00:01
For this problem, we're trying to determine how many moles of nh4cl, which would be the same thing as this nh4 plus up here, that we would need to add to some ammonia to make a buffer solution with a ph equal to 9.
00:18
So ph and h plus are related to each other.
00:24
So to go from h plus to ph, it's 10 to the negative ph.
00:30
So 1 times 10 to the negative ninth, because our ph was 9, equals our ka.
00:39
So we have kb for ammonia as this.
00:41
So we take 1 times 10 to the negative 14th, divided by this kb, and we will end up with 5 .6 times 10 to the negative 10th.
00:49
So that's our ka, 5 .6 times 10 to the negative 10th.
00:54
And then we want our acid information on the top and our base information on the bottom.
00:58
What we're trying to figure out is our acid information.
01:01
So initially, we have zero of that acid, and we are going to add some moles of that.
01:05
We need to figure out how many moles of the ammonia we have.
01:09
So we take 2 liters times 0 .1 molar.
01:12
So 2 times 0 .1 equals 0 .2.
01:15
So we start out with 0 .2 molar.
01:18
And then we are going to subtract from there because we're adding acid.
01:24
And we don't know how much of that.
01:26
That is what we are trying to determine.
01:30
So let's go ahead and solve this...