00:01
You have 50 milligrams of calcium phosphate in a 250 milliliter solution.
00:06
Find the concentrations of the ions, so calcium and your phosphate ions, and we have to do it in milli equivalents per liter.
00:13
So let's first talk about milli equivalents per liter and how to convert them from parts per million and back again.
00:19
So a milli equivalents to parts per million is just the ion concentration, so let's do that, divided by the charge times the molar mass.
00:28
Now if you're going from parts per million to milli equivalents per liter, you take the concentration in parts per million, divide it by the molar mass, and then multiply it by the charge.
00:38
So what we're going to be using is we're going to be using the second one, converting from parts per million to milli equivalents per liter.
00:45
Now i chose parts per million because parts per million, the units, are just milligrams per liter.
00:50
So we have milligrams, we have milliliters, but we can easily convert these milliliters to liters by dividing by a thousand.
00:57
So that's going to be 0 .2500 liters of our solution.
01:05
So let's first consider the 50 milligrams of calcium phosphate, and let's figure out how many moles that is.
01:13
So we have the molar masses for our calcium and our phosphate.
01:17
So for calcium 3 -phosphate, what we're going to have to do is we're going to take 3 times 40 .08, and we're going to add that to 2 times 94 .971, which is the molar mass for the phosphate.
01:36
So let's do that math.
01:38
We have 30 times 40 .08 plus 2 times 94 .971, and our total molecular weight is going to be 310 .182 grams.
01:52
And note this is grams of calcium phosphate.
01:56
There we go.
01:57
So now let's convert 50 milligrams to moles.
02:03
So we can say one mole over 310 .182 grams, or we can say millimole to milligrams.
02:17
And that way we don't have to convert at all from milligrams to grams and back again.
02:24
So we're going to take 50 .0, divide it by our molar mass, and we're going to come up with 0 .161196 millimoles.
02:36
And this is millimoles of calcium phosphate.
02:45
So i'm going to scroll to give us a little bit more room.
02:48
So now we want to figure out for calcium ions.
02:51
So if we're starting with 0 .161196 millimoles of our calcium phosphate, we're going to use a ratio of 3 to 1.
03:08
So we have one millimole.
03:11
I'm just going to shorten that to cp for calcium phosphate.
03:14
That's going to have three millimoles of calcium.
03:18
So now we're in millimoles of calcium for every one millimole that we have.
03:25
That weighs 40 .08 milligrams.
03:29
Now let's do the same thing with our phosphate.
03:33
We have 0 .161196, and we're just going to shorten that.
03:40
For here we have one millimole of cp...