Chapter 8 (3.1.2/3/4)

Question 1

Configuration of Group 2 metals

Answer 1

• 2 outer electrons: 2 in outer s sub-shells
• end in s²
• undergoes redox reactions - loses its electrons to form 2+ ions - it is a reducing agent - reduces other substances by donating its electrons

Question 2

G2 redox reactions with oxygen

Answer 2

• react to form MO - metal oxide

- metal is oxidised, oxygen is reduced

Question 3

G2 redox reactions with water

Answer 3

• react with water to form alkaline hydroxide, M(OH)₂ and hydrogen gas
• reactivity increases down the group, reactions become more vigorous

Question 4

G2 reactions with dilute acids

Answer 4

• react to form a salt and hydrogen gas

- metal is oxidised, hydrogen is reduces

Question 5

G2 Trend in reactivity + FIE

Answer 5

• requires the input of 2 ionisation energies
• ionisation energies decrease down the group
• 1st and 2nd ionisation energies make up most of the energy input
• reactivities increase down the group

Question 6

G2 oxides with water

Answer 6

• releases hydroxide ions, OH⁻, and form alkaline solutions of the metal hydroxide
  CaO + H₂O –> Ca²⁺ + 2OH⁻
• G2 hydroxides are only slightly soluble in water
• when solution gets saturated, any further metal + hydroxide ions will form a solid precipitate
  Ca²⁺ + 2OH⁻ –> Ca(OH)₂ (s)

Question 7

Solubility of G2 hydroxides

Answer 7

• increases down the group, so resulting solutions contain more OH⁻ ions and are more alkaline - have a higher pH
• down the group: solubility, pH and alkalinity increases

Question 8

Test for solubility of G2 hydroxides

Answer 8

• add spatula of each group 2 oxide to insufficient water in a test tube
• shake mixture so solution is unsaturated
• measure pH of solution

Question 9

Uses of G2 compounds

Answer 9

• Agriculture - Ca(OH)₂ added to fields as lime by farmers to increase pH of acidic soils - it neutralises the acid, forming neutral water
  Ca(OH)₂ + 2H⁺ —> Ca²⁺ + 2H₂O
• Medicine - used as antacids for treating acid indigestion, e.g. magnesium + calcium carbonates.
  Mg(OH)₂ + 2HCl —> MgCl₂ + 2H₂O
  CaCO₃ + 2HCl —> CaCl₂ + H₂O + CO₂

Question 10

Physical properties of halogens

Answer 10

• most reactive non-metal group
• exist as diatomic molecules at RTP
• down the group = more electrons = stronger London forces = more energy to break IM forces = boiling point increases
• Appearance at RTP: F₂ = pale yellow gas; Cl₂ = pale green gas; Br₂ = red/brown liquid; I₂ - shiny grey/black crystalline solid; At₂ = has never been seen
• simple molecular lattices in the solid state

Question 11

Chemical properties of the halogens

Answer 11

• 7 outer shell electrons: s²p⁵
• redox reactions - halogen atom reduced, gaining an electron to form a 1- halide ion
• halogens = oxidising agents
• halides = reducing agents

Question 12

Halogen displacement reactions

Answer 12

If the halogen added is more reactive than the halide present, then the halogen displaces the halide from solution, and the solution changes colour.