[vmaggio]

Tell me if i did this totally wrong.

heres the question
What is the pH of a buffered system made by dissolving 10.70 g of ammonium chloride and 20.00 mL of 12.0 M ammonia in enough water to make 1.000 L of solution? Kb = 0.000018 for ammonia.


Ok, so heres what i did.

10.70g/(53.49)(1.)L) = .20M
(12.0M)(.020L)= .24mol/1.0L= .24M

pKa= 14-(-log(.000018)) = 9.255

therefore,   pH= 9.255 + log (.24/.20)  = 9.33



and the choices are.

A. 7.00
B  9.18
C. 9.26
D. 9.33
E. 11.32


so i got one of the answers, but did i do it right?

[Nick]

Yes, you used the Henderson-Hasselbalch equation correctly.