14. Solutions
Parts per Million (ppm)
11PRACTICE PROBLEM
WHO guidelines recommend that the amount of residual chlorine in drinking water should not be higher than 5 parts per million (ppm). The amount of chlorine can be determined by back titration with potassium iodide:
Cl2(aq) + 2 I−(aq) → 2 Cl−(aq) + I2(aq)
The iodine formed as a result of the reaction above is then titrated with a solution of sodium thiosulfate:
2 Na2S2O3(aq) + I2(aq) → 2 NaI(aq) + Na2S4O6(aq)
A 350.0 mL water sample was added with excess solid sodium iodide and the resulting solution was then titrated against a 2.25×10−3 M sodium thiosulphate solution. The solution required 14.5 mL of Na2S2O3 to reach the equivalence point. How many grams of chlorine are there in the water sample?
WHO guidelines recommend that the amount of residual chlorine in drinking water should not be higher than 5 parts per million (ppm). The amount of chlorine can be determined by back titration with potassium iodide:
Cl2(aq) + 2 I−(aq) → 2 Cl−(aq) + I2(aq)
The iodine formed as a result of the reaction above is then titrated with a solution of sodium thiosulfate:
2 Na2S2O3(aq) + I2(aq) → 2 NaI(aq) + Na2S4O6(aq)
A 350.0 mL water sample was added with excess solid sodium iodide and the resulting solution was then titrated against a 2.25×10−3 M sodium thiosulphate solution. The solution required 14.5 mL of Na2S2O3 to reach the equivalence point. How many grams of chlorine are there in the water sample?