Everyone should know how to find a mass of a substance

The course of school chemistry is an introductory textbook in a complex science. From the very beginning, students are trying to understand how to solve design problems. Let them have little practical application at the first stages, but if the student has learned about how to find the mass of substances that have reacted, then he can claim serious achievements.

Consider a simple example of a problem, on the basis of which you can learn to solve more complex ones. Suppose that for the complete combustion of carbon monoxide (II), you need 11.2 liters. How many grams of CO2 did you get?

1. We will formulate the reaction equation.

CO + O2 = CO2

2. Equalize for oxygen. There is some rule that in most cases can help you. Begin to arrange the coefficients from that substance whose number of atoms is odd. In this case, it is oxygen in the CO molecule. To it we put the coefficient 2. Since on the left two carbon atoms were formed, and on the right one is one, we put 2 before CO2. Thus, we get:

2CO + O2 = 2CO2

As you can see, there are four oxygen atoms in the left and right parts. Carbon is also in balance. Consequently, they called correctly.

3. Next, find the number of O2. The determination of the molecular weight for schoolchildren is too cumbersome and difficult to remember, so we will use a different method. Recall that there is a molar volume, which is 22.4 liters / mol. You need to find how many moles (n) reacted: n = V / V m. In our case, n = 0.5 mol.

4. Now make up the proportion. The amount of oxygen reacted is half that of n (CO2). This follows from the fact that 0.5 mol / 1 = x mol / 2. A simple ratio of the two quantities helped to form the correct equation. When we found x = 1, we can get an answer to the question of how to find mass.

5. Truth for the beginning it is necessary to recollect one more formula: m = M * n. The last variable was found, but what to do with M? The molar mass is the experimentally established value relative to hydrogen. It is designated by the letter M. Now we know that m (CO2) = 12 g / mol * 1 mole = 12 g. So we got the answer. As you can see, there is nothing complicated.

This task is very easy with respect to many others. But the main thing is to understand how to find mass. Imagine a molecule of some substance. It has long been known that a mole consists of 6 * 10 ^ 23 molecules. At the same time, in the Periodic Table there is an established mass of the element per mole. Sometimes it is necessary to calculate the molar mass of the substance. Assume M (H20) = 18 grams / mole. That is, one molecule of hydrogen has M = 1 gram / mol. But the water contains two H atoms. Also, do not forget about the presence of oxygen, which gives us another 16 grams. Summarizing, we get 18 grams / mole.

Theoretical calculation of the mass will subsequently have practical application. Especially for students who are waiting for a chemical workshop. Do not be afraid of this word if you are studying in a non-core school. But if chemistry is your core subject, it is better not to run the basic concepts. So, now you know how to find mass. Remember that in chemistry it is very important to be a consistent and considerate person who not only knows some algorithms, but also knows how to apply them.