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., Ca2+Ca^{2+} & NO<em>3−NO<em>3^{-}$, gives Ca(NO</em>3)2Ca(NO</em>3)_2).

Covalent Compounds

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

  • E.g., Nitrogen monoxide (NO), Nitrogen dioxide (NO2NO_2).

Chemical Equation
State Symbols

  • (s), (l), (g), (aq)

Balancing Equations

  • Equal atoms on both sides using coefficients.

  • E.g., MgCl<em>2(aq)+Na</em>2CO<em>3(aq)→MgCO</em>3(s)+2NaCl(aq)MgCl<em>2 (aq) + Na</em>2CO<em>3 (aq) \rightarrow MgCO</em>3 (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., Ca2+(aq)+SO<em>42−(aq)→CaSO</em>4(s)Ca^{2+} (aq) + SO<em>4^{2-} (aq) \rightarrow CaSO</em>4 (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: Ar×(no. of atoms)Mr of compound×100%\frac{Ar \times (no. \ of \ atoms)}{Mr \ of \ compound} \times 100\%

Mole

  • 1 mole = 6.02×10236.02 \times 10^{23} particles (Avogadro's constant).

  • Molar Volume: 1 mole gas = 24 dm3dm^3 (room temp).

  • No. of particles=mole×6.02×1023\text{No. of particles} = \text{mole} \times 6.02 \times 10^{23}

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

  • 1 mole of gas = 24dm3dm^3

Concentration

  • Amount of solute in solution.

  • Ways to measure: gdm-3 or moldm-3.

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

  • No. of moles=Concentration×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)+2HCl(aq)→CaCl<em>2(aq)+H</em>2(g)Ca (s) + 2 HCl (aq) \rightarrow CaCl<em>2 (aq) + H</em>2 (g)

Stoichiometry for Gas

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

  • E.g., N<em>2(g)+2O</em>2(g)→2NO2(g)N<em>2 (g) + 2 O</em>2 (g) \rightarrow 2 NO_2 (g)

Limiting Reagent

  • Reactant fully used up first.

Percentage Yield & P