weak acid question

[SN1]

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Consider hydrozoic acid, HN3. The Ka at 25 degree celsius is 2 x 10^-5. Which of these statements will be true if HN3 was put into solution.

a) [N3-] = [H+] at equilibrium
b) [H+] = 3[N-] at equilibrium
c) [H+]>[N-3] at equilibrium
d) A .10 M solution of HN3 has a pH of 5.2


the correct answer is "a" but I don't understand why. If I write equilibrium constant for the acid wouldn't it be

HN3 <----> H+ + 3N- ?

then shouldn't concentration of N- be 3 times as much as concentration of H+?

or is there something wrong with my equilibrium constant ?

thanks.

 

[jwest88]

So hydrozoic acid HN3 does not dissociate into 3N-(three nitrogen anions) and H+. Instead, it will dissociate into H+ and N3-(known as an azide ion), which is 3 N's bonded together with an overall negative charge. Does that make sense?

 

[SN1]

So hydrozoic acid HN3 does not dissociate into 3N-(three nitrogen anions) and H+. Instead, it will dissociate into H+ and N3-(known as an azide ion), which is 3 N's bonded together with an overall negative charge. Does that make sense?

Oh I didn't know that HN3 dissociate to H+ and N3-

is this because N3- is actually an anion and therefore I can NOT change the formula?

is there another weak acid that is similar to this?