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

Hint: 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.