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The application of the difference method in chemical calculation is based on the chemical change before and afterThe amount of matterThe changes that occur to find out the so-called "theoretical differences". The differences mainly include:

Difference in quality, difference in quantity of substance, difference in volume of gas, difference in pressure, difference in heat during reaction, etc.

Metallic zinc of unknown quality was put into 100 g of dilute sulfuric acid.

After the solution is completely dissolved, the mass of the solution becomes, and the mass of metal zinc is obtained.

Zn+H2SO4=ZNSO4+H2In this reaction, the solid (Zn) and the solution (dilute sulfuric acid) react to form a solution (ZnSO4) and a gas (H2), and the mass of the solution increases after the reaction m = the mass of Zn participating in the reaction minus the mass of hydrogen generated. Let the mass of zn be m g, then the column formula is:

zn+h2so4=znso4+h2 △m，65 63，m （m=65*（

Difference Method Application:

Mg + H2SO4 = Mg SO4 + H2 2AL +3H2SO4 = Al2(SO4)3 +3 H2 Fe + H2SO4 = Fe SO4 + H2 Zn + H2SO4 ==ZNSO4 + H2 Cu does not react with dilute sulfuric acid because copper is not active.

mg: Violent reaction, a large number of bubbles are produced, the solution is still colorless, and the test tube wall is hot.

The resulting gas is capable of combustion, and produces a pale blue flame.

zn: The reaction is more violent, a large number of bubbles are produced, the solution is still colorless, the gas produced can be burned, and a light blue flame is produced.

The solution is as follows:

1.Analyze the topic.

2.Determine if the difference method can be used.

3.Write the correct chemical equations.

4.According to the meaning of the question, determine the "theoretical difference" and the "actual difference" provided in the question, list the proportional relationship, and find the answer.

Precautions

x and y can represent the mass of the substance and the quantity of the substance.

The volume of the gas, etc., so the difference can refer to the difference in mass (m), the difference in the quantity of a substance (n) or the difference in the volume of a gas (v), etc.

Distinguish whether the "difference" is increasing or decreasing. In more complex cases, there are multiple reactions, and the direction of increase or decrease of the difference may not be consistent, which is to take the algebraic sum. If the direction is the same, the total difference is equal to the sum of the individual fractions.

Correctly analyzing the causes of the difference and finding out the corresponding "theoretical difference" derived from the equation is the key to solving the problem of the difference method.

Differential development is to find out the mass difference of homomorphic substances in chemical reactions, and this mass difference is also proportional to the change of the quantity of other substances, which is the difference method, which is not only to study the reduction and increase of solids, but also to use gases or liquids.

For example, if an iron sheet is inserted into a copper sulfate solution, if the mass of the solid is considered, then it will definitely increase, according to the equation, 56 parts of iron will produce 64 parts of copper, so the mass of the solid is increased, and 8 parts will be increased, that is to say, if the mass of the solid is increased by 8 parts, there must be 56 parts of iron reacting, and 64 parts of copper will be produced at the same time.

Fe+CuSO4 ==FeSO4+Cu solid mass increases m

If the mass of the solution is considered, then 56 parts of iron enter the solution and come out of 64 parts of copper, and the mass of the solution is reduced, and 8 parts are reduced, that is to say, if the mass of the solution is reduced by 8 parts, there must be 56 parts of iron reacting, and 64 parts of copper are produced at the same time.

Fe+CuSO4 ==FeSO4+Cu solution mass reduction m

For gases, the differential method can also be used, such as carbon monoxide to reduce copper oxide, which can be calculated by the amount of gas mass increase.

For example, 10g of mixed gas of carbon monoxide and carbon dioxide passes through the calcireal copper oxide, and the mass of the gas increases after the full reaction to find the mass ratio of carbon monoxide and carbon dioxide in the mixed gas.

According to the difference, the mass of carbon monoxide in the gas mixture is x

CO+ Cuo = =Cu + CO2 gas mass increase m

x28/x=16/

x= then the mass of carbon dioxide =

The ratio is 56:44

The mass of solids, gases, or liquids increases or decreases before and after a chemical reaction. Some problems often have very little data, only one or two or even no data, and it is often impossible to solve them with conventional methods. If you can look closely at the chemical equation, analyze and find the quantity corresponding to the actual mass change.

According to the actual difference is proportional to its relative quantity and the actual quantity of each reactant or product in the chemical equation corresponds to the relative quantity, the difference is listed at the right end of the chemical equation with m as part of the chemical equation. It can be solved in a proportional way, which is the difference method, which often simplifies the problem.

Example When reducing hematite powder with carbon monoxide, after heating for a period of time (impurities do not decompose), the weight of the solid is found to be reduced by g, and how many grams of iron are generated?

Analysis: The reactions that occurred were: The conventional solution of 3CO+Fe2O3==2Fe+3CO2 is that if the mass of the formed iron is X, then the ferric oxide participating in the reaction is G+X, and the proportional formula can also be listed:, but it is more troublesome to solve. If the difference rule is much simpler, the difference can be expressed by m, and it can be seen through observation and analysis that the mass of the solid after the reaction is caused by the loss of oxygen by ferric oxide and turning into iron, the difference is the oxygen element lost, and the chemical equation corresponds to three oxygen atoms 3O, and the solution is as follows:

Solution: Let the mass of the formed iron be x, 3Co+Fe2O3==2Fe+3CO2

112 △m =3o=48x gx=5．6 g 。

Answer: Let the iron g.

If you need it, you can leave an email and I'll send you a copy of the information about some examples of the difference method

That's what you're asking.

Example: CaCO3 + HCl = CACl2 + H2O + CO2 (gas arrow) mkg before the reaction, nkg after the reaction

then the difference (m-n)kg

What needs to be calculated is the amount of CO2, and the gas runs away, so the difference is the amount of CO2. According to the formula of CO2, find the molar quantity of CO2 and then proceed to other calculations. Hope it helps.

Let the amount of iron be m1 and the amount of magnesium be m2. Then, to maintain the balance between the two sides, the following equation must be true:

m1 - m1/56) *2 = m2 - m2/24) *2

Therefore, m1 m2 = 77 81

Conservation is done with the spilled hydrogen equally.

The bar of the high school attached to Hangzhou Normal University (

To solve it, each method must be used once.

You're also from the high school attached to the National Normal University, right?

The reduced mass of the solids is Fe2O3 with Cuo in the mass of oxygen set with x grams of iron oxide and containing Y grams of oxygen.

Then there are grams of copper oxide, which contain oxygen.

fe2o3－－－3o

x y160y＝48x

cuo－－－o

Solution: x grams.

The mass ratio of Fe2O3 to Cuo in the original mixture was :(1

Full reaction, then the remaining solid matter is only iron and copper, then the mass of the solid reduction is the mass of the reduction of oxygen, I don't know if you have learned the amount of matter, if there is it is simpler, I don't need it here, because if you learn it, then you will definitely use it after reading it.

Let the mass of Fe2O3 be Xg, and the mass of Cuo is Yg, so X+Y=, in iron oxide, there is 48g of oxygen for every 160g, then Xg iron oxide has 48 160xg of oxygen (simplified.

In the same way, there is 16 80yg oxygen in yg copper oxide (that's it.

In the end, we find how much x y is equal to, which can be solved by using this equation. The answer is 1:1 The so-called difference method is a solution method based on the fact that some "difference" (difference in solid quality, solution quality, gas volume difference, difference in the amount of gaseous substances, etc.) before and after a chemical reaction is proportional to the change in reactants or products.

In this method, the "difference" is regarded as one of the right ends of the chemical equation, and the known difference (the actual difference) is proportional to the corresponding difference (theoretical difference) in the chemical equation, and the other steps are exactly the same as the proportional solution of the chemical equation. The key to solving the problem with the difference method is to find the theoretical difference correctly.

Hope it helps!

If you don't understand, please ask!

The grams reduced should be the mass of oxygen in the mixture.

Hence the total mass of iron and copper is.

The mass fraction of oxygen in iron oxide is 48 160 = 3 10 = 30%, copper oxide: 16 80 = 1 5 = 20%.

Let the mass of iron oxide be XG and the mass of copper oxide be YG

So get x+y=

30%x+20%y=

The solution is x=y=so the mass ratio is 1:1

In this question, you have to calculate how much hydrogen is released when magnesium is added. For every 24 grams of magnesium, 2 grams of hydrogen will be released, so just add 22 grams of copper, because copper does not react with dilute sulfuric acid.

The reactions are as follows:

It can be seen that the mixture of 25 4 grams of NaHCO3 and AgNO3 finally becomes a mixture of nano3 and Agno3, that is, there is no change in Agno3, and the increase in grams is because NaHCO3 becomes an equimolar nano3 [Na conservation].

So: δm NaHCO3

nano3－nahco3＝1 84x x＝

The mass of agno3 in the original mixture grams.