Question

To prepare 0.1 M $KMn{O}_4$ solution in 250 mL flask, the weight of $KMn{O}_4$ required is:

• A. $4.80g$
• B. $3.95g$
• C. $39.5g$
• D. $0.48g$

Answer 1

Answer: (B)

$3.95g$

Definition:

Molarity is a measure of the concentration of a solute in a solution or of any chemical species, in terms of amount of a substance in a given volume. A commonly used unit for molar concentration used in chemistry is mol/L. A solution of concentration 1 mol/L is also denoted as 1 molar (1 M).

Molar concentration or molarity is most commonly expressed in units of moles of solute per litre of solution. For use in broader applications, it is defined as amount of solute per unit volume of solution, or per unit volume available for the species, represented by lowercase c:

$c=\frac{n}{V}$

where,

$n$= no. of moles of solute.

$V$= volume of solution in litres.

Calculation:

Let the weight required be $x$ g.

Molarity $c=0.1M$

Number of moles of $KMn{O}_4$ is $n=\frac{x}{158.034}$ moles

The volume of solution in litrs is $V=\frac{250}{1000}=0.25$ litres

Molarity of the given solution is given as $c=\frac{n}{V}$

$c=\frac{\frac{x}{158.034}}{0.25}=0.1⟹x=158.034\times 0.1\times 0.25⟹x=3.95$ g

Therefore, weight of $KMn{O}_4$ required is $3.95$ g.