Asked a chemistry question which stumped our teacher .

Strictly speaking, this question is not rigorous.

The meaning of the answer is: if A is more acidic than B, then the ionization of H+ in the solution is more than B, so when the pH of the two is the same, the volume of A will be more than B when neutralizing the equivalent amount of OH-.

For example, hydrochloric acid and acetic acid with pH=2, hydrochloric acid is completely ionized, and acetic acid is partially ionized, then the concentration of hydrochloric acid should be 10 negative quadratic per liter, and the H+ concentration ionized by acetic acid is already 10 negative quadratic per liter, and the unionized H+ is in solution in a molecular state. When they neutralize the same amount of OH-, the volume of HCl consumed must be greater than the volume of acetic acid consumed.

When both are strong acids, the acidity is also judged according to this, that is, although HCI and HBR are both strong acids, the degree of ionization of hydrochloric acid is still greater than that of hydrogen bromide. It's just that the difference between the two is very small and negligible.

Therefore, this question is not rigorous.

For the second question, it cannot be explained in this way.

Because Hno3 is more acidic than HCI, it is not because of the high degree of ionization, but because the N in nitric acid has extremely strong oxidizing properties. The rate of dissolution of CaCO3 is determined by the concentration of H+. Therefore, the rate of dissolution of CaCO3 is the same, and CaCO3 is not soluble in water, the contact area is limited, and the "advantage" of Hno3 being more acidic than HCI may not necessarily be brought into play.

Does that make sense??

Don't get into the nitty-gritty, the language of the current answer books is not rigorous, and the answers are often good and the answers are rubbish. Reading these books requires the ability to correct mistakes.

1. Choose B, because only the "Carbon-12 atom has a relative atomic mass of 24" in B, and the carbon-12 atom is limited by the original title condition and can be determined, and the other three terms contain other undefined elements, and there are isotopic uncertainties.

2. Select the exact value of b x or y in order to determine the relationship between other quantities and calculate.

3. The method is (add a sufficient amount of existing soapy aqueous solution to the four solutions to be tested, and the order of at least the resulting precipitate is: 1% mgCl2 solution; 1% CaCl2 solution; CaCl2 solution ; Distilled water. ）

In fact, no precipitate is formed in distilled water. This order is due to the fact that the number of Ca ions or Mg ions in these four solutions to be measured is at least ranked by the most. The same is 1% MgCl2 solution and CaCl2 solution, because the atomic mass of Mg ions is smaller than that of Ca ions, the number of Mg ions is greater than that of Ca ions.

The number of Ca ions in the CaCl2 solution of " is of course less than the number of Ca ions in the CaCl2 of "1%".

A word of caution in advance, Ha ......I'm just a freshman in high school, so I'll talk about whether I'm right or not, and I'll just talk about my personal opinion......

The isotopes of oxygen should change, after all, the number of neutrons is different.

B: This shouldn't change.

C: I don't think this will change (he doesn't seem to say a few sulfuric acid......It may be a mistake in the statement, I don't know about this)

D: The pressure will definitely change depending on the temperature.

2.Every 2 3valent metal atoms lose 6 electrons, and every 6 hydrogen ions gain 6 electrons to produce hydrogen, so the ratio of the metal to the amount of hydrogen-forming substances is 1:3, and in the same way, the bivalent is 1:

1, the price of one is 2:1 ......So, let's look at the answer again: first of all, D is definitely not right (it has nothing to do with the concentration of acid, anyway, it is excessive), B should not be (if you only know X and Y, you can't do it in the next step, and the reaction formula is not equal) After that, you can see that the valency of metal A is MX M, and B is ...... Ny N(according to the conservation of electrons) so.

The ratio of the valency of the two metals is mxn nym (which is important) and because of the ......The title says "at least", so the values of m and n should be known, so the values of m and n are important. So ......Choose C

3.Distilled water is certainly simple, and non-foaming is definitely it; The lower concentration of CaCl2 is definitely simpler, and the least precipitated must be; As for the same concentration of CaCl2 and MgCl2, it ......I quite agree with the opinion upstairs: the same 1% MgCl2 solution and CaCl2 solution, since the atomic mass of the Mg ion is smaller than the Ca ion, the number of Mg ions is greater than the Ca ion.

However, you should ensure that the density of the solution is the same at ......the same temperature and concentration

Hmmm......That's it, if it's wrong, don't spray ...... if you don't like it

The first question is the relative molecular weight, the change of carbon 12 is relative to the change of molecular weight, and the relative molecular weight of other molecules changes based on it. Only the mass of the carbon atom is not based on it, so it does not change. Pick B

I only figured out question 2, choose b

Fe elemental and Fe3+, Cu2+ in the solution reaction to form Fe2+ and Cu element, the solid residue must contain Cu element, and the solid residue is treated with hydrochloric acid, and there is gas release, indicating that there is Fe element. The above can obtain an excess of Fe element, and the Cu2+ reaction is complete. Therefore, the most ions in the solution are Fe2+, so B is chosen

1. The starch blue color just fades.

Cu2+ +4 i- = cui i23, by titration reaction equation.

2 na2s2o3 + i2 = 2 nai + 2 na2s4o6· x

So the amount of matter of i2 x = 2 = mol consists of 2 cu2+ +4 i- = cui i2y mol so cu2+ amount of substance y = * 2 = molCuCl2·2H2O amount of substance = mol, mass = * 171 = mol

Mass Score = =

(3) Starch aqueous solution The solution changes from colorless to blue and does not fade for half a minute 2 divalent copper ions (the chemical formula is not easy to write, forgive me) + 5 iodine negative ions = 2cui + iodine trianion.

2S2O3 2- + Iodine trianion = S4O6 2- +3I-2 1N(I3-) =

2cu2+ +5i- = 2cui↓ +i3-2 1

nn(cu2+)=

m(cu2+)=

m(cucl2) pure =

Percentage = (There seems to be a discrepancy.)

Do this question.

First of all, it is necessary to clarify a guiding idea: since the mass of Na is, the conversion is, so the final generation is 4G (Na-NaOH can be calculated) NaOH, so the mass of the solute is equal. Then the magnitude of the mass fraction of the solute will depend on the mass of the solution.

Then, the chemical reaction that occurs after these substances are dissolved in water is analyzed, and the greater the mass of which substance increases the solution, the larger the mass concentration denominator, and therefore the smaller

2Na - 2H2O - 2NaOH - H2 A Na2O - H2O - 2NaOH B.

Na2O2 - H2O-2NaOH - (1 2)O2 Propylene is added to generate hydrogen and escape, and the solution increases the mass.

With the addition of Na2O (i.e., sodium oxide), no gas escapes, and the mass of the solution is net increased.

The Na2O2 (i.e., sodium peroxide) added by C. oxygen escapes, and the mass of the solution is net increased.

Ding was added, directly dissolved in water, and the mass of the solution increased by 4g.

The third step is to compare the size of the increase in the mass of the solution, and the fourth step is D, C=B, and the fourth step, according to the larger the mass of the solution, the smaller the solute mass fraction, then there is D: C=B, and A chooses B

Question 4.

The answer is C, yes.

a's water made an oxidizing agent.

b Reaction is non-redox.

C is the redox reaction, but the reaction is a disproportionation reaction, and Na2O2 is an oxidant and a reducing agent, and D is a non-redox reaction.

The c in the fourth question is the disproportionation reaction of sodium peroxide, the valency of oxygen in sodium peroxide is -1 valence, and after the reaction, oxygen and water are generated, which become 0 valence and -2 valence respectively, and the water in the reactant is only equivalent to the reaction to the final generation of sodium hydroxide, and there is no change in valency. Sodium peroxide is both an oxidizing agent and a reducing agent. Water does not undergo redox reactions.

Got it? If you are satisfied, please like it, thank you!

Question 5: Choose B

200 ml of water, definitely excessive. Since the added sodium is of the same mass, all the sodium remains in the beaker at the end. That is to say, the solute in the four beakers is all sodium hydroxide, so the solute in the four beakers is equal because the sodium ions and hydroxides are 1 to 1.

So to compare the mass fraction, as long as you compare the amount of water in the final beaker, the more water, the lower the mass fraction. Note that the water may react with the additives or turn into some other gas, so that the amount of water is less.

Sodium oxide and sodium hydroxide are added to water, and all substances only go in and out, and sodium oxide goes in and reacts with water, so B&D. The extra oxygen atoms in C just turn into oxygen and run away, which is the same as B, so B = C. As for the nail, sodium turns the hydrogen element in one part of the water molecule into hydrogen, and the other part takes away the hydroxide group, which further reduces the water molecule, so the mass fraction in the nail is the largest.

In the end it was BA" B = C "D".

4. Choose C. The analysis is as follows:

A, during the reaction, the h element in the water decreases from +1 valence to zero valence in H2.

b. In the reaction process, there is no rise and fall of the valence of the elements.

c. When water reacts with sodium peroxide, only the -1 valence oxygen in sodium peroxide loses both electrons and electrons, and the hydrogen and oxygen elements in the water do not gain and lose electrons, so the C term is in line with the topic;

d. Sulfur dioxide reacts with water, without gaining or losing electrons, and is not a redox reaction.

5. When the four substances of Na, Na2O, Na2O2 and NaOH in the title are dissolved in water, the first three react with water, and the relationship and analysis are as follows:

2Na - 2H2O - 2NaOH - H2 A.

Na2O——H2O——2NaOH B.

Na2O2 – H2O—2NaOH – (1 2)O2 C.

Analysis: Ding and NaOH were directly dissolved, no water was consumed, and after dissolved in water, the mass of water was the largest, and the mass fraction of solute was the smallest;

In A, B, C, the amount of solute is the same, while the amount of water consumed in A is the largest, and after the reaction, the amount of solvent is the least, and the mass fraction of solute is the largest;

In B and C, the amount of water consumed is the same, and after the reaction is over, the amount of solvent is also the same, and the mass fraction of the solute is the same.

From the above analysis, it can be seen that the mass fraction of the solute is:

A" B = C "D".

As you can see, the correct option is b.

It's okay, it's fun.