Answer to Question #120786 in Inorganic Chemistry for Jamie koonoolal

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

T₂ = - 5.00 ^oC; T₁ = 0.00 ^oC; K_f = 1.86 ^oC*kg/mol; m_H2O = 0.050 kg; M_NH4Cl = 53.5 g/mol

T₁ - T₂ = K_f*b

b = n_NH4Cl/m_H2O = m_NH4Cl/(M_NH4Cl*m_H2O)

T₁ - T₂ = K_f*m_NH4Cl/(M_NH4Cl*m_H2O)

m_NH4Cl = M_NH4Cl*m_H2O*(T₁ - T₂)/K_f = 53.5*0.050*5/1.86 = 7.2 g