The following substances can undergo chemical reactions, and the mass of the solution is reduced aft

The mass of hydrogen produced in a is smaller than that of iron, so the mass of the solution increases.

The solution of copper and zinc sulfate in b does not react, so the quality of the solution remains unchanged.

The iron in the iron and copper chloride solution in c is smaller than the zinc mass, so the mass of the solution decreases.

No gas or precipitate is formed, so the mass of the solution remains the same.

So choose C and wish you progress in your studies!

Answer a...Except for a gas that is released and the mass of the solution is reduced, everything else is in the solution and there is no precipitation and gas.

So the mass of the solution does not change.

Problem solving ideas: a. Iron and dilute sulfuric acid, iron replaces the hydrogen in sulfuric acid and turns the solution into ferrous sulfate solution;

b. Add dilute nitric acid to potassium hydroxide solution, and the solution will gradually become potassium nitrate solution;

c. Iron sheets are added to the copper sulfate solution, and the iron sheets replace the copper in the copper sulfate to make the solution become ferrous sulfate solution;

d. When calcium hydroxide solution is mixed with potassium carbonate solution, calcium hydroxide reacts with potassium carbonate to form calcium carbonate precipitate, and the solution becomes potassium hydroxide solution

a. After iron is mixed with dilute sulfuric acid, iron replaces the hydrogen in sulfuric acid to form ferrous sulfate solution, and the mass of dissolved iron is greater than the mass of hydrogen released, so the mass of the solution increases after the reaction, so a is incorrect;

b. Potassium hydroxide reacts with nitric acid to form potassium nitrate and water, and the quality of the solution is not lost, so the quality of the solution will continue to increase with the addition of dilute nitric acid after the reaction, so B is incorrect;

c. Iron replaces the copper in the copper sulfate solution and changes the solution to ferrous sulfate solution, according to the chemical equation, it can be seen that the mass of dissolved iron is less than the mass of precipitated copper, so the mass of the solution decreases after the reaction, so C is correct;

d. Calcium hydroxide reacts with potassium carbonate to form calcium carbonate precipitate, and the mass of potassium ions increased in the solution is greater than the mass of precipitated calcium ions, so the mass of the solution increases after the reaction, so D is incorrect;

Therefore, c: Comments:

Test points for this question: Metal activity sequence and its application; chemical properties of the acid; The Law of Conservation of Mass and Its Applications

Test site comments: According to the change of solution composition before and after the reaction, the change of the solution quality before and after the reaction is judged by the comparison of the dissolved mass and the precipitated mass

The answer should be b, the question is about the quality of the solution before and after the reaction, and the chemical reaction follows the law of conservation of mass (the specific reaction formula will not be written, I am not very good at typesetting...).

a。Before the reaction, the solution is dilute sulfuric acid, and after the reaction, the iron sheet is dissolved in dilute sulfuric acid and becomes a mixed solution containing ferrous sulfate, and H2 is precipitated. The mass of the iron dissolved in it is much greater than the mass of the hydrogen that is spilled. So the mass of the solution after the reaction becomes larger.

b。The iron sheet is immersed in copper sulfate solution, and the displacement reaction occurs, and the elemental copper is precipitated, and the ratio of the amount of iron to copper before and after the reaction is 1:1. The relative molecular mass of copper is greater than that of iron, so the mass of the solution after the reaction decreases.

c。The products after the reaction are in solution. So the mass becomes larger.

d。Sodium bicarbonate is added to dilute hydrochloric acid to produce carbon dioxide gas, and the carbon dioxide in the whole reaction comes from sodium bicarbonate, and it is not difficult to understand that the mass of the solution increases after the reaction.

So choose B

option A, because Fe is dissolved into the solution, the solution mass increases.

Option b. Iron dissolves, precipitates copper, enters Fe with a mass fraction of 56 and precipitates copper with a mass fraction of 64, so it decreases.

c option. There is no change, neither precipitation nor gas.

d option. Naci H2O is left after the reaction. CO2 Escape... Judging by the quality score. The solution still increases.

To sum up, I hope it will help you.

Select BFE+H2SO4=FESO4+H2

56 2 The mass of the solution increases.

fe+cuso4=feso4+cu

56 64 The mass of the solution decreases.

The mass of Fe2O3+HCl=FeCl2+H2O solution remained unchanged, and the mass of NaHCO3+HCl=NaCl+H2O+CO2 73 44 increased.

Only after the B reaction, due to the substitution of Cu2- with Fe2-, the mass decreases, and the products of other reactions increase in solution.

The following information is provided about the possibility that the quality of the solution obtained after the reaction may remain the same compared to before the reaction.

The mass of the solution obtained after the reaction may remain unchanged compared with the mass of the solution before the reaction, because the reaction of zinc with silver nitrate reduces the mass of the dissolved oak and increases the mass of the solution when it reacts with ferrous nitrate, so the mass of the solution may remain unchanged. Therefore, the reaction of zinc with silver nitrate reduces the mass of the solution, and when it reacts with copper nitrate, the mass of the solution increases, so the quality of the solution may not change.

Answer A analysis: According to the law of conservation of mass, if no precipitate and gas are formed after the metathesis reaction between acids and alkalis, the mass of the solution may remain unchanged or increase; The reaction between metals and acids and salts should be analyzed and compared with the quality of the hydrogen and metal displaced

Answer: a. After the magnesium strip is mixed with dilute sulfuric acid, the magnesium replaces the hydrogen in the sulfuric acid to form a magnesium sulfate solution, and the mass of the dissolved magnesium is greater than the mass of the released hydrogen, so the mass of the solution increases after aging; Therefore, the option is correct

b. The reaction of sodium chloride solution and silver nitrate solution will generate silver chloride precipitate, and the quality of the solution will decrease, so the option is wrong

c. After the reaction of dilute sulfuric acid and sodium hydroxide solution, no precipitation and gas are formed, and the quality of the solution remains unchanged, so the option is wrong

d. The sodium carbonate solution can react with dilute hydrochloric acid to generate carbon dioxide gas, and the quality of the solution will be reduced, so the option is wrong

Therefore, choose a Comment: This question examines the connotation and application of the law of conservation of mass, and pays attention to the fact that the quality of the solution does not include precipitation and gas To judge the change in the quality of the solution after the reaction, first consider the quality of the solution before the reaction, and then see if there is gas and precipitation after the reaction

aa naoh+hcl=nacl+h2o

Neither gas nor precipitation is generated, so the mass of the solution is not reduced.

b They do not react, so they cannot be chosen.

b will generate baso4 white precipitate and the quality of the solution will change.

A: The relative molecular mass of copper is 65, and silver is 108, so the copper wire is put into the silver nitrate because the activity of copper metal is stronger than that of AG, so the silver will be replaced, and it will become copper ions dissolved in water, and the silver will not be included in the solution mass after becoming a precipitate, so the solution mass will be reduced.

B: Carbon dioxide reacts with clarified lime water to form a precipitate, so that after the solute becomes a precipitate, the mass of the solution decreases.

C: The ion equation is: Na2CO3 + 2H + ====2Na + H2O CO2, it can be seen that whenever a carbon dioxide molecule runs out of the solution, there are 2 sodium ions and an oxygen atom that become part of the solution, (the oxygen atom refers to the oxygen atom in the water molecule, which was originally in sodium carbonate), so the difference between one gain and one loss is 2 23 16 44 (the relative molecular mass of carbon dioxide) >0, and the gain is greater than the loss, so the mass increases.

D: The answer is uncertain, the concentration of silver nitrate is uncertain.

D belongs to the neutralization reaction of B, C and D, but the mass of the solution remains unchanged after the B reaction, only D reduces the total mass of the solution due to the formation of precipitation.

dFirst, acid and alkali are called neutralization.

Second, BaSO4 precipitates and the total mass decreases.

d.There are both hydrogen ions and hydroxide ions that react, and precipitation is generated.

Analysis: 1. When the reactants are all solutions and the products have neither precipitation nor gas, the mass of the solution before the reaction is equal to the mass of the solution after the reaction.

2. When the reactants are all solutions and the products have precipitation or gas production, the mass of the solution before the reaction is greater than the mass of the solution after the reaction.

3. When one reactant is a solution and the other is a solid, the product has precipitation or gas. It is necessary to compare the mass ratio of the solid in the reactant to the gas in the product according to the chemical equation, if "large for small", the mass of the solution before the reaction is greater than the mass of the solution after the reaction, and vice versa, the mass of the solution before the reaction is less than the mass of the solution after the reaction.

Now seated, ASodium hydroxide solution and dilute hydrochloric acid belong to the first case; b.Sodium carbonate solution and dilute hydrochloric acid belong to the second case; c.Water and dilute sulfuric acid do not undergo chemical changes, none of the three; d.This is the third case.

So the answer is (b, d).