00:01
If you have 4 .8 327 grams of sodium chromate and you dilute it to 500 milliliters of water and we assume a density of 1 .0 grams per milliliter, find the molarity of sodium in the compound.
00:18
And we're given the molecular weights for sodium chromate and sodium.
00:23
So what we're going to do is we're going to take 4 .8 of 327 grams of our sodium chromate.
00:36
We're going to convert this to moles by saying one mole weighs 161 .97 grams.
00:47
And if we notice, our grams will cancel here.
00:51
Next, we're going to convert from one mole of the na2.
00:59
Cr -04, sodium chromate.
01:02
And this is going to give us two moles of sodium.
01:08
In fact, sodium plus ions.
01:10
That's what the little two represents, the little subscript after the sodium.
01:15
It just represents how many atoms that will be in there or how many moles that you will have per one mole of the entire compound.
01:24
So from here, we see that our moles of our sodium chromate cancel out.
01:30
Now i'm going to create a little gap because the next question asks us to convert from molarity to parts per thousand.
01:41
And we're going to need a mass for that.
01:45
But i don't want to have to calculate it twice.
01:48
So i'm just going to leave a gap.
01:49
And we're going to say moles of sodium.
01:54
And then we're going to convert those moles of sodium to grams right here.
01:58
So one mole of sodium is 22 .989.
02:09
So from here, all we have to do is a little bit of math.
02:13
So we're going to start with 4 .8 .327 divided by 161 .97, multiply that by 2, and we're going to end up with 0 .05967.
02:30
6, 7 moles of sodium plus, or our sodium ion.
02:37
Now, molarity for big m is just moles over liters.
02:49
So from here, we can just divide by 0 .50 liters, and we will get our molarity.
03:00
And our molarity is going to be 0 .11935 molarity of our sodium plus ion.
03:15
So now let's figure out the mass that we have so that we can answer the second question.
03:22
So if we take our previous answer and multiply it by 0 .5, we'll get back to the number of moles of sodium that we have.
03:29
So then we just take that number, multiply it by 22 .9898, and you will get 1 .37189 grams of sodium.
03:48
So now let's go down and let's calculate our molarity to parts per thousand.
03:55
So if we convert our grams, we'll say 1 .37189 grams of sodium plus.
04:07
I know it says convert molarity to parts per thousand, but parts per thousand is really just grams per liter.
04:16
So all we have to do is take our grams and divide it by 0 .5 and we will get our parts per thousand...