Dropping stannous chloride solution into the hot mixed solution of ferric chloride and dilute hydrochloric acid can turn the yellow ferric chloride solution into colorless.
Add 1 drop of iodine solution to 10 ml of 0.5% starch solution to form a blue solution. Adding stannous chloride solution dropwise can turn the blue solution into colorless.
Add 10 ml of 0.1% potassium permanganate solution with dilute hydrochloric acid to adjust the acidity. Dropwise addition of stannous chloride solution can turn the red potassium permanganate solution into colorless.
The above three identifications make full use of the strong reducing property of stannous chloride solution.