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20 mL of 0.2 M NaOH are added to 50 mL of 0.2 M CH3COOH (Ka = 1.8 x 10^-5) the pH of the solution is

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20 mL of 0.2 M NaOH are added to 50 mL of 0.2 M CH3COOH (Ka = 1.8 x 10-5) the pH of the solution is

(a) 4.56

(b) 4.73

(c) 9.45

(d) 6.78

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Answer is (a) 4.56

Explanation:

NaOH + CH3COOH ⇌ CH3COONa + H2O

20x0.2  50x0.2         0                  0

4           10               0                 0

0           6                 4                 4

Conc. = \(\frac{Millimoles}{Total\;Volume}\)

[CH3COOH] = \(\frac{6}{70}\); [CH3COONa] = \(\frac{4}{70}\)

pH = -log 1.8 x 10-5 + log \(\frac{\frac{4}{70}}{\frac{6}{70}}\)

pH = 4.56

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