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02/01/2022 4:37 pm
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Calculate the mass of ascorbic acid (Vitamin C, C6H5O6) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. Kf = 3.9 K kg mol-1.
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02/01/2022 4:44 pm
Mass of acetic acid, w1 = 75 g
Molar mass of ascorbic acid (C6H8O6), M2 = 6 × 12 + 8 × 1 + 6 × 16
= 176 g mol-1
Lowering of melting point, ΔTf = 1.5 K
We know that,
ΔTf = \(\frac{K_f \times w_2 \times 1000}{M_2 \times w_1}\)
⇒ w2 = \(\frac{\Delta T_f \times M_2 \times w_1}{K_f \times 1000}\)
= \(\frac{1.5 \times 176 \times 75}{3.9 \times 1000}\)
= 5.08 g (approx)
Hence, 5.08 g of ascorbic acid is needed to be dissolved.