The following methods can change the solute mass fraction in the solution .

Answer: AABecause the saturated solution is cooled down. The solubility of salt in general will be reduced. As a result, crystals are precipitated. And the quality of the water has not changed. As a result, the dissolved salt is smaller. So the quality score has changed!

b.Warm up the solution of ordinary salts. will increase his solubility.

And the solution that is already saturated becomes unsaturated. And there is no salt to dissolve in the outside world. If the temperature does not reach the boiling point of water, the quality of the water does not change.

Therefore the b is unchanging!

c.If you evaporate at a constant temperature, there will be less water. But at the same time.

Because it is a saturated solution, the salt will also precipitate. At the junior high school level, the saturated solution of salt here is generally considered saturated all the time. Even if it heats up, it is saturated.

So it doesn't change. You know, in fact, it's changing.

d.Because it's already saturated. It's useless to add more. It doesn't change. It will only sink below the solution on the outside.

Answer: AA: The solubility of ammonium chloride increases with the increase of temperature, and the mass fraction decreases when it cools down, because the mass fraction of saturated solution = s (100+s) * 100%.

b: The solubility of potassium nitrate increases with the increase of temperature, and the mass of the solute and solvent remains unchanged when the temperature rises, so the mass fraction remains unchanged.

C: The saturated solution of sodium chloride evaporates at constant temperature, although the solvent becomes smaller, and the solute is precipitated at the same time, but the solubility remains unchanged, because the mass fraction of the saturated solution = s (100+s)*100%, so it does not change.

D: It's similar to the C principle, but it doesn't change.

Just change the solubility of the solution.

d is already a saturated solution, and it will not dissolve again with the addition of sucrose.

c. Evaporation at a constant temperature, and water is reduced.

Answer: Analysis: Changing the mass fraction of solute is mainly from two aspects: changing the solute mass and changing the quality of the solvent (solution) (1) Changing the solute mass:

The solute mass fraction increases with the increase of solute mass, but the increase in solute mass is not necessarily proportional to the multiple of the increase in solute mass fraction.

If you want to increase the solute mass fraction of a solution, you can often use the following methods for source nuclei

Adopt methods of increasing solutes; If the method of evaporating solvent is used; Raise or decrease the temperature to increase the solubility of the substance

So the answer is: increase solute; evaporation dissolution Zheng agent; Increase or decrease the temperature

The mass fraction of a solution refers to the ratio of solute mass and mass of solution in solution, ie.

Post-variant: <>

The mass fraction of a solution refers to the ratio of solute mass to mass of solution in solution.

That is: solute mass fraction = solute mass solution mass * 100%;

After the variant, it is obtained: solute mass = solution mass * solute mass fraction;

Solution mass = solute mass solute mass fraction.

In fact, it is a variation of the formula, where the mass of the solute is equal to the mass of the solution multiplied by the mass fraction of the solution; The mass of the solution is equal to the mass of the solute divided by the mass fraction of the solution.

The mass fraction of a solution refers to the ratio of solute mass to solution mass in solution, i.e., solute mass or solution mass obtained after fractional variation.

When measuring water with a graduated cylinder, looking up at the scale marks on the water surface to read the volume will cause the water to be taken more, making the solution thinner, so it will be smaller;

When weighing the solid, the weighed object should be placed on the left plate, and the actual mass should be weight-to-game code when it is reversed, resulting in a decrease in solute, so it is small;

After cleaning the beaker, a small amount of water remains in the beaker, which will also increase the quality of the water, and the mass fraction is small Therefore, the answer is: when measuring water, look up at the reading; When weighing solids, the weights and solids are reversed; Clean the beaker and there is a small amount of water left in the beaker

Answer D analysis early Danhe: The saturated solution is the maximum amount of solute dissolution at a certain temperature, therefore, when the solute solid is added again, it will not be dissolved again So the quality of saturated salt water in A will not change and the solute in B is calcium hydroxide, which can react with carbon dioxide in the air to form insoluble calcium carbonate, therefore, the mass of the solution in B decreases (according to the chemical equation comparison, The mass of calcium carbonate is more than the mass of the absorbed sulfur dioxide) and when the potassium nitrate saturated solution is raised to temperature in C, it will only become an unsaturated solution, but the mass of the solute and solvent will not change, so the mass of the solution will not change In the D term, after adding sucrose to the sucrose solution, the sucrose is dissolved, therefore, the mass of the solute increases, and then the mass of the solution also increases

Select C, potassium nitrate saturated solution heats up, because the amount of potassium nitrate is fixed, so he does not change, and the sodium chloride saturated solution is evaporated at a constant temperature: the amount of solvent is reduced, and the amount of NaCl is also reduced, and finally it is saturated sodium chloride solution, so he also remains unchanged.

The sodium chloride saturated solution is cooled, and the cooling of the solution causes the solubility of NaCl in water to decrease, and NaCl is precipitated, while the volume of the solvent remains unchanged. So the solute mass fraction in the solution changes.

Add a small amount of sucrose to the saturated solution of sucrose: other conditions do not change, and when saturated, it no longer dissolves.

Option C Decrease the temperature of potassium nitrate solubility A is not true.

cThe solubility of the saturated solution decreases after cooling (although the solubility of sodium chloride does not change much with temperature, it still decreases), so a small amount of sodium chloride will be precipitated, so that the solute mass fraction will decrease.

c When the temperature is cooled, sodium chloride will be precipitated.

a (100*10%+10) empty mu 100 + 10 = b 100 * 10% Judgment 50 = 20%.

c 20/(20+100)=

d 20/(100*

Therefore, B is the most fighting and punching.

bc。The amount of sodium, sodium oxide, and sodium peroxide is respectively, and sodium hydroxide is. The equations for the reaction of sodium, sodium oxide, sodium peroxide, and water are as follows:

2Na+2H2O 2NaOH+H2, the mass of the solution Na2O+H2O2O2, the mass of the solution 2Na2O2+2H2O=4NaOH+O2, the mass of the solution Add sodium hydroxide to water, the mass of the solution is 50g

According to the conservation of sodium atoms, the amount of sodium hydroxide obtained by sodium, sodium oxide, sodium peroxide, and sodium hydroxide dissolved in water is all, so through the above analysis, it can be seen that the mass fraction in option BC is the largest and equal, so the answer is BC.