Experimental analysis (1) Add all 5.0g of coarse salt to 10mL of water, and the sodium chloride in it may not be fully dissolved, so the yield obtained is low;

(2 ) When evaporating a liquid, when a large amount of solid appears in the evaporating dish, the heating should be stopped and let the residual heat of the evaporating dish evaporate the liquid. Otherwise, the solids will splash. In this operation, the role of the glass is to stir the liquid so that the liquid is heated evenly. To prevent droplets from splashing due to excessive local temperature, analysis of the options given shows that option B is correct, so choose B;

Experimental design ① Magnesium chloride can react with sodium hydroxide to form a white precipitate. The chemical equation of this reaction is: MgCl2+2NaOH═Mg(OH)2↓+2NaCl;

②Calcium chloride can react with sodium carbonate to form white calcium carbonate precipitate. The chemical equation of this reaction is: CaCl2+Na2CO3═CaCO3↓+2NaCl．

So the answer is: Experimental analysis (1) Add all 5.0g of coarse salt to 10mL of water;

(2) Stop heating when the liquid evaporates to dryness; B;

Experimental design ① White precipitate appears; MgCl2+2NaOH═Mg(OH)2↓+2NaCl;

②Sodium carbonate (Na2CO3); CaCl2+Na2CO3═CaCO3↓+2NaCl.