Question

 A solution containing 8.32 g of para-aminobenzoic acid (PABA) and 150 g of chloroform boils at 62.62℃. At the same pressure, pure chloroform boils at 61.15℃. What is the molecular mass of PABA? The K_b for chloroform is 3.63℃/m.

Answer 1

The empirical formula for PABA$= C_7H_2NO_2$ , with a molar mass of $137.14g/mol$

Chloroform$CHCl_3$ has a molar mass of $119.38g/mol$

$\therefore$ $W_{C_7H_{2}NO_2}$ $=8.2g$

$W_{CHCl_3}=150g$

$\Delta _{{T}_{b}}$ $=61.15°C$

$m=$ $W_{C_7H_2NO_2}\over mC_7H_2NO_2$ $\times$ $1000\over w$

$m=$ $8.2\over 137.14$ $\times$ $1000\over 1000$ $=0.0598$

$0.62\over 3.63\times 0.0598$ $\times$ $1000$ $=134.60$

Molecular mass of PABA$=134.60g/mol$