Why should the test tubes used for the silver mirror reaction experiment be washed with hot NaOH sol

The first test tube used for the experiment should be washed with dilute nitrate pickling, and the only commonly used acid that can dissolve silver is nitric acid. Before the test, because I was afraid that the grease on the glass would adhesion and affect the formation of the silver mirror, I washed it with hot Naoh.

Second, because the concentrated ammonia is not easy to control, the preparation of silver ammonia solution is to dissolve the precipitate to the best of the last drop of ammonia.

Addendum: Do you think you can still put something on the glass if there is oil on it?

In addition, the problem that they said is easy to produce ** silver azonate is actually not a big problem, because only the silver ammonia solution that has not been used for a long time will be produced, and it will be nothing if it is cleaned after the experiment.

As for why you should use hot water, don't you think that hot water is better to wash dishes to remove oil? Of course, it enhances the effect of oil hydrolysis!

Besides, you can't just divide the questions into several questions! You're also lazy to ask so many questions in one question. Commonly used cleaning agents are stearates, alkyl sulfonates, etc., because most of them are sodium or potassium salts, so they are hydrolyzed into alkaline.

I don't want to say any more, Baidu on a bunch.

The silver mirror reaction must be done with an absolutely clean test tube. Washing with sodium hydroxide is to remove the oil stain on it, otherwise the reduced silver will not be deposited into a flat silver mirror.

Destroy the silver ammonia solution to form a precipitate. Prevent conversion into ** silver thunderate.

When configured, it is easy to use concentrated ammonia to make OH- excessive, which affects the presence of complexes and makes the poor quality of the silver produced turn black.

Washing with hot NaOH solution is to keep the tubes alkaline, and an alkaline environment is required for the silver mirror reaction.

It is difficult to prevent excess with concentrated ammonia, and it is easy to form explosive silver azide.

Concentrated ammonia is volatile and has a very unpleasant smell

If you are in a place with ammonia for a long time, it will be very itchy.

The tubes after the silver mirror reaction are washed with hydrochloric acid solution. The silver mirror reaction is a chemical reaction in which the solution of silver compounds is reduced to metallic silver, and it is called the silver mirror reaction because the metallic silver produced is attached to the inner wall of the container and is as bright as a mirror.

A common silver mirror reaction is a silver-ammonia complex.

Ammonia-silver complexes.

Also known as Toren's reagent) is reduced to silver by aldehydes and oxidized to the corresponding carboxylic ions, but in addition, certain silver compounds (such as silver nitrate.

It can also be reduced by reducing agents (such as hydrazine) to produce a silver mirror.

Add 1ml of 2% silver nitrate solution to a clean test tube, then add sodium hydroxide aqueous solution, and then shake the test tube while the black precipitate can be seen. Then drop 2% dilute ammonia water drop by drop until the initial precipitate happens to dissolve (the resulting solution is called silver ammonia solution).

Silver mirror reaction of acetaldehyde: 3 drops of acetaldehyde are dropped, and the test tube is warmed in hot water after shaking. Soon you can see that a layer of metallic silver is attached to the inner wall of the test tube, which is as bright as a mirror. (During this process, do not shake the tube, otherwise you will only see a black precipitate without a silver mirror.) ）

This layer of black substance is still silver, but it is not well adhered to, and it becomes fine particles, which look black.

This is because when the silver adheres evenly to the surface of the test tube, it forms a smooth flat surface, and the reflection of light is very regular. When silver is scattered in the solution in the form of small particles, the direction of reflection of light on each small particle is very scattered, and it looks black.

Shaking can cause the silver to not adhere well to the walls of the tube. This will also affect the results of the experiment.

Because the product is ag after the silver mirror reaction, it will be adsorbed around the test tube, and it is not easy to wash with water, because silver is an inactive metal and cannot react at room temperature and pressure.

If silver is used as the anode of the electrolytic cell, and sodium hydroxide is used as an electrolyte solution, then the two react.

Anode: 2AG

2e(-)2oh(-)

ag2oh2o

Cathode: 2h (+).

2e(-)h2↑

Total reaction: 2ag

H2O === (Condition: Electrolysis, NaOH) Ag2O

H2 So I don't think that the test tube that has been done with the silver mirror reaction can be washed with a hot sodium hydroxide solution, I think it should be done with concentrated and dilute nitric acid.

3AG+4HNO3 (dilute) = 3AGnO3+NO +2H2O2AG+4HNO3 (concentrated) = 2AGnO3+2NO2 +2H2O

After the experiment, do not wash with sodium hydroxide at all, clean with dilute nitric acid, and wash the test tube with a hot sodium hydroxide solution before doing the silver mirror reaction.

Probably because the solubility of silver ions increases at high temperatures, they react with sodium hydroxide to form silver hydroxide, and because of high temperatures, they decompose into silver oxide. Silver is a highly soluble metal (compared to other metals such as iron and copper).

The landlord is wrong, it is to wash with hot sodium hydroxide before doing the silver mirror reaction, in order to get out the acidic impurities, and the test tube that has done the silver mirror reaction should be cleaned with dilute nitric acid!

Used to wash test tubes Otherwise granular silver will form.