Exam 2 Study Guide: Stoichiometry, Solubility, and Solutions

Key vocabulary and foundational concepts for General Chemistry Exam 2 covering Chapter 3 (Stoichiometry) and Chapter 4 (Solubility and Aqueous Solutions).

Avogadro's Number

A fundamental constant defining the number of constituent particles found in one mole of a substance.

Mole

The standard unit for amount of substance, related directly to Avogadro's number.

Molar Mass

The mass in grams of one mole of a substance, determined from the formula weight by summing the atomic masses of the atoms in the compound formula.

Percent Composition

The percentage by mass of each element present in a compound, calculated from the compound formula.

Empirical Formula

The chemical formula showing the simplest whole-number ratio of the elements in a compound, determinable from percent composition or a molecular formula.

Molecular Formula

The chemical formula specifying the actual number of atoms of each element present in a molecule of a compound.

Water of Hydration

Water molecules chemically bound in a definite ratio within the crystalline structure of a hydrated compound.

Hydrated Compound

A compound that incorporates water of hydration into its solid structure.

Reactant

A starting substance consumed during the course of a chemical reaction.

Product

A substance formed as a result of a chemical reaction.

Stoichiometric Factors

Ratios of balancing coefficients derived from a balanced chemical equation used to convert between moles of reactants and products.

Limiting Reactant

The reactant that is completely consumed first in a reaction, determining the theoretical maximum amount of product that can form.

Excess Reactant

The reactant that remains unreacted after the limiting reactant has been completely consumed.

Theoretical Yield

The maximum quantity of product that can be formed from a specified quantity of reactants based on stoichiometric calculations.

Actual Yield

The amount of product obtained from a chemical reaction in practice.

Percent Yield

The percentage efficiency of a chemical reaction calculated as the actual yield divided by the theoretical yield multiplied by $100\%$.

Combustion Analysis

An experimental technique used to determine the empirical formula of a compound containing only carbon, hydrogen, and oxygen by burning it completely in oxygen.

Combustion Reaction

A type of chemical reaction where a substance reacts rapidly with oxygen gas.

Decomposition Reaction

A chemical reaction in which a single compound breaks down into two or more simpler substances.

Single Displacement Reaction

A chemical reaction in which an uncombined element displaces another element from a compound.

Double Displacement Reaction

A chemical reaction where ions of two reacting compounds exchange places in aqueous solution to form two new compounds.

Solution

A homogeneous mixture composed of two or more substances: the solvent and one or more solutes.

Solvent

The component of a solution that dissolves the solute and is present in the greatest amount.

Solute

The component of a solution that is dissolved by the solvent.

Aqueous Solution

A solution in which water serves as the solvent.

Solvated

The state of solute particles interacting with and being surrounded by solvent molecules.

Hydrated

The specific case of being solvated where the solvent surrounding the solute particles is water.

Electrolyte

A substance that dissociates into free ions when dissolved in an aqueous solution.

Strong Electrolyte

A substance that dissociates completely (or nearly completely) into ions in aqueous solution.

Weak Electrolyte

A substance that dissociates only partially into ions in aqueous solution.

Precipitate

An insoluble solid product that forms and separates from a solution during a reaction between soluble reactants.

Saturated Solution

A solution that contains the maximum amount of dissolved solute at a given temperature in equilibrium with undissolved solute.

Unsaturated Solution

A solution that contains less than the maximum amount of solute capable of being dissolved at a given temperature.

Supersaturated Solution

An unstable solution containing more dissolved solute than is normally soluble at a given temperature.

Precipitation Reaction

An aqueous reaction in which soluble reactants combine to produce an insoluble precipitate.

Spectator Ions

Ions in a complete ionic equation that do not take part in the chemical reaction and remain unchanged in solution.

Monoprotic Acid

An acid capable of donating only one proton ($H^+$) per molecule in aqueous solution.

Diprotic Acid

An acid capable of donating two protons ($H^+$) per molecule in aqueous solution.

Triprotic Acid

An acid capable of donating three protons ($H^+$) per molecule in aqueous solution.

Gas-Forming Reaction

An aqueous reaction in which a carbonate, hydrogen carbonate, sulfite, or hydrogen sulfite salt reacts with an acid to generate a gas.

Oxidation

The loss of one or more electrons by a substance in a chemical reaction.

Reduction

The gain of one or more electrons by a substance in a chemical reaction.

Oxidizing Agent

The reactant that causes oxidation in another substance by gaining electrons and being reduced.

Reducing Agent

The reactant that causes reduction in another substance by losing electrons and being oxidized.

Half-Reaction

A theoretical construct showing an oxidation-only reaction where electrons appear as products, or a reduction-only reaction where electrons appear as reactants.

Oxidation Numbers

A theoretical construct assigned to elements to keep track of electron distribution and electron transfer in redox reactions.

Concentration

A quantitative measure of the amount of solute dissolved in a specified quantity of solution or solvent.

Molarity ($M$)

A concentration unit defined as moles of solute per $1\text{ L of solution}$, denoted by $M$ and represented by square bracket notation, $[\text{solute}]$.

Indicator

A chemical compound used in titrations that undergoes a noticeable color change to signal the equivalence point or endpoint.

Equivalence Point

The point in a titration where the exact stoichiometric amount of titrant has been added to react completely with the analyte.

Standardization

The analytical procedure of determining the exact concentration of a solution, often by titration against a primary standard.

Primary Standard

A highly pure, stable substance of known composition used as a reference material to standardize solutions.