[3.2.4] Properties of Period 3 Elements & their Oxides

Question 1

Describe the conditions/observations and the equation for the reaction between Na and water.

Answer 1

• Sodium reacts with cold water. It fizzes around on the surface.
• 2 Na (s) + 2 H₂O (l) -> 2 NaOH (aq) + H₂ (g)

Question 2

Describe the conditions/observations and the equation for the reaction between Na and oxygen.

Answer 2

• Sodium burns with a yellow flame to produce a white solid.
• 4Na (s) + O₂ (g) -> 2Na₂O (s)

Question 3

Describe the conditions/observations and the equation for the reaction between Mg and water.

Answer 3

• Magnesium reacts very slowly with cold water to form the hydroxide.
• Mg (s) + 2 H₂O (l) -> 2 Mg(OH)₂ (aq) + H₂ (g)

Question 4

Describe the conditions/observations and the equation for the reaction between Mg and steam.

Answer 4

• Magnesium reacts readily with steam to form the oxide.
• Mg (s) + H₂O (g) -> MgO (s) + H₂ (g)

Question 5

Describe the conditions/observations and the equation for the reaction between Mg and oxygen.

Answer 5

• Magnesium burns with a white flame to give a white solid.
• 2Mg (s) + O₂ (g) -> 2MgO (s)

Question 6

Describe the conditions/observations and the equation for the reaction between Al and oxygen.

Answer 6

• Aluminum burns with a white flame to give a white solid.
• 4Al (s) + 3O₂ (g) -> 2Al₂O₃ (s)

Question 7

Describe the conditions/observations and the equation for the reaction between Si and oxygen.

Answer 7

• Silicone burns with a white flame to give a white solid.
• Si (s) + O₂ (g) -> SiO₂ (s)

Question 8

Describe the conditions/observations and the equation for the reaction between P and oxygen.

Answer 8

• Phosphorus burns with a white flame to give a white solid.
• 4P (s) + 5O₂ (g) -> P₄O₁₀ (s)

Question 9

Describe the conditions/observations and the equation for the reaction between S and oxygen.

Answer 9

• Sulfur burns with a blue flame to form an acidic choking gas.
• S (s) + O₂ (g) -> SO₂ (g)

Question 10

Describe and explain the melting points of the oxides of the elements Na-S.

Answer 10

MACROMOLECULAR OXIDES

• SiO₂ is macromolecular.
  
  • It has many very strong covalent bonds between atoms.
  • High energy is needed to break many strong covalent bonds therefore, it has a very high melting and boiling point.

IONIC OXIDES

• The metal oxides (Na₂O, MgO, Al₂O₃) are ionic.
• They have giant ionic lattice structures: strong forces of attraction between oppositely charged ions.
  
  • Therefore, they have high melting points.
    
    • The increased charge on the cation makes the ionic forces stronger going from Na to Al so leading to increasing melting points.

SIMPLE MOLECULAR OXIDES

• P₄O₁₀ and SO₂ are simple molecular with weak intermolecular forces between molecules (van der waals + permanent dipoles) so have lower melting points.
• P₄O₁₀ is a molecule containing 4P’s and 10 O’s. As it is a bigger molecule and has more electrons than SO₂, it will have large vdW between molecules and thus a higher melting point.

Question 11

Explain why although Al₂O₃ is ionic, it displays a covalent character.

Answer 11

• This can be explained by the small aluminium ion with the high charge being able to get close to the oxide ion and distort the oxide charge cloud.

Question 12

Describe the equation for the reaction between Na₂O and water. What is the pH of the resulting solution?

Answer 12

• Na₂O (s) + H₂O (I) -> 2Na⁺ (aq) + 2OH⁻ (aq).
• pH 13 - this is a vigorous exothermic reaction.

Question 13

Describe the equation for the reaction between MgO and water. What is the pH of the resulting solution?

Answer 13

• MgO (s) + H₂O (I) -> Mg(OH)₂ (s).
• pH 9 - Mg(OH)₂ is only slightly soluble in water as its lattice is stronger so fewer free OH⁻ ions are produced and so lower pH.

Question 14

Describe and explain the reaction between Al₂O₃ and water and SiO₂ and water. What is the pH of the resulting solutions?

Answer 14

• Al₂O₃ and SiO₂ do not dissolve in water because of the high strength of the Al₂O₃ ionic lattice and the SiO₂ macromolecular structure.
• Therefore, they give a neutral pH 7.

Question 15

Describe the equation for the reaction between P₄O₁₀ and water. What is the pH of the resulting solution?

Draw the structure of the acid and describe the ionic equation that shows the formation of the anion when P₄O₁₀ reacts with water.

Answer 15

• P₄O₁₀ (s) + 6H₂O (I) -> 4H₃PO₄ (aq)
• pH 0 - this is a vigorous exothermic reaction.
• P₄O₁₀ + H₂O -> H⁺ + HPO₄⁻

Question 16

Describe the equation for the reaction between SO₂ and water. What is the pH of the resulting solution?

Draw the structure of the acid and describe the ionic equation that shows the formation of the anion when SO₂ reacts with water.

Answer 16

• SO₂ (g) + H₂O (I) -> H₂SO₃ (aq)
• pH 3 (weak acid).
• SO₂ + H₂O -> H⁺ + HSO₃⁻

Question 17

Describe the equation for the reaction between SO₃ and water. What is the pH of the resulting solution?

Draw the structure of the acid and describe the ionic equation that shows the formation of the anion when SO₃ reacts with water.

Answer 17

• SO₃ (g) + H₂O (I) -> H₂SO₄ (aq)
• pH 0 .
• SO₃ + H₂O -> H⁺ + HSO₄⁻

Question 18

Explain the trends in the reactions of the oxides with water.

Answer 18

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

Question 19

The ionic oxides react with acids to make salts.

Write equations to show the reaction between Na₂O with HCl and H₂SO₄.

Write the ionic equation that represents BOTH these reactions.

Answer 19

• Na₂O (s) + 2HCl (aq) -> 2NaCl + H₂O (l)
• Na₂O (s) + H₂SO₄ (aq) -> Na₂SO₄ (aq) + H₂O (l)
• IONIC: Na₂O (s) + 2H⁺ (aq) -> 2Na⁺ (aq) + H₂O (l)

Question 20

The ionic oxides react with acids to make salts.

Write the equation to show the reaction between the magnesium oxide with HCl.

Write the ionic equation that represents this reaction.

Answer 20

• MgO (s) + 2HCl (aq) -> MgCl₂ + H₂O (l)
• IONIC: MgO (s) + 2H⁺ (aq) -> Mg²⁺ (aq) + H₂O (l)

Question 21

Aluminium oxide can act as both an acid and an alkali.

Show aluminium oxide acting as a base in a reaction with H₂SO₄ and HCl using equations.

Write the ionic equation that represents BOTH these reactions.

Answer 21

• Al₂O₃ (s) + 3H₂SO₄ (aq) -> Al₂(SO₄)₃ (aq) + 3H₂O (l)
• Al₂O₃ (s) + 6HCl (aq) -> 2AlCl₃ (aq) + 3H₂O (l)
• IONIC: Al₂O₃ + 6H⁺ -> 2Al³⁺ + 3H₂O

Question 22

Aluminium oxide can act as both an acid and an alkali.

Show aluminium oxide acting as an acid in a reaction with NaOH using an equation.

Write the ionic equation that represents this reaction.

Answer 22

• Al₂O₃ (s) + 2NaOH (aq) + 3H₂O (l) -> 2NaAl(OH)₄ (aq)
• IONIC: Al₂O₃ (s) + 2OH⁻ (aq) + 3H₂O (l) -> 2Al(OH)₄⁻ (aq)

Question 23

Simple molecular acidic oxides react with bases to form salts.

Write the equation to show the reaction between the phosphorus oxide and NaOH. Write the ionic equation that represents this.

Write the equation to show the reaction between the phosphorus oxide and Na₂O.

Answer 23

• P₄O₁₀ (s) + 12NaOH (aq) -> 4Na₃PO₄ (aq) + 6H₂O (l)
• IONIC: P₄O₁₀ (s) + 12OH⁻ -> 4PO₄³⁻ + 6H₂O (l)
• P₄O₁₀ + 6Na₂O -> 4Na₃PO₄

Question 24

Simple molecular acidic oxides react with bases to form salts.

Write the equation to show the reaction between the sulfur dioxide and NaOH. Write the ionic equation that represents this.

Answer 24

• SO₂ (g) + 2NaOH (aq) -> Na₂SO₃ (aq) + H₂O (l)
• IONIC: SO₂ (g) + 2OH⁻ (aq) -> SO₃²⁻ (aq) + H₂O (l)

Question 25

Simple molecular acidic oxides react with bases to form salts.

Write the equation to show the reaction between the sulfur trioxide and NaOH. Write the ionic equation that represents this.

Answer 25

• SO₃ (g) + 2NaOH (aq) -> Na₂SO₄ (aq) + H₂O (l)
• IONIC: SO₃ (g) + 2OH⁻ (aq) -> SO₄²⁻ (aq) + H₂O (l)

Question 26

Silicon dioxide has a giant covalent structure with strong bonds so it doesn’t react with water or weak solutions of alkali. However, it will react with concentrated NaOH. Write an equation to represent this.

Answer 26

• 2NaOH (I) + SiO₂ (s) -> Na₂SiO₃ (aq) + H₂O