The second year of junior high school science questions, the second year of junior high school scien

The answer is cYou have to read the topic clearly. Yes"The atmosphere goes from high to low"

It means from the atmosphere to the ground. You should know that with the altitude rises. The density of the atmosphere decreases gradually.

Now it is a drop with altitude. It is the gradual increase in the density of the atmosphere. So choose C.!

Dizzy! Of course it's C! This is still a question! You still dare to refute the teacher.

How do you have two C's?

It should be that the density is getting bigger. Because as the altitude increases, the Earth's gravitational pull on the gas becomes smaller and smaller, so the atmosphere tends to be thinner and thinner as it moves towards space. We can take a certain volume of air at different heights, and since density = mass volume, when the volume is the same, the mass is proportional to the density.

Obviously, the density of the gas gradually increases as the height decreases, as the gravitational pull increases and the mass of the gas accumulates per unit volume as it gets closer to the ground.

Faint! Come on.

I don't see the questions clearly, from high to low, not from low to high!

c,, do you know why the atmosphere is thin in one layer? Because the oxygen content is determined by the magnitude of the density, the lower the density, the lower the oxygen content.

1) Troposphere: It is the lowest layer of the atmosphere, its lower boundary is the ground, and the upper boundary varies depending on latitude and season. The average thickness of the troposphere is 17-18 km at low latitudes, 10-12 km at mid-latitudes and 8-9 km at high latitudes.

The troposphere is the most closely related level of the atmosphere to all living things, and it also has the greatest impact on human production and life. The phenomenon of air pollution that usually occurs occurs mainly in this layer, especially within 1-2 km of the ground.

2) Stratosphere: Stratosphere from the top of the troposphere to about 55 km.

3) Mesosphere: From the top of the stratosphere to an altitude of 85 km is the mesosphere.

4) Ionosphere: From the top of the mesosphere to an altitude of 800 km, it belongs to the warm layer.

5) Fugitive layer: The atmosphere above the top of the ionosphere, that is, above an altitude of 800 km, is called fugitive.

Look at this, air also has weight, for a long time, air is deposited at low altitudes, and the density also increases, so you can live in the world, otherwise, you would have hung up a long time ago.

If you're right, you're superhuman – don't breathe.

c I called 110 and the police told me.

It has nothing to do with friction.

Float f float = g object = g row = v row g = m 1000kg cubic meter 10n kg = 801504n

m matter = g object g = m bomb = m object - m tank =

26 tons does not take into account the area and speed of the track contact with the ground.

f = 10 * 1000 * is the density of water, 10 of the gravitational constant) g = 54 * 1000 (1000 is the conversion of tons to kg) f-g 10 = 26 tons of goods.

(1) x= (because the first time every 20ghcl can react 2g and the fourth time only reacts to the excess of hydrochloric acid, and the rest is impurity).

2) The limestone sample should be 10g (otherwise it cannot be calculated), CaCO3%=(3) Solution: Let the first reaction use (x)GhClCaCO3+2HCl====CaCl2+H2O+CO2 100 73

2 (x）g

x=hcl%=

Hope to solve the problem

First of all, you should know that this is a calculation question about chemistry. The reaction in the question is CaCO3 + 2HCl = CaCl2 + H2O + CO2 (g) to explain that CaCO3 is calcium carbonate and HCl is hydrochloric acid.

1) You can see that since only 1g of sample was reacted in the first addition, it means that there are other impurities, and they react before calcium carbonate. The first three additions of hydrochloric acid consumed 2g of samples, and only consumed when the fifth or fourth time was added, indicating that the hydrochloric acid had been excessive, and the excess hydrochloric acid would no longer react. Then x=

2) According to the above analysis, the mass of calcium carbonate in the sample is m=, so the mass fraction of calcium carbonate is w=(

3) According to the reaction equation:

caco3+2hcl=cacl2+h2o+co2(g)100 73

2g x So, x = (73*2) 100 = g....Then the mass fraction of dilute hydrochloric acid is m=(