00:01
When we add hcl to a solution of ammonia, the hcl reacts with the ammonia making ammonium and chloride.
00:08
If we don't add any more moles of hcl, then we have ammonia.
00:12
We'll still have some ammonia, but having made the ammonium, we now have a buffer solution.
00:18
But in this case, we've added more moles of hcl, 100 milliliters versus the 50 milliliters.
00:25
Thus we have excess hcl, and ph is governed solely by the excess hcl.
00:31
So to calculate the excess hcl concentration, which will be equal to the hydronium concentration, we'll take the moles of hcl total that we added.
00:42
100 milliliters is 0 .100 liters.
00:46
If we multiply that by its concentration of 0 .10 moles per liter, that'll give us moles hcl we add.
00:53
We then subtract off the moles of hcl that reacted.
00:56
That's going to be the 50 milliliters of ammonia, or 0 .050 liters, at a concentration of 0 .12 moles per liter.
01:09
So this is the moles of hcl we added.
01:12
This is the moles of hcl that reacted, which corresponds to the moles of ammonia present.
01:17
The difference is the excess.
01:20
We then divide that by the new total volume...