Chapter 13 – Properties of Mixtures: Solutions and Colloids

A comprehensive set of question-and-answer flashcards covering definitions, principles, equations, and applications from Chapter 13 on solutions, colligative properties, and colloids.

What is a solution?

A homogeneous mixture of two or more substances that exists as a single phase.

In a solution, which component is the solvent?

The component present in the greatest amount—the substance in which the solute is dissolved.

Define solubility (S).

The maximum amount of solute that dissolves in a fixed quantity of solvent at a given temperature.

What does it mean if two liquids are miscible?

They are soluble in each other in any proportion.

State the ‘like-dissolves-like’ rule.

Substances with similar types of intermolecular forces tend to dissolve in each other.

What must happen to intermolecular forces when a solution forms?

Solute–solute and solvent–solvent attractions are replaced by solute–solvent attractions of similar strength.

List six principal intermolecular forces important in solutions.

Ion-dipole, hydrogen bonding, dipole-dipole, ion-induced dipole, dipole-induced dipole, and dispersion forces.

Describe an ion-dipole force.

Attraction between an ion and the partial charge on a polar molecule (e.g., Na⁺ surrounded by H₂O).

What is a hydration shell?

A layer of oriented water molecules surrounding a dissolved ion due to ion-dipole attraction.

What is meant by the dual polarity of alcohols?

They have a polar –OH group and a non-polar hydrocarbon tail, allowing interactions with both polar and non-polar solvents.

How does increasing hydrocarbon chain length affect alcohol solubility in water?

Solubility decreases because the growing non-polar portion outweighs the polar –OH group.

What type of alloy is brass, and how is it formed?

A substitutional alloy where Zn atoms replace some Cu atoms in the lattice.

Name the three enthalpy steps in solution formation and their signs.

1) Separating solute particles (endothermic), 2) separating solvent particles (endothermic), 3) mixing solute and solvent (exothermic).

Define heat (enthalpy) of solution (ΔHₛₒₗₙ).

The overall enthalpy change when solute and solvent form a solution; it may be exothermic or endothermic depending on the magnitudes of the component steps.

What is solvation? What is hydration?

Solvation is surrounding a solute particle with solvent molecules; when the solvent is water the process is called hydration.

How does ionic charge density influence heat of hydration?

Higher charge and smaller ionic radius (higher charge density) give more negative (more exothermic) ΔHₕᵧ𝒹.

Write the expression that relates ΔHₛₒₗₙ, lattice energy, and heats of hydration for an ionic solid.

ΔHₛₒₗₙ = ΔHlattice + ΣΔHhydr(ions).

What is lattice energy?

The energy required to separate one mole of an ionic solid into gaseous ions (always positive).

How do enthalpy (ΔH) and entropy (ΔS) changes together decide whether a solution forms?

A solution tends to form if the decrease in enthalpy (or only a small increase) is offset by a favorable increase in entropy.

Distinguish saturated, unsaturated, and supersaturated solutions.

Saturated: holds equilibrium amount of solute with undissolved excess present; unsaturated: holds less than equilibrium amount; supersaturated: temporarily holds more than equilibrium amount and is unstable.

How does temperature generally affect solubility of solids?

Most solids become more soluble as temperature increases.

How does temperature affect gas solubility in liquids?

Gas solubility decreases as temperature rises.

State Henry’s law for gas solubility.

Sgas = kH × P_gas, where S is solubility and P is the gas’s partial pressure above the solution.

Give two everyday examples that illustrate Henry’s law.

Soda going flat after opening (lower P_CO₂) and ‘the bends’ in divers who ascend quickly (decreasing gas solubility in blood).

Define molarity (M).

Moles of solute per liter of solution.

Define molality (m).

Moles of solute per kilogram of solvent.

Which concentration term depends on mass of solvent rather than solution?

Molality (m).

List five common concentration terms and their basic ratios.

Molarity (mol/volume), Molality (mol/mass_solvent), Parts by mass, Parts by volume, Mole fraction (mol component/total mol).

What are colligative properties?

Properties that depend only on the number of solute particles present, not their identity.

What is vapor-pressure lowering?

The reduction in a solvent’s vapor pressure caused by addition of a nonvolatile solute.

State Raoult’s law for a nonvolatile solute.

Psolvent = Xsolvent × P°_solvent.

Why does a nonvolatile solute raise a liquid’s boiling point?

Lowering the vapor pressure means the liquid must reach a higher temperature before its vapor pressure equals external pressure (boiling point elevation).

Give the equation for boiling-point elevation.

ΔTb = i Kb m.

Give the equation for freezing-point depression.

ΔTf = i Kf m (subtracted from the pure solvent value).

Define osmotic pressure (Π) and give its equation.

The pressure required to stop osmosis; Π = i M R T.

During osmosis, which way does solvent flow?

From the more dilute solution (or pure solvent) to the more concentrated solution.

What is the van’t Hoff factor (i)?

The number of particles the solute yields in solution; accounts for dissociation of electrolytes in colligative property equations.

Why do strong electrolytes exhibit non-ideal behavior in solution?

Ion pairing and formation of an ionic atmosphere reduce the effective number of independent particles.

How are colligative formulas modified for strong electrolytes?

ΔTb, ΔTf, Π, and ΔP all include the van’t Hoff factor, i, to account for multiple ions.

What is a colloid?

A heterogeneous mixture in which dispersed particles (1–1000 nm) are distributed throughout a continuous medium and do not settle out.

Give two examples of colloid types.

Fog (liquid aerosol) and milk (liquid emulsion).

What is the Tyndall effect?

Scattering of light by colloidal particles, making the beam visible.

Name four main steps in municipal water treatment.

Screening/settling, coagulation–flocculation, filtration, disinfection.

What role does ion-exchange resin play in water softening?

It swaps hard-water cations (Ca²⁺, Mg²⁺) for Na⁺ or H⁺ ions on the resin, removing hardness.

Explain reverse osmosis in desalination.

Applying pressure greater than the osmotic pressure to force water through a semipermeable membrane, leaving ions behind.

How do isotonic, hypotonic, and hypertonic solutions affect red-blood-cell shape?

Isotonic: cells retain shape; hypotonic: cells swell/lyse; hypertonic: cells shrink (crenate).

Differentiate substitutional and interstitial alloys.

Substitutional: solute atoms replace host atoms (e.g., Zn in Cu for brass); interstitial: smaller atoms occupy holes between host atoms (e.g., C in Fe for steel).

Define ionic charge density.

Ratio of an ion’s charge to its volume; higher charge and smaller radius give higher charge density.

Why is ion hydration always exothermic?

Strong ion-dipole attractions release energy when water molecules surround the ion.

How does increasing external pressure affect gas solubility in a liquid?

It increases solubility by forcing more gas molecules into solution until equilibrium is re-established (Henry’s law).

Why are soap molecules effective cleaning agents?

Their polar heads interact with water while their long non-polar tails embed in greasy dirt, allowing micelles to suspend and wash away oils.