Question

$5$ moles of $AB_2$ weigh $125 \times 10^{-3}\; kg$ and $10$ moles of $A_2B_2$ weigh $300 \times 10^{-3} \; kg$. The molar mass of $A(M_A)$ and molar mass of $B(M_B) $ in $kg\, mol^{-1}$ are :

• A. $M_A = 50 \times 10^{-3} $ and $M_B = 25 \times 10^{-3}$
• B. $M_A = 25\times 10^{-3} $ and $M_B = 50\times 10^{-3}$
• C. $M_A = 5 \times 10^{-3} $ and $M_B = 10 \times 10^{-3}$
• D. $M_A = 10 \times 10^{-3} $ and $M_B = 5 \times 10^{-3}$

Answer 1

Answer: (C)

$5[M_A + 2M_B] = 125$
$M_A + 2M_B = 25$ ....(1)
$2M_A + 2M_B = 30$ ....(2)
from eq. (1) & (2)
$M_A = 5$
$M_B = 10$