Question

50 ml of an alkaline water sample requires 10.4 ml of 0.05 N HCl upto phenolphthalein end point and total 14.3 ml of the acid for complete neutralization. Find types and amount of alkalinities in water.

Answer 1

$V_b = 50ml\\ V_a\ (incomplete) = 10.4 ml \\ C_a = 0.05 N = 0.05M\\ V_a = 14.3ml$

The reaction is;

$HCl + xOH \to H_2O + xCl$

During incomplete neutralisation, the phenolphthalein concentration is;

$\dfrac{0.05 × 10.4 }{50} = C_b = 0.0104M$

However, during complete neutralisation, the final concentration of the alkali water is;

$\dfrac{0.05 × 14.3 }{50} = C_b = 0.0143M$