Practicing Success

Target Exam

CUET

Subject

Chemistry

Chapter

Physical: Solutions

Question:

The elevation in boiling point for 13.44 g of CuCl2 dissolved in 1 kg of water as solvent will be (Kb = 0.52 kg/J, molar mass of CuCl2 = 134.4 g/mol)

Options:

0.05

0.10

0.16

0.20

Correct Answer:

0.16

Explanation:

To calculate the elevation in boiling point caused by the addition of CuCl2 to water, we can use the formula:

\(\Delta T_b = K_b \cdot m \cdot i\)

where:
\(\Delta T_b\) is the elevation in boiling point,
\(K_b\) is the ebullioscopic constant of the solvent (water),
\(m\) is the molality of the solute (CuCl2), and
\(i\) is the Van't Hoff factor, which represents the number of particles formed when the solute dissolves.

First, we need to calculate the molality of CuCl2. Molality (\(m\)) is defined as the moles of solute per kilogram of solvent. Since we have 13.44 g of CuCl2 and 1 kg of water, we need to convert the mass of CuCl2 to moles:

\(\text{moles of }CuCl_2 = \frac{{\text{mass of }CuCl_2}}{{\text{molar mass of }CuCl_2}}\)
\(\text{moles of }CuCl_2 = \frac{{13.44 \, \text{g}}}{{134.4 \, \text{g/mol}}} = 0.1 \, \text{mol}\)

Now we can calculate the molality:

\(m = \frac{{\text{moles of solute}}}{{\text{mass of solvent kg}}} = \frac{{0.1 \, \text{mol}}}{{1 \, \text{kg}}} = 0.1 \, \text{mol/kg}\)

The Van't Hoff factor (\(i\)) for CuCl2 is 3 because it dissociates into three particles (Cu2+ and 2 Cl-) when it dissolves.

Now we can calculate the elevation in boiling point:

\(\Delta T_b = K_b \cdot m \cdot i = 0.52 \, \text{kg/J} \cdot 0.1 \, \text{mol/kg} \cdot 3 = 0.156 \, \text{K}\)

The elevation in boiling point is 0.156 K, which is approximately equal to 0.16 K. Therefore, the answer is option (3).