a. To a 25 mL volumetric flask at 25.0°C was added 0.100 g of ethylene glycol, H

Question

a. To a 25 mL volumetric flask at 25.0°C was added 0.100 g of ethylene glycol, HOCH2CH2OH; the flask was filled to the calibration mark with water. What was the osmotic pressure of the resultant aqueous solution? b. What mass in grams of calcium chloride must be used at 25.0°C to prepare 50.0 mL of an aqueous solution with the same osmotic pressure as the solution in Part a above has? c. If equal masses of sodium chloride and calcium chloride were added to separate samples of water to give equal volumes of aqueous solution at the same temperature, will the osmotic pressure of the aqueous sodium chloride solution be greater than, less than, equal to, or cannot be determined compared with the osmotic pressure of the aqueous calcium chloride solution? Justify your choice.

Explanation / Answer

a)

mass of ethylene glycol = 0.100 g

moles of ethylene glycol = 0.1 / 62.07 = 1.611 x 10^-3 mol

volume = 25 mL = 0.025 L

Molarity = moles / volume = 1.611 x 10^-3 / 0.025

              = 0.0644 M

temperature = 25 oC = 298 K

osmatic pressure = M x S x T

                          = 0.0644 x 0.0821 x 298

                          = 1.58 atm

osmatic pressure = 1.58 atm

b)

osmatic pressure = M x S x T

1.58 = 3 x M x 0.0821 x 298

M = 0.02148 M

Molarity = moles / volume

0.02148 = moles / 0.050

moles = 1.074 x 10^-3 mol

mass of CaCl2 = 1.074 x 10^-3 x 110.98

                        = 0.119 g CaCl2

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