400 mL of a buffer contains 0.50 M HA and 0.50 M NaA. Find the magnitude of the pH change (two decimals) when 0.020 mol of HCl is added, assuming no volume change.

Numerical answer type, tolerance 0.01.

Answer: 0.0872

HA = 0.200 mol, A

^{-}

= 0.200 mol. After HCl: HA = 0.220, A

^{-}

= 0.180.

Δ pH = lo g (0.180/0.220) = - 0.0872

; magnitude 0.09.

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