Homework Help: CHEMISTRY> HELP QUICK! pls

Posted by Lucinda on Friday, June 4, 2010 at 9:32pm.

I GOT THIS WRONG IN AN ASSIGNMENT. I HAVE AN EXAM IN 2 DAYS. CAN YOU SHOW ME HOW TO DO IT PLS.
What is the pH of a 2.62 x 10 -1 M NaNO2 solution ? NB the pKa for HNO2 = 3.153.

12.13
13.42
1.87
8.29
0.58

CHEMISTRY> HELP QUICK! pls - DrBob222, Saturday, June 5, 2010 at 12:21am
NaNO2 is the salt of a strong base (NaOH) and a weak acid (HNO2). The NO2^- is hydrolyzed.
NO2^- + HOH ==> HNO2 + OH^-

Kb = (Kw/Ka) = (HNO2)(OH^-)/(NO2^-)
Set up an ICE chart.
You know Kw. You can calculate Ka from pKa. (HNO2) will be x. (OH^-) will be x. (NO2^-) = 0.262. Solve for x, convert to pOH, then to pH. I found pH = 8.285 which I would round to 8.28 but I would pick the 8.29 for the answer.

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