Mole Concept & Chemical Equations Notes

Chapter Analysis

• Practice needed.

• 5 key concepts, heavily tested, often as add-ons.

• 8% of past papers.

Key Concepts

• Chemical Equation, Formula, Balancing

• Ionic Equation

• Mole Concept (Ar, Mr, Mole)

• Concentration

• Stoichiometry, Limiting Reagent

• % Yield & Purity

• Empirical/Molecular Formula

Chemical Formula

Ionic Compounds

• Common anions: Carbonate, Nitrate, Phosphate, Sulfate, Chloride.

• Forming compounds: Balance charges (e.g., Ca^{2+} & NO3^{-}$, gives Ca(NO3)_2).

Covalent Compounds

• Use prefixes: Mono (1), Di (2), Tri (3), Tetra (4), Pent (5).

• E.g., Nitrogen monoxide (NO), Nitrogen dioxide (NO_2).

Chemical Equation

State Symbols

• (s), (l), (g), (aq)

Balancing Equations

• Equal atoms on both sides using coefficients.

• E.g., MgCl2 (aq) + Na2CO3 (aq) \rightarrow MgCO3 (s) + 2 NaCl (aq)

Ionic Equation

• Shows only reacting aqueous ions.

• Steps: Balanced equation, write aqueous ions, remove spectator ions, final ionic equation.

• E.g., Ca^{2+} (aq) + SO4^{2-} (aq) \rightarrow CaSO4 (s)

Relative Mass

• Ar: Average mass vs. 1/12 of carbon-12.

• Mr: Average mass of molecule vs. 1/12 of carbon-12.

• Percentage by mass: \frac{Ar \times (no. \ of \ atoms)}{Mr \ of \ compound} \times 100\%

Mole

• 1 mole = 6.02 \times 10^{23} particles (Avogadro's constant).

• Molar Volume: 1 mole gas = 24 dm^3 (room temp).

• \text{No. of particles} = \text{mole} \times 6.02 \times 10^{23}

• \text{No. of moles} = \frac{\text{Mass (in g)}}{Mr}

• 1 mole of gas = 24dm^3

Concentration

• Amount of solute in solution.

• Ways to measure: gdm-3 or moldm-3.

• \text{Concentration} = \frac{\text{Mole}}{\text{mass volume}}

• \text{No. of moles} = \text{Concentration} \times \text{volume}

Chemical Calculations

• Steps: Balanced equation, calculate moles, molar ratio, calculate mass.

• E.g., Ca (s) + 2 HCl (aq) \rightarrow CaCl2 (aq) + H2 (g)

Stoichiometry for Gas

• Mole ratio = volume ratio (constant temp/pressure).

• E.g., N2 (g) + 2 O2 (g) \rightarrow 2 NO_2 (g)

Limiting Reagent

• Reactant fully used up first.

Percentage Yield & P