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Calcium lactate is a salt of a weak organic acid and is represented as Ca(Lac)_2. A saturated solution of Ca(Lac)_2 contains 0.13 mol of this salt in 0.5 litre solution. The pOH of this solution is 5.6. Assuming complete dissociation of the salt, calculate K_a for latic acid.

Answer»

Solution :`Ca(LAC)_2(s) to Ca(Lac)_2(aq) TOCA^(2+)(aq) + 2LAC^(-) (aq) `
`Lac^(-) (aq)+ H_2O hArrLaCH(aq) + OH^(-) (aq)`
Since it is salt of strong base and weak acid, its PH is CALCULATED as
pH=14-pOH=14-5.6=8.4
`8.4= 1/2[14+pK_a + log 0.52]` (`therefore`c = 2 × 0.13/0.5)
`pK_a`=(2 × 8.4) – 14 – log 0.52 = 3.08
`thereforeK_a=8.31xx10^(-4)`


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