1.0 g of a weak monobasic acid HA in 100 g water lowers the freezing point by 0.155 K. If 0.45 g, of same acid requires 15 mL of N/5 NaOH solution for complete neutralistion then %, degree ofionization of acid is `(K_f " of H"_(2)O="1.86 K kg mol"^(-1))`. a)0.2 b)0.25 c)0.4 d)0.5

Options

A. 0.2
B. 0.25
C. 0.4
D. 0.5

Answer

B

Explanation

`triangleT_(f)=K_(f) xx (W_("acid"))/(M_("acid") xx W_(H_(2)O)) xx 1000, " "M_("acid") ("observed")=120`
Normal molecular mass of acid can be calculated as milli-equivalents of acid =milli-equivalents of base (for HA and NaOH, N=M)
`(0.45)/(M_("acid")) xx 1000 =15 xx 1/5 rArr M_("acid(normal)")=150, i=(150)/(120) rArr 1.25`
`i=1+alpha rArr 0.25 therefore % alpha=25`