MolSynapsequestion bank

MolSynapse / Question bank / Solutions and Colligative Properties / Concentration units and Henry's law

JEE Advanced levelSingle correct optionDifficulty 3 of 3so018

A solution of a solute (molar mass $M_{2}$ , in $g mo l^{- 1}$ ) has molarity $C$ ( $mol L^{- 1}$ ) and density $d$ ( $g m L^{- 1}$ ). The correct expression for its molality $m$ is

A $m = \frac{1000 C}{1000 d - C M _{2}}$
B $m = \frac{1000 C}{1000 d + C M _{2}}$
C $m = \frac{1000 C}{d - C M _{2}}$
D $m = \frac{C}{d - 1000 C M _{2}}$

Answer: A

Take

1000 mL

of solution: mass of solution

= 1000 d

g, solute mass

= C M_{2}

g, so solvent mass

= (1000 d - C M_{2})

g. Solute moles

= C

, hence

m = C / [(1000 d - C M_{2}) /1000] = 1000 C / (1000 d - C M_{2})

. Units of the other options do not balance or the sign is wrong.

Practice Solutions and Colligative Properties More on Concentration units and Henry's law

Previous questionNext question

More questions on Concentration units and Henry's law