2012 Xicheng junior high school second mode chemistry question 28

The calcium hydroxide produced by calcium oxide must be greater than , so it must be a saturated solution, and its mass fraction is.

Analysis: Calcium oxide is dissolved in water to form calcium hydroxide, and the calcium hydroxide produced by calcium oxide must be greater than that, so it must be a saturated solution of calcium hydroxide.

So the mass fraction of the solute in the solution is.

cao+h2o=ca(oh)2xx=

So the mass fraction of the solute is.

Select: The p-point indicates the solution after the non-reaction. Instead of pH equal to 7b:m, the point contains more than one solute, sodium hydroxide and sodium chloride.

C: The sodium hydroxide solution added from point M to point N is 20g, and Azi did not mention other solutions.

D: The point of p indicates that the solute mass of the solution in the same mass is more delayed, so the solute mass fraction is small.

Pick the D answer. A Answer: The point p indicates that the copper chloride has completely reacted. It cannot be expressed that pH is equal to 7, in fact PH is already greater than 7.

B Answer: Point M contains two kinds of copper chloride and sodium chloride, and point M also indicates that the added hydrogen car carries only sodium oxide and the hydrochloric acid in it.

C answer: The increment of the mass of the solution from point M to point N should be less than 20g, because there is a precipitation of copper oxide in the hydrogen hidden mu at the same time as the solution is added.

D Answer: Obviously, the mass of sodium chloride does not increase after the n point, so there is more mass of the solution in the solute of the same mass, so the solute mass fraction is smaller.

There are places on the first floor that are incorrectly analyzed, so you can take a second look. In fact, when doing this type of question, if you are not sure, use the elimination method to analyze, so that you can better select the answer.

In this reaction process, sodium hydroxide first reacts with hydrochloric acid, that is, the process from point 0 to point m, and the hydrochloric acid completely reacts to point m, at this time, the solutes in the solution are only copper chloride and sodium chloride. Then from point M to point N, sodium hydroxide reacts with copper chloride, and copper chloride is completely converted into copper hydroxide precipitate at point N, and the solute at this point is only sodium chloride, the solution is neutral, and the pH is 7. Then continue to add sodium hydroxide, and there is no reaction process.

It's just that the alkalinity of the solution continues to increase the pH value. 20g of sodium hydroxide was added from point m to point n, and copper hydroxide precipitation was precipitated at the same time, so the mass of the solution was reduced. So ABC is wrong.

In D, because the mass of sodium chloride remains unchanged and the total mass of the solution increases, the absolute mass fraction of the chain at point P is smaller than that at point N. Hope it helps.

Select the last Biyan answer. The analysis is as follows:

A---P point through the meditation hall through the amount of sodium hydroxide He Huiyin, alkaline, excluded.

Point b---m has sodium chloride and copper chloride.

c – the mass of the precipitate is increased by 20 g.

Carbonate reacts with hydrogen cations in dilute hydrochloric acid to form carbonic acid, which destabilizes into water and carbon dioxide.

Precipitation is observed when carbon dioxide is introduced into the clarified lime water. The presence of carbonate is proven.

If you don't understand, please ask, I'm also in the third year of junior high school.

If it contains calcium carbonate, dilute hydrochloric acid and its hardening will generate carbon dioxide, and the resulting gas will be passed into lime water, if it becomes turbid, it will prove to be carbon dioxide, and then it must contain calcium carbonate.

The final temperature and solubility values of the students are a little incomprehensible, but if you add a punctuation point to divide it, it will ......be clearBut I vaguely feel that it should be potassium nitrate in the beaker and potassium carbonate in the beaker. Option B, if the solids in the beaker are completely dissolved, there are three methods, one is that the mass of the solute and solvent remains unchanged, and the temperature is increased, and the mass fraction of the solute increases; Second, the temperature does not change to improve the quality of the solvent, and the mass fraction of the solute is reduced; The third is to increase the temperature and increase the mass of the solvent, and the mass fraction of the solute is also reduced, so option B is wrong. Option D is similar to B, if the beaker becomes an unsaturated solution, there are also three methods, one is that the mass of the solute and solvent remains unchanged, and the temperature is increased, and the mass fraction of the solute is increased; Second, the temperature remains unchanged, increasing the mass of the solvent, and the mass fraction of the solute is reduced; The third is to increase the temperature, but also increase the quality of the solvent, at this time the mass fraction of the solute is also reduced.

So option d is correct, and the mass fraction of the solute is likely to increase. A is wrong, the beaker may be a saturated solution, C may be correct, at this time, the temperature range of T1 should be determined, and the solubility value given by the classmate is not divided by symbols, so I can't see what is what, so I can't do further analysis.

b. If all the solids in the beaker are dissolved, the solute mass fraction in the solution must increase. If water is added until it is just dissolved and the temperature does not change, the solute mass fraction will not change.

d. If the solution in the beaker becomes an unsaturated solution, the solute mass fraction in the solution may increase. In the example above, if water is added, the solution becomes an unsaturated solution, and the solute mass fraction decreases. However, if the temperature is increased, the solute mass fraction will increase until the solute is just dissolved.

As the temperature continues to rise, the solution becomes an unsaturated solution, and the solute mass fraction remains unchanged again.

The sodium carbonate in the sample that reacts with hydrochloric acid, the sodium hydroxide in the sample, and the sodium hydroxide added later all form sodium chloride, and the cl in hydrochloric acid all becomes cl in sodium chloride

hcl ～ nacl

100 x x= hi I reed.

The final solid is sodium chloride, which is resistant to travel rent, and the total mass of sodium is unchanged, only the total mass of sodium before the reaction is required, and then divided by the mass fraction of sodium in sodium chloride.

From the question, it can be seen that the hydrochloric acid is excessive, and later sodium hydroxide is used to neutralize the skull, or the ruler base, so it can be seen that the salt trapped inchic acid in this question happens to be completely reacted. Therefore, the amount of sodium chloride produced can be calculated according to the amount of hydrochloric acid.

naoh+hcl=nacl+h2o na2co3+2hcl=2nacl+h2o+co2 naoh+hcl=nacl+h2o