K 3 [Fe (C2O4) 3] 3H2O is a water-soluble potassium iron (Ⅲ) oxalate crystal, which can be used in photography and blue printing. Take iron filings as raw materials

( 1)A？ (2) Prevent the hydrolysis of Fe 2+? British Council

(3)① exhaust the air in the device to prevent interference with the experimental results? Prevent liquid from flowing back (or sucking back)? Carbon dioxide and carbon monoxide

② In Scheme C, the samples were dissolved with hydrochloric acid, and chloride ions could also be oxidized by acidic MnO 4-.

Test analysis: (1) When absorbing impurity gas, the connection mode of the air passage is long inlet and short outlet, the long air passage should be submerged under the liquid surface, and the short air passage can be slightly exposed from the rubber plug. Therefore, the option is a. (2) Add a small amount of h2so 4 to the prepared FeSO 4 solution for acidification, so as to prevent Fe2+ from hydrolysis and make the solution turbid. In order to obtain FeSO4 7H2O from the solution, the necessary experimental operations are evaporation and concentration, cooling and crystallization, filtration and washing, and drying. So what's the choice? University of Cambridge, UK. (3)① After the air tightness inspection of the device is completed, it is necessary to pass N 2 for a period of time to exhaust the air in the device to prevent interference with the experimental results. During the experiment, it was observed that the clarified limewater in B became turbid, indicating that it contained CO 2, red solid was generated in E, and the clarified limewater in F became turbid, indicating that the gas product contained CO, so the gas product was CO 2 and CO. ② The solid product obtained by decomposition contained K 2 CO 3, FeO and Fe, which was dissolved in water, filtered, washed and dried to obtain iron-containing samples. Answer: Add enough nitric acid to dissolve the sample ag to get Fe(NO 3) 3, and add enough NaOH solution to get Fe(OH) 3 precipitate. After filtering and washing, the reaction is burning: 2Fe(OH) 3 Fe 2 O 3 +3H 2 O. The solid mass obtained after drying is the mass of Fe 2 O 3. Then calculate the mass of Fe element. Therefore, according to the quality of iron-containing samples and the quality of Fe, the content of each component in solid products can be obtained. Correct. B: Add enough dilute sulfuric acid to the iron-containing sample for reaction: Fe+H2SO4 = FeSO4+H2write. According to the volume of hydrogen released, the mass of Fe can be calculated, and then the mass of FeO can be calculated, and then the contents of three components in solid samples can be solved. Correct. C: the sample reacts when it is dissolved with sufficient hydrochloric acid: Fe+2 HCl = FeCl 2+H2 ↑; FeO+2HCl=FeCl 2 +H 2 O. When titrating 25ml solution with acidic KMnO4 solution, both Fe 2+ and Cl- are oxidized by acidic potassium permanganate, so the amount of Fe2+ in the solution cannot be determined according to the amount of substances consumed in the potassium permanganate solution. Therefore, it is impossible to determine the content of each component in the sample. Mistake. Therefore, in these three schemes, C cannot determine the composition of matter.