Question

The $10.6$ gm of a substance of molecular weight $106$ was dissolved in $100ml$. $10ml$ of this solution was pipetted out into a $1000ml$ flask and made up to the mark with distilled water. The molarity of the resulting solution is:
A.$1M$
B.${10^{ - 2}}M$
C.${10^{ - 3}}M$
D.${10^{ - 4}}M$

Answer 1

The molarity can be calculated from the number of moles and volume of solution in liters. Moles of solute can be calculated from weight and molar mass of a substance. The volume and molarity have the relation and the molarity can be calculated by substituting the volume in that formula.

Formula used:
${M_1}{V_1} = {M_2}{V_2}$
${M_1}$ is the initial molarity
${V_1}$ is the initial volume
${M_2}$ is the final molarity
${V_2}$ is the final volume

Complete answer:
Molarity is also known as molar concentration. Given that the $10.6$ gm of a substance of molecular weight $106$ was dissolved in $100ml$.
Molarity will be obtained by dividing weight by molar mass and volume of solution in litres. Its volume is in millilitres molarity should multiply with $1000$ .
By substituting the values, will get
Thus, molarity will be $\dfrac{{10.6}}{{106}} \times \dfrac{{1000}}{{100}} = 1M$
The initial molarity ${M_1}$ is $1M$
Initial volume ${V_1}$ is $10ml$
The final volume ${V_2}$ is $1000ml$
By substituting the values in the formula, will get the value of final molarity.
${M_2} = \dfrac{{1 \times 10}}{{1000}} = {10^{ - 2}}M$
Thus, the final molarity is ${10^{ - 2}}M$. Therefore, Option (B) is the correct option.

Note:
While calculating the molarity, the volume of solution must be in litres. If the volume of solution is not in litres it should multiply with the value of $1000$ as molarity is defined as the number of moles of solute dissolved in volume of solution in litres.