00:02
In this video, we're going to be looking at a few questions related to solutions.
00:06
Let's take a look at the first part.
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We're asked to figure out the mass of sodium chloride needed to make a 2 % solution, 2 % solution by mass, with 85 grams of water.
00:19
Now, mass percent is going to be the mass of the solute over the mass of the total solution than times 100.
00:27
So let's take a look at how we would set this up.
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We want to know the mass of the sodium chloride.
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So i'm going to use that as an x.
00:35
We'll put an x there.
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Now that's divided by the total mass of the solution.
00:41
So we have 85.
00:42
That's the 85 grams.
00:45
But remember that we are adding at least a certain mass of sodium chloride to that.
00:50
So whatever it is, the total mass of the solution is also going to be the 85 grams of water plus whatever mass of the sodium chloride we have to add is.
00:59
Now we're going to multiply that by 100 in order to get the mass percent.
01:04
Of course, if we don't do that, it's still going to end up as just 0 .02.
01:09
Okay, so just set up really a little algebra question for ourselves.
01:12
Whatever the mass is, x, divided by the total mass, 85 grams plus x, is going to equal our 2%.
01:20
That's going to be 0 .02.
01:23
So we need to simply solve for x.
01:26
So we'll multiply both sides by 85 .0 plus.
01:30
Plus x and so let's go ahead and look at a little bit of the algebra so that's going to give us x equals 85 times 0 .02 is 1 .7 plus 0 .02x now we're going to isolate x and we're going to subtract 0 .02x from both sides so we get 0 .98x equals 1 .7 of course get x by itself and that turns out to be 1 .73 .3 grams of nacl.
02:07
You could also do it by trial and error, but this setting of this up algebraically gives you a definitive answer.
02:14
Okay, the second question is a little bit different.
02:17
It says in an aqueous solution of calcium chloride, which end of the water molecule is going to be facing the calcium ions? this is kind of interesting...