(Multiple choice) Calculate the pH of the solution resulting from the addition of 30.0 mL of....?

Question

Calculate the pH of the solution resulting from the addition of 30.0 mL of 0.15 M NaOH to 75 mL of 0.80 M HCN solution. [Ka = 4.9x10^-10 for HCN.]

A) 8.22
B) 3.60
C) 10.40
D) 8.18
E) 8.15

okay I keep getting 8.2, must be a sig fig problem, what do you guys get?

Answer 1

a

Answer 2

i'm getting 12.22 :S. If (for some unusual reason, nevertheless my uni chem textbook has executed this a pair of cases) you anticipate that the addition of the NaOH doesnt impact the quantity (as quickly as lower back, i can't see why, yet I even have seen it executed) then i'm getting 11.3. the only thank you to get an answer off that checklist is that if u use 10mL because of the fact the quantity :S. and that's for e) 13.0 does all human beings else have any clue? undesirable question?

Answer 3

just remember that the digits in front of the decimal don't count towards sig figs for the pH. So, if there are 2 sig figs then there should be 2 digits after the decimal. 8.22 is the answer I got if that helps