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MCAT Physics Question — pH

A NaOH solution has an  OH concentration of 1x10-5M. What is the pH of the solution?


A. 2

B. 5

C. 9

D. 12

Click for Explanation

Two relationships are necessary for this solution:

pOH = -log[OH]     and    pOH + pH = 14

pOH = -log[1×10-5] = 5, and 14 – 5 = 9.


A. 2, incorrect, This results from subtracting the pOH from 7.

B. 5, incorrect, This is the pOH.

C. 9, correct.

D. 12, incorrect, This results from adding the pOH to 7.

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