The mass percent is the relation of mass of any component of solution, alloy or mix to the lump of the substances which are in this solution, expressed as a percentage. The it is higher than a percent, the maintenance of a component is more.
Instruction
1. Remember the task set for the great scientist Archimedes the tsar Giyeron and alter it a little. Let's assume, Archimedes found out that the roguish master jeweler stole a part of gold, having replaced it with silver. As a result, alloy of which the royal crown was made consisted of 150 cubic centimeters of gold and 100 cubic centimeters of silver. Task: to find mass percent of gold in this alloy.
2. Remember density of these precious metals. 1 cubic cm of gold contains 19.6 grams, in 1 cubic cm of silver – 10.5 grams. For simplification, you can round these sizes to 20 and 10 grams, respectively.
3. Further make calculations: 150*20 + 100*10 = 4000 grams, that is 4 kilograms. Such is the mass of the alloy which went for production of a crown. As in statements of the problem nothing is told about "production wastes", receive the answer: 150*20/4000 = 3/4 = 0.75. Or in a different way, 75%. Here the mass percent of gold in allegedly "purely gold" to Giyeron's crown was it.
4. And if you dealt with solution? For example, you were given such task: to define mass percent of table salt (sodium chloride) in its two-molar solution.
5. And there is nothing difficult at all. Remember what is molarity. It is molal quantity is 1 liter of solution. Mol, respectively, amount of substance which mass (in grams) is equal to its weight in atomic units. That is you should write only a formula of table salt and to learn the mass of its components (in atomic units), having looked in Mendeleyev's Table. The mass of sodium – 23 and. e. m, the mass of chlorine – 35.5 and. e. m. In the sum at you 58.5 grams/mol turn out. Respectively, mass of 2 moths of table salt = 117 grams.
6. Therefore, 1 liter water 2M solutions of chloride sodium contains 117 grams of this salt. What density of this solution? According to the table of density, you find that it is approximately equal to 1.08 g/ml. Therefore, 1 liter of such solution will contain about 1080 grams.
7. And further the problem is solved in one action. Having divided the mass of salt (117 grams) into the solution lump (1080 grams), receive: 117/1080 = 0.108. Or as a percentage – 10.8%. Such is mass percent of table salt in it 2M solution.