Question

How many grams of ammonium chloride must be added to 0.050 kg of water to produce a

solution that freezes at -5.00 °C? The cryoscopic constant of water is 1.86 °C kg mol-1

. The

molar mass of ammonium chloride is 53.5 g mol-1

.

Answer 1

W_B - ?; M_B = 53.5 g/mol; W_A = 0.05 kg; ∆T = 5 °C

∆T = (K_f×W_B)/(M_B×W_A)

W_B = (∆T×M_B×W_A)/K_f

W_B = (5 °C × 53.5 g/mol × 0.05 kg)/(1.86 °C kg/mol) = 7.19 g

Answer: 7.19 g