Which of the following solutions will have the lowest freezing point? a) 2.5 g o

Question

Which of the following solutions will have the lowest freezing point? a) 2.5 g of KCl in 100 g water b) 2.5 g of NH4Cl in 100 g water c) 2.5 g of NaOH in 100 g water Which of the following solutions will have the lowest freezing point? a) 2.5 g of KCl in 100 g water b) 2.5 g of NH4Cl in 100 g water c) 2.5 g of NaOH in 100 g water Which of the following solutions will have the lowest freezing point? a) 2.5 g of KCl in 100 g water b) 2.5 g of NH4Cl in 100 g water c) 2.5 g of NaOH in 100 g water a) 2.5 g of KCl in 100 g water b) 2.5 g of NH4Cl in 100 g water c) 2.5 g of NaOH in 100 g water

Explanation / Answer

dT = Kf x m x i

dT = (Freezing point of pure solvent) - (Freezing point of solution)

Kf = freezing point depression constant of solvent

i = van't hoff factor

m = molality of the solution.

All the solutions are made in water as a solvent so Kf constant,

all these 3 solutes have a van't hoff factor of 2 ( they can form 2 ions per molecule in solution).

so we need to determine molality.

molality = moles of solute / kg of solvent

the mass of the water is the same.

which solute has the greatest number of moles of solute

2.5g / 74.45g/mole
2.5g / 53.45g/mole or
2.6g / 40g/mole

this would be the NaOH, So NaOH solution will have the lowest freezing point

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