Happens that there is such task: how to find the mass of the substance which is contained in any given volume of solution? The course of its decision depends on what basic data you have. It can be and very simple, literally in one action, and more difficult.
Instruction
1. For example, you should learn what amount of table salt contains in 150 milliliters of 25% solution. Decision: 25% solution – it means what contains in 100 milliliters of solution gram25 the dissolved substance (in this case table salt). In 150 milliliters, respectively, one and a half times more. Make multiplication: 25 * 1.5 = 37.5. Here and answer: 37.5 grams of table salt.
2. Alter statements of the problem a little. Let's assume, you were given the same 150 milliliters of solution of table salt. But instead of mass concentration molar is known – 1 M. Skolko of table salt contains in solution in this case? And there is nothing difficult. First of all, remember a chemical formula of table salt: NaCl. Having glanced in Mendeleyev's table, specify the atomic masses (rounded) of the elements making this substance: sodium – 23, chlorine – 35.5. Therefore, the molar mass of table salt – 58.5 g/mol.
3. And what is molar concentration? It is the number of moles of the dissolved substance 1 1 liter of 1-molar solution of table salt would contain 58.5 grams of this substance. How many does it contain in 150 milliliters? Having made multiplication, receive: 58.5 * 0.15 = 8.775 g. If you do not need high precision, it is possible to take result for 8.78 grams or for 8.8 grams.
4. Let's assume, the exact volume of solution and its density is known to you, but concentration of substance is unknown. How in that case to define its quantity in solution? Here the decision will take a little more time, but again will not cause difficulties. It is only necessary to find any reference book where there are tables of density of solutions. For each indicator of density the corresponding values it mass and molar concentration are given there.
5. For example: 200 milliliters of water solution of substance X, with a density of 1.15 g/ml are given. According to the table of solubility you found out that such density corresponds to 30% concentration of solution. How many substance X is in solution? Decision: if 100 milliliters of solution contain 30 grams of substance X, then in 200 milliliters: 30*2 = 60 grams.