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Chapter 13: Problem 62

How does increasing the concentration of a nonvolatile solute in water affect the following properties: (a) vapor pressure, (b) freezing point, (c) boiling point; (d) osmotic pressure?

Short Answer

Expert verified
Increasing the concentration of a nonvolatile solute in water: (a) lowers the vapor pressure due to solute molecules occupying the solvent's surface positions; (b) lowers the freezing point because solute particles interfere with the formation of an ordered lattice structure; (c) raises the boiling point as the solution needs to be heated to a higher temperature to reach atmospheric pressure; and (d) increases osmotic pressure due to a stronger osmotic gradient caused by the higher solute concentration.

Step by step solution

01

(a) Vapor Pressure

When a nonvolatile solute is added to water, the vapor pressure of the solution decreases compared to the pure solvent (water). This is because the solute molecules occupy some of the solvent molecules' surface positions, reducing the number of solvent molecules on the surface that can escape into the vapor phase. Hence, the vapor pressure of the solution is lower than that of the pure solvent.
02

(b) Freezing Point

Adding a nonvolatile solute to water lowers its freezing point. This phenomenon is known as freezing point depression. The reasoning behind this is that solute particles interfere with the formation of an ordered lattice structure, which is required for a substance to freeze. With a higher solute concentration, more particles cause this interference, resulting in a lower freezing point for the solution compared to the pure solvent.
03

(c) Boiling Point

The presence of a nonvolatile solute in water raises its boiling point. This effect is called boiling point elevation. When a solute is added, the vapor pressure of the solution is lowered compared to the pure solvent. To reach atmospheric pressure (which is required for boiling), the solution needs to be heated to a higher temperature than the pure solvent. Consequently, a higher temperature is needed for the solution to boil, thus raising its boiling point.
04

(d) Osmotic Pressure

Osmotic pressure is the pressure required to prevent osmosis from occurring when two solutions of different concentrations are separated by a semipermeable membrane. Increasing the concentration of nonvolatile solute in water increases the osmotic pressure of the solution. Higher solute concentration leads to a stronger osmotic gradient, and thus, a greater pressure is required to prevent water from flowing in through osmosis to dilute the solute-rich side.

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Most popular questions from this chapter

Using data from Table \(13.3,\) calculate the freezing and boiling points of each of the following solutions: (a) \(0.25 \mathrm{~m}\) glucose in ethanol; (b) \(20.0 \mathrm{~g}\) of decane, \(\mathrm{C}_{10} \mathrm{H}_{22}\), in \(50.0 \mathrm{~g} \mathrm{CHCl}_{3} ;\) (c) \(3.50 \mathrm{~g}\) \(\mathrm{NaOH}\) in \(175 \mathrm{~g}\) of water, (d) 0.45 mol ethylene glycol and \(0.15 \mathrm{~mol} \mathrm{KBr}\) in \(150 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}\)

Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of \(5.00 \mathrm{~g}\) of lauryl alcohol in \(0.100 \mathrm{~kg}\) of benzene freezes at \(4.1^{\circ} \mathrm{C}\). What is the approximate molar mass of lauryl alcohol?

Consider two solutions, one formed by adding \(10 \mathrm{~g}\) of glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) to \(1 \mathrm{~L}\) of water and the other formed by adding \(10 \mathrm{~g}\) of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) to \(1 \mathrm{~L}\) of water. Are the vapor pressures over the two solutions the same? Why or why not?

Water and glycerol, \(\mathrm{CH}_{2}(\mathrm{OH}) \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH},\) are miscible in all proportions. What does this mean? How do the OH groups of the alcohol molecule contribute to this miscibility?

How does the lattice energy of an ionic solid affect its solubility in water? [Section 13.1\(]\)
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