Periodicity

Question 1

Describe the trend in the reaction of period 3 elements with water.

Answer 1

Only sodium and magnesium react - sodium much more quickly than magnesium. Chlorine will form green chlorine water.

Question 2

Give the equation for, and describe, the reaction between sodium and water.

Answer 2

2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)

This is a vigorous reaction that lets off hydrogen gas.

Question 3

What is the pH value for sodium hydroxide?

Answer 3

13-14

Question 4

Give the equation for, and describe, the reaction between magnesium and water.

Answer 4

Mg(s) + 2H2O(l) –> Mg(OH)2(aq) + H2(g)

Very slow, only a few bubbles of hydrogen formed.

Question 5

Give the equation for, and describe, the reaction between magnesium and steam.

Answer 5

Mg(s) + H2O(g) –> MgO(s) + H2(g)

Fast reaction due to more energy.

Question 6

What is the pH value for magnesium hydroxide?

Answer 6

9-10

Question 7

Give the equation for, and describe, the reaction between sodium and oxygen.

Answer 7

4Na(s) + O2(g) –> 2Na2O(s)

This gives a bright yellow flame and forms white sodium oxide.

Question 8

Give the equation for, and describe, the reaction between magnesium and oxygen.

Answer 8

2Mg(s) + O2(g) –> 2MgO(s)

This gives a bright white flame and forms white magnesium oxide.

Question 9

Give the equation for, and describe, the reaction between aluminium and oxygen.

Answer 9

4Al(s) + 3O2(g) –> 2Al2O3(s)

This gives a bright white flame and forms white aluminium oxide.

Question 10

Give the equation for, and describe, the reaction between silicon and oxygen.

Answer 10

Si(s) +O2(g) –> SiO2(s)

White flame, if in pure oxygen.

Question 11

Give the equation for, and describe, the reaction between phosphorus and oxygen.

Answer 11

4P(s) + 5O2(g) –> P4O10(s)

This spontaneously ignites in air, and gives off a white smoke.

Question 12

Give the equation for, and describe, the reaction between sulphur and oxygen.

Answer 12

S(s) + O2(g) –> SO2(g)

Burns with a blue flame, and gives off colourless sulphur dioxide gas, and a little sulphur trioxide.

Question 13

Which period 3 elements do we have to burn in a jar of oxygen?

Answer 13

Aluminium, silicon, sulphur

Question 14

Which period 3 oxides have a giant ionic lattice structure?

Answer 14

Na2O, MgO and Al2O3.

Question 15

Why do the period 3 metal oxides have high boiling points?

Answer 15

Strong forces of attraction between ions make them very hard to melt.

Question 16

Which has a higher boiling point - Na2O or MgO - and why?

Answer 16

MgO has a higher melting point than Na2O because it forms 2+ ions, which are able to bond more strongly.

Question 17

Which has a lower boiling point - MgO or Al2O3 - and why?

Answer 17

Al2O3 because it’s 3+ ions distort the oxygen’s electron cloud, causing the bonds to have covalent character.

Question 18

Which period 3 oxides have a giant covalent structure, and how does this affect their melting point?

Answer 18

Only SiO2. It means that it’s melting temperature is very high compared to other non-metal oxides, because to melt it we are required to break strong covalent bonds, not just intermolecular forces.

Question 19

Which period 3 oxides have a simple covalent structure, and how does this affect their melting point?

Answer 19

P4O10 and SO2. This means their melting point is very low, because we only need to overcome very weak van der Waals forces.

Question 20

Give the equation and pH value for the reaction between sodium oxide and water.

Answer 20

Na2O(s) + H2O(l) –> 2Na^(+)(aq) + 2OH^(-)

pH = 14

Question 21

Give the equation and pH value for the reaction between magnesium oxide and water, and explain the pH value.

Answer 21

MgO(s) + H2O(l) –> Mg(OH)2(s) –> Mg^(2+)(aq) + 2OH^(-)(aq)
pH = 9
Because magnesium hydroxide is sparingly soluble in water.

Question 22

Give the equation and pH value for the reaction between aluminium oxide and water.

Answer 22

Aluminium oxide is insoluble in water.

Question 23

Give the equation and pH value for the reaction between silicon oxide and water.

Answer 23

Silicon oxide is insoluble in water.

Question 24

Describe, and give the equation and pH value for the reaction between phosphorus oxide and water.

Answer 24

P4O10(s) + 6H2O(l)–> 4H3PO4(aq)
pH = 0-1
This is quite a vigorous reaction.

Question 25

Give the equation and pH value for the reaction between sulphur dioxide and water, and explain the pH value.

Answer 25

SO2(g) + H2O(l) –> H2SO3(aq) –> H^(+)(aq) + HSO3^(-)(aq)
pH = 2
Because sulfurous acid only partly dissociates in water.

Question 26

Give the equation and pH value for the reaction between sodium trioxide and water, and explain the pH value.

Answer 26

SO3(g) + H2O(l) –> H2SO4(aq) –> H^(+)(aq) + HSO4^(-)(aq)
pH = 0-1
Sulfuric acid completely dissociates in water.

Question 27

Give the equation for sodium oxide with hydrochloric acid.

Answer 27

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

Question 28

Give the equation for magnesium oxide with sulfuric acid.

Answer 28

MgO(s) + H2SO4(aq) –> MgSO4(aq) + H2O(l)

Question 29

Give the equations for aluminium oxide with both sulfuric acid and sodium hydroxide, and state what character this shows.

Answer 29

Al2O3(s) + 3H2SO4(aq) –> Al2(SO4)3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) + 3H2O(l) –> 2NaAl(OH)4(aq)
This shows amphoteric character.

Question 30

Give equations for reactions between the acidic oxides and sodium hydroxide.

Answer 30

SiO2(s) + 2NaOH(aq) –> Na2SiO3(aq) + H2O(l)
P2O10(s) + 12NaOH(aq) –> 4Na3PO4(aq) + H2O(l)
SO2(g) + 2NaOH(aq) –> Na2SO3(aq) + H2O(l)
SO3(g) + 2NaOH(aq) –> Na2SO4(aq) + H2O(l)