Stoichiometry, Volumetric analysis, Gravimetric analysis

Stoichiometry

Using balanced chemical equations to calculate amounts of reactants and products; based on conservation of mass.

Process for Stoichiometry Questions

1. Write & balance equation

2. Convert units where necessary (mL → L, kg → g, mg → g).

3. Convert known quantities to moles (mass → moles, volume → moles, etc).

• n = m/M

• n =C×V (V in litres)

3. Use mole ratios (from the balanced equation) to find unknown moles.

4. Convert back to required units (mass, volume, concentration, etc).

Dilution

n₁ = n₂ → C₁×V₁ = C₂×V₂.

Volumetric analysis

Analysis using measurement of volumes.

Titration

Process to determine concentration of reactant by adding one solution to a known volume of another.

Standard solution

Solution of accurately known concentration

Primary standard

Pure

Secondary standard

Substance whose concentration is determined by standardisation against primary standard.

Concentration

Measure of solute in solution; g L⁻¹ = m/V

Diluted

Solution with reduced concentration.

Titre

Volume of titrant needed to reach end point.

End point

Indicator colour change marking completion.

Equivalence point

Reactants have reacted in correct mol ratio.

Aliquot

Volume measured by pipette.

Electronic balance

Measures mass precisely.

Concordant titres

Titres within ±0.10 mL of each other.

Average titre

Mean of concordant titres; used in calculations.

Precision

Closeness of repeated measurements.

Accuracy

Closeness to true value.

Random errors

Unpredictable variations.

Systematic errors

Consistent errors in one direction.

Volumetric flask

Used to prepare solutions of precise volume.

Funnel

Used to fill burette without spillage.

Conical flask

Used in titration; easy to swirl without spilling.

Beaker

General container; not accurate for volume.

Bulb pipette

Calibrated tube to measure fixed volume accurately.

Burette

Graduated tube with tap delivering known volumes accurately.

Titration method

Prepare standard solution → pipette aliquot → add indicator → fill burette → add titrant slowly → record titre → repeat for concordant titres.

Gravimetric analysis

Quantitative determination by measuring mass.

Precipitation

Formation of solid when two soluble salts react.

Analyte

Substance being measured.

Precipitate

Solid product formed.

Filtration

Separates solid precipitate from solution.

Washing

Rinses precipitate to remove impurities.

Drying/Igniting

Removes moisture or converts precipitate to stable form.

Stoichiometry

Used to relate mass of precipitate to amount of analyte.

Purity

Proportion of precipitate that is desired compound.