Chemistry is a science of extremes. In the sense that the actual, real, describing the reality of the numbers in it are either extremely small or extremely large. Too many would be scared by a number with 23 zeros. This is really a lot. But so many units (pieces) are contained in one mole of substance. Would you like to carry out calculations with such colossal numbers? It is not comfortable. But nowadays, any student solves chemistry problems with a sheet of paper and a simple calculator. This is possible thanks to the special simplification language created by chemists. And one of the main phrases of this language is “molar mass”.
Formula by definition
Determining molar mass is simple: the mass of a substance should be divided by its chemical amount. That is, you will find out how much one mole of a given substance weighs. There is another way to determine the molar mass, but the main thing here is not to get confused. The molar mass is numerically equal to the atomic or molecular mass. But the units are different.
But why?
In what situations might you need a molar mass? A classic example is the need to identify the formula of a substance. Not all substances and in all situations can be determined by chemical properties and appearance; sometimes it is necessary to consider quantitative ratios. If you know the actual quantities of substances, you can calculate the type of atoms and their proportions in the substance. And you will need the help of an old chemist. Really very old. Mendeleev himself.
Relationships of concepts
How will the table of the great scientist help us? The molar mass of a substance is equal in number to atomic (for atomic substances and pure metals) or molecular weight, but is measured in other units. This characteristic of the substance will be listed in grams per mole, molecular - in atomic units of mass. How is it that these numbers are the same? Those values that you see in the table for the elements were calculated empirically. We managed to weigh each type of atom and determine its mass in convenient units. Therefore, you see not minus the twenty-seventh degree, but quite decent numbers, most often within one and a hundred. There are heavyweight elements, but they are not usually mentioned in school books.
If not all numbers are at hand
But what if a substance consists of molecules and you know what it is? How is the molar mass of a substance sought if there is no mass of it and no chemical quantity at the same time according to the conditions of the problem? It's simple, find each type of atom (element) in the table and multiply the atomic mass by the number of atoms in the molecule for different elements. And then just summarize - and you get a molecular mass that will exactly match the molar mass. Everything has already been prepared for modern young chemists - for the well-known formula of the substance, the desired value is not a problem to calculate.
If you understand the essence of chemistry, it will seem very easy to you. The main burden in mastering this science is to study and memorize the properties of specific substances, but the general processes and descriptions are nowhere simpler. Once you understand, practice, you will never get confused in life.