Calculate the pH of 9.2E-8 M NaOH, ignoring activity coefficients. Report the pH

Question

Calculate the pH of 9.2E-8 M NaOH, ignoring activity coefficients. Report the pH using the correct number of decimal places. The concentration of NaOH is given to two significant figures.  Therefore, your final pH should be reported to the nearest 0.01 pH unit (because Moodle does not check significant figures, it is safe to report an extra digit, such as 8.000). Calculate the pH of 9.2E-8 M NaOH, ignoring activity coefficients. Report the pH using the correct number of decimal places. The concentration of NaOH is given to two significant figures.  Therefore, your final pH should be reported to the nearest 0.01 pH unit (because Moodle does not check significant figures, it is safe to report an extra digit, such as 8.000).

Explanation / Answer

C = 9.2 x 10^-8 M

H2O ----> H+ + OH-

Ksp = 10^-14 = X * (9.2 x 10^-8 + X)

=> X = 6.41 x 10^-8

=> [OH-] = (9.2 +6.41) x 10^-8

=> [OH-] = 1.561 x 10^-7 M

=> pOH = 6.81

=> pH = 7.19

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