Question

The addition of sodium cyanate to a cyanic acid solution causes the pH to?

Answer 1

A.Increase, due to the common ion effect
B.decrease due to the common ion effect
C.remain constant because a buffer forms
D.remain constant because sodium cyanate is a neutral salt

Answer 2

@Rushwr

Answer 3

\[NaOCN \rightarrow Na ^{+} + ^{-} OCN \] sodium cyanate

Answer 4

and cyanic acid, is a weak acid

\[CHOCN \rightarrow COCN + [H] \]

Answer 5

I think sodium cyanate isn't a neutral salt because NaOH strong base HOCN weak acid, so the salt would be basic I think so i think D is out

Answer 6

Yeah I think so, @Woodward what do you think? i think this would be a buffer

Answer 7

Honestly I don't know, I was thinking that it could do that but I haven't really played around with acid base stuff in a long time so I barely remember what a buffer is or how to do titrations. I was thinking the common ion effect in terms of this:

\[\large K = \frac{[H^+][^-OCN]}{[HOCN]}\]

So adding \([^-OCN]\) in the form of sodium cyanate would cause the numerator to increase. Since that would move it away from equilibrium, then it would have to bond with hydrogen ions to form the acid back to restore equilibrium again so that the denominator could increase, thus lowering the hydrogen ion concentration.

So I was thinking that the common ion effect would be increasing the pH, however I don't really know for sure if this is the right way of thinking about it or not.

Answer 8

@Woodward you are correct the answer is that it increases the pH

Answer 9

I thought it would be a buffer, I guess I was confused at that point

Answer 10

you see I guess we were adding only additional [-oCN] ions, like I thought that in solution we would have NaOCN and OCN- The weak acid and it's salt, so I guess my question was why wasn't this a buffer

Answer 11

yeah that was an amazing explanation

Answer 12

Yeah I think it will form a buffer, but it will not stay constant pH because of it! However if you add other acids or bases to the solution, the pH will not shift very much. At least that's my understanding of how buffers work but I forget the details past this of like the explanation haha! XD

Answer 13

You explained it perfectly, and I see that. I'm still a bit confused I guess I will have to look at buffers again usually it's weak acid and it's salt but I guess we aren't adding any acid or base just a common ion so maybe it wouldn't act as a buffer in this case?

Answer 14

I'm going to post one more another question