Cross method (Note: only applicable to the mixture of two substances M A: molar mass M B: molar mass M Mix: molar mass N of the mixture formed by A and B: amount of substance B.

According to:

Hybrid merger-hybrid merger

M- mixing

B: m, b, m, a, m.

Draw:

N A: N B =(M mixed -M B): (M A -M mixed)

{M, a, m and m, b must be quantities of the same nature (that is, if they are molar masses, they must all be molar masses, if they are formula quantities, they must all be formula quantities). The relationship between X, Y and M: X, Y and M can be mutually calculated in the chemical reaction formula (for example, in the chemical reaction formula, the amount of substance N and the thermal change Q in the reaction can be mutually calculated, then the ratio of Q is Q A/Q B =(N N- mixing < N A, the ratio of N A /n B =(Q mixing -q mixing) /(Q A-q mixing) Q.

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1 cross multiplication

2 Cross comparison method

3 cross elimination method

4 application

Edit this paragraph | Back to the top cross multiplication This is a method of writing the chemical formula of a substance with valence, which is suitable for compounds composed of two elements or two groups. Its principle is the law of price number: the algebraic sum of the total number of positive prices and the total number of negative prices is 0 or the absolute value of the total number of positive prices and the total number of negative prices is equal. Now let's take a look at its operation steps with the following example.

Edit this paragraph | Back-to-Top Cross Comparison Method The cross comparison method we often say is actually a cross comparison method, which is a graphic method. In fact, the cross diagram method is a simple algorithm to replace the summation formula. It is especially suitable for calculating the mixture of two quantities and two relationships (that is, the calculation of 2-2 mixture) and calculating the ratio of two components in the mixture.

Edit this paragraph | Go back to the top cross elimination method. Cross elimination method is called cross elimination method for short. This is a solution to the problem of ion reasoning. Using "cross-elimination method" can narrow the range of unknown substances, so as to determine substances under given conditions and find out the correct answer.

In fact, the intersection method is a simple method to solve binary linear equations. If you are really not used to it, you can solve the equation, but I will tell you. For example, the density of A is 10 B, and the density of their mixture is 9, so you can put 9 in the middle, write 10 and 8 on the left, and then subtract 9 respectively to get the ratio of 1 and 1 on the right. 438+0: 1 This example is relatively simple, but the difficulty is the same. Please experience for yourself. This method actually saves time, especially when it comes to comprehensive examination.

Edit the cross method in the calculation of | topping application (1) mixed gas in this paragraph.

Example At room temperature, 1 volume of ethylene is mixed with a certain amount of gaseous unknown hydrocarbon, the relative density of mixed gas and hydrogen is measured as 12, and the volume of the hydrocarbon is calculated.

According to the calculation of relative density, the average molecular formula of mixed gas is 24, and the molecular formula of ethylene is 28, so the molecular formula of unknown hydrocarbons must be less than 24, and the hydrocarbons less than 24 are only methane. By using the cross method, we can find that the volume of methane is 0.5.

(2) Cross method for calculating the atomic percentage of isotopes.

There are two isotopes of bromine. In nature, these two isotopes account for about half. It is known that bromine has an atomic number of 35 and an atomic weight of 80, so the neutron number of two isotopes of bromine is equal to.

(A)79、8 1 (B)45、46 (C)44、45 (D)44、46

According to the cross method, the difference between the atomic weights of two isotopes and bromine is equal, so their neutron numbers should be different by 2, so the answer is D.

(3) Cross method in solution preparation calculation

Example A Students should prepare100g of 40% NaOH solution, and there are 10% NaOH solution and NaOH solids in the laboratory. How many grams of each of the above substances should this student take?

The analysis shows that the solute of 10%NaOH solution is 10, the solid solute of NaOH is 100, and the solute of 40%NaOH solution is 40. The required 10% NaOH solution was obtained by orthogonal method.

× 100 = 66.7g, and NaOH solid is×100 = 33.3g ..

(4) Cross method in calculation of mixed reaction.

For example,100g mixture of lithium carbonate and barium carbonate consumes the same amount of hydrochloric acid when they react with hydrochloric acid of a certain concentration as when100g calcium carbonate reacts with hydrochloric acid of this concentration. Calculate the molar ratio of lithium carbonate to barium carbonate in the mixture.

The formula amount of calcium carbonate can be understood as the average formula amount of the mixture of lithium carbonate and barium carbonate, and the ratio of lithium carbonate to barium carbonate can be calculated by cross method, which is 97:26.

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