Inorganic 2 Section 2 - Unit 22: Periodicity

Question 1

Deduce the type of bonding in phosphorus oxide (1 mark)

Answer 1

Simple molecular

Question 2

Write an equation for the reaction between phosphorus oxide and water (1 mark)

Answer 2

P₄O₁₀ + 6H₂O → 4H₃PO₄

Question 3

State the meaning of the term amphoteric (1 mark)

Answer 3

Reacts with acids and bases

Question 4

Explain why sodium oxide forms an alkaline solution when it reacts with water (2 marks)

Answer 4

• Sodium oxide contains O²⁻ ions

- Which react with water forming OH– ions

Question 5

Write two equations to show the amphoteric nature of aluminium oxide (2 marks)

Answer 5

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

Al₂O₃ + 6HCl → 2Al³⁺ + 6Cl⁻
+ 3H₂O

Question 6

Write an ionic equation for the reaction of phosphorus(V) oxide with an excess of sodium hydroxide solution (1 mark)

Answer 6

P₄O₁₀ + 12OH⁻ → 4PO₄³⁻ + 6H₂O

Question 7

Describe what you would observe when magnesium is heated with steam (2 marks)

Answer 7

• White solid

- White light / flame

Question 8

Describe what you would observe when sodium is heated in oxygen (2 marks)

Answer 8

• White solid

- Yellow flame

Question 9

State the observation when magnesium reacts with oxygen (2 marks)

Answer 9

• Burns with a white flame

- To give a white solid smoke

Question 10

State the observation when aluminium reacts with oxygen (2 marks)

Answer 10

• Burns with a white flame

- To give a white solid smoke

Question 11

State the observation when silicon reacts with oxygen (2 marks)

Answer 11

• Burns with a white flame

- To give a white solid smoke

Question 12

State the observation when phosphorus reacts with oxygen (2 marks)

Answer 12

• Burns with a white flame

- To give a white solid smoke

Question 13

State the observation when sulfur reacts with oxygen (2 marks)

Answer 13

• Burns with a blue flame

- To produce an acidic choking gas

Question 14

Explain why aluminium oxide shows some covalent character as well as ionic character (2 marks)

Answer 14

• Small aluminium ion has high charge (3+) so pulls the electrons from O²- towards itself
• This distorts the oxide charge cloud and creates covalent character

Question 15

Suggest why P₄O₁₀ and SO₂ are simple covalent oxides (1 mark)

Answer 15

• Small electronegativity difference between the non-metal and the O atoms

Question 16

Suggest and explain how aluminium metal is protected from corrosion in moist air (3 marks)

Answer 16

• Thin layer of aluminium oxide
• As it has a high lattice strength and is insoluble in water
• So makes this layer impermeable to air and water

Question 17

State the pH of the solution formed when sodium oxide reacts with water and explain why it has this pH (2 marks)

Answer 17

• pH 13

- Oxide ions accept protons and become hydroxide ions

Question 18

State the pH of magnesium hydroxide and suggest why it is lower than the pH of sodium hydroxide (3 marks)

Answer 18

• pH 9
• It’s lattice is stronger so it is only slightly soluble in water
• So fewer OH- ions are produced

Question 19

State the pH of the solution formed when phosphorus oxide reacts with water (1 mark)

Answer 19

• pH 0

Question 20

State the pH of H₂SO₃ (1 mark)

Answer 20

pH 3

Question 21

State the pH of H₂SO₄ (1 mark)

Answer 21

pH 0

Question 22

State the ionic equation in which aluminium oxide acts as a base (1 mark)

Answer 22

Al₂O₃ + 6H+ –> 2Al³+ + 3H₂O

Question 23

State the ionic equation in which aluminium oxide acts as an acid (1 mark)

Answer 23

Al₂O₃ + 2OH- + 3H₂O –> 2Al(OH)₄-

Question 24

Explain why magnesium has a higher melting point than sodium (2 marks)

Answer 24

• Magnesium has a higher charge

- So delocalised electrons pulled in more closely

Question 25

Other than a high melting point, give two physical properties of silicon dioxide that are characteristic of its structure and bonding (2 marks)

Answer 25

• Hard
• Insoluble
• Brittle

Question 26

Write an equation for the reaction between the acidic oxide, phosphorus(V) oxide, and the basic oxide, magnesium oxide (1 mark)

Answer 26

P4O10 + 6MgO → 2Mg3(PO4)2

Question 27

By reference to the structure of, and the bonding in, silicon dioxide, suggest why it is insoluble in water (3 marks)

Answer 27

• Macromolecular
• Covalent Bonding
• Water cannot (supply enough energy to) break the covalent bonds / lattice

Question 28

Ions are formed when SO₂ reacts with water - write and equation for this reaction and suggest why sulfur dioxide forms a weakly acidic solution (2 marks)

Answer 28

• SO₂ + H₂O –> H+ + HSO₃

- Reaction is an equilibrium / reversible reaction displaced mainly to the left

Question 29

State and explain the trend in electronegativities across Period 3 from sodium to sulfur (4 marks)

Answer 29

• Electronegativity increases
• Proton number increases (increase in nuclear charge)
• Same number of electron shells/levels
• Attraction of bond pair to nucleus increases

Question 30

Explain why the oxides of the Period 3 elements sodium and phosphorus have different melting points. In your answer you should discuss the structure of and bonding in these oxides, and the link between electronegativity and the type of bonding (6 marks)

Answer 30

• Big difference in electronegativity leads to ionic bonding, smaller covalent
• Sodium oxide ionic lattice
• Strong forces of attraction between ions
• P4O10 covalent molecular
• Weak (intermolecular) forces between molecules
• Melting point Na2O greater than for P4O10

Question 31

Write an equation for the reaction of sodium hydroxide with silicon dioxide (1 mark)

Answer 31

2NaOH + SiO2 → Na2SiO3 + H2O