The third major question of chemistry equations in junior high school, and the third question of che

cu+hgno3=cuno3+hg

NaHCO3+HCl=NaCl+H2O+CO2 precipitation).

precipitation) Na2SO4 + BACL2 = 2NaCl + BaSO4 (precipitation) (hand beating is not easy, hope).

.The relative molecular weight of 71% ammonium nitrate = 80 n The mass fraction in ammonium nitrate is 28 80 = 7 20= Ammonium nitrate fertilizer has other components for the year, with 30%.

In this topic, you can see that the ratio of the number of sulfur atoms to oxygen atoms is 1:4, and in addition to iron, the mixture is sulfate.

Because iron accounts for 31%, sulfate accounts for 69%.

The mass fraction of sulfur in sulfate = 32 32 + 16 * 4 = 1 3 sulfate accounts for 69%.

So sulfur contains 69% * 1 3 = 23%% in the mixture Your question is incorrect, it should be oxygen 22%.

All three substances can be regarded as Na2S O4, Na2S O3, and the ratio of sodium to sulfur atoms is 2:1

So the mass ratio of sodium to sulfur is 46:32

Oxygen accounts for 22%, then the total mass fraction of sodium and sulfur is 78% and the mass fraction of sodium in Na2s is unique = 46 46 + 32, because the total mass fraction of sodium and sulfur is 78%.

Therefore, the mass fraction of sodium is 46 (46+32)*78%=46%, don't forget to give and pei.

Dude, you haven't finished writing yet!!

71% The relative molecular weight of ammonium nitrate = 80 n The mass fraction in ammonium nitrate is 28 80 = 7 20= Ammonium nitrate fertilizer has other components, use 30%.

In this topic, you can see that the ratio of the number of sulfur atoms to oxygen atoms is 1:4, and in the mixture, except for iron, it is sulfur and acid roots.

Because iron accounts for 31%, sulfate accounts for 69%.

The mass fraction of sulfur in sulfate = 32 32 + 16 * 4 = 1 3 sulfate accounts for 69%.

So sulfur contains 69% * 1 3 = 23%% in the mixture Your question is incorrect, it should be oxygen 22%.

The three types of reed substances can be regarded as Na2S O4, Na2S O3, and the ratio of Na2S sodium to sulfur atoms is 2:1

So the mass ratio of sodium to sulfur is 46:32

Oxygen accounts for 22%, then the total mass fraction of sodium and sulfur is 78% Mass fraction of sodium in Na2s = 46 46 + 32, because the total mass fraction of sodium and sulfur is 78%.

So the mass fraction of sodium is 46 (46+32)*78%=46%.

1) Sure, possibly, reason: the air is mainly nitrogen and oxygen, so the hydrogen element in the air can be ignored, so the pure matter must have hydrogen element, and the oxygen element can not be determined, because organic matter can basically be burned with water to produce, so there may be oxygen element.

2) Not greater than, reason: the law of conservation of mass I believe you should have learned, in short, the total mass of reactants is equal to the total mass of products, and this question does not explain that x and y happen to be completely reacting, there may be reactants remaining, so the total mass of products must not be greater than the total mass of reactants.

Clearly, right?

The presence of water in the product of the aerial combustion of a pure substance indicates that this substance.

Definitely (definitely may not have) contains hydrogen, probably certainly not maybe) contains oxygen.

Reason: Because the air contains oxygen, oxygen is involved in the combustion process, but there is no hydrogen in the air, so it must contain hydrogen and may contain oxygen.

2.The chemical reaction formula x+y=z, if the x of a g and the y of b g are fully reacted under a certain condition, the mass of the product is not greater than greater than equal and less than not greater than a + b ).

Explanation of the reason: According to the law of conservation of mass, if it happens to be a complete reaction, it is equal! There is also an excess of reactants, that is, the total mass before the reaction is greater than the mass of the product!

1.Definitely possible.

Analysis: Because this substance burns in the air, that is, it reacts with O2 in the air. According to the law of conservation of mass, the types of elements before and after the chemical reaction are the same, and there is water in the products of combustion, that is, there are elements H and O.

The element h is only ** from the pure substance, while the element oxygen may come from some of the pure substance or all of it.

2.Not greater.

Also according to the law of conservation of mass.

There are 3 possibilities:

are exactly complete reaction, then the mass of the product = (a+b)g complete reaction, y has a surplus, then the mass of the product <(a+b)g complete reaction, x has a surplus, then the mass of the product is <(a+b)g, and the mass of the product is not greater than a + b

These questions are very basic, you have to work hard. There are many similar problems according to the law of conservation of mass, and only by doing more practice will you improve.

1.The presence of water in the product of the aerial combustion of a pure substance indicates that the substance (definitely) contains hydrogen and (possibly) oxygen.

The product of combustion in the air of the pure substance is water, which is composed of two elements, hydrogen and oxygen, and the air provides oxygen for combustion, so the pure substance must contain hydrogen. The presence or absence of anaerobic elements has no effect on the product, so it may contain oxygen.

2.The chemical reaction formula x+y=z, if the x of a g and the y of b g are fully reacted under a certain condition, the mass of the product is (not greater than a + b).

According to the law of conservation of mass, the sum of the masses of the substances participating in the reaction is equal to the sum of the masses of the substances produced after the reaction. If x of a g and y of b g happen to be perfectly reacted, the mass of the resulting product is equal to (a + b) gIf there is an excess of x of a g and y of b g (the excess is neither a reactant nor a product), the mass of the product is less than (a + b) g

So the mass of the product is not greater than ( a + b)g

1.Definitely possible.

Because water contains oxygen atoms and hydrogen atoms, but the pure substance is burned in the air, and the combustion agent in the air is oxygen, which contains oxygen atoms, so the first blank is definitely filled, and the second blank is possible.

2.(equal).

Because of the law of conservation of mass: in a chemical reaction, the sum of the masses of the substances before participating in the reaction is equal to the sum of the masses of the substances produced after the reaction. This law is called the law of conservation of mass.

In any system that is isolated from its surroundings, the total mass remains the same, regardless of the changes or processes that occur. In other words, any change, including chemical reactions and nuclear reactions, cannot eliminate matter, but only change the original form or structure of the material, so this law is also called the law of immortality of matter.

Since the reactive formula has already been written, x+y=z, it is certain that the answer is equal.

1.Definitely possible.

Reason: Combustion in the air, that is, generally only the oxygen in the air supports combustion, and the reactant has water, indicating that the pure substance must have H, but not necessarily O

2.Not greater.

Reason: If the x of ag and the y of bg react exactly exactly according to the balance of mass, z is a+b g;

The incomplete reaction product is less than a+b

1.It definitely contains hydrogen and possibly oxygen.

Because the combustion of the substance is also a reaction with oxygen, since water is generated, water is composed of hydrogen and oxygen, and oxygen does not contain hydrogen, so according to the law of conservation of mass, it must contain hydrogen; Whereas oxygen already contains oxygen, so the substance may contain oxygen.

2.The mass of the product is equal to a + b

According to the law of conservation of mass, the mass of the product is equal to the total mass of the reactants involved in the reaction, and since the reaction is sufficient, the mass of the product is equal to a + b.

Definitely water is made up of two elements, hydrogen and oxygen, so hydrogen definitely has, but oxygen may be better than air.

Not greater than, including equal to or less than, equal to the sum of the two if the full reaction is made, and less than the sum of the two if there is one of the remainders.

13.(1) After closing the switch, the phenomenon observed in tubes A and B is that bubbles appear on the electrodes, and after a period of time, the volume ratio of gas collected in tubes A and B is about 1:2

The phenomenon in the C tube is the rise of the liquid level.

The reason for this phenomenon is that the hydrogen and oxygen produced by the decomposition of water by electricity increase the pressure in the AB pipe, and the water is pressed into the C pipe.

2) The reason why the gases generated in the A and B pipes are concentrated in the upper part is that the density of hydrogen and oxygen is smaller than that of water, and hydrogen and oxygen are insoluble in water.

14.There are 1234 in physics and 56 in chemistry

15.(1) Both can produce oxygen. (2) The text expression of the third method is to write Chinese without writing the chemical formula. (3) Choose 3, because it is clean, the reaction is also easy to carry out, and it is more economical.

15 1, Heat.

2. Hydrogen peroxide is heated to produce oxygen and water.

3. Choose three, simple, convenient and easy to operate.

14 Physics 1, Chemistry 2, 5, 6

Nature 3, 4

13.(1) The phenomenon of tubes A and B observed by the closing switch is that bubbles are generated on the electrodes, and after a period of time, the volume ratio of gas collected in tubes A and B is about 1:2

The phenomenon in the C tube is the rise of the liquid level.

Reason: Water electrolysis produces oxygen and hydrogen in tubes A and B, respectively, and turns from liquid to gas, and the volume becomes larger, so water is pressed into tube C.

14. Physical Properties: 1,2 Chemical Properties: 5,6 Uses:

3,415·(1) chemical reactions occur to produce oxygen (2) potassium chlorate (arrow) potassium chloride + oxygen; Hydrogen peroxide (arrow) water oxygen (3) choose three, choose one of the reasons: 1, the product is water and oxygen, no pollution to the environment; 2. No need to heat or electrify, save energy, 3, simple and convenient operation.

1.Increasing 10GC, they continue to reflect that when it is completed, A and C are exactly consumed, that is, when A is 15G and C is 25G, they happen to be completely reactive, and the mass ratio of A and C is 3:5;

According to this, when 30GD is generated, the mass of C is 15G, A is 9G, and B is 30G-15G-9G=6G, so the mass ratio of A to B is 9G:6G 3:2

And 2GB happens to be fully reactive.

5ga is required and so a may be 5g or.

3.The metal reacts with the oxygen in the air, increasing the mass of the oxygen.

It does not react because no water, gas, or precipitate is formed.

It does not react because no water, gas, or precipitate is formed.

1) Fe(OH)2+H2SO4===FeSO4+2H2O2) do not react, because there is no precipitation after they exchange components with each other, and gas or water is generated 3) Cu+2AGno3===Cu(NO3)2+2AG4) does not react, it should be a reaction between salt and salt, salt must be soluble in water, but calcium carbonate is insoluble in water.