Chapter 14 Solutions — Practice Flashcards

Q&A flashcards covering core concepts from Section 14 (Solutions) including definitions, laws, and key relationships such as solubility, enthalpy of solution, Raoult’s and Henry’s laws, colligative properties, osmotic pressure, and concentration units.

What is a solution?

A homogeneous mixture of two or more substances in which the solute is dissolved in the solvent; the solvent is the majority component and the solute is the minority.

What are solvent and solute?

The solvent is the substance present in the greatest amount; the solute is the substance dissolved in the solvent.

What is spontaneous mixing?

When a barrier between pure water and a solution is removed, mixing occurs spontaneously to form a uniform solution, often driven by a decrease in free energy due to entropy.

What factors influence solubility?

Nature’s tendency toward mixing and the types of intermolecular forces between solute and solvent determine solubility.

What does the rule ‘like dissolves like’ mean?

Polar solutes tend to dissolve in polar solvents, and nonpolar solutes tend to dissolve in nonpolar solvents; similar structures/polarities promote dissolution.

What is miscible vs. immiscible?

Miscible liquids mix in all proportions to form a solution; immiscible liquids do not mix to form a homogeneous solution.

What is solubility?

The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature (and pressure), depending on intermolecular forces and entropy.

Which ions and compounds are generally soluble in water according to common rules?

Group 1A and ammonium salts; nitrates and acetates; chlorides, bromides, and iodides (except Ag+, Pb2+, Hg2^2+); sulfates (with exceptions such as Ca^2+, Sr^2+, Ba^2+, Ag+, Pb^2+). Insoluble rules include carbonates, phosphates, sulfides, and hydroxides with few exceptions (e.g., NH4^+ or Group 1A).

What is the enthalpy of solution (ΔHsoln)?

The overall heat change when a solution forms, composed of ΔHsolute + ΔHsolvent + ΔHmix; the sign determines whether the process is endothermic or exothermic.

What is the enthalpy of hydration?

The energy released when gaseous ions dissolve in water; part of the overall enthalpy of solution for ionic compounds.

What is lattice energy?

The energy required to separate the ions in an ionic solid into gaseous ions; positive magnitude for breaking the solid structure.

How is ΔHsoln related to ΔHhydration and lattice energy?

ΔHsoln = ΔHhydration − ΔHlattice (the balance determines whether dissolution is exothermic or endothermic for ionic compounds).

What is Raoult’s Law?

The vapor pressure of a volatile solvent above a solution equals its mole fraction in the solution times the vapor pressure of the pure solvent: Psolution = χsolvent × P°_solvent.

What is Henry’s Law?

The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas: S = kH × Pgas.

What is the Van’t Hoff factor (i)?

The ratio of moles of solute particles in solution to moles of formula units dissolved; for ideal electrolytes i equals the number of particles produced, but real solutions often have a smaller i due to ion pairing.

What is osmotic pressure?

The pressure required to stop osmosis; π = MRT, proportional to the molarity of solute particles.

What is osmosis?

The flow of solvent through a semipermeable membrane from a region of lower solute concentration to higher solute concentration.

What are colligative properties?

Properties that depend on the number of solute particles in solution, not their identity; include vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure.

What is freezing point depression?

ΔTf = i × Kf × m; the presence of solute lowers the freezing point of a solvent, with the depression proportional to molality and the van’t Hoff factor.

What is boiling point elevation?

ΔTb = i × Kb × m; the presence of solute raises the boiling point of a solvent, proportional to molality and the van’t Hoff factor.

What are the three steps in the solution process for enthalpy changes?

(1) Separate the solute particles (endothermic); (2) separate solvent particles to make room (endothermic); (3) mix solute and solvent (exothermic).

What determines whether a solution’s dissolution is overall exothermic or endothermic?

If the energy cost to break existing attractions is less than the energy released by new solute–solvent attractions, the process is exothermic; otherwise it is endothermic.

What is the heat of hydration vs lattice energy in ionic solutions?

Heat of hydration is the energy released when ions are hydrated; lattice energy is the energy required to break the ionic lattice; ΔHsoln = ΔHhydration − ΔHlattice.

What is a saturated, unsaturated, and supersaturated solution?

Saturated: solution in dynamic equilibrium with dissolved solute; dissolution rate equals deposition rate. Unsaturated: more solute can dissolve. Supersaturated: more solute than the solubility limit; typically a metastable state that can crystallize.

What is solubility curve interpretation?

Graphs showing how solubility of a solute in a solvent changes with temperature; solids typically become more soluble as temperature rises, gases less so.

What is the difference between a mole fraction and mole percent?

Mole fraction XA = nA/(nA + nB); sum of all Xi in a solution equals 1. Mole percent is XA × 100%.

What are common concentration units and their definitions?

Molarity (M) = moles solute per liter solution; Molality (m) = moles solute per kilogram solvent; Mole fraction (X); Mole percent; Percent by mass; Parts per million (ppm); Parts per billion (ppb).

What is a micelle and its role in soaps?

A spherical aggregate formed by soap molecules in water, with a hydrophilic (polar) head outside and hydrophobic (nonpolar) tails inside; aids emulsification and cleaning.

What is the Tyndall effect and Brownian motion?

Tyndall effect: scattering of light by colloidal particles; Brownian motion: random movement of colloidal particles in suspension.

What is the difference between a colloid and a suspension?

Colloids are heterogeneous but do not settle under gravity and show Tyndall effect; suspensions are heterogeneous and settle/segregate over time.

What is a solution’s vapor pressure behavior when a nonvolatile solute is added?

The solvent’s vapor pressure lowers (Raoult’s law); the decrease is proportional to the solvent’s mole fraction in the solution.

What is the concept of osmolality and medical solutions?

Isosmotic solutions have the same osmotic pressure as the cell interior; hyperosmotic solutions have higher osmotic pressure causing water to leave cells; hypoosmotic solutions have lower osmotic pressure causing water to enter cells.