A chemical experiment was carried out in the senior high school entrance examination, and the following three problems emerged: ① purification of raw salt; ② preparation and collection of carbon dioxi

A chemical experiment was carried out in the senior high school entrance examination, and the following three problems emerged: ① purification of raw salt; ② preparation and collection of carbon dioxide; ③ Preparation and collection of oxygen. (1) As shown in figure 1, the name of instrument A is iron shelf; According to the fact that there is hydrogen peroxide in the medicine pumped by A, A absorbs the preparation and collection of oxygen; The laboratory uses manganese dioxide and hydrogen peroxide to prepare oxygen, so there is a lack of a drug, that is, manganese dioxide; The chemical equation of this experimental reaction is 2H2O2? MnO2？ . ? 2H2O+O2↑；

(2) Hydrogen peroxide is liquid and manganese dioxide is solid, so the reaction does not need heating, so according to the fact that the generating device of carbon dioxide is a solid-liquid mixing device without heating, it is concluded that carbon dioxide can also be made from calcium carbonate and dilute hydrochloric acid, and the chemical equation is CaCO3+2HCl ═ CaCl2+CO2 ↑+H2O; ?

(3) Sodium hydroxide reacts with magnesium chloride to produce magnesium hydroxide precipitate and sodium chloride, so the raw salt usually contains soluble impurities such as MgCl2 in addition to insoluble magazines such as silt. In order to remove MgCl2, the reagent that can be added is sodium hydroxide solution;

(4) As can be seen from the figure, when weighing, the positions of the articles and the weights are reversed, and when the object code is reversed, the mass of the weighed articles = the mass of the weights-the mass of the row code, so the actual mass of the beaker = 30g-2.6g = 27.4g；;

So the answer is: (1) iron platform; ③; Manganese dioxide; 2H2O2？ MnO2？ . ? 2H2O+O2↑；

(2)caco3+2hcl═cacl2+co2↑+h20；

(3) sodium hydroxide solution;

(4) inversion of articles and weights; 27.4.