Composition of Substances and Solutions – VOCABULARY Flashcards

Vocabulary flashcards covering key terms from the lecture notes on moles, molar mass, formulas, and solution concentration.

Mole (mol)

A unit for amount of substance equal to 6.022×10^23 elementary entities; the amount that contains Avogadro’s number of particles.

Avogadro’s Number

The number 6.022×10^23; the quantity of particles in one mole used to convert between atoms/molecules and moles.

Molar Mass

The mass in grams of one mole of a substance; numerically equal to the atomic/formula mass in amu.

Atomic Mass Unit (amu)

A unit defined as 1/12 the mass of a carbon-12 atom; used to express atomic and molecular masses.

Carbon-12 Standard

The reference isotope used to define amu; 12C has exactly 12 amu.

1 Mole of Carbon‑12 Equals 12.00 g

One mole of carbon-12 atoms has a mass of 12.00 g.

Formula Mass

Sum of the atomic masses (in amu) of all atoms in a formula unit of a compound.

Molar Mass of a Compound

The mass in grams per mole of a compound; numerically equal to its formula mass in amu.

Atomic Mass Unit (amu) vs. Molar Mass

amu measures mass at the atomic scale; molar mass (g/mol) scales that mass to grams per mole.

Empirical Formula

The simplest whole-number ratio of elements in a compound.

Molecular Formula

The actual number of each type of atom in a molecule; an integral multiple of the empirical formula.

Percent Composition (Mass Percent)

The mass percent of each element in a compound: (mass of element ÷ mass of compound) × 100%.

Mass Percent as a Conversion Factor

A way to use percent composition to relate grams of one component to grams of the whole.

Determining Empirical Formula from % Composition

Convert each element’s mass percent to moles, then find the smallest whole-number ratio.

Determining Molecular Formula from Empirical Formula

Use n = (molar mass of compound) ÷ (molar mass of empirical formula); multiply empirical formula by n.

Solution

A homogeneous mixture of solute dissolved in a solvent.

Solute

The substance dissolved in a solution.

Solvent

The substance in which the solute dissolves; usually present in greater amount.

Aqueous Solution

A solution in which the solvent is water.

Molarity (M)

Moles of solute per liter of solution (mol/L).

Molality (m)

Moles of solute per kilogram of solvent (mol/kg).

Percent by Mass

Mass percent; mass of solute divided by total mass of solution, times 100%.

Percent by Volume

Volume percent; volume of solute divided by total volume of solution, times 100%.

Parts Per Million (ppm)

Mass of solute per mass of solution times 10^6 (or μg of solute per g solution).

Parts Per Billion (ppb)

Mass of solute per mass of solution times 10^9 (or ng of solute per g solution).

Mole Fraction

XA = nA ÷ (nA + nB + …); the fraction of moles of component A in a mixture.

Density

Mass per unit volume (g/mL or g/cm^3); used to convert between mass and volume.

Conversion Factors

Factors that relate different units (e.g., gram ⇄ mole via molar mass; mole ⇄ number via Avogadro’s number).

Preparation of a Solution

Dissolve a known amount of solute and dilute with solvent to a final volume.

Dilution

Lowering a solution’s concentration by adding solvent; in calculations M1V1 = M2V2.

Molarity in Calculations

Use mol/L units in problems to ensure proper cancelation of units.

1 Liter = 1000 Milliliters

A volume relation used to convert between L and mL in solution calculations.

Concentration Units Conversion

Ability to convert between molarity, molality, percent by mass/volume, ppm, ppb, and mole fraction.

Density in Conversions

Sometimes needed to convert between mass-based and volume-based concentrations.

Example Context

Problems may involve determining molarity, molality, percent composition, or molecular formulas from data such as mass, volume, and density.