Concentration of solution is the size showing what mass of any given substance contains in a certain volume or mass of solution. Even the person, farthest from chemistry, faces this concept literally continually: for example, buying in shop 9% vinegar for house conservation, or 20% cream to add them to coffee. How concentration of solution is calculated?
Instruction
1. Let's assume, in number of 200 or 300 milliliters of water dissolved 58.5 grams of chloride sodium, that is table salt well familiar to all. Then, flowing water, brought solution lump to one kilogram. It is simple to guess that solution will contain in this case 58.5 grams of salt and 941.5 grams of water. What will be a mass fraction of salt?
2. To calculate it as easy as shelling pears, for this purpose divide amount of salt into the lump of solution and increase by 100%, it will look as follows: (58.5/1000) * 100% = 5.85%.
3. Formulate a task a little in a different way. The same amount of salt was dissolved in water, then brought solution volume to one liter. What will be molar concentration of solution?
4. Remember definition molar concentration. It is the number of moles of the dissolved substance which is contained in one liter of solution. And to what the mol of table salt is equal? Its formula – NaCl, molar weight – about 58.5. In other words, one liter of solution at you contains exactly one mol of salt. You receive 1.0 molar solution.
5. Well, and now return to initial statements of the problem – where the total weight of solution was exactly one kilogram. How to you to find a molyalnost of such solution?
6. And here too there is nothing difficult. Above you already calculated that 941, 5 grams of water are the share of 58.5 grams of table salt. Substituting the known sizes in formula m = to v/M where m is value of a molyalnost, v is molal quantity in solution, and M - the mass of solvent in kilograms, receive: 1.0/0.9415 = 1.062 molal solution.