AP Chemistry Unit 4 Notes: Quantifying Reactions with Stoichiometry and Titrations

Stoichiometry

The quantitative “accounting system” of chemistry that uses a balanced chemical equation to predict reactant needs, product amounts, limiting reactants, and reaction efficiency.

Balanced chemical equation

A chemical equation adjusted so the number of atoms of each element is the same on both sides; its coefficients determine correct mole ratios.

Mole ratio

The fixed whole-number ratio between substances in a balanced equation, used to convert moles of one species to moles of another.

Mole

A counting unit for particles; 1 mol corresponds to a specific number of atoms, molecules, or formula units.

Avogadro’s number

The number of particles in 1 mole: 6.022 × 10^23 particles/mol.

Molar mass

The mass of 1 mole of a substance (g/mol), numerically equal to its atomic or molecular mass from the periodic table.

Mass-to-mass stoichiometry

Stoichiometry where a mass of one substance is used to calculate the mass of another using grams → moles → mole ratio → moles → grams.

Mole road map

A standard stoichiometry workflow: balance equation → convert given to moles → use mole ratio → convert to desired units.

Limiting reactant

The reactant that is consumed first in a reaction mixture, limiting the maximum amount of product that can form.

Excess reactant

A reactant present in more than the stoichiometric amount required; some remains after the limiting reactant is used up.

Theoretical yield

The maximum amount of product predicted by stoichiometry from the limiting reactant.

Actual yield

The amount of product actually obtained/isolated in the lab.

Percent yield

A measure of reaction efficiency: (actual yield ÷ theoretical yield) × 100%.

Molarity (M)

Solution concentration defined as moles of solute per liter of solution: M = n/V.

n = M × V

A relationship used to find moles of solute from molarity and solution volume (with volume in liters).

Dilution

A process where solvent is added to decrease concentration while the moles of solute stay the same.

Dilution equation (M1V1 = M2V2)

A relationship for dilutions where initial concentration × initial volume equals final concentration × final volume.

Titration

A lab method to determine an unknown concentration (or amount) by reacting it with a solution of known concentration in carefully measured volumes.

Titrant

The solution of known concentration delivered from a buret during a titration.

Analyte

The solution of unknown concentration placed in a flask; the substance being analyzed in a titration.

Standard solution

A solution whose concentration is accurately known (often used as the titrant).

Equivalence point

The point in a titration when reactants have been combined in exact stoichiometric proportions according to the balanced equation.

Endpoint

The observed signal (often a color change) used to estimate that the equivalence point has been reached.

Indicator

A substance that changes color near a particular condition (commonly a certain pH) to help detect the endpoint.

Buret

A precise piece of glassware used to deliver titrant; volume delivered is found by subtracting initial from final buret readings.