The mass fraction is the size showing what relation of mass of any component which is a part of solution or alloy, or mix to the lump of all components. She can say or in unit shares, or as a percentage. It is easy to understand that the mass fraction is closer to unit, the maintenance of this component in solution, alloy or mix is more.
Instruction
1. Let's review an example with substance – sodium chloride, or, in a different way, table salt. Let's assume, you have 200 milliliters of water solution of table salt, and you should calculate its mass fraction.
2. There are different ways of the solution of this task. For a start consider the simplest. If you had 200 pure milliliters how many its such quantity would weigh? Certainly, 200 grams or 0.2 kilograms. Density of fresh water is almost equal to unit. And how many solution of table salt weighs? Weigh at first the container with solution, it is desirable on laboratory scales for best accuracy.
3. Let's assume, the total weight was 320 grams. Pour solution in some other ware, and weigh empty capacity. It turned out that it weighs exactly 100 grams. Therefore, the weight of solution of salt will be: 320 – 100 = 220 grams. That is its density is equal: 220/200 = 1.1 grams/ml.
4. For simplicity of calculations it is admissible that at dissolution of salt in water its volume increased so slightly that it can be neglected. It turns out that contains in 200 milliliters of solution: 200 pure grams and 20 grams of chloride sodium, making totally those 220 grams. What mass fraction of chloride sodium? The problem is solved in one action: 20/220 = 0.909. Or, if to consider as a percentage, 9.09%. It is possible to accept the rounded value: 9.1%.
5. Well, and if you for any reason could not neither measure the volume of solution of chloride sodium, nor learn its weight? How then to define a mass fraction of solution? Very simply. At first you should measure salt solution density by the special device – the densitometer. And then to determine by special tables (they are in many chemical or physical reference books) to what percentage concentration of solution of table salt there corresponds such density. Percentage concentration, as you know, one of expressions of a mass fraction. Here so you found the answer to the question posed.