00:01
Okay, we have 100 cubic centimeters of a .2 molar solution of methylamine in a conical flask, titrated with a 0 .1 molar solution of hydrochloric acid until the equivalence point is reached.
00:12
This is essentially what's happening.
00:15
We're looking for the equivalence point.
00:18
Okay, given the kb of methylamine, what is the volume of acid required in cubic centimeters? so the balanced chemical equation is the methylamine reacts with the hydrochloric acid.
00:33
To form ch3nh3 plus plus cl minus.
00:44
And essentially the chlorine is a spectator and because it doesn't really matter which acid is reacting with as long as it's a strong acid.
00:53
Anyway, but we know that it is a balanced chemical equation.
00:55
It's one to one.
00:56
You always want to check that because since it's one to one, i can just use m1 v1 equals m2 to v2 to find the volume at the equivalent point.
01:07
So our molarity of methylomeen is .20000.
01:11
Our volume is the 100 cubic centimeters.
01:15
Our new molarity, i'm sorry, the molarity of the hcl is 0 .10 -0 molar and the volume is what we're looking for, the volume of acid required.
01:26
So you can just solve her v .2 times 100 divided by the point one and you get 200 cubic centimeters of the acid to reach equivalence point.
01:42
Now for part ii, wants the number of moles of the base in the flask and to find moles, it's just molarity times the cubic decimeters.
01:54
Excuse me times cubic decimeters will give us the moles of the substance.
01:59
So for you use the point two zero zero of the for the molarity of the methylamine and then change the cubic centimeters into cubic decimators, which would be a 0 .1 .00 cubic decimeters there and you'll get the moles.
02:19
So when you multiply, you get 0 .02 0 .0 moles of the methylamine, ch3 and h2.
02:31
Okay, so we found the 200 cubic centimeters for the acid and 0 .0200 two zero zero moles of the methylamine and our equation was th3 and h2 plus the acid whatever it is.
02:50
The chlorine remember is a spectator ion.
02:52
We'll form our conjugate acid which is the th3nh3 plus.
02:57
So i'm writing it, i'm rewriting the equation this way because i just want to ignore the chlorine the spectator ion.
03:03
Now to find the number of moles of conjugate acid in the flask because we're at equivalence point, right? so we started with point 0200 .2 .0.
03:13
Moles of the base and we're going to use up that base to reach equivalence point 0 .0 to 0 0 0moles of the acids were used to get to that equivalence point.
03:31
We didn't have any of the acid to begin with but we're going to completely use those up.
03:35
So this would be the initial and this would be the final or the equilibrium amounts.
03:42
Essentially, you're going to use the 1 to 1 to 1 ratio there.
03:46
Everything has a coefficient of 1, and you'll get 0 to 0 -200 moles of the conjugate acid at equivalence point.
03:57
And that is your answer for part 3.
04:06
Then to find the concentration of the conjugate acid in the flask, we're going to take our moles of conjugate acid at equivalence point and divide by our total volume at equivalence point.
04:18
And so we had 100 cubic centimeters of the base and 200 cubic centimeters of the acid.
04:27
So we're at 300 cubic centimeters total or 0 .30 cubic decimeters...