REDOX TITRATIONS

Unit 3 PPA 3 REDOX TITRATIONS. REDOX TITRATIONS (Unit 3 PPA 3). The balanced redox equation for the reactions is:- C 6 H 8 O 6 + I 2 C 6 H 6 O 6 + 2H + (aq) + 2I - (aq).

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Unit 3 PPA 3 REDOX TITRATIONS

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  1. Unit 3 PPA 3 REDOX TITRATIONS

  2. REDOX TITRATIONS (Unit 3 PPA 3) The balanced redox equation for the reactions is:- C6H8O6 + I2 C6H6O6 + 2H+(aq) + 2I-(aq) The aim of the experiment is to determine the mass of vitamin C in a tablet by carrying out a redox titration using a solution of iodine of accurately known concentration and starch solutions as an indicator. (1) How many moles of iodine react with one mole of vitamin C (C6H8O6 )? (1) 1 mole of iodine. (2) What colour change indicates the end-point of the titration? (2) The appearance of a permanent blue- black colour. (3) Describe in detail how a vitamin C tablet can be dissolved to form exactly 250 cm3 of a vitamin C solution. (3) Place some distilled water (50 to 100cm3) in a beaker. Add a vitamin C tablet and stir until it has completely dissolved. Transfer the vitamin C solution from the beaker to a 250cm3 standard flask. Add distilled water to the standard flask until the solution is just below the mark on the stem of the flask. Add distilled water using a dropper until the bottom of the meniscus lies on top of the mark. Stopper the flask and shake to ensure the solution is thoroughly mixed.

  3. 0.040 mol l-1 iodine solution 0.0 12.0 23.7 12.0 23.7 35.6 11.7 11.9 12.0 25 cm3 of vitamin C solution + starch indicator The above results were obtained when a 25 cm3 sample taken from a standard flask containing 250 cm3 of vitamin C was titrated. Use the results to calculate the mass of vitamin C in the flask. Volume of iodine solution used = 11.7 + 11.9 /2 = 11.8 cm3. Number of moles of iodine used = 11.8/1000 x 0.04 0 = 0.000472 So number of moles of vitamin C in 25 cm3 sample = 0.000472. So the number of moles of vitamin C in 250 cm3 flask = 0.00472 The mass of vitamin C present = no. of moles x gfm of Vitamin C gfm of vitamin C (C6H8O6) = 176 g Mass of vitamin C = 0.00472 x 176 = 0.831 g

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