Chemical gas identification questions for junior high school, chemical identification questions for

First of all, the smell is definitely wrong, unless it is to be poisoned. In addition, the above gases are colorless.

1. Combustion, what cannot be burned is ammonia and nitrogen (in the air). What burns in oxygen is ammonia.

2。The rest of the water is methane and hydrogen, lime water, and cloudy methane.

3. What does not produce water is carbon monoxide.

Smell first, the smell is ammonia, the rest is covered with a beaker on the ignition, the non-burning is nitrogen, the burning on the beaker wall without water beads is co, and then pour lime water into the beaker with water mist, and the turbidity is methane.

Calciferous copper oxide and clarified lime water can distinguish carbon monoxide and hydrogen--- can reduce copper oxide, carbon monoxide can make the clarified lime water turbid, and hydrogen has water droplets.

Odor identification: Ammonia or moist litmus test paper, ammonia is alkaline and turns blue.

Nitrogen and methane can burn methane.

Nitrogen can be found from the color, ammonia can be found from the smell, and the rest is burned, and a beaker with clear lime water on the inner wall is covered with it, only the water droplets are hydrogen, the water droplets are cloudy is methane, and the only thing that becomes cloudy is carbon monoxide.

Because NaOH+HCl=NACl+H2O, NACl must be there! However, sodium hydroxide hydrochloric acid may be excessive, choose a, you can use 2 methods:

1: Elimination method: Because B substances can not identify whether hydrochloric acid is excessive, but can identify whether sodium hydroxide is excessive, C, D sodium hydroxide and hydrochloric acid can not identify whether it is excessive, (no phenomenon), so choose B

2: positive selection method: colorless phenolphthalein can identify whether sodium hydroxide is excessive, if it turns red, sodium hydroxide is excessive, if it does not turn red, then add sodium carbonate solution, there are bubbles to produce hydrochloric acid excess, if not, it just reacts.

Pure hand hit.

Select a sodium hydroxide and hydrochloric acid to react to produce sodium chloride and water, sodium chloride must be there, but it is not necessarily a good reaction.

Phenolphthalein test solution can be added first, if it turns red, sodium hydroxide is excessive, if it does not turn red, then sodium carbonate solution is added, and if there are bubbles, hydrochloric acid is excessive, if not, it is just the reaction.

A indeterminate solute is sodium hydroxide or hydrochloric acid. So the essence of this question is how to test the presence of sodium hydroxide and hydrochloric acid. According to the difference in the properties of the two substances.

The sodium hydroxide solution is alkaline, and the phenolphthalein test solution turns red. But hydrochloric acid does not. Hydrochloric acid plus carbonate has bubbles, sodium hydroxide does not.

There must be sodium chloride, which does not interfere with their inspection, so choose A.

A, uncertain is either HCL or NAOH, if there is NAOH alkaline, use phenolphthalein to identify, if there is HCL with sodium carbonate.

A NaOH is also known as caustic soda, caustic soda, etc., which is easy to absorb CO2 in the air and deliquescent. NaOH reacts with CO2 to form Na2CO3. Since the amount of hydrochloric acid is uncertain, it is possible that sodium carbonate remains after the hydrochloric acid reaction.

1.Distinguish between water and hydrogen peroxide solutions.

Hydrogen peroxide is hydrogen peroxide, and manganese dioxide is used as a catalyst to produce oxygen. In this way, it is natural to think of using manganese dioxide for identification, because hydrogen peroxide meets manganese dioxide and releases oxygen. Water, on the other hand, does not, but only by electrolysis.

2. Just ignite it in oxygen.

3. Add silver nitrate to the two bottles of reagent, and if there is precipitation, it is salt water. It's okay to smell, but you have to "fan into your nose" (standard operation)!

Hope you understand! Thanks, I'm on a task.

1.Manganese dioxide.

2.Hydrogen peroxide solution.

3.Sniff. In short, there are many ways to identify them, and it is best to think about them often.

Scheme A (because the sodium hydroxide solution is introduced into B first, and then the concentrated sulfuric acid is introduced, and a small amount of water vapor is brought into the concentrated sulfuric acid when the sodium hydroxide solution is introduced, so the A scheme is correct) Because the concentrated sulfuric acid is heavier, there must be methane (because there is hydrogen in the methane), and because the first step is to clarify the lime water is not turbid, the gas must have no carbon dioxide, so it is necessary to prove whether carbon monoxide exists. From the third step, it can be seen that the gas is burned to produce H2O and CO2, assuming that the gas is all methane, CH4+4O2=(ignition)=CO2+2H2O

m solution gives m = which corresponds to the mass of the gas, so the composition of the gas is methane.

A correct. Scheme B: The gas will carry the water vapor in the sodium hydroxide solution into the concentrated sulfuric acid.

a, composed of carbon monoxide, methane.

The first step is to prove that there is no carbon dioxide.

The second step is to prove that the gas composition is only methane or methane and carbon monoxide, which means that there must be methane.

The third step is to further prove the presence of carbon monoxide. In scheme B, if the gas passes through the sodium hydroxide first, the water in the product will enter the solution, or the gas will carry the water into the concentrated sulfuric acid, or the concentrated sulfuric acid will absorb the water in the sodium hydroxide solution along the direction of the gas flow. In scheme A, concentrated sulfuric acid absorbs water first, and carbon dioxide is absorbed through sodium hydroxide solution, then the problem in scheme B will not occur.