Experimental Techniques and Chemical Analysis

You will be able to

• Calculate Rf values from a chromatogram: distance moved by the substance ÷ distance moved by the solvent front.
• Deduce the substances in a mixture by matching its spots and Rf values with those of known substances, and state that a pure substance gives one spot.
• Explain why the baseline is drawn in pencil above the solvent level, and describe the use of a locating agent for colourless substances.

You will be able to

• Describe and explain methods of separation: filtration, evaporation, crystallisation, simple distillation, fractional distillation and chromatography.
• Deduce the most suitable separation method for a given mixture from the properties of its parts (solubility, boiling point).
• State that a pure substance melts and boils at a fixed temperature, and that impurities lower the melting point and raise the boiling point.

You will be able to

• Describe the tests for the cations Al³⁺, NH₄⁺, Ca²⁺, Cr³⁺, Cu²⁺, Fe²⁺, Fe³⁺ and Zn²⁺ with aqueous sodium hydroxide and aqueous ammonia, and the flame tests for Li⁺, Na⁺, K⁺, Ca²⁺, Ba²⁺ and Cu²⁺.
• Describe the tests for the anions CO₃²⁻, Cl⁻, Br⁻, I⁻, SO₄²⁻, SO₃²⁻ and NO₃⁻, and for the gases NH₃, CO₂, Cl₂, H₂, O₂ and SO₂.
• Deduce the identity of an unknown salt or gas from a set of test results.