Question

A compound h2x with molar weight of 80 gram is dissolved in solvent having density of 0.4 gram ml assuming no change in volume up on dissolution the molarity of a 3.2 molar solution is ??

Answer 1

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So, this question can be solved by conversion of Molarity into molality

As we know that ,

Molarity = 3.2 M

let volume of solution = 1000ml = Volume of solvent

Mass of solvent = 1000 × 0.4 = 400 g

since, Molarity of solution = 3.2 molar

so, N(solute) = 3.2 mol

Molarity (m) =
$\frac{3.2}{ \frac{400}{1000} } = \frac{3.2 \times 1000}{400}$ = 8
1000
400
​

3.2
​
=
400
3.2×1000
​
=8
Hence, Correct integer by solving is 8

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Answer 2

Molarity (M) = (No of moles of solute / Volume of solution in ml) *1000 …..(i)

Molarity of solution =3.2M

Molality (m) = (No of moles of solute /Mass of solvent in gm) *1000……. (ii)

Dividing (i) by (ii) we get,

M/m =[ (No of moles of solute / Volume of solution in ml) *1000]/ [(No of moles of solute /Mass of solvent in gm) *1000]

M/m = Mass of solvent in gm/ Volume of solution in ml

As we assume no change in the volume we get

M/m = Density

m= M/density

m =3.2/0.4

m= 8 molal