Part A: Calculate the mass of solute required to make a sodium chloride solution

Question

Part A: Calculate the mass of solute required to make a sodium chloride solution containing 158 g of water that has a melting point of -2.7 C

Part B: Calculate the mass of solute required to make 255 mL of a magnesium sulfate solution that has an osmotic pressure of 3.99 atm at 301 K

Part C: Calculate the mass of solute required to make an iron(III) chloride solution containing 265 g of water that has a boiling point of 112 C.

Using the vant Hoff factors in the table below, calculate the mass of solute required to make each aqueous solution. Van't Hoff factors at 0.05 m concentration in aqueous solution Solute Expected Measured 1 1 Nonelectrolyte 2 NaCl 1.9 2 MgSO4 1.3 MgCl2 2.7 S04 2.6 4 FeCl3 3.4

Explanation / Answer

A)

for NaCl = i = 1.9

delta Tf = i x Kf x m

To - Tf = 1.9 x 1.86 x m

2.7 = 3.534 m

m = 0.764

molality = moles of solute / mass of solvent

0.764 = moles / 0.158

moles = 0.1207

mass / molar mass = 0.1207

mass / 58.5 = 0.1207

mass of solute = 7.06 g

B)

osmatic pressure = i x M x S x T

3.99 = 1.3 x M x 0.0821 x 301

M = 0.124

Molarity = moles / volume

0.124 = moles / 0.255

moels = 0.03167

mass of solute = 3.81 g

c)

delta Tb = i x Kb x m

12 = 3.4 x 0.512 x m

m = 6.893

moles / mass of solvent = 6.893

moles / 0.265 = 6.893

moles = 1.827

mass of solute = 296.3 g

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