Guide

1

To determine the mole

**share**of a substance, you will need to first calculate the number of moles, and the substance and all other substances contained in the mixture (solution), and then substitute these values inthe following formula: X = n1 / Σn, where X - mole fraction of the substance of interest to us, n1 - the number of its moles and Σn - the sum of the number of moles of all the available materials. 2

Consider an example.Before you is the following problem: there is a mixture of 29 grams of sodium chloride and 33.3 grams of calcium chloride.It was dissolved in 540 grams of water.It is necessary to calculate the mole fraction of

**sodium chloride in the resulting solution.** 3

First, write the formula of all substances, then determine their molar masses by means of the periodic table, which shows the atomic weights of all the elements: NaCl - molar mass equal to 58. Since the atomic weight of sodium 23 and chlorine- 35 (23 + 35 = 58); CaCl2 - molar mass equal to 110 atomic mass of 40, calcium, chlorine - 35 (40 + (35 + 35)) = 110); H2O - the molar mass is 18. The atomic mass of hydrogen 1,oxygen - 16 (1 + 1 + 16 = 18).

4

To simplify the calculations, you can also round off the value.If the desired high precision, even then you need to take into account in the calculations that the atomic weight of calcium - 40.08, chlorine - 35.45, and sodium - 22.98.

5

Determine the number of moles of each of the starting material.To do this, you divide the number of known sodium chloride, calcium chloride and water on their molar mass, and get the following results: - for sodium chloride: 29/58 = 0.5 mol - for calcium chloride: 33.3 / 111 = 0,3 mol; - water: 540/18 = 30 mol.

6

Put all of the above values in the formula and determine the mole fraction of

**sodium chloride.The formula is as follows: 0.5 / (0.5 + 0.3 + 30) = 0.5 / 30.8 = 0.0162.** Sources:

- Calculate the molar