Chapter 13 – Ions in Aqueous Solutions & Colligative Properties

20 question-and-answer flashcards covering dissociation, electrolyte strength, nonvolatile solutes, and all major colligative properties discussed in Chapter 13.

What is meant by dissociation in the context of ionic compounds dissolving in water?

Dissociation is the separation of an ionic compound into its constituent ions when it dissolves in water.

Write the dissociation equation for Al2(SO4)3 in water.

Al2(SO4)3(s) → 2 Al³⁺(aq) + 3 SO4²⁻(aq)

How many total moles of ions are produced when 1 mol of Al2(SO4)3 dissociates completely?

Five moles of ions (2 mol Al³⁺ + 3 mol SO4²⁻).

Define an electrolyte.

A substance whose aqueous solution conducts electricity because it produces ions in solution.

What distinguishes a strong electrolyte from a weak electrolyte?

Strong electrolytes ionize or dissociate almost completely in water, whereas weak electrolytes produce only a small fraction of ions in solution.

Give two examples of strong electrolytes mentioned in the notes.

Any two of: HCl, HBr, HI, or any soluble ionic compound.

What are colligative properties?

Properties of solutions that depend only on the concentration of solute particles, not on their identity.

List four key colligative properties.

Vapor-pressure lowering, freezing-point depression, boiling-point elevation, and osmotic pressure.

What is a nonvolatile solute?

A solute with little tendency to become a gas under existing conditions.

How does adding a nonvolatile solute affect the boiling and freezing points of a solvent?

It raises the boiling point and lowers the freezing point of the solvent.

Define freezing-point depression (Δtf).

The difference between the freezing point of the pure solvent and that of the solution; it is directly proportional to the solution’s molal concentration.

What is the molal freezing-point constant (Kf)?

The freezing-point depression of a solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute.

Define boiling-point elevation (Δtb).

The difference between the boiling point of the pure solvent and that of the solution; it is directly proportional to the solution’s molal concentration.

What is the molal boiling-point constant (Kb)?

The boiling-point elevation of a solvent in a 1-molal solution of a nonvolatile, nonelectrolyte solute.

What is a semipermeable membrane?

A barrier that allows certain particles (usually solvent molecules) to pass while blocking others (solute particles).

Explain osmosis.

The movement of solvent through a semipermeable membrane from the side with lower solute concentration to the side with higher solute concentration.

Define osmotic pressure.

The external pressure required to stop osmosis across a semipermeable membrane.

Why do electrolyte solutions cause larger changes in colligative properties than nonelectrolyte solutions of the same molality?

Because electrolytes dissociate into multiple ions, increasing the total number of solute particles that affect the property.

For equal molal solutions, how does the colligative effect of NaCl compare to that of sucrose?

The effect for NaCl is expected to be roughly twice as large because NaCl produces two ions (Na⁺ and Cl⁻) per formula unit, whereas sucrose remains as one particle.

If Ba(NO3)2 completely dissociates, how many ions result from one formula unit, and what implication does this have for colligative properties?

Three ions (one Ba²⁺ and two NO3⁻); thus, colligative effects are expected to be about three times as large as for a nonelectrolyte of the same molality.