Chemistry choice questions for junior 3, chemistry multiple choice questions for junior 3

From the question, it can be seen that 25g of A and 15g of B can react completely, that is, the mass ratio of A and B participating in the reaction is 25:15, that is, 5:3, so in the first reaction, the mass ratio of A and B participating in the reaction is also 5:

3, i.e., 15ga all participate in the reaction, and only 9GB participates in the reaction. Then there is the law of conservation of mass, and the mass of c participating in the reaction is 30g-15g-9g=6g

Therefore, in the first reaction, a reacts 15g, and the remaining 0g;

B reaction 9g, remaining 6g

c reacts 6g, and the remaining 9g

So in the second reaction, a reacts 25g, and the remaining 0g

b reaction 15g, remaining 0g

The mass ratio of C to B participating in the reaction is 6:9=2:3, so in the second reaction, C reacts 10g, and the remaining 5g

So you have all the answers.

Answer A: After the first reaction stops, B is left with 6g, false.

Answer B: After the second reaction stops, D is 50g, false.

Answer C: The mass ratio of A to C in the reaction is 15:6 or 25:10, and it is 5:2 after simplification, which is false.

Answer D: The mass ratio of B to C in the reaction is 9:6 or 15:10, which is 3:2 after simplification, which is correct.

Observe the second reaction first, only C is left after the reaction stops, indicating that A and B happen to be completely reacted, that is, the mass ratio of A and B meets the conditions of complete reaction (otherwise there must be a substance that has not been reacted completely), so the mass ratio of A and B consumed by the reaction is (15+10): 15 = 5:3

Then look at the first reaction, since adding A will continue to react, it means that only A has all the reactions in the first reaction, so A consumes 15g, according to the ratio found above, B should react 9g, and 30gd is generated, so C reacts 6g

So the mass ratio of A and C consumed in the reaction is 5:2

b also needs to be connected to the device.

c, solid does not use.

You can also do it with elimination.

If the purity of the gas is not pure, it will be **, so d is right In the third year of junior high school, the teacher in the next class was ** when he was producing hydrogen, so he was particularly impressed.

b. When not, it is not right to check the air tightness in the test, it should be before the test, and the device needs to be connected first.

c. Liquids need to be preheated, while solids are not needed.

Before preparing gas, the airtightness of the device should be checked.

B: Check the air tightness after connecting the experimental equipment.

c: Not used for solids (e.g. copper oxide is not required for hydrogen reaction).

Select CA, hydrogen density is less than air, physical properties.

b, carbon dioxide does not support combustion, chemical properties.

c. Graphite hardness is small, physical properties, graphite (carbon element) chemical properties are stable, not easy to fade, chemical properties.

d, diamond hardness, physical properties.

b Chemical properties: CO2 does not support combustion.

Physical properties: The density of CO2 is greater than that of air.

19 The "corrosive fluid" of printed copper circuit boards is FeCl3 solution. It is known that copper and iron can react with FeCl3 solution, and the reaction equation is: Cu + 2FeCl3 2FeCl2 + CuCl2; fe + 2fecl3 ＝ 3fecl2。

Now a package of mixed powder of copper and iron is added to the beaker containing FeCl3 solution, and there is still a small amount of solids in the beaker after the full reaction, and the statement about the composition of the substances in the beaker is correct.

A solution must contain FeCl3, solid must be Fe and cub solution must contain FeCl2, solid must contain Cuc The solution must contain FeCl2, solid may contain Fed, the solution may contain FeCl3, and the solid may contain Cu20 The following experimental operation process of impurity removal is correct (impurities in parentheses) A O2 (CO2) Add sufficient amount of hydrated lime and wash.

B NaOH solution (lime water) Add an appropriate amount of soda ash solution and filter.

c cuo(cu) add sufficient dilute hydrochloric acid, filter, wash, and dry.

D mno2 (KCL) is dissolved, filtered, evaporated, and crystallized with water.

Answer: If there is a solid, there must be a Cu and there may be FeExcess iron reacts with divalent copper to precipitate copper, and if the bivalent copper is exhausted, there will be Fe precipitation.

In both equations, the product is FeCl2, so there must be FeCl2B(2)ACO2 cannot be removed with hydrated lime. Hydrated lime is used to test CO2 applications NaohbPair of caCO3 precipitates are generated.

c.Dilute hydrochloric acid reacts with Cuo and does not react with Cu.

Insoluble in water The process should be.

Add water to dissolve, filter, wash, and dry.

According to the law of conservation of mass, the types of elements before and after a chemical reaction remain the same, and the number of atoms does not change

Limestone reacts with dilute hydrochloric acid to produce carbon dioxide Magnesium is a very reactive metal, and it reacts with acid to release a lot of heat, and sodium hydroxide is dissolved in water to release heat.

Quicklime calcium oxide reacts with water to exothermic.

The answer is: b If it is pure copper oxide, the mass fraction of oxygen is 20% Again, according to the pure spine, the oxygen element of each of the following elements is b, c is 40%, and if the copper oxide element is reached in the impurities, then the oxygen element of another impurity is higher than 20%, and if it is lower than 20%, then its oxygen element will never be reached.

Dry ice is solid CO2 and is pure.

Select C. a. There are a lot of inorganic salts in mineral water, which are mixtures.

b. Gasoline and diesel are mixtures.

d. Air and milk are mixtures.

c Mineral water has a lot of trace elements in it.

Gasoline and diesel are not explained.

Air... There's a lot of stuff in there.

Pure milk, no matter how pure it is, it has fat, protein and so on in it.

I hope it helps