Period Three Oxides

Question 1

Predict the pH of the solution when phosphorus oxide reacts with water and write an equation (2)

Answer 1

P₄O₁₀(s) + 6H₂O(l) -> 4H₃PO₄(aq)
Acidic (0-2)

Question 2

Explain why excess MgO can be used to neutralise acidic compounds. (1)

Answer 2

Weakly ionising

Question 3

Describe the observations and give the equation for the reaction of magnesium with water at a high temperature. (3)

Answer 3

Mg(s) + H₂O(l) -> MgO(s) + H₂(g)
-White precipitate
-White flame

Question 4

Give the formula, structure and bonding shown in phosphorus oxide. (4)

Answer 4

-P₄O₁₀
-simple molecular structure
-covalent bonding
-VDWs between molecules

Question 5

Write an equation for the reaction between sulphur dioxide and water. (1)

Answer 5

SO₂(g) + H₂O(l) -> H₂SO₃(aq)

Question 6

Write an equation for the reaction between aluminium oxide and hydrochloric acid.(1)

Answer 6

Al₂O₃(s) + 6HCl(aq) -> 2AlCl₃(aq) + 3H₂O(l)

Question 7

Write an equation for the reaction between Na₂O and HCl. (1)

Answer 7

Na₂O(s) + 2HCl(aq) -> 2NaCl(aq) + H₂O(l)

Question 8

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

Answer 8

Al₂O₃(aq) + 6HCl(aq) -> 2AlCl₃(aq)
+ 3H₂O(l)

Al₂O₃ + 2NaOH + 3H₂O -> 2Na⁺ + 2[Al(OH)₄]⁻

Question 9

Explain why phosphorus oxide has a higher melting point than sulfur oxide. (2)

Answer 9

P₄O₁₀ is a bigger molecule
Therefore, VDWs between molecules are stronger

Question 10

State the type of bonding in sodium oxide and explain why it reacts to form an alkaline solution in water. (3)

Answer 10

ionic
O²⁻ reacts with water (accepts protons)
forming OH⁻ ions

Question 11

Compare and explain the melting points of phosphorus oxide and sulphur dioxide. (3)

Answer 11

lower melting point
molecular with covalent bonding
weak van der Waals between molecules

Question 12

Write an equation for the reaction between aluminium and oxygen. (1)

Answer 12

2Al(s) + 3/2O₂(g) + Al₂O₃(aq)

Question 13

Explain why sodium oxide has a high melting point. (2)

Answer 13

Ionic lattice
strong forces of attraction between oppositely charged ions

Question 14

Write the equation for the reaction between phosphorus oxide and magnesium oxide. (1)

Answer 14

P₄O₁₀(s) + 6MgO(s) -> 2Mg₃(PO₄)₂(s)

Question 15

Predict the pH of the solution when sodium oxide reacts with water and write an equation. (2)

Answer 15

Na₂O(s) + H₂O(l) -> 2Na(OH)
pH 14

Question 16

Give the equation for phosphoric acid with magnesium oxide. (1)

Answer 16

MgO(s) + H₃PO₄(aq) -> MgHPO₄(aq) + H₂O(l)

Question 17

Write an equation for the reaction between silicon dioxide and sodium hydroxide. (1)

Answer 17

SiO₂(g) + 2NaOH(aq) -> Na₂SiO₃(aq) + H₂O(l)

Question 18

Explain why sodium oxide has a high melting point. (2)

Answer 18

ionic lattice
strong attraction between oppositely charged ions

Question 19

Explain why the melting point of silicon dioxide is high (2)

Answer 19

giant covalent structure
strong covalent bonds

Question 20

Write an equation for the reaction of phosphorus oxide with sodium hydroxide

Answer 20

P₄O₁₀(s) + 12NaOH(aq) -> 4Na₃PO₄(aq) + 6H₂O(l)

Question 21

Write an equation for the acid-base reaction that occurs between sodium oxide and phosphorus oxide. (1)

Answer 21

6Na₂O(s) + P₄O₁₀(s) -> 4Na₃PO₄(s)

Question 22

Outline an experiment that could be used to show that aluminium oxide contains ions. (2)

Answer 22

-heat until molten
-if its conducts electricity then the compound contains ions

Question 23

Explain why sulphur trioxide has a higher melting point than sulphur dioxide. (2)

Answer 23

-sulphur trioxide is a larger molecule
-so van der Waals forces between molecules are stronger

Question 24

Explain why the melting point of phosphorus oxide is higher than the melting point of sulphur dioxide. (2)

Answer 24

-phosphorus oxide is a bigger molecule
-stronger van der Waals between molecules

Question 25

Write an equation for the reaction of sulfur oxide with water and give the pH of the solution formed. (2)

Answer 25

SO₂(g) + H₂O(l) -> H₂SO₄(aq) pH 1

Question 26

Write an equation to show MgO acting as a base with another reagent. (2)

Answer 26

MgO(s) + 2HCl(aq) -> MgCl₂(s) + H₂O(l)

Question 27

Explain, with the aid of an equation, why silicon oxide is an acidic oxide. (2)

Answer 27

-reacts with bases -SiO₂ + 2NaOH -> Na₂SiO₃ + H₂O

Question 28

Write an ionic equation to show how aluminium oxide reacts with hydrochloric acid. (1)

Answer 28

Al₂O₃(s) + 6HCl(aq) -> 2AlCl₃(l) + 3H₂O(l)

Question 29

Explain why the melting point of phosphorus oxide is low. (1)

Answer 29

weak van der Waals between molecules

Question 30

Describe observations when sulfur burns in oxygen. Write an equation for the reaction that occurs and state the type of bonding in the oxide formed. (4)

Answer 30

-blue flame -choking gas -S + O₂ -> SO -covalent

Question 31

Write an equation for the reaction between sodium and oxygen. State the observations observed. (3)

Answer 31

2Na + ½O₂ -> Na₂O -white ash -yellow flame

Question 32

Explain why sodium oxide and phosphorus oxide have different melting points. (6)

Answer 32

-sodium oxide forms an ionic lattice - strong forces of attraction -big difference in electronegativity between sodium and phosphorus -P₄O₁₀ simple molecular covalent -weak van der Waals between molecules -melting point of sodium oxide is greater than phosphorus oxide

Question 33

State the structure and bonding in sulfur dioxide and 2 properties. (4)

Answer 33

-simple molecular structure -covalent bonding -hard -insoluble

Question 34

Suggest why SO₂ is insoluble in water. (3)

Answer 34

-simple molecular structure -covalent -water doesn't supply sufficient energy to break the strong bonds

Question 35

State the meaning of the term amphoteric. (1)

Answer 35

reacts with acids and bases

Question 36

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

Answer 36

P₄O₁₀ + 6H₂O -> 4H₃PO₄

Question 37

Write an ionic equation to show how aluminium oxide reacts with aqueous sodium hydroxide. (1)

Answer 37

Al₂O₃ + 2OH⁻ + 3H₂O -> 2Al(OH)₄⁻

Question 38

Write an equation for the reaction between sodium and water. (1)

Answer 38

2Na + 2H₂O -> 2NaOH+ H₂

Question 39

Write an equation for the reaction between sodium oxide and phosphorus oxide. State the general type of reaction shown. (2)

Answer 39

6Na₂O + P₄O₁₀ -> 4Na₃PO₄ acid-base

Question 40

Suggest why silicon dioxide does not react with HCl. (1)

Answer 40

it is acidic