Edexcel A Level Chemistry Topic 4: Inorganic Chemistry and the Periodic Table Exam Questions

About Edexcel A Level Chemistry Topic 4: Inorganic Chemistry and the Periodic Table

Topic 4 of Edexcel A Level Chemistry applies atomic structure and redox to Group 2 and Group 7. For Group 2 you study reactions with oxygen, chlorine and water, the reactions of oxides and hydroxides, solubility trends, thermal stability of nitrates and carbonates explained by polarisation, and flame tests. For Group 7 you cover physical trends, oxidising ability of the halogens, disproportionation of chlorine with water and cold and hot alkali, reactions of halides with concentrated sulfuric acid and silver nitrate, and the hydrogen halides. The topic ends with inorganic tests for ions. It is examined in Paper 1, and examiners frequently ask for observations, equations and explanations of trends.

What you need to know

• Group 2 reactions Reactivity increases down the group as ionisation energies decrease. The metals react with water to form hydroxides and hydrogen (Mg with steam forms MgO), and with oxygen and chlorine to form MO and MCl2.
• Group 2 trends Hydroxides become more soluble down the group and sulfates less soluble. Thermal stability of nitrates and carbonates increases down the group because larger cations polarise the anion less.
• Flame tests Li red, Na yellow, K lilac, Ca orange-red, Sr red, Ba pale green. Colours arise when excited electrons fall back to lower energy levels, emitting light of specific frequencies.
• Group 7 trends Volatility decreases down the group. Oxidising ability decreases, shown by displacement reactions in aqueous solution and the colours of halogens in organic solvents (Br2 orange, I2 purple in cyclohexane).
• Disproportionation Cl2 + 2NaOH → NaCl + NaClO + H2O in cold alkali; 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O in hot alkali.
• Halide reactions With concentrated H2SO4, NaCl gives HCl, NaBr gives HBr, Br2 and SO2, and NaI gives I2, SO2, S and H2S, because reducing power increases down the group. Silver halides are white, cream and yellow, with different solubilities in ammonia.
• Tests for ions CO3 2- with acid gives CO2 that turns limewater milky; SO4 2- gives a white BaSO4 precipitate with acidified BaCl2; NH4+ gives ammonia with warm NaOH, turning damp red litmus blue.

Common mistakes in Topic 4: Inorganic Chemistry and the Periodic Table

• Saying thermal stability decreases down Group 2; it increases.
• Explaining flame colours by electrons absorbing light; the colour comes from energy emitted as electrons return to lower levels.
• Forgetting to add dilute nitric acid before silver nitrate when testing for halides.
• Mixing up halogen colours in aqueous and organic layers; iodine is brown in water but purple in cyclohexane.
• Stating that chloride ions reduce concentrated sulfuric acid; chloride is not a strong enough reducing agent.

Try three Topic 4: Inorganic Chemistry and the Periodic Table exam-style questions