Junior High School Chemistry Competition Questions 10, Junior High School Chemistry Competition Ques

The relative atomic mass of element M is a, the formula of compound RM2 is b, and the relative atomic weight of r is (b—2a).

Using the proportional relation, the ratio of the relative atomic weight of r to RM2 is equal to the ratio of the actual mass of one of its atoms (molecules).

i.e. (b-2a) b = a rm2

Find the actual mass of a rm2 a*b (b-2a), then rm2 in w grams has w (a*b (b-2a)) and ask the number of m atoms just multiply by 2.

I don't know how to leave QQ,

The formula of r is (b-2a), and r in rm2 of wg has (b-2a)wg b, then the number of r is (b-2a)wg ab, and the number of m is twice it, that is, 2(b-2a)wg ab

The relative atomic mass of the r element is =b-2a

The mass of the R element contained in B-2AW gram RM2 = ———w(g)b B-2A

The atomic number of R contained in compound RM2 = ——— BW(G)A(G) and the atomic number of element M is 2 times that of R.

2（ b-2a）×w

The atomic number of element m = ———

B A score is not easy to play, you move the number to the score line.

Solution: 1 mg generates 1 h2

1 Al generates H2, so 2 3 Al generates 1 H21 Fe generates 1 H2

Because the relative molecular mass of metals of the same mass is greater and the amount of matter is less and the mass of acids is equal, it can be divided into 2 situations:

1) When the acid is insufficient, the amount of hydrogen released is certain, so the quality of the three metals must be the same.

2) In case of acid excess, Al>mg>Fe

The title is classic.

First, let's learn a point of view.

The greater the amount of metal formula of the same mass, the less the amount of matter.

Then, since Al is trivalent, we think of it as a bivalent metal (one part aluminum produces one part hydrogen), then the formula for Al is 27*(2, 3)=18

Then we know that acids are equal parts.

a。If all the acids are insufficient, then all three metals are of equal mass (unfortunately there is no answer)b. If there is an excess of acid, then the large amount of H2 is released, so it is less so that C, Al Mg Fe is selected

Write their reaction formulas separately, since the mass of the resulting hydrogen is equal, and the relative atomic masses of iron, magnesium, and aluminum are 56, 24, and 27, respectively, the mass ratio is 56 2 : 24 2 :(2 27 6) = 28:12:9

So choose D

Potassium chlorate is indeed produced by simply heating it.

If manganese dioxide is added, manganese dioxide will first react with potassium chlorate to produce potassium chloride and another substance, and then the other substance will decompose to produce manganese dioxide and oxygen, after which manganese dioxide will continue to participate in the reaction.

The junior high school textbook says that manganese dioxide does not participate in the reaction in order to simplify teaching, but if it is a chemistry competition, it should be a more in-depth test.

There are two versions of the intermediate product: one is potassium permanganate (KMno4) and the other is manganese heptaoxide (Mn7O2).

Don't doubt it, generate it at the same time.

It should be at the same time, because manganese dioxide is a catalyst in the reaction, and it can be combined with potassium chlorate to form an intermediate in the reaction, and then the oxygen is released, and the intermediate becomes manganese dioxide and potassium chloride.

Solution: Because the mass of the dilute sulfuric acid solution in the two beakers before the reaction is equal, the sum of the remaining substances in the two beakers after the reaction should be equal

Specifically, the change of the mass of the substances in the left disc beaker after the reaction was analyzed, because there was no escape of substances in the reaction of sulfuric acid and calcium oxide, so the mass of the substances in the left disc beaker increased grams

a. Add grams of magnesium, according to the chemical equation, the mass of hydrogen can be calculated as grams, and the mass of the solution increases grams, so the balance is balanced.

b. Add calcium carbonate, because calcium carbonate and sulfuric acid can not react completely, assuming that calcium carbonate can react with sulfuric acid, then according to the chemical equation, the maximum mass of CO2 gas can be calculated, and the mass of the substance in the beaker is the least, so the balance will not be balanced

c. Add 2 grams of magnesium carbonate, then according to the chemical equation, the maximum mass of CO2 gas released can be calculated as grams, and the mass of the substance in the beaker is the balance balance

d. Add copper-aluminum mixture, assuming that all copper, because copper does not react with sulfuric acid, no gas escapes, so the balance is balanced; Assuming that it is all aluminum, to release gas, then the mass of the substance in the remaining beaker will be less than and the balance will be unbalanced; So if it is a mixture, the mass of the remaining material in the beaker is also less than the gram, and the balance will not be balanced

So choose AC