(2) Filtration can be used to separate soluble solids from insoluble solids, so the name of operation a in step 3 is: filtration, in which sodium carbonate solution reacts with calcium hydroxide solution to generate calcium carbonate precipitation and sodium hydroxide, so there is sodium hydroxide in the filtrate besides sodium chloride and sodium carbonate, so the purpose of adding appropriate amount of hydrochloric acid in step 4 is to remove Na2CO3 and NaOH from the filtrate;
(3) When heating and evaporating, use a glass rod to continuously stir, which is to prevent droplets from splashing due to local high temperature. When the refined salt water evaporates to a large amount of solid precipitation, stop heating, and then continue stirring to obtain refined salt;
(4) The calcium hydroxide solution reacts with magnesium chloride to generate magnesium hydroxide precipitate and soluble calcium chloride, so if the order of step (1) and step (2) is reversed, the final refined brine still contains CaCl2；;
(5) After two times of filtration, the filtrate is still turbid. The reasons may be: the filter paper is damaged or the liquid level is higher than the edge of the filter paper or the instrument is not clean;
(6) The yield of refined salt after purification calculated by Xiao Li is much lower than that of other students in the same period, which may be caused by the splashing of liquid droplets during heating evaporation without stirring with a glass rod.
So the answer is: (1) MgCl2+Ca (OH) 2 ═ Mg (OH) 2 ↓+CaCl2;
(2) filtering, NaOH；;
(3) The local temperature is too high, causing droplets to splash; When more solids precipitate;
(4) calcium chloride;
(5) The filter paper is damaged or the liquid level is higher than the edge of the filter paper;
(6) When heating and evaporating, the glass rod is not used to stir, resulting in droplets splashing.