How to review and master the knowledge of acids, alkalis, and salts in junior high school

Take a look at your notes from the beginning of the lesson, find a workbook with specific exercises, and concentrate on the exercises, or find all your papers, concentrate on these kinds of questions, and memorize more equations.

1. Solubility of acids, alkalis and salts.

1. Solubility of common salts and alkalis: (If you don't read the words in parentheses, is it a good memory slip?) ）

Potassium (salt), sodium (salt), and ammonium salt are all soluble, and nitrate is nowhere to be seen in water.

Sulfate is insoluble barium sulfate, chloride is insoluble silver chloride.

Carbonate only dissolves potassium (salt), sodium (salt), and ammonium (salt).

Solubility of alkalis: only potassium (hydroxide), sodium (hydroxide), calcium (hydroxide), and barium (hydroxide) are soluble.

2. Eight common precipitates: silver chloride, barium sulfate, silver carbonate, barium carbonate, calcium carbonate, magnesium hydroxide, copper hydroxide, iron hydroxide.

3. Four microlytic substances: Ca(OH)2 (the reason why lime water is marked as "clarified"), CASO4 (the reason why dilute sulfuric acid is not used when making carbon dioxide in the laboratory), AG2SO4 (the reason why silver nitrate is not used when distinguishing SO42- and CL-), and MGCO3 (the reason why carbonate ions cannot be used to remove magnesium ions in solution).

4. Three non-existent substances: the so-called silver hydroxide, aluminium carbonate, and iron carbonate.

2. Conditions under which the decomposition reaction occurs After the reaction, gas, water or precipitation are generated. (i.e., there are substances that do not exist in solution or do not easily ionize in aqueous solution).

1) Insoluble bases can only neutralize with acidity.

2) Insoluble salts, only carbonates can react with acids.

3) Kno3, nano3, agno3 and baso4 cannot be reactants of metathesis reaction.

3. Determination of the acidity and alkalinity of the solution.

1. The acidic and alkaline purple litmus test solution of the indicator ——— solution turns red when the acidic solution is encountered; In case of alkaline solution, it turns blue.

The colorless phenolphthalein test solution only turns red when the alkali solution is encounteredNote: insoluble alkali has no effect on the indicator, and the alkaline solution is not necessarily a solution of alkali (special case: the aqueous solution of sodium carbonate is alkaline).

2. pH value——— pH of the solution, pH >7, the solution is acidic (the smaller the acidity, the stronger the acidity), the pH = 7 solution is neutral,

Fourth, the detection of ions.

Cl- (in solution) - silver nitrate solution is added to the test solution, and if a white precipitate insoluble in nitric acid is generated, the original test solution contains chloride ions.

SO42- (in solution) - Add barium chloride (or barium nitrate, or barium hydroxide) solution to the test solution, if a white precipitate insoluble in nitric acid (or hydrochloric acid) is generated, the original test solution contains sulfate ions.

CO32-(1) (solid or solution) – a dilute acid solution is added to the substance to be measured, and if a gas is produced that can make the clarified lime water turbid, the original substance to be tested contains carbonate ions.

2) (in solution) - add barium chloride or silver nitrate solution to the test solution, if a white precipitate dissolved in nitric acid is produced, and at the same time a gas can make the clear lime water turbid, then the original test solution contains carbonate ions.

Acid is a compound with ionized cations that are all hydrogen ions, which can react with the indicator to make the purple litmus test solution red, and the green bromothymol blue test solution yellow, and can not change the color of the colorless phenolphthalein test solution, and can also react with alkaline jujube burying sheds and alkaline oxides to form salt and water, and react with salts to form another salt and another acid, and react with active metals (generally non-oxidizing acids) to generate salt liquid mill and hydrogen. Acids can be divided into oxygenated acids and anaerobic acids, and generally anaerobic acids are mixtures because it is an aqueous solution of gas.

The alkali is a compound in which the ionized anions are all hydroxide ions, which can react with the indicator to make the purple litmus test solution and the green bromothymol blue test solution blue, and the colorless phenolphthalein test solution to turn red, and can also react with acids and acidic oxides to form salt and water, and react with salts to form another salt and another base. Bases can be divided into monobasic bases, dibasic bases, and terbasic bases.

Salt is a compound composed of metal elements and acid groups, which can form another salt and acid or base with alkalis and acids, and if it reacts with salts, it will form two other salts, and if it reacts with metals, it will form another salt and metal. Salts can be divided into normal salts, acid salts, and alkaline salts.