Junior High School Chemistry Questions, Junior High School Chemistry Questions

A is not true. First of all, the temperature has an effect on the solubility, such as the 30 degrees of potassium nitrate saturated solution to 40 degrees, it is no longer a saturated solution, and then add a little potassium nitrate, less than the saturated state, but its concentration is already larger than the concentration of the saturated solution at 30 degrees, in addition, the solubility of some substances is reduced with the rise of temperature. Such as some gases.

b generally remains saturated.

d Not right, such as potassium nitrate, sodium chloride, etc.

C's account is inaccurate and can be considered correct.

A is false, the solubility of the same substance is not the same at different temperatures, so it is possible that the concentration of saturated solution at low temperature is smaller than that of unsaturated solution at high temperature.

B is wrong, after the precipitation of the crystal, it becomes a saturated solution at low temperature, and it is still saturated.

c correct. Dfalse, the solubility of some substances decreases with increasing temperature.

A: False, provided that the temperature is the same and the solvent is the same.

B: False, it's still a saturated solution.

C: Yes, if the temperature of the solution increases, if the mass of the solution does not change, the mass of the solvent and the solute remain the same, so the mass fraction of the solute does not change.

D: False, if the temperature of Ca(OH)2 saturated solution decreases, there is no crystal precipitation.

The answer is c....A: Different temperatures B:

After the crystal is precipitated by lowering the temperature, it is known from the meaning of the question that it is still a saturated solution under the condition d: potassium nitrate c: the mass of the solution does not change, and the solute solution does not change, so the mass fraction of the solute does not change.

cThe mass of the solution remains unchanged, indicating that there is no crystallization, no water evaporation, and the solute mass fraction remains unchanged.

Pick C is definitely right. If it is precipitated, it is not considered a solute. The score of Baohe is unchanged.

Strictly carbon monoxide, sulfur dioxide, nitrogen dioxide.

In general, it should be nitrogen oxides, hydrocarbons, and sulfur dioxide, and the reason why nitric dioxide is said is because it is too easy to become nitrogen dioxide (famous poisonous gas) and cannot exist in nature, so it is considered harmful by default, nitric oxide is actually harmless, and it can also be used for cancer!

The decay of the corpse is a slow oxidation, even if some poisonous gas is released, it is only a small amount, and nature itself also has the ability to purify these gases.

Otherwise, how many creatures have died since ancient times, isn't the earth still fine, until now it is caused by human interference).

Sulfur dioxide, nitric oxide, carbon monoxide.

The decay of animal carcasses is chronic, the oxidation is relatively thorough, and these reducing gases are not produced. Why is nitrogen dioxide excluded? Because nitric oxide easily combines with oxygen to become nitrogen dioxide, nitrogen dioxide combines with water and releases nitric oxide.

It should be sulphur dioxide, carbon monoxide and nitrogen dioxide. Carbon dioxide is not considered pollution. Nitric oxide is also not right because it is not stable in the air and will be oxidized to nitrogen dioxide! Upstairs wrong @@

To be precise, there are two types of pollutants that cause air pollution: dust pollution and gas pollution. Among the gas pollutants are carbon monoxide, sulfur dioxide, nitrogen dioxide.

Carbon dioxide gas is non-toxic, it is not a polluting gas, although it will bring harm to human beings in large quantities, but there must be a certain amount of carbon dioxide in the air. Because the oxygen that people breathe needs it to photosynthesize with green plants.