Question

Molecular weight of urea is 60. A solution of urea containing 6g urea in one liter is
A) $1$ molar
B) $1.5$molar
C) $0.1$molar
D) $0.01$molar

Answer 1

Hint: The amount of solute dissolved in a given amount of the solvent is known as concentration. Molarity is a way to express the concentration of a solution. We will determine the moles of urea by using mole formula. Then by using molarity formula determine the molarity.

Complete step by step solution:
Determine the mole of urea as follows:
${\text{Mole}}\,{\text{ = }}\,\dfrac{{{\text{Mass}}}}{{{\text{Molar}}\,{\text{mass}}}}$
Molar mass of the urea is $60\,{\text{g/mol}}$ .
Substitute $60\,{\text{g/mol}}$ for molar mass and $6$ gram for mass.
\[{\text{Mole}}\,{\text{ = }}\,\dfrac{{6\,{\text{g}}}}{{60\,{\text{g/mol}}}}\]
\[\Rightarrow {\text{Mole}}\,{\text{ = }}\,0.1\,{\text{mol}}\]
Formula of molarity is as follows:

${\text{Molarity}}\,{\text{ = }}\,\dfrac{{{\text{Moles}}\,{\text{of}}\,{\text{solute}}}}{{{\text{Litter}}\,{\text{of}}\,{\text{solution}}}}$

Substitute $0.1$ for mole of solute (urea) and one liter for volume of solution.
${\text{Molarity}}\,{\text{ = }}\,\dfrac{{{\text{0}}{\text{.1}}\,{\text{Mol}}}}{{{\text{1}}\,{\text{L}}}}$
$\Rightarrow {\text{Molarity}}\,{\text{ = }}\,0.1\,{\text{mol/L}}$

So, a solution of urea containing $6\,{\text{g}}$ urea in one liter is known as $0.1$ molar.

Therefore, option (C) $0.1$ molar, is correct.

Note: Molarity is defined as the amount of solute dissolved in a volume of solution. The amount of solute is taken in the form of mole and the volume of the solution is taken as per litre. When the concentration is defined in terms of molarity the solution is known as molar solution.
Concentration is also defined in some other terms as a molality, mole concentration, normality. Molality is defined as the moles of the solute dissolved in per ${\text{kg}}$of the solvent. When the concentration is defined in terms of molality the solution is known as molal solution. Normality is defined as the gram equivalent of the solute dissolved in per litter of the solution.