20% of acetic acid is dissociated when its 5 g is added to 500 mL of water. The depression in freezing point of such water is °C.

Atomic mass of C, H and O are 12, 1 and 16 a.m.u. respectively.

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Question

20% of acetic acid is dissociated when its 5 g is added to 500 mL of water. The depression in freezing point of such water is  °C.

Atomic mass of C, H and O are 12, 1 and 16 a.m.u. respectively.

[Given: Molal depression constant and density of water are 1.86 K kg mol⁻¹ and 1 g cm⁻³ respectively.]

Canvas Classes · Accepted Answer

Strategy:
 Calculate the molality of the acetic acid solution, then find the van't Hoff factor from the degree of dissociation. Finally, compute the freezing point depression.

Step 1: Calculate molality ()
- Mass of Acetic acid = 5 g. Molar mass = 60 g/mol.
- Moles = .
- Mass of solvent (water) = 500 g = 0.5 kg.

Step 2: Determine van't Hoff factor ()
Dissociation = 20%, so .

Step 3: Calculate 
.

Step 4: Express as 
.

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