In ordinary life we extremely seldom should face an issue of finding of amount of substance unless in case of the joint solution of problems on chemistry with the child school student.
Instruction
1. As is well-known from an initial course of chemistry, the amount of substance (n) is measured in moths and defines the number of the structural units of substance (electrons, protons, atoms, molecules, etc.) which are contained in the set weight (or volume).
2. It is convenient to use this physical quantity at the description of chemical reactions as molecules interact in quantity multiple to an integer, it is not dependent on their weight (coefficients reflect a ratio between amounts of the substances which reacted in the chemical equations).
3. Considering that in real experiments quantity of molecules (atoms) of substance too big, it it is inconvenient to apply in calculations. Instead it is accepted to express number of molecules in moths.
4. Thus amount of substance in one pier of in number equally constant Avogadro (NA = 6,022 141 79(30) ×1023 моль−1). When rounding we will receive NA = 6.02.1023
5. The uniqueness of this constant is that if number of molecules N = NA, then their weight in and. e. the m (atomic units of mass) is in number equal to their weight in grams. In other words, to translate and. e. m in grams, it is necessary just to increase them by NA.6.02.1023 * and. e. m = 1 g
6. Such portions of molecules (atoms) of substance are called mole of a substance. Means, the mol is a measure of amount of substance. 1 mol is equal 6.02.1023 structural particles of this substance.
7. Weight of one mole of a substance is called the molar mass (M). Molar weight is defined by multiplication of molecular mass of substance by constant Avogadro (NA).
8. Molecular weight is by addition of atomic mass of all atoms which are a part of a molecule of this substance. For example, for molecules of water (H2O) it will make: 1*2+16=18 gmol.
9. So, the amount of substance is calculated on a formula: n = mM where m is the mass of substance. The number of molecules is defined: N = NA*n, and for gases: V = Vm * n where Vm is the molar volume of gas equal 22.4 lmol (under normal conditions).
10. We receive the general ratio: n = mM = NNA = VVm