Q: A solution is prepared by dissolving 0.35 mol of pantothenic acid in 1.00 kg of water. If the freezing point depression constant $$K_f$$ for water is $$1.86\ ^\circ\mathrm{C}\cdot\mathrm{kg}\cdot\mathrm{mol}^{-1}$$, what is the expected decrease in freezing point?

$$\Delta T_f = 0.35 \times 1.86 = 0.65\ ^\circ\mathrm{C}$$

Question 1

Which of the following statements best explains why the freezing point of a solution is lower than that of the pure solvent when a nonvolatile solute is added?

Accepted Answer

The solute disrupts the equilibrium between solid and liquid phases, requiring a lower temperature to reestablish equilibrium.

Question 2

Given the equation $$\Delta T_f = m \cdot K_f$$, what does the variable $$m$$ represent?

Accepted Answer

Molality of the solute

Question 3

A solution is prepared by dissolving 0.35 mol of pantothenic acid in 1.00 kg of water. If the freezing point depression constant $$K_f$$ for water is $$1.86\ ^\circ\mathrm{C}\cdot\mathrm{kg}\cdot\mathrm{mol}^{-1}$$, what is the expected decrease in freezing point?

Accepted Answer

$$\Delta T_f = 0.35 	imes 1.86 = 0.65\ ^\circ\mathrm{C}$$

Question 4

Which of the following solutions will produce the largest increase in boiling point upon addition to 1 kg of water?

Accepted Answer

2 mol KCl

Question 5

The osmotic pressure $$\Pi of a $$solution is given by $$\Pi = MRT. $$What does $$R$$ represent in this equation?

Accepted Answer

The gas constant

Question 6

A biological cell is placed in a solution with a higher solute concentration than the cell's interior. What will happen due to osmosis?

Accepted Answer

Water will move out of the cell, causing it to shrink.

Question 7

Which of the following best describes a colligative property?

Accepted Answer

A property that depends on the amount of solute particles present, not their identity.

Question 8

For a solution of NaCl, which van't Hoff factor ($$i) $$should be used in colligative property calculations, assuming complete dissociation?

Accepted Answer

$$i = 2$$

Question 9

A solution is made by dissolving 0.186 g of an unknown organic substance in 2.18 g of camphor. The freezing point of pure camphor is $$179.8\ ^\circ\mathrm{C}$$ and the mixture freezes at $$176.7\ ^\circ\mathrm{C}. If$$ $$K_f$$ for camphor is $$40.0\ ^\circ\mathrm{C}\cdot\mathrm{kg}\cdot\mathrm{mol}^{-1}$$, what is the approximate molar mass of the solute?

Accepted Answer

109 g/mol

Question 10

Which of the following is true regarding the boiling point elevation of ionic solutions compared to non-ionic solutions of the same molarity?

Accepted Answer

Ionic solutions have a higher boiling point elevation due to the greater number of particles produced upon dissociation.

Question 11

If the osmotic pressure of a solution is measured to be 2.5 bar at 25$$^\circC$$, and the molarity is 1.0 mol/L, what is the value of the gas constant $$R$$ used in the calculation?

Accepted Answer

$$R = 0.08314\ \mathrm{bar}\cdot\mathrm{L}\cdot\mathrm{mol}^{-1}\cdot\mathrm{K}^{-1}$$

Question 12

Which of the following best describes the effect of adding a nonvolatile solute to a solvent on its vapor pressure?

Accepted Answer

The vapor pressure of the solution decreases.

Question 13

Which equation correctly represents the freezing point depression for an ionic solute?

Accepted Answer

$$\Delta T_f = i K_f m$$

Question 14

A solution of 0.1 mol/L NaCl and a solution of 0.1 mol/L glucose are prepared. Which will have the higher boiling point elevation and why?

Accepted Answer

The NaCl solution, because it produces more particles upon dissociation.

Question 15

Which of the following is the correct van't Hoff factor ($$i) $$for Al$$_2(SO$_4$$)$$_3$$ assuming complete dissociation?

Accepted Answer

$$i = 5$$

Question 16

Which of the following statements about osmosis is correct?

Accepted Answer

Osmosis is the net movement of solvent from the less concentrated solution into the more concentrated one.

Question 17

If a pressure greater than the osmotic pressure is applied to a solution separated by a semipermeable membrane, what will happen?

Accepted Answer

Solvent will move from the more concentrated solution to the less concentrated one (reverse osmosis).

Question 18

Which of the following is a method for determining the molar mass of a substance using colligative properties?

Accepted Answer

Using the freezing point depression to calculate the number of moles of solute.

Question 19

Substance A has a greater molecular weight than substance B. If 50 grams of each are dissolved in 250 grams of water in separate beakers, which statement is correct?

Accepted Answer

The vapor pressure of solution A will be lower than the vapor pressure of solution B.

Colligative Properties of Solutions: Freezing-Point Depression, Osmosis, and Determination of Molar Mass

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