00:01
Hi, in this case we want to know what is the mass of sodium nitrate that we need to add to 400 grams of water to prepare a 0 .0525 molal solution.
00:19
So remember that the definition of molality is equal to mol of solute over kilogram of solvent.
00:30
So the first thing that we need to do is convert this 400 grams of water into kilograms, which is 0 .4 kilograms, and employ the information that we get from the molality.
00:46
So since molality is equal to amount of mol divided by mass in kilograms of the solvent, the amount of mol of the solute, in this case, of sodium nitrate, is going to be equal to to the molality times the mass of the solvent in kilograms.
01:03
So the amount of mol that we require of the solute is equal to 0 .0525 mol per kilogram times 0 .4 kilograms, giving us 0 .021 mol of sodium nitrate.
01:26
Now the mass of sodium nitrate that we're going to get is going to be equal to 0 .021 mol of sodium nitrate multiplied by its molecular weight, which is 85 grams per mole.
01:45
So 85 grams is equal to 1 mol of sodium nitrate...