# Colligative properties of solutions concept questions and answers

1. What are colligative properties?

Colligative properties are properties of solutions that depend on the number of solute particles in solution, not the nature or type of solute particles.

2. What are the main colligative properties?

The main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

3. How does the addition of a solute affect the boiling point of a solution?

Adding a non-volatile solute to a solution elevates the boiling point of the solution compared to that of the pure solvent. This is because the solute particles interfere with the vaporization of the solvent.

4. What is the concept behind freezing point depression?

The freezing point of a solution is lower than that of the pure solvent. This is because the presence of solute particles disrupts the ability of the solvent particles to form a regular crystal lattice, which is necessary for freezing.

5. What is osmotic pressure and why does it occur?

Osmotic pressure is the pressure required to stop osmosis, the movement of solvent particles from an area of lower solute concentration to an area of higher solute concentration. Osmosis occurs because systems tend towards equilibrium; the solvent moves to balance the solute concentrations on both sides of a semipermeable membrane.

6. Why does adding a solute to a solvent decrease its vapor pressure?

Adding a solute to a solvent decreases its vapor pressure because fewer solvent molecules are at the surface and can enter the vapor phase. This is because the solute particles block the solvent particles from escaping.

7. What is Raoult’s law and when can it be applied?

Raoult’s law states that the partial pressure of a solvent over a solution is equal to the vapor pressure of the pure solvent times its mole fraction in the solution. It can be applied when the solute and solvent are very similar chemically (such as two volatile liquids), meaning the solution is nearly ideal.

8. How can colligative properties be used to determine molar mass?

The molar mass of an unknown solute can be determined by measuring one of the colligative properties (e.g., boiling point elevation or freezing point depression) and using the appropriate formula.

9. What is the van’t Hoff factor and why is it important?

The van’t Hoff factor (i) is the ratio of actual solute particles to theoretical solute particles in a solution. It is important because it accounts for solute particles that may dissociate or associate in solution, affecting the observed colligative properties.

10. What are ideal and nonideal solutions?

Ideal solutions obey Raoult’s law at all concentrations and temperatures, whereas nonideal solutions do not. In ideal solutions, the interactions between solvent and solute particles are the same as those among the solvent particles themselves.

1. How do colligative properties change with the amount of solute added?

As more solute is added, the colligative properties become more pronounced – the vapor pressure decreases further, and the boiling point increases and the freezing point decreases further.

1. What does it mean when a solution is hypertonic?

A hypertonic solution has a higher solute concentration compared to another solution. When a cell is placed in a hypertonic solution, water moves out of the cell (due to osmosis), causing it to shrink.

1. What happens to the osmotic pressure when you increase the temperature?

The osmotic pressure increases with an increase in temperature. This is because osmotic pressure is directly proportional to temperature.

1. What is the difference between volatile and nonvolatile solutes?

A volatile solute has a noticeable vapor pressure and can readily evaporate, while a nonvolatile solute has no significant vapor pressure and does not evaporate.

1. How does the solute-solvent interaction influence the colligative properties?

If the solute-solvent interaction is strong, the solute particles will tend to stay in the liquid phase, further lowering the vapor pressure and increasing the boiling point and osmotic pressure. If the interaction is weak, the solute may tend to go into the vapor phase, reducing the effect on colligative properties.

1. Why is the boiling point elevation and freezing point depression greater for ionic solutes than for nonionic solutes?

Ionic solutes dissociate into two or more particles in solution, thereby increasing the number of particles in solution, which leads to a greater boiling point elevation and freezing point depression.

1. How is the semipermeable membrane involved in osmosis?

A semipermeable membrane allows only certain particles to pass through. In osmosis, the solvent particles move through the membrane from an area of low solute concentration to an area of high solute concentration.

1. What role does entropy play in colligative properties?

Entropy, a measure of disorder, tends to increase in a solution when solute is added. This increase in entropy can help drive changes in colligative properties.

1. Can colligative properties be observed in gases?

Colligative properties are usually discussed in terms of liquid solutions. However, they can also apply to gaseous solutions, but the effects are often less noticeable and harder to measure.

1. How do colligative properties apply in everyday life?

Colligative properties have many real-world applications. For example, salt is added to icy roads in the winter to lower the freezing point of water and prevent ice formation. Similarly, antifreeze added to car radiators works by elevating the boiling point and depressing the freezing point of the water, preventing it from boiling off in the heat or freezing in the cold.

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