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17. SOLUBILITY OF SUBSTANCES. WAYS OF EXPRESSION OF CONCENTRATION OF SOLUTIONS.
Solutions call the uniform mixtures of variable structure containing two or more substances.
From solution components one substance is considered solvent, the others - solutes. For each couple the dissolved substance-solvent exists mixing border which characterizes solubility of substance. Solutions can be saturated and unsaturated. Such solution in which the dissolved substance does not pass into solution is called saturated.
If the content of substance in solution is less than solubility of this substance, then such solution is unsaturated.
The quantitative composition of solution can be quantitatively set in several ways. We will consider two ways of expression of concentration: percentage (mass fraction of solute) and molar concentration.
| Percentage, mass fraction of solute |
|
The mass fraction of the dissolved substance is the relation of mass of solute to the mass of solution.
For calculation of percentage the formula is used:
Solution consists as it has been told above, from solute and solvent. The mass of solution can be determined on formula:
These formulas are used for the solution of different tasks on рвсчёт concentration. |
| Molar mass |
|
Molar concentration is size in number equal to the relation of amount of solute to solution volume. Mol/l unit of measure.
Zadacha:98 of H2SO4 sulphuric acid was diluted up to the volume of 2 liters. Define molar strength of acid in solution. 2. On above to the given formula we define molar concentration from =1mol/2l =0,5 mol/l. Answer: 0,5 mol/l. |
At problem solving the formula which you studied on physics, density formula is often used. I will bring her here.
