2.1Periodicity of period 3

Question 1

Trends in the reactions of the elements with water, limited to Na and Mg

Answer 1

Sodium fizzes in cold water
around on surface
2Na(s) + 2 H2O (l) –> 2 NaOH (aq) + H2 (g)

Magnesium reacts very slowly with cold water to form the hydroxide but reacts more readily with steam to form the oxide
Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g)
Mg(s) + H2O (g) –> MgO (s) + H2 (g)

Question 2

Trends in the reactions of the elements Na, Mg, Al, Si, P and S with oxygen symbol equations only (6)

Answer 2

4 Na (s) + O₂ (g) → 2 Na₂O (s)
2Mg (s) + O₂ (g) → 2MgO (s)
4Al (s) + 3O₂ (g) → 2Al₂O₃ (s)
Si (s) + O₂ (g) → SiO₂ (s)
4P (s) + 5O₂ (g) → P₄O₁₀ (s)
S (s) + O₂ (g) → SO₂ (g)

Question 3

What is the colour of the flame in the reactions of the elements Na, Mg, Al, Si, P and S with oxygen

Answer 3

Sodium burns with a yellow flame to
produce a white solid.
Mg, Al, Si and P burn with a white flame to give white solid smoke.
S burns with a blue flame to form an acidic choking gas.

Question 4

Just read this papi

Answer 4

• The metal oxides (Na2O, MgO, Al2O3) are ionic.
• They have high melting points. They have ionic giant lattice structures: strong forces of attraction between
  oppositely charged ions : higher mp. - They are ionic because of the large electronegativity difference
  between metal and O
• The increased charge on the cation makes the ionic forces stronger (bigger lattice enthalpies of
  dissociation) going from Na to Al so leading to increasing melting points.

Question 5

How do you prove that Na2O MgO and Al2O3 compounds contain ions

Answer 5

Melt the solids and show they
conduct electricity.

Question 6

The reactions of the oxides of the elements Na –> S with water

Answer 6

Metal ionic oxides solutions across the period. tend to react with water to form hydroxides which are alkaline
Na2O (s) + H2O (l) –> 2Na+ (aq) + 2

Question 7

Show the reaction of magneisum oxide with water

Answer 7

MgO (s) + H2O (l) –> Mg(OH)2 (s) pH 9
Mg(OH)2 is only slightly soluble in water as its lattice is stronger
so fewer free OHions are produced and so lower pH.

Question 8

Do Al2O3 and SiO2 dissolve in water and why also what is their pH

Answer 8

Al2O3 and SiO2 do not dissolve in water because of the high strength of the Al2O3 ionic lattice and the SiO2 macromolecular structure,

Neutral pH 7

Question 9

Why is MgO better than NaOH for treating acid in rivers and the stomach

Answer 9

It is only sparingly soluble and weakly alkaline so using an excess
would not make the water excessively alkaline.

Question 10

Give the reactions for simple molecular, covalent, oxides react with water to give acids. and give the pH too

Answer 10

P₄O₁₀ (s) + 6 H₂O (l) → 4 H₃PO₄ (aq) pH 0 (this is a vigorous exothermic reaction)
SO₂ (g) + H₂O (l) → H₂SO₃ (aq) pH 3 (weak acid)
SO₃ (g) + H₂O (l) → H₂SO₄ (aq) pH 0

Question 11

What are the pattern most reactions follow for acid and base reactions

Answer 11

acid + base –> salt + water
Know the charges on the ions e.g. PO4^3-
SO4^2-

Question 12

Equations showing formation of ions in solution

Answer 12

SO₂ + H₂O → H⁺ + HSO₃⁻
SO₃ + H₂O → H⁺ + HSO₄⁻

Question 13

Trend in ionic metal oxides and non metal oxides

Answer 13

• The trend is the ionic metal oxides show basic behaviour
• The non-metal covalent oxides show acidic behaviour.

Question 14

Acid base reactions between period 3 oxides and simple acids and bases. (5) Na2O (2) MgO (1) 2 ionic equations

Answer 14

Na₂O (s) + 2 HCl (aq) → 2NaCl (aq) + H₂O (l)

Na₂O (s) + H₂SO₄ (aq) → Na₂SO₄ (aq) + H₂O (l)

MgO (s) + 2 HCl (aq) → MgCl₂ (aq) + H₂O (l)

Or ionic equations
Na₂O (s) + 2H⁺ (aq) → 2Na⁺ (aq) +
H₂O (l)

MgO (s) + 2 H⁺ (aq) → Mg²⁺ (aq) + H₂O (l)

Question 15

Give the reactions where Al₂O₃ (aluminum oxide) is acting as a base

Answer 15

Al₂O₃ (s) + 3H₂SO₄ (aq) → Al₂(SO₄)₃ (aq) + 3H₂O (l)

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O

Or ionic: Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O

Question 16

Define amphoteric

Answer 16

Can act as both an acid and as an alkali

Question 17

Give the reactions where Al₂O₃ (aluminum oxide) is acting as an acid

Answer 17

Al₂O₃ (s) + 2NaOH (aq) + 3H₂O (l) → 2NaAl(OH)₄ (aq)

Al₂O₃ (s) + 2OH⁻ (aq) + 3H₂O (l) → 2Al(OH)₄⁻ (aq)

Question 18

Equations for p4o10 and so2 and so3 and how they react with bases to form salts.

Answer 18

P₄O₁₀ (s) + 12 NaOH (aq) → 4Na₃PO₄ (aq) + 6 H₂O (l)
P₄O₁₀ + 6 Na₂O → 4Na₃PO₄
SO₂ (g) + 2NaOH (aq) → Na₂SO₃ (aq) + H₂O (l)
SO₃ (g) + 2NaOH (aq) → Na₂SO₄ (aq) + H₂O (l)
Or ionic equations:
P₄O₁₀ (s) + 12 OH⁻ (aq) → 4PO₄³⁻ (aq) + 6 H₂O (l)
SO₂ (g) + 2OH⁻ (aq) → SO₃²⁻ (aq) + H₂O (l)
SO₃ (g) + 2OH⁻ (aq) → SO₄²⁻ (aq) + H₂O (l)