(2009? The principle and method of indirect iodometry for the determination of copper in vitriol are as follows:

The way to solve the problem: (1) According to the analysis, the solution after sulfuric acid dissolution contains Fe 3+, which can oxidize I- to generate I2;

(2) According to the acidity of Cu 2+ hydrolysis reaction solution;

(3) According to the fact that the solution of iodine measuring bottle is not in contact with oxygen in the air, but can be in contact with oxygen in the air with an ordinary conical bottle, and oxygen can react with potassium iodide to generate elemental iodine;

(4) According to the relationship: 2cu2+~ I 2 ~ I 3-~ 2S2O3 2-, first calculate the quantity and quality of cu2+, and then divide the quality of Cu 2+ by the quality of the sample.

(1) The sulfuric acid solution dissolved with acid contains Fe3+, which can oxidize I- to I2, producing a large amount of Cu, which affects the determination results. When a small amount of NaF is added, Fe3 ++ 6f-=[Fe F6]3- and FeF63- cannot oxidize I-.

So the answer is: shielding Fe3+ to prevent big errors;

(2)Cu2+ can undergo hydrolysis reaction, and the solution is acidic, which provides acidic conditions to inhibit the hydrolysis of Cu2+, so the answer is: provide acidic conditions to inhibit the hydrolysis of Cu2+;

(3) iodine flask solution is not in contact with oxygen in the air, but can be in contact with oxygen in the air with an ordinary conical flask, and oxygen can react with potassium iodide to generate elemental iodine, so iodine flask is used to prevent oxygen in the air from reacting with potassium iodide.

So the answer is: prevent the oxygen in the air from reacting with potassium iodide;

(4) Copper sulfate solution reacts with potassium iodide solution to generate white precipitate (cuprous iodide) and separate out iodine. Ionic equation is 2Cu2++4I-=2CuI↓+I2, so the answer is 2cu2++4i-= 2cui ↓+I2;

(5) (5) The amount of substance in the standard solution of Na2S2O3 is cmol/L×V× 10-3L, and the amount of substance of cu2+ is cmol/L×V× 10-3L according to the relation: 2cu2+~ I2 ~ i3-~ 2S2O3-.

The mass of Cu2+ is cmol/L×V× 10-3L×64g/mol, so ω(Cu)= 1

cmol/L×V× 10？ 3L×64g/mol

ag× 100% =[64cV/ 1000 a]× 100%，

So the answer is: [64cv/1000a] ×100%.

Comments:

Test center of this topic: explore the composition of substances or determine the content of substances; Redox reaction; Neutralization titration.

Test center comments: This question mainly examines chemical experiments and calculations, involving more knowledge points, and the (1) question is more difficult. Through inspection, it is found that the solution contains Fe3+.