00:01
That we have this reaction between the hc and hydrogen cyanide and oxygen at 25 degree which is hcn plus oh h produce water and cyanide ion so first of all we would know that uh we want we we actually know that the k a of the acid hydrogen cyanide is a weak acid and has a k a of uh 6 .2 times 10 to the negative 10 power now the next step, we want to find out the conjugated base, cn, this one has a base dissociation constant, kb.
00:52
So how do we get the kb? in our case, we know that kb basically is the reverse reaction here.
01:02
Cn, this is the conjugated base plus water, produce hcn plus oh.
01:12
So kb is this reaction constant.
01:18
So we know that the kb is for this reverse reaction.
01:25
So from there, you can see that since we know that base has a base dissociated constant of kb, now we want to find out the relationship between ka and kb.
01:37
So what we know is that kb of cn -ion, the cyanide ion can be calculated by the kw divided by ka.
01:48
Kw is the, we call it water dissociation equilibrium constant, and this is always a constant number, which is 1 .0 times 10 to negative 14.
02:03
So if we know ka, we can calculate kb.
02:07
So 1 times 10 to negative 14 divided by 6 .2 times 10 to the negative 14.
02:14
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