Question

10.0 g
kcl is dissolved in 1000g of water .if the density of the solution is 0.997g cm-3. calculate molarity and molality of the solution​

Answer 1

The molarity and molality are 0.1325 M and 0.1342 respectively.

Given:

10.0 g KCL is dissolved in 1000g of water. if the density of the solution is 0.997g cm-3.

To Find:

The molarity and molality of the solution.

Solution:

To find the molarity and molality of the solution we will follow the following steps:

As given in the question:

Mass of KCl = 10g

Mass of water = 1000g

Mass of the solution = 10 + 1000 = 1010g

The density of solution = 0.997g/ml

Also,

The molecular mass of KCl = 39 + 35.5 = 74.5 g

The volume of solution =

$\frac{mass}{density} = \frac{1010}{0.997} = 1013 \: ml$

As we know,

Molarity =

$\frac{given \: mass}{molecular \: mass \times volume \: of \: solution \: in \: ml} \times 1000$

Now,

Putting values in the above formula we get,

$\frac{10}{74.5 \times 1013} \times 1000 = 0.1325 \: mol \: {l}^{ - 1}$

Also,

Molality formula =

$\frac{given \: mass}{molecular \: mass \times mass \: of \: solvent \: in \: g} \times 1000$

Now,

Putting values we get,

Molality =

$\frac{10}{74.5 \times 1000} \times 1000 = 0.1342 \: mol \: {kg}^{ - 1}$

Henceforth, molarity and molality are 0.1325 M and 0.1342 respectively.

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