Question

Magnesium chloride is often used 10 melt ice on sidewalks. Considering that the solubility of magnesium chloride (95.21 g/mol) in water is 54.3 g per 100.0 g of water, what is the lowest temperature that you would expect to be able to melt ice with magnesium chloride? Assume ideal behavior. [K_f(water) = 1.86 degree C/m]

Answer 1

Answer – We are given, solubility of MgCl₂ = 54.3 g, mass of water = 100 g

Molar mass of MgCl₂ = 95.21 g/mol , Kf = 1.86^oC/m

First we need to calculate the moles MgCl₂

Moles of MgCl₂ = 54.3 g / 95.21 g.mol^-1

                          = 0.570 moles

So, molality of MgCl₂ = 0.570 moles / 0.100 kg

                                    = 5.70 m

So, ∆Tf = i*Kf*m

             = 2*1.86^oC/m * 5.70 m

            = 21.20 ^oC

So, Freezing point of solution = 0.0^oC - 21.20 ^oC

                                             = -21.20 ^oC

We know, freezing point and the melting point temp is same, so -21.20 ^oC would expect to be able to melt ice with magnesium chloride.