Acid/Base & pH question

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AlwaysLucky

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From TPRH (Pg 370, Question 5):

If 90% of 1.0 M NaOH is neutralized during the dissolution of HCl gas, then the pH of the final solution is:

A) 0.9
B) 7.0
C) 8.0
D) 13.0

The answer is D.

Can anyone explain their steps in getting this answer? I read the answer key, but don't really understand.

My steps were the following: Because 10% of NaOH remains, the solution will be basic (so the answer is either C or D). But I don't know how to solve it from here .. help! Thanks!
 
From TPRH (Pg 370, Question 5):

If 90% of 1.0 M NaOH is neutralized during the dissolution of HCl gas, then the pH of the final solution is:

A) 0.9
B) 7.0
C) 8.0
D) 13.0

The answer is D.

Can anyone explain their steps in getting this answer? I read the answer key, but don't really understand.

My steps were the following: Because 10% of NaOH remains, the solution will be basic (so the answer is either C or D). But I don't know how to solve it from here .. help! Thanks!
10% or 0.1 OH .......pH + pOH = 14....
pOH = -log (OH).... pOH = -log(0.1) = -log(10^-1) = 1
pH + 1 = 14 .....pH = 13
 
since ten percent of NaOH is remain, the concentration to consider would be .1 M NaOH. From there find pOH as so:
pOH= -log(OH)
pOH=-log(.1M) -->(1x10^-1)
pOH=-log(1)+-log(10^-1)
pOH=0+1
pOH=1
now find pH from pOH as so:
pkw=pH+pOH
14=pH+1
pH=14-1
pH=13

hope that helped
 

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