The molar share is the size characterizing the relation of number of moles of this substance to total number of moths of all substances which are in mix or solution. To define molar shares of substances, only Mendeleyev's table and elementary ability to make calculations is necessary.
Instruction
1. To define a molar share of any given substance, you need to calculate at first number of moles and this substance and all other substances which are contained in mix (solution) then to substitute these sizes in the following formula: X = n1/Σn, where X – a molar share of the substance interesting us, n1 – the number of his moths, and Σn – the sum of number of moles of all available substances.
2. Review an example. You are faced by the following task: there is a mix from 29 grams of chloride sodium and 33.3 grams of chloride calcium. It was dissolved in 540 grams of water. It is necessary to calculate a molar share of chloride sodium in the formed solution.
3. First of all, write formulas of all substances, after that determine their molar masses by Mendeleyev's table where atomic masses of all elements are specified: NaCl – molar weight is equal to 58. As the atomic mass of sodium 23, and chlorine – 35 (23+35=58); CaCl2 – molar weight is equal to 110. The atomic mass of calcium 40, chlorine – 35 (40+(35+35))=110); H2O – molar weight is equal to 18. The atomic mass of hydrogen 1, oxygen – 16 (1+1+16=18).
4. For simplification of calculations you can round sizes also. If high precision is desirable, then already you need to consider in calculations that the atomic mass of calcium – 40.08, chlorine – 35.45, and sodium – 22.98.
5. Determine the number of moles of each initial substance. For this purpose divide amount of chloride sodium known to you, chloride calcium and water into their molar masses, and receive the following results: - for chloride sodium: 29 / 58 = 0.5 asking; - for chloride calcium: 33.3 / 111 = 0.3 asking; - for water: 540 / 18 = 30 moths.
6. Substitute all above-stated sizes in a formula and define a molar share of chloride sodium. The formula will look as follows: 0.5 / (0.5 + 0.3 + 30) = 0.5/30.8 = 0.0162.