How can you tell if a gas or precipitate is formed in chemistry?

The reaction between hydrogen and oxygen is generated, and the judgment of gas should not be verbose.

If the metathesis reaction gives H2CO3 after exchanging components, it will be decomposed into water and carbon dioxide gas.

The judgment of the formation of precipitation needs to be judged according to the solubility law of acid and alkali salts, and if the product is insoluble in water, it is a precipitation.

Solubility law of acid and alkali salts:

alkali-soluble potassium, calcium, sodium, barium;

Ammonium salt, potassium salt, sodium salt and nitrate are completely soluble in salt;

Barium sulfate is insoluble in sulfate;

Silver chloride in chloride is insoluble;

Carbonate is mostly insoluble, only dissolved in ammonium, potassium, sodium and magnesium.

In the reaction of acid-base salt solution, if the product is insoluble in water, there will be precipitation.

The main precipitations are: calcium carbonate, barium carbonate, barium sulfate, silver chloride, silver carbonate, copper carbonate; Iron hydroxide, copper hydroxide, magnesium hydroxide, aluminum hydroxide, etc. If these substances are formed in solution, precipitation will be formed.

In addition, calcium hydroxide and barium hydroxide solutions react with carbon dioxide to form precipitation.

CaCO3+2HCl=CaCl2+H2 Upward arrow Indicates that there is gas formation.

Na2CO3+BA(NO3)2===2nano3+BACO3 was judged to have precipitated formation.

Because only by equations, there is only memorization, remembering which gases are precipitated.

If you do experiments, there are many ways, and you can usually look at it.

In the reaction of acid-base salt solution, if the product is insoluble in water, there will be precipitation.

The main precipitation is: calcium carbonate.

barium carbonate, barium sulfate, silver chloride, silver carbonate, rubber carbonate copper; Iron hydroxide, copper hydroxide, magnesium hydroxide, aluminum hydroxide, etc. If these substances are formed in the spinal solution, a precipitate is formed. In addition, calcium hydroxide, barium hydroxide solution with carbon dioxide.

The reaction also has a precipitate formation.

Identifying precipitates or gases actually requires you to memorize them. For example, we know that Cu(OH)2 is a blue precipitate and CaCO3 is a white precipitate. Whether it is a precipitate or not can be seen in the solubility table of the substance at the back of the chemistry book, if it is slightly soluble, insoluble is a precipitate.

Tell you 2 ways to remember:

1.Write it down according to the substance dissolution table at the back of the textbook.

Formula: 1. Solubility of salt.

Substances containing potassium, sodium, nitrate, and ammonium are all soluble in water.

Only AgCl is insoluble in water, and the others are soluble in water;

Only BaSO4 is insoluble in water, and the others are soluble in water.

Only K2CO3, Na2CO3, (NH4)2CO3 are soluble in water, and the others are insoluble in water.

2. Solubility of alkali.

The alkalis soluble in water are: barium hydroxide slag mupei, potassium hydroxide, calcium hydroxide, sodium hydroxide and ammonia, and other alkalis are insoluble in water. Fe(OH)3 is a reddish-brown precipitate, Cu(OH)2 is a blue precipitate, and other insoluble bases are white.

including Fe(OH)2) Note: AgCl and Baso4 in the precipitate are insoluble in dilute nitric acid, and other precipitates are soluble in acid. Such as:

Mg(OH)2 CaCO3 BaCO3 AG2 CO3 etc.

3. Most acids and acidic oxides can be soluble in water, (acidic oxides, water acids) most alkaline oxides are resistant to positive insoluble in water, and the soluble ones are: barium oxide, potassium oxide, calcium oxide, sodium oxide (alkaline oxide water alkali).

2.Do more questions, read more, and you will know naturally. Here's a list of common precipitations:

Salts: (white) agcl, baso4, baco3, ag2co3, cuco3, zn(oh)2, znco3, al(oh)3, mg(oh)2, caco3, blue precipitate cu(oh)2

Reddish-brown )Fe(OH)3 Please note: 2-valent iron ions are green, and 3-valent iron ions are yellow.

1. The scale in the kettle is caused by calcium carbonate deposition;

2. The rust in the iron pot is ferric oxide and ferric oxide deposits;

3. The dirt in the toilet bowl is calcium carbonate;

4. The combustion of materials such as paper or wood produces water and carbon dioxide;

5. Iron rust produces rust.

Then it depends on whether the ions can coexist.

First of all, you need to memorize the chemical formulas that precipitate, as well as the chemical equations that can produce gases, and understand their characteristics.

After that, it's easy, if the two chemicals are mixed and the ions are separated, if you can combine the insoluble precipitate, then you can generate a precipitate.

1. Judged by experimental phenomena.

2. Rote memorization.

Add the corresponding reagent to see if there is a reaction.