Question

How many grams of ammonia chloride must be added to 0.05kg of water to produce a solution that freezes at -5°C? The cryoscopic constant of water is 1.86°C kg mol-1. The molar mass of ammonium chloride is 53.5gmol-1

Answer 1

W_B = unknown

M_B = 53.5 g/mol

W_A = 0.05 kg

∆T = 5 °C

K_f = 1.86 °C×kg/mol

∆T = (K_f×W_B)/(M_B×W_A)

W_B = (∆T×M_B×W_A)/K_f

W_B = (5×53.5×0.05)/1.86 = 7.19 g

Answer: 7.2 g