Calculate the mass of ascorbic acid (Molar mass = 176 g mol–1) to be dissolved in 75 g of acetic acid, to lower its freezing point by 1·5^oC.
(K_f = 3·9 K kg mol–1)

Mass of ascorbic acid ( W _A ) = 75 g = 0.075 kg (W_A)=75 g=0.075 kg
Depression in melting point ( Δ T_f ) = 1.5^∘C = 1.5 K
ΔT_f)=1.5^∘C=1.5 K Molar mass of ascorbic acid ( M_B ) = ( 12 × 6 ) + ( 8 × 1 ) + ( 16 × 6 ) = 176 g mol − 1 (MB)=(12×6)+(8×1)+(16×6)=176 g mol-1
Molal depression constant ( K _f ) = 3.9 K kg mol – 1
(K_f) = 3.9 K kg mol^-1
W _B = (176 g mol ⁻¹) × ( 1.5 K ) × ( 0.075 kg ) ( 3.9 K kg mol⁻¹ ) = 5.08g