00:02
Here, this question is asking about the colligative property known as freezing point depression.
00:17
And freezing point depression tells us that when we add a solute to a solvent, the freezing point is going to be lowered.
00:27
The more the freezing point is lowered, the lower the freezing point, of course.
00:31
So this is called a colligative property because it's only dependent upon the number of particles that are present, not the actual identity of the substance.
00:41
Alright, so we're dealing with freezing point depression here, and to calculate how much the freezing point changes, we need to use the equation that says the change in the freezing point is equal to the constant, the freezing constant for the solvent, which is kf, multiplied times the molality of the substance, multiplied times i, which is the vantahoff factor.
01:08
And this is the number of particles the solute breaks into.
01:21
When we put it into water, since water's our solvent here.
01:30
Okay, so for each of these, we are given the molality.
01:35
Kf is going to be the same for each one, because kf for water is 1 .86, and that's degrees celsius per molal.
01:45
All right, so let's go ahead and calculate how much the freezing point changes for each of these solutions.
01:53
So for our first one, 1 .86 degrees celsius per molal times its molality, which is 0 .25, times the vantahoff factor.
02:11
So we have sodium sulfate, 2 sodium and 1 sulfate.
02:19
So we have 2 sodium, 1 sulfate for a total of 3 particles.
02:24
When this breaks apart, we'll get 2 sodium and 1 sulfate.
02:27
So i is 3.
02:30
When we multiply these together and express it to just two significant figures, since our molality only has two, we get 1 .4 degrees celsius.
02:39
That's how much the temperature is going to change.
02:42
Repeating this for each of our other ones.
02:45
Change in freezing point for the second one.
02:48
1 .86.
02:50
The freezing constant is not going to change because the solvent is the same for each of these.
02:56
This molality is 0 .50.
03:00
And for i, we have kcl...