The essence of the decomposition reaction

There are a large number of free moving hydrogen ions and chloride ions in hydrochloric acid solution, and a large number of free moving calcium ions and hydroxyl ions in calcium hydroxide solution. According to the charge conservation in the solution, the ratio of the number of hydrogen ions to chloride ions in hydrochloric acid solution is 1:1, and the ratio of calcium ions to hydroxyl ions in calcium hydroxide solution is 1:2. < / P > < p > when the two solutions are mixed, the cation and anion collide with each other, because the product calcium chloride is a strong electrolyte and exists in the form of free moving calcium ion and free moving chloride ion in the solution. However, hydrogen ions and hydroxyl ions collide to form new water molecules, which reduces the concentration of hydrogen ions and hydroxyl ions in the original solution, and the reaction takes place. Similarly, it can be seen from the solubility table that calcium chloride, potassium carbonate and potassium chloride exist in the form of free moving ions in the solution. When calcium chloride solution is mixed with potassium carbonate solution, calcium ion and carbonate ion collide to form calcium carbonate precipitate, which reduces the concentration of calcium ion and carbonate ion in the original solution, and the reaction occurs. When dilute hydrochloric acid reacts with sodium carbonate solution, the total number of chloride ions and sodium ions remains unchanged, but the reaction occurs because water and gas are generated after the collision of hydrogen ion and carbonate ion, and carbon dioxide escapes in the air, resulting in the decrease of hydrogen ion and carbonate ion concentration in the original solution. It can be found from the microscopic diagram that after the mixture of dilute hydrochloric acid and magnesium nitrate solution, the concentration of any ions in the original solution does not decrease, so the reaction can not take place. Take sodium chloride as an example. We know that matter can be made up of molecules, atoms or ions. Sodium chloride is a substance composed of sodium ions and chloride ions. In sodium chloride solid, sodium ion and chloride ion cannot move freely due to strong electrostatic effect. However, when sodium chloride is dissolved in water, the strong electrostatic effect is destroyed under the action of water molecules. Therefore, sodium ions and chloride ions can move freely in sodium chloride solution. 2. Salt is the representative. The “dissolution” of salts belonging to the “solubility table” in the appendix of the textbook indicates that in aqueous solution, the cation and anion in the substance are free to move in the solution. “No” means that the salt is insoluble in water in aqueous solution, and the concentration of anions and cations composed of the salt in the aqueous solution can be ignored. In order to understand the essence of metathesis reaction, we must first master the “solubility table of common substances” in the textbook. Because even if you don’t want to recite in junior high school, you will also ask for it after high school. CUISINE&HEALTH