Question

The density of an aqueous solution of salt (Formula weight = 60) is 1.080 g.cm^-3, and contains 18 % (W/V) of salt. The molality of the solution is
(A) 1.0
(B) 3.3
(C) 6.66
(D) 2.0​

Answer 1

answer : option (B)

explanation : The density of an aqueous solution of salt , d = 1.08g/cm³

so, mass of 1000ml solution = volume of salt solution × density of solution

= 1000ml × 1.08g/cm³ = 1080g

again, it is given that salt contains 18% (W/V) .

means, in 100ml of solution it contains 18g.

or, in 1000ml of solution , salt contains 180g.

so, mass of solvent = mass of solution- mass of solute

= 1080 - 180 = 900g

given, molecular weight of solute (salt) = 60g/mol

and mass of solute = 180g

so, number of mole of solute = 180/60 = 3moles

now, molality = number of moles of solute/mass of solvent in kg

= (3moles) × 1000/900g

= 30/9 = 10/3 = 3.3 m

hence, option (B) is correct choice.