3) What is the freezing point of a 3.0 m aqueous solution of NaCl? (The freezing point depression constant for water is 1.86 °C kg solvent/mol solute.) a) 5.6 °C b) -5.6 °C c) 11°C d) -11°C

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**Question 3: Freezing Point Depression Calculation**

**Problem Statement:**
What is the freezing point of a 3.0 m (molal) aqueous solution of NaCl (Sodium Chloride)? The freezing point depression constant (\(K_f\)) for water is 1.86°C kg solvent/mol solute.

**Options:**

a) 5.6°C  
b) -5.6°C  
c) 11°C  
d) -11°C

### Explanation:

To solve this problem, we'll use the freezing point depression formula:

\[ \Delta T_f = i \times K_f \times m \]

where:
- \(\Delta T_f\) is the freezing point depression,
- \(i\) is the van't Hoff factor (which represents the number of particles the solute splits into),
- \(K_f\) is the freezing point depression constant,

For NaCl, which dissociates into two ions (Na\(^+\) and Cl\(^-\)), the van't Hoff factor (\(i\)) is 2.

Given:
- \(K_f = 1.86^\circ\)C kg/mol,
- \(m = 3.0\) mol/kg (molality).

Plug these values into the formula to find \(\Delta T_f\):

\[ \Delta T_f = 2 \times 1.86 \,^\circ\text{C kg/mol} \times 3.0 \,\text{mol/kg} \]
\[ \Delta T_f = 2 \times 5.58 \,^\circ\text{C} \]
\[ \Delta T_f = 11.16 \,^\circ\text{C} \]

The freezing point of pure water is 0°C. The freezing point of the solution will be lowered by 11.16°C from pure water's freezing point. Thus, the new freezing point is:

\[ 0^\circ\text{C} - 11.16^\circ\text{C} = -11.16^\circ\text{C} \]

However, the closest match to this calculation in the options provided is:

**d) -11°C**
Transcribed Image Text:**Question 3: Freezing Point Depression Calculation** **Problem Statement:** What is the freezing point of a 3.0 m (molal) aqueous solution of NaCl (Sodium Chloride)? The freezing point depression constant (\(K_f\)) for water is 1.86°C kg solvent/mol solute. **Options:** a) 5.6°C b) -5.6°C c) 11°C d) -11°C ### Explanation: To solve this problem, we'll use the freezing point depression formula: \[ \Delta T_f = i \times K_f \times m \] where: - \(\Delta T_f\) is the freezing point depression, - \(i\) is the van't Hoff factor (which represents the number of particles the solute splits into), - \(K_f\) is the freezing point depression constant, For NaCl, which dissociates into two ions (Na\(^+\) and Cl\(^-\)), the van't Hoff factor (\(i\)) is 2. Given: - \(K_f = 1.86^\circ\)C kg/mol, - \(m = 3.0\) mol/kg (molality). Plug these values into the formula to find \(\Delta T_f\): \[ \Delta T_f = 2 \times 1.86 \,^\circ\text{C kg/mol} \times 3.0 \,\text{mol/kg} \] \[ \Delta T_f = 2 \times 5.58 \,^\circ\text{C} \] \[ \Delta T_f = 11.16 \,^\circ\text{C} \] The freezing point of pure water is 0°C. The freezing point of the solution will be lowered by 11.16°C from pure water's freezing point. Thus, the new freezing point is: \[ 0^\circ\text{C} - 11.16^\circ\text{C} = -11.16^\circ\text{C} \] However, the closest match to this calculation in the options provided is: **d) -11°C**
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