How to solve a problem using the chemical difference method? It s better to have sample questions

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.

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 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 introduction of carbon dioxide into the solid (which increases the mass of the solid) and the discharge of oxygen (which decreases the mass of the solid), then according to the law of conservation of mass, the change in the mass of the solid is the difference between the masses of the two gases.

Write the chemical equation equation, in this question, the relationship between the carbon of the acacia dioxide group, oxygen, and the increase in solid mass m is:

2co2 ~ o2 ~ m

x y can be solved to x=88* (cross method).

So the percentages are.

2CO2 + 2Na2O2 = 2Na2CO3 + O2--- solid loss and body mass increase stove plus.

2*44g---2*78g---2*106g---2*106-2*78)=56g

m = CO2 mass fraction = Sakura 10 = 88%.

A analysis: the first thermite reaction happens to be completely reactive, which means that all the electrons given by Al are transferred to the Fe element, and all Fe is reduced to elemental matter. Reacting with a sufficient amount of hydrochloric acid, since Fe can only be oxidized to +2 valence, fewer electrons will be given than it accepts, so less hydrogen will be generated.

The second part reacts with a sufficient amount of caustic soda, and Al transfers electrons directly to hydrogen to produce hydrogen, and we can assume that the second time also transfers electrons to Fe first, and then Fe releases all the accepted electrons to produce hydrogen.

Because the mixture is equal twice. Assuming that the amount of xfeo·yfe2o3 in the mixture is 1, then the first part produces hydrogen: x+2y, and the second part produces hydrogen:

2x+2y*3]/2。So [x+2y] [x+3y]=5:7, so x:

y=1:2First:[2(x+3y) 3]Al+xfeO·yFe2O3=(x+2y)Fe+[(x+3y) 3]Al2O3; fe+2hcl=fecl2+h2

xfeo·yfe2o3 (x+2y)fe (x+2y) h2 second part: 2al+2naoh+2h2o=2naalo2+3h2;

xfeo·yfe2o3~[2x+2y*3]/2 h2