Chemistry 102: The Mole, Solutions, and Chemical Reactions

Comprehensive vocabulary flashcards covering the mole concept, stoichiometry, solution chemistry, molarity, dilution, balancing equations, and reaction classifications.

Mole

A chemical counting word that fixes a specific number ($6.022 \times 10^{23}$ items), not a mass, allowing macroscopic mass measurements to relate directly to whole-number ratios of combining atoms.

Avogadro's Number ($N_A$)

The constant $6.022 \times 10^{23}\text{ per mole}$, representing the exact number of atoms, molecules, or formula units contained in one mole of any substance.

Atomic Mass Unit ($\text{u}$)

A standard unit of mass close to the mass of a single proton or single neutron, equal to $1.6605 \times 10^{-27}\,\text{kg}$, such that $N_A \times 1\,\text{u} = 1.000\,\text{g}$ exactly.

Molar Mass

The mass in grams of one mole of a substance ($\text{g/mol}$), found on the periodic table by summing the atomic masses in the chemical formula, which serves as the conversion factor between grams and moles.

Mole Ratio (Formula Subscripts)

The stoichiometric relationship derived from subscripts inside a chemical formula (e.g., $1\,\text{mol } CO_2 = 1\,\text{mol } C$ and $2\,\text{mol } O$) that provides conversion factors to relate moles of atoms within a compound.

Density (Mole Conversions)

The physical property relating volume to mass ($\text{g/mL}$), used as the first conversion bridge before molar mass to convert a liquid volume into moles ($\text{mL} \rightarrow \text{g} \rightarrow \text{mol}$).

Neutralization Reaction

A reaction where an acid reacts with a base (e.g., $HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$) in which one molecule of base neutralizes exactly one molecule of acid in a $1:1$ mole ratio, not a mass or volume ratio.

Percent Composition

The fraction of total molar mass attributed to a specific element in a compound, calculated as: $\left(\frac{\text{mass in } 1\,\text{mol}}{\text{molar mass}}\right) \times 100$.

Pure Liquid

A liquid consisting of only one compound with no other substances dissolved in it (e.g., pure $H_2O$ or octane).

Solution

A homogeneous mixture formed by dissolving two or more compounds together in a liquid phase.

Solute

The dissolved component within a solution, typically present in a smaller amount than the solvent (e.g., $NaCl$ in salt water).

Solvent

The major liquid component of a solution that dissolves the solute (e.g., water in salt water, blood, or vinegar).

Aqueous Solution

A solution where water ($H_2O$) serves as the solvent.

Molarity ($M$)

A concentration unit defined as moles of solute per liter of solution ($M = \frac{n}{V}$, expressed in $\text{mol/L}$), representing a concentration ratio rather than a total amount of substance.

Dilution

The process of adding solvent to a solution to decrease its concentration while keeping the total amount of solute constant ($\text{moles in} = \text{moles out}$).

Dilution Equation

The relationship $M_1 V_1 = M_2 V_2$, where $M_1$ and $V_1$ are the concentration and volume before dilution, and $M_2$ and $V_2$ are the concentration and volume after dilution.

Reactants

The starting substances that react during a chemical process, written on the left side of a chemical equation.

Products

The new chemical substances formed as a result of a reaction, written on the right side of a chemical equation.

Subscript

A fixed number written below and to the right of an element's symbol in a formula that indicates the exact number of atoms of that element per unit; changing a subscript changes the substance's identity.

Stoichiometric Coefficient

A whole number placed in front of a formula in a balanced equation that specifies how many formula units participate and multiplies all subscripts within that formula.

Synthesis Reaction (Combination)

A reaction family where two or more simpler elements or compounds combine to form a single, more complex substance ($A + B \rightarrow AB$; 'two in, one out').

Decomposition Reaction

A reaction family where a single compound breaks down into two or more simpler elements or compounds ($AB \rightarrow A + B$; 'one in, two out').

Single Replacement Reaction

A reaction where an element and a compound react such that like replaces like: a metal replaces a metal cation, or a nonmetal replaces a nonmetal anion ($A + BC \rightarrow AC + B$).

Double Replacement Reaction

A reaction where two ionic compounds in aqueous solution switch ionic partners to produce two new compounds ($AB(aq) + CD(aq) \rightarrow AD + CB$), typically driven by the formation of a precipitate, gas, or liquid.

Precipitate

An insoluble solid substance formed during an aqueous chemical reaction that falls out of solution, labeled with the state symbol $(s)$.

State Symbol $(aq)$

A notation indicating that a compound is dissolved (soluble) in water and its constituent ions or molecules are free to move and react.

State Symbol $(s)$

A notation indicating that a substance is in the solid state, representing an insoluble compound or precipitate in aqueous reactions.

State Symbol $(g)$

A notation indicating that a substance exists as a gas and can leave the reaction mixture.

Combustion Reaction

A chemical reaction where a hydrocarbon compound ($C_n H_m$) burns in the presence of oxygen ($O_2$) to produce strictly carbon dioxide ($CO_2$) and water ($H_2O$).

Balancing Order for Hydrocarbon Combustion

The sequential procedure for balancing combustion reactions: balance carbon first, then hydrogen, and oxygen last, followed by doubling all coefficients if a fractional coefficient ($\frac{\#}{2}$) remains.

Spectator Ion

An ion that remains unchanged in solution throughout a chemical reaction and simply pairs with the newly formed or remaining ions without undergoing oxidation or reduction (e.g., $SO_4^{2-}$ in $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$).

Lead(II) Iodide ($PbI_2$)

A bright yellow insoluble solid precipitate produced by the double replacement reaction of aqueous lead(II) nitrate with potassium iodide: $Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)$.