2.2.4Physical Chemistry
Uses of Group 2 Elements — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 59 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Neutralising Acids
Basic Group 2 compounds neutralise acidity in people, soils and lakes.
Calcium hydroxide
- Calcium hydroxide Ca(OH)₂ is spread on fields to neutralise acidic soil, since it is cheap and not too strongly alkaline.
Magnesium hydroxide
- Magnesium hydroxide Mg(OH)₂ in indigestion remedies reacts with stomach acid: Mg(OH)₂(s) + 2HCl(aq) → MgCl₂(aq) + 2H₂O(l).
Calcium carbonate
- Calcium carbonate CaCO₃ is another antacid and also treats acidic lakes: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g).
Why they are safe
- Why they are safe Their low solubility keeps the pH moderate, so they are gentler than soluble strong alkalis.
Part 2 of 4Flue Gas Desulfurisation
Burning coal and heavy fuel oil releases sulfur dioxide, which causes acid rain, so power stations remove it from waste gases.
1
Waste gases are passed through a slurry of calcium oxide or calcium carbonate in water.
2
Sulfur dioxide is an acidic gas and reacts with the basic calcium compound.
3
With calcium oxide the equation is CaO(s) + SO₂(g) → CaSO₃(s).
4
With calcium carbonate the equation is CaCO₃(s) + SO₂(g) → CaSO₃(s) + CO₂(g), releasing some carbon dioxide.
5
The calcium sulfite formed can be oxidised to calcium sulfate, which can be used to make plasterboard.
Part 3 of 4Other Uses
Other Uses
Magnesium in alloys
- Magnesium in alloys Magnesium is used in light alloys because it has low density and reasonable strength.
Reducing agent
- Reducing agent Magnesium displaces titanium from titanium(IV) chloride in a high-temperature reaction under an inert atmosphere.
Barium sulfate
- Barium sulfate Because it is insoluble, it passes through the body without releasing toxic barium ions.
| Use | Compound or element | Reason |
|---|---|---|
| X-ray imaging | BaSO₄ | Insoluble and absorbs X-rays |
| Extracting titanium | Mg metal | Reducing agent: TiCl₄ + 2Mg → Ti + 2MgCl₂ |
| Fireworks and flares | Mg | Burns with a bright white flame |
Part 4 of 4Exam Checklist & Tips
2.2.4 – Key Points for the Exam
- Neutralisation A reaction between an acid and a base that produces a salt and water.
- Flue gas desulfurisation Removal of sulfur dioxide from power-station emissions by reacting it with a basic calcium compound.
- Acid rain Rain made acidic by dissolved sulfur dioxide and nitrogen oxides.
- Antacid A base used to neutralise excess acid in the stomach.
Common Mistakes
- Writing the product of CaO + SO₂ as CaSO₄ instead of CaSO₃.
- Forgetting that the CaCO₃ route releases CO₂.
- Saying that barium compounds are safe in general; only the insoluble BaSO₄ is used.
- Using magnesium as an oxidising agent, when it is a reducing agent.
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