Properties of period 3 elements and their oxides (3.2.4)

How do Mg and Na react with water?

Sodium

2Na_(s) + 2H₂O_(l) → 2NaOH_(aq) + H_2(g)

Na reacts vigorously with water, melting into a ball and fizzing. Na floats on water

Magnesium

Mg reacts slowly with water:

Mg_(s) + H₂O_(l) → Mg(OH)_2(aq) + H_2(g)

Mg(OH)₂ is sparingly soluble and is a weak alkaline

Mg reacts much faster with steam:

Mg_(s) + H₂O_(g) → MgO_(s) + H_2(g)

What are the ionic oxides that are formed by sodium and magnesium?

Sodium - Na₂O - white solid - when made from Na and O₂ orange/yellow flame

Magnesium - MgO - white solid - burns bright white

How do the ionic oxides react with water?

Na₂O_(s) + H₂O_(l) → 2NaOH_(aq)

MgO_(s) + H2O_(l) → Mg(OH)_2(aq)

These form alkaline solutions with pH of 10-14

What are the simple molecular oxides that are formed from sulfur and phosphorus? 

Phosphorus - P₄O₁₀

Sulfur - SO₂ , SO₃

SO₃ requires a catalyst and high temperature to be formed

How do simple molecular oxides react with water?

P₄O_10(s) + 6H₂O_(l) → 4H₃PO_4(aq) - phosphoric (V) acid

SO_2(g) + H₂O_(l) → H₂SO_3(aq) - sulfurous acid

SO_3(l) + H₂O → H₂SO_4(aq) - sulfuric (VI) acid

They form acidic solutions with a pH of 0-2

What are the oxides formed by silicon and aluminium?

Silicon - SiO₂ - insoluble in water. It’s an acid as it reacts with a base. Macromolecular structure

Aluminium - Al₂O₃ - It’s both covalent and ionic and it’s insoluble in water. It’s amphoteric as it reacts with both bases and acids to form salts.

What are the melting points and reactivities of the oxides?

How do the basic oxides react with acids?

Na₂O_(s) + H₂SO_4(aq) → Na₂SO_4(aq) + H₂O_(l)

MgO_(s) + 2HCl_(aq) →MgCl_2(aq) +H₂O_(l)

Base + acid → salt + water

How do acidic oxides react with bases?

SiO_2(s) + 2NaOH_(aq) → Na₂SiO_3(aq) + H₂O_(l)

P₄O_10(s) + 12NaOH_(aq) → 4Na₃PO_4(aq) + 6H₂O_(l)

SO_2(g) + 2NaOH_(aq) →Na₂SO_3(aq) + H2O_(l)

SO₃(l) + 2NaOH(aq) → Na₂SO_4(aq) + H₂O_(l)

How do amphoteric oxides react?

Acting as an acid - Al₂O_3(s) + 2NaOH_(aq) + 3H₂O_(l) → 2NaAl(OH)_4(aq)

Acting as a base - Al₂O_3(s) + 3H₂SO4_(aq) → Al₂(SO₄)_3(aq) + 3H₂O_(l)

How do you test for the oxides?

Thus by adding universal indicator the trend can be seen with the ionic oxides turning into a purple/blue solution and the simple molecular oxides having a orange/red solution