Question 1 – REDOX titration
Sodium hypochlorite is a solution that has been used for centuries as a bleach. We need to find the concentration of our sample of sodium hypochlorite. By following the steps below.
i) A 50 ml sample of bleach is taken out from the 880ml bottle.
ii) The solution is diluted up to 200ml volumetric flask.
iii) A 20 ml aliquote sample is taken out of the volumetric flask and transferred into conical flask.
iv) Iodide is added to the conical flask which creates iodine.
ClO-(aq) + 2 H+(aq) + 2 I-(aq) –> I2(aq) + Cl-(aq) + H2O(l)
Finally, after all the sodium hypochlorite solution is reacted, the resulting solution is diluted with another 50 ml of water and it is titrated using sodium thisulfate. The average titre used was 8.43ml, the concentration of the sodium thiosulfate was 23.2g/L.
2 S2032- (aq) + I2 (aq) –> 2 I- (aq) + S4O62- (aq)
a) Find the concentration of sodium thiosulfate in molarity.
(1 mark)
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b) Find the concentration of thiosulfate ions in molarity.
(1 mark)
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c) Find the amount (in mol) of iodine in the reaction involving sodium
hypochlorite solution. (3 marks)
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d) Using your answer in (c) find the amount of hypochlorite solution in the
20 ml aliquote. (1 mark)
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e) Find the amount (in mol) of hypochlorite solution in the 880ml bottle.
(3 marks).
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f) Find the mass of hypochlorite in the 880ml bottle (2 marks)
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