# pH

#### Temperature101

##### Membership Revoked
Removed
Which one of the following best approximates the pH of a solution when 99.9% of the acid in a pH 1 solution is neutralized?
A. 1
B. 4
C. 6.7
D. 7

I know the answer is B, can someone explain? I forgot the log properties.

#### chiddler

##### Full Member
10+ Year Member
pH 1 = 0.1 M H+

get rid of 99.9% of that and 0.1% remains which, in decimal form, is 0.001

so 0.1 * 0.001 = 0.0001 M H+

pH = -log(0.0001) = 4

do you mean you need help with converting -log(0.0001) into 4?

if so:

-log(0.0001) = -log(10^-4) = pH

put negative on other side

-pH = log(10^-4)

raise pH to the 10th power

10^-pH = 10^-4

so -pH = -4, and pH = 4

#### Temperature101

##### Membership Revoked
Removed
pH 1 = 0.1 M H+

get rid of 99.9% of that and 0.1% remains which, in decimal form, is 0.001

so 0.1 * 0.001 = 0.0001 M H+

pH = -log(0.0001) = 4

do you mean you need help with converting -log(0.0001) into 4?

if so:

-log(0.0001) = -log(10^-4) = pH

put negative on other side

-pH = log(10^-4)

raise pH to the 10th power

10^-pH = 10^-4

so -pH = -4, and pH = 4

Thanks...

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