8. What is the concentration of ammonia in a popular window...

8. What is the concentration of ammonia in a popular window cleaner if 25.34 ml of 1.162 M HCl is needed to titrate a 10.00 ml sample of the cleaner? 9. If only 0.160 g of Ca(OH)$_2$ dissolves in 0.100 L of water, what is the $K_{sp}$ value for calcium hydroxide at that temperature? 10. What is the solubility of calcite (CaCO$_3$) in grams per milliliter at a temperature at which its $K_{sp} = 9.9 \times 10^{-9}$?

Transcript

00:01 So there's a lot going on in the question that's been posed.

00:03 So i'm going to, you know, kind of point out each little bit as we go.

00:08 The very first part was a strong acid and a strong base titration.

00:12 Those are very simple and very straightforward.

00:15 I've got the information kind of listed right there.

00:19 And it's a very simple little calculation.

00:23 The molarity of the acid times the volume of the acid is going to be equal to the molarity of the base times the volume of the base times the volume of the base and in titration, you end up having neutralization of a strong acid and a strong base to where the amount of acid is exactly the same at the equivalence point as the amount of base.

00:40 So all you have to do to solve that one is just plug in that 24 .5 here, plug those in over here and solve for ma right there.

00:50 So that one's very simple and straightforward.

00:52 The rest of it is about solubility product, which is equilibrium of a fairly insoluble solid.

01:00 In solution.

01:01 So they gave you magnesium hydroxide.

01:04 When solid magnesium hydroxide dissolves in water, it breaks into the magnesium plus two ion and two hydroxide ions.

01:13 That's because to make it a balanced equation.

01:16 That leaves you with a ratio for every one of these.

01:19 There will be one of those.

01:20 There will be two of those.

01:22 So it's a one to one to two.

01:23 The first question tells you that you have a concentration of hydroxide of 7 .44 times 10 the negative 5 molarity.

01:31 And then they ask you to find ksp, but then they also ask you to show or to tell how you find the concentration of the magnesium ion.

01:42 And it's very, very simple to find the magnesium concentration because for every one magnesium ion, there's two hydroxides.

01:50 So to go from this 7 .44 times 10 and negative 5 back to magnesium, you would just need to divide that by two.

01:59 So if you divide this number, the hydroxide by two, you're going to get the concentration of mg2 plus.

02:07 Very simple, just very simple mole ratio concepts there.

02:13 Then to find the value of ksp, this is the ksp equation that you would need to use.

02:21 So you would plug in the concentration of magnesium that you found when you divide it by two.

02:26 You would plug that in right here.

02:28 Then you would plug in that 7 .44 times 10 and negative 5 into the oh.

02:33 But what you have to watch out for on this one is you've got to make sure that you square that 7 .44 times 10 to the negative 5.

02:42 So the easiest way to solve that question or to solve what the value for ksp would be to take that 7 .44 times 10 to the negative 5 and square it, get that answer, and then multiply it by what you got for the magnesium.

02:56 And remember the magnesium was this right here.

02:59 That gives you the magnesium...

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