2 chemistry problems for junior high school, solve, thank you!

Qualitative: Water is made up of the elements hydrogen and oxygen.

Quantitative: Each water molecule is made up of two hydrogen atoms and one oxygen atom; In other words, the ratio of hydrogen to oxygen in water is 1:8

Quantification may be related to quantity).

Since H always shows +1 in the compound, the valency of Ro(2N-1) should be -nn+x+16(2N-1)=m

So, x=m-33n+32

1. "Chemical formula" is a very important chemical term in chemistry, with a wide range of meanings. Please take "H2O" as an example and explain a little bit from the perspectives of "qualitative" (macro) and quantitative (quantitative).

1) "Qualitative" angle Water is made up of the elements hydrogen and oxygen 2) "Quantitative" angle There are two hydrogen atoms and 1 oxygen atom in each water molecule.

2. If the chemical formula of a compound is known to be HNRO(2N-1) [2N-1 is the lower right corner of O], and the relative molecular mass is M, then the valency of the atomic cluster of RO(2N-1) is N, and the relative molecular mass of the element R is M+16-33N.

hn means that there are n hydrogen atoms in the molecule, and qualitative refers to the consideration of macroscopic properties, such as male and female classmates in your class.

Quantification is from the measurement aspect, such as 20 male classmates, etc.

1) "Qualitative" Perspective Water is made up of oxygen and hydrogen.

2) "Quantitative" Perspective A water molecule is made up of one oxygen atom and one hydrogen atom.

If the chemical formula of a compound is known to be HNRO(2N-1) [2N-1 is the lower right corner of O] and the relative molecular mass is M, then the valency of the atomic cluster Ro(2N-1) is -N, and the relative atomic mass of the element R is m-33N+16

H in hnro(2n-1) is +1 valence, so according to the algebraic sum of its valency is 0, then the valency of the atomic group of RO(2N-1) is (0-1*n)=-n

The relative atomic mass of the element r is m-((2n-1)*16+n*1)=m-33n+16

hn where n is the subscript, which denotes n h atoms. Qualitative refers to the composition and properties of a substance (it is usually not necessary to have specific data, as long as its properties are analyzed from a macroscopic perspective). Quantitatively refers to the amount of various components contained in a substance (usually with specific data, to be analyzed from the microscopic level). ）

①.Mass fraction of iron in Fe2O3.

56*2/(56*2+16*3)*100%=70%②。800t of hematite containing 60% Fe2O3. Theoretically, how many tons of pure iron can be smelted.

According to the equation.

Fe2O3+3Co=High temperature=2Fe+3CO2160 112800T*60% x solution x=336T

2 The mass of the caCO3 precipitate formed after the reaction is:

Conservation of mass 50g+70g=precipitation+115

Pellet = 5 g of Na2CO3 participating in the reaction.

cacl2+na2co3=caco3↓+2nacl111 106 100x 5

Solved x = mass fraction of solute in the solution after filtration (exactly.

Because it happens to react, the solute is only NaCl

cacl2+na2co3=caco3↓+2nacl111 106 100 117g

5 xx = so the mass fraction of the solute is.

1.①112÷160×100%=70%

Fe2O3 + 3Co = High temperature = 2Fe + 3CO2160T 112T800 60%T m m = 336T

2.The total mass before the reaction is 50 + 70 = 120g and the filtered solution is 115g

m=120-115=5g

cacl2+na2co3=caco3↓+2nacl106g 100g 117gn 5g q n=53g q=③

Question 1: 1Mass fraction of iron element: Fe%=56 2 (56 2+16 3)=70%.

mass = 800000000g 60% = 480 tons.

Fe2O3 + 3Co = High temperature = 2Fe + 3CO2

480 tonnes m(fe) mass of iron = 480 112 160 = 336 tonnes.

Question 2:1Obviously, the reduced mass is the precipitated mass, then m(caCO3) = 50 + 70-115 = 5g

m 5g m(naco3)=106×5/100=

5g m m(nacl)=2×

So the mass fraction of the solute is == rounded)

This can be obtained according to the formula: 56*2 (56*2+16*3 x100% according to the reaction formula to 160 grams of iron oxide to obtain 112g of iron, first calculate the mass of iron oxide, and then calculate it according to the proportion.

According to the reaction equation, we can get the overall mass reduction, which is the precipitated mass, and then find the mass of sodium carbonate according to the calcium carbonate (precipitation).

According to the reaction formula, it can be seen that the latter solution is the sodium chloride solution, and the mass of sodium chloride is calculated according to the reaction formula, and the rest is simple.

1 ① w（fe）=m（fe）/m(fe2o3)*100%=(56/160)*100%=35%

M(Fe2O3) = 800T*60%=480TBecause Fe accounts for 35% of Fe2O3, M(Fe)=480T*35%=168T is generated according to the law of conservation of mass

2 According to the law of conservation of mass m(CaCl2) + m(Na2CO3) = m(CaCO3) + m(2NaCl).

So m(CaCO3)=50g+70g-115g=5g Solution: Let the mass of Na2CO3 participating in the reaction be x

cacl2+na2co3=caco3↓+2nacl1 1

x 5g solution gives x = 5g

What is the amount of solute in solution? You didn't say yes.

Hello landlord: The correct answer is b. (Analysis:.)

a.Hydrogen peroxide is catalytically decomposed into water and oxygen by manganese dioxide, in which the quality and properties of manganese dioxide remain unchanged, that is, it is a catalyst that does not participate in the reaction, so a is correct; b.Oxygen is chemically active, but it cannot react with all substances at room temperature, such as noble gases, so B is wrong; c.

When the thin iron wire burns in oxygen, the sparks are scattered and a black solid is generated, which is the phenomenon of the iron wire burning in oxygen, so c is correct; d.It is true that the drainage method is used to collect gases that are not easily soluble in water, because the gases are insoluble in water and do not react with water to ensure the success of gas collection, so d is correct).

Khan: Study hard

This kind of problem can react with all substances at room temperature.

It's not that nothing can exist in the air.

The answer is definitely B, where A is absolutely correct, and manganese dioxide is the catalyst, which is mentioned in the textbook;

The chemical properties of b oxygen are indeed very active, but it must react with carbon under the condition of combustion;

Among them, C iron is burned in oxygen to form ferric tetroxide, which is a black solid, and when burned, it is full of sparks, which is found in textbooks;

Among them, d uses drainage to collect insoluble gases, which is more right, although some gases can be collected by exhausting air, but it is still easy to collect impure gases, which may contain air, if the drainage method is adopted, the air is insoluble in water, and the collected gases are not soluble in water, so that the collected gases are purer.

b.At room temperature all substances are false; The chemistry of oxygen is also less reactive.

bBecause although the chemical properties of oxygen are active, it cannot chemically react with all substances at room temperature, such as gold, even at high temperature.

b, obviously wrong, that is, if we can chemically react with all substances at room temperature, as the title says, it is difficult to imagine what our lives will become.

Choose B, the first half of the sentence is correct, but oxygen cannot react with all substances, because there is activity and inertia.

A does not need to be explained B, oxygen cannot react with all substances at room temperature, C black solid ferric tetroxide lz Note that it is oxygen, pure oxygen D dissolved in water can also be understood as reacting with water, and the reaction with water cannot be collected, as for the gas, it is not explained.

The ferric oxide formed by the reaction of the iron wire with oxygen in B and C is black. D. Gases that are insoluble in water can be drained, such as oxygen and carbon monoxide.

Pick B. Obviously. Everything else is correct.

Choose B, because although oxygen is active, other substances are not active, and oxygen is also impossible. Noble gases, for example, do not react with oxygen.

b Some reactions require heating, such as hydrogen.

1. Decrease. This question examines metal mobility and solution calculations. Iron can be replaced with copper and silver, but not aluminum, and the chemical equation is as follows:

fe+cu(no3)2=fe(no3)2+cu、fe+2agno3=fe(no3)2+2ag。

After the full reaction, it is filtered, and bubbles are generated when dilute sulfuric acid is added dropwise to the filtered solid. It is stated that there is iron so both Cu and Ag are also replaced.

Judging by the equation:

By Fe+Cu(No3)2=Fe(No3)2+Cu Fe+2AGno3=Fe(NO3)2+2AG

When 56 parts of iron enter the solution, 64 parts of copper and 216 parts of silver become solid and precipitate out of the solution, so the mass of the solution decreases.

2. Answer: cu

The equation is corrected to generate 3fecl2:

cu+2fecl3=2fecl2+cuci2 fe+2fecl3=3fecl2

Because it is a certain amount of ferric chloride solution, and the activity of iron is greater than that of copper, the reaction between iron and ferric chloride also occurs at the same time as the reaction of iron replacing copper, so there must be copper.

1. There are bubbles in dilute sulfuric acid dropwise added to the filter residue, indicating that there is iron in the filter residue, that is, the iron powder added is excessive. Therefore, the copper ions and silver ions in the original solution are completely replaced, and the ferrous ions of equal charge are replaced in the solution. Because the atomic weight of iron is less than that of copper and silver, the mass of the solution becomes smaller.

2. The knowledge point of this topic is high school、、、 essence is because the reducing property of iron is greater than that of copper, and the oxidation of copper ions is greater than that of iron ions

First of all, find out who reacts with the solution first: if copper reacts first, copper ions are formed, but copper ions are replaced by iron to form copper, so iron reacts with the solution first, that is, copper can only participate in the reaction after the iron reaction is completed, so there must be copper if there is a surplus solid.

Becoming smaller Iron is located before copper and silver in the table of metal activity sequences, so copper nitrate and silver nitrate can be displaced, and there are bubbles formed indicating that there is iron surplus and the relative atomic mass of iron is smaller than copper and silver completely displaced, so: small.

Small. Because iron replaces silver, because dilute sulfuric acid and silver do not react, so it can be seen from the bubbles of dropwise sulfuric acid that copper is also replaced, and the mass of ferrous ions is lower than that of copper ions and silver ions, because it is ferrous ions that are replaced with ferrous ions, so the final mass becomes smaller.

Copper. Because even if the first reaction occurs, because iron reacts with acid to form ferrous chloride more easily than copper, a displacement reaction will occur, so if all copper has the first reaction first, there will also be a displacement reaction due to the presence of iron solid residues, so that the solid residue will turn into copper, and it can be inferred from this point that iron must have reacted with ferric chloride first.

Ignite. +o2 ==so2

For every 1 gram of sulfur and 1 gram of Hona oxygen, 2 grams of sulfur dioxide are combusted and burned.

Ignite. +5o2 ==p2o5