Question

$5$g of an unknown solute is dissolved in $295$ g solvent. If molarity and density of solution are $0.05$M and $1.5$ g/cc respectively. The molecular weight of unknown solute is:

• A. $375$
• B. $425$
• C. $400$
• D. $500$

Answer 1

Answer: (D)

$500$

Given,

Weight of Solute = 5 gm

Weight of Solvent=295 gm

molarity = 0.05 m

density = 1.5 g/cc

$Molarity=\frac{WeightofSolute}{MolecularWeightofSolute\times VolumeofSolutioninLitre}$

$0.05=\frac{5}{M\times V}$

$M.V.=\frac{500}{5}=100$ (1)

$density=\frac{m}{v}$

$1.5=\frac{295+5}{v}$

$v=200cc$ (2)

equation (1) and (2)

$M=\frac{100}{200}\times 1000=500$