Properties of Solutions
The ratio of solubility acid per unit volume of n-heptane to that in 97.5% acetic acid is 4.95.
How many extractions of 10mL solution of stearic acid in 97.5% acetic with successive 10mL portions of n-petane are needed to reduce the residual stearic acid content of the acetic acid layer to less than 0.5% of its original value?
The answer is 3.
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1 solution
The ratio in each extraction is 4 . 9 5 1 . 0 0 ). The ratio of the concentration in the acetic acid to the total concentration is 1 . 0 0 + 4 . 3 9 1 . 0 0 = 5 . 9 5 1 . 0 0
But n repeated extractions leaves a concentration of 0.005:
5 . 9 5 1 . 0 0 =0.005 -nlog5.95=log0.05 n=2.97
Three extractions will suffice.