CHEM2133 QUIZ 3 – 50 points 1. (10 points) Iodine is a toxic, volatile and corrosive solid that attacks mucous membranes and absorbs strongly to skin. Spills are conveniently treated. Explain how to treat spilled iodine. Drop concentrated solution of sodium thiosulfate until discoloration and follow by water. 2. (5 points) If you use Cu wire instead of Cu wool to prepare CuI, the rate of reaction will be very slow. Explain why using Cu wool significantly increases the rate of reaction. Increasing in surface area of Cu increases the rate of reaction. 3. (5 points) CuI is white solid but the solution of CuI in concentrate ammonia is blue. They appear in different color because copper in those two systems have different oxidation state. 4. (5 points) What is the role of acetic acid added into the mixture of Cu wool, NaI and I2 in preparation of CuI? Remove CuO on the surface of Cu. 5. (5 points) Why is NaI3 less stable than Me4NI3? Size miss-match makes ionic compound unstable. Na+ -- small cation I3- -- big anion Me3+ -- big cation 6. (10 points) What is the observation at the end point of a titration of iodine solution with bisulfate solution? Solution color changes from brown to colorless. 7. (10 points) 1.563 g of CuI was obtained from the experiment. In determination of per cent purity of prepared CuI, 1.452 g of CuI was used to react with excess NaBH4 yielding 0.411 g of Cu. Calculate percent purity of prepared CuI. (Cu = 63.54, I = 126.9) Molar mass of CuI = 190.44 1.452 g of crude CuI = 7.624 mmol 0.411 g of yielded Cu = 6.468 mmol
%purity of prepared CuI =
%purity of prepared CuI =
mass or moles of CuI which is converted into Cu mass or moles of crude CuI
6.468 7.624
100 84.8
100