Question

When dissolved in 1000 g of water, which chemical compound will produce a solution with the greatest freezing point depression?

a) 5.0 g of sodium chloride (NaCl)
b) 9.2 g of potassium chloride (KCl)
c) 11 g of calcium fluoride (CaF2)
d) 20 g of glucose (C6H12O6)

Answer 1

c) 11 g of calcium fluoride (CaF2)

Step-by-step explanation:

Given :

Mass of solvent = M = 1000 g = 1 kg

Formula:

The depression in freezing point is given as:

`\Delta T = k_(f)*m`

where kf = freezing point depression constant for solvent

`m = molality = (moles of solute)/(kg solvent)`

`moles = (mass)/(molar mass)`

Calculation:

a) Mass of NaCl = 5.0 g

Molar mass = 58.44 g/mol

`Moles NaCl = (5)/(58.44) =0.0856`

`Molality(NaCl) = (0.0856 moles)/( 1 kg water) = 0.0856 m`

`\Delta T = k_(f)*0.0856`

b) Mass of KCl = 9.2 g

Molar mass = 74.55 g/mol

`Moles KCl = (9.2)/(74.55) =0.1234`

`Molality(KCl) = (0.1234 moles)/( 1 kg water) = 0.1234 m`

`\Delta T = k_(f)*0.1234`

c) Mass of CaF2 = 11.0 g

Molar mass = 78 g/mol

`Moles CaF2= (11)/(78) =0.1410`

`Molality(CaF2) = (0.1410 moles)/( 1 kg water) = 0.1410 m`

`\Delta T = k_(f)*0.1410`

d) Mass of glucose = 20.0 g

Molar mass = 180 g/mol

`Moles glucose = (20)/(180) =0.1111`

`Molality(glucose) = (0.1111 moles)/( 1 kg water) = 0.1111 m`

`\Delta T = k_(f)*0.1111`

Therefore, CaF2 will produce the greatest freezing point depression

Answer 2

The correct answer among the choice presented above would be option C. The solution that will have the greatest freezing point depression is 11 g of calcium fluoride (CaF2). This is because it has higher concentration among other solutions. Also, when it ionizes 3 ions are formed.