00:01
The first thing we need to do is calculate the hydronium concentration from the ph.
00:05
Ph is 10 to the, sorry, hydronium is 10 to the negative ph.
00:10
Having that and recognizing that ka for any weak acid, in this case the ammonium concentration, is equal to the hydronium concentration squared divided by the concentration of the ammonium minus the hydronium concentration.
00:32
We want to calculate this concentration knowing ka for ammonium.
00:37
They didn't give that to us, so we'll have to look it up.
00:44
Kw is 1 .0 times 10 to the negative 14.
00:48
If we divide that by kb for ammonia at 1 .8 times 10 to the negative 5, we will get ka for ammonium.
00:56
We then set that equal to the hydronium concentration, 6 .92 times 10 to the negative 6.
01:04
We square that and then divide by the concentration of ammonium minus 6 .92 times 10 to the negative 6.
01:18
So if we multiply both sides by this entire denominator, we get 5 .56 times 10 to the negative 10 minus, whoops, times ammonium minus 3 .84 times 10 to the negative 15 equals 6 .92 to the negative 6 squared, or 4 .79 times 10 to the negative 11...