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 06-01-2012, 01:03 PM #1 Banned   Status: Pre-Health Join Date: Jan 2011 Posts: 580 weak acid question SDN Members don't see this ad. (About Ads) 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.
 06-01-2012, 01:21 PM #2 Member   Status: Pre-Dental Join Date: Feb 2012 Posts: 44 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?
06-01-2012, 01:32 PM   #3
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Quote:
 Originally Posted by 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?
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?

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