Super simple chemical equations, super not simple questions! 25

Ask a rhetorical question. Aluminum oxidizes in the air, and it only takes a dozen seconds to plant. If you first polish three aluminum sheets, then add hydrochloric acid to the first part, observe the phenomenon, and then add sulfuric acid to the second part, then it will be too late, and the surface will oxidize. How do you do that?

Also, talk about it. Even an oxide of aluminum can react with hydrogen ions. So it does not hinder the reaction of aluminum in acid.

But we do see passivation of aluminum in concentrated sulfuric acid. It's not that there is no reaction, but that the reaction speed suddenly becomes very slow, and we call this a "kinetic-dominated" reaction.

The phenomenon you observe should be that some kind of condition affects the reaction rate of the aluminum surface material and the dilute and concentrated sulfuric acid. It is advisable to have the opportunity to heat the reaction system, and you will find that if it is a little hotter, the reaction will go smoothly.

Passivation. Aluminum and iron react with concentrated sulfuric acid and concentrated nitric acid, forming a dense oxide layer on the surface of aluminum and iron, preventing the reaction from proceeding.

There are three reasons why it does not react with dilute sulfuric acid:1I didn't sandpaper it clean2The concentration of dilute sulfuric acid is not enough.

3.To heat.

Passivation occurs in concentrated sulfuric acid, as for dilute sulfuric acid, there may still be an oxide film, so the reaction is hindered, pure aluminum will definitely react with dilute sulfuric acid, there is no reaction here, only the presence of other substances may affect the occurrence of the reaction.

This is a troublesome experiment, theoretically, dilute hydrochloric acid and dilute sulfuric acid can react with freshly ground aluminum. In fact, if the concentration of dilute sulfuric acid is too low, the reaction is very slow, and it can be heated at this time, because the reaction of dilute sulfuric acid with zinc is also (slower than this); If the concentration of dilute sulfuric acid is too high, passivation may occur, and this concentration is difficult to control. The reaction with concentrated sulfuric acid will be passivated, and a dense oxide film will be formed that will hinder the continuation of the reaction.

In fact, it can be thought of as this, even if aluminum reacts with the limited hydrogen ions of dilute sulfuric acid, the generated aluminum ions will be hydrolyzed, and the hydrolyzed hydroxide will inhibit the continuation of the displacement reaction.

I remember that there was a chemistry competition question...

The reaction of aluminum and iron with concentrated sulfuric acid and concentrated nitric acid creates a dense oxide layer on the surface of aluminum and iron, preventing the reaction from proceeding.

The reasons for not reacting with dilute sulfuric acid may be:

1.It was not sanded with sandpaper, and there was an oxide film on the aluminum surface that hindered the reaction.

2.The concentration of dilute sulfuric acid is not enough, and there are not enough hydrogen ions in the solution to allow aluminum to replace to produce hydrogen gas.

Dilute sulfuric acid in sufficient concentrations reacts with pure aluminum without heating.

Wow! It's amazing! Because it changes so strongly that you can't see it!

Fe + 2O2 = ignition = Fe3O4 . Burns violently, sparks in all directions, and generates a black solid. Spread fine sand or a small amount of water to prevent high-temperature splashes from bursting the cylinders.

2. CO2 + Ca(OH)2=H2O+CaCO3 (precipitation H2O2=MNO2=2H2O+O2 (gas) 2KCLO3=MNO2 heating = 2KCl + 3O2 (gas) 2kmNO4 = heating = K2Mno4 + MNO2 + O2 (gas) 4, CaCO3 + 2HCl = CaCl2 + H2O + CO2 (gas).

3Fe+2O2=Fe3O4 Sprinkle to prevent the beaker from being damaged by high temperatures.

2 Kick to see if there is too much carbon dioxide?

(Ignited) sparks, the walls of the bottle heat up, producing a black solid. The sand spread is to prevent the bottom of the flask from breaking if it comes into contact with the overheated product.

precipitation) + H2O (CO2 insufficient).

CO2 + CaCO3 + H2O = Ca(HCO3)2 (CO2 excess) gas) (mNO2 catalysis).

2kClO3==2kCl+3O2 (gas) (mNO2 catalyzed and heated) 2kmNO4 = K2mno4+mno2+O2 (gas) (heated) 4CaCO3 + 2HCl = CaCl2 + H2O + CO2 (gas).

cu+2h2so4=cuso4+2h2o+so2n(so2)=

So the reacted H2SO4 is , and the unreacted H2SO4 is n(H2SO4)=c*v=7*, so originally n(H2SO4)total=

So the original c(h2so4)=

To earn points! The next thing is useful!

Since it's super easy, answer it yourself.

The error is the largest, so it is removed.

Because it is a millimeter scale.

Therefore, it is also necessary to give it up.

Average the rest as, choose a

A: I think it's A

First of all, the millimeter scale is excluded, and one more person is estimated).

Closest to analysis: The fourth data has to be discarded.

First of all, because this is a millimeter scale, the data should be the effective value + the estimated reading of the next digit, then the data should be rounded, and the obvious error should also be rounded, there are still 3 data left, add them up, and then divide by 3, the result should be A

The true value of the five data three times is nearby, so C&D is excluded, and the two estimations are read as, so the true value is the closest, that is, option A.

I think to choose A, first of all, because the ruler can't read three decimal places, the remaining numbers, only one is too far away from the other three numbers, don't want it, the remaining two are so choose A

(1) Insoluble salts are prepared from soluble alkalis.

Ba(OH)2+Na2SO4=2NaOH+BaSO4 (2) Insoluble salts are prepared from acids.

BaCl2 + H2SO4 = BaSO4 + 2HCl (3) oxide is prepared from salt.

CaCO3 = High temperature = Cao + CO2

4) There is a metathesis reaction of oxide generation.

NaOH + HCl = NaCl + H2O (water is an oxide) (5) only produces the reaction of gas and water.

H2CO3 = Heating = CO2 + H2O