Period 3 Elements

Question 1

What is the equation and observation for the reaction between sodium and cold water

Answer 1

It fizzes around on surface
2Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2(g)

Question 2

What is the equation for the reaction between magnesium and cold water

Answer 2

Mg(s) + H2O(l) → Mg(OH)2 + H2(g)

This is a very slow reaction

Question 3

What is the observation and equation for the reaction between magnesium and steam

Answer 3

Mg (s) + H2O (g) → MgO (s) + H2 (g)

Reacts faster than it does with cold water

Question 4

Reaction and observation for the reaction between sodium and oxygen

Answer 4

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

Question 5

Reaction and observation for the reaction between magnesium and oxygen

Answer 5

2Mg (s) + O2 (g) → 2MgO (s)
Burns with a white flame to give a white solid smoke

Question 6

Reaction and observation for the reaction between aluminium and oxygen

Answer 6

4Al (s) + 3O2 (g) → 2Al2O3 (s)
Burns with a white flame to give a white solid smoke

Question 7

Reaction and observation for the reaction between silicon and oxygen

Answer 7

Si (s) + O2 (g)→ SiO2 (s)
Burns with a white flame to give a white solid smoke

Question 8

Reaction and observation for the reaction between phosphorous and oxygen

Answer 8

4P (s) + 5O2 (g) → P4O10 (s)
Burns with a white flame to give a white solid smoke

Question 9

Reaction and observation for the reaction between sulfur and oxygen

Answer 9

S (s) + O2 (g) → SO2 (g)
Burns with a blue flame to form an acidic choking gas

Question 10

How is sodium stored and why

Answer 10

Under oil to stop it from coming into contact and reacting with air

Question 11

How is phosphorous stored and why

Answer 11

Under water to stop it from coming into contact and reacting with air

Question 12

Describe the structure and bonding in sodium/magnesium/aluminium oxide

Answer 12

The metal oxides are ionic. They have have a giant ionic lattice with strong electrostatic forces of attraction between the oppositely charged ions. They have high MP’s

Question 13

Explain why the melting point of the oxides increases from Na to Al

Answer 13

The increased charge on the cation makes the ionic forces stronger (bigger lattice enthalpies of dissociation) so increased MP.

Question 14

Explain the boiling point of SiO2 with reference to its structure and bonding

Answer 14

SiO2 is macromolecular. It has a giant covalent lattice with many strong covalent bonds between atoms. High amounts of energy is needed to break the many strong covalent bonds. It has a very high BP

Question 15

Describe the structure of phosphorous and sulfur oxides

Answer 15

They are simple molecular with weak Van der Waals and permanent dipole forces between their molecules so have lower BP’s.

Question 16

Why does Phosphorous oxide have a higher melting poiunt than sulphur dioxide

Answer 16

Phospohorous oxide is a bigger molecules and has more electrons so will have stronger Van der Waals forces between its molecules

Question 17

How can you prove a compound is ionic

Answer 17

Melt the solid and test its electric conductivity. It will conduct electricity

Question 18

Why is aluminium metal protected from corrosion in moist air

Answer 18

It is protected by a thin layer of aluminium oxide. The high lattice strength of aluminium oxide and its insolubility in water make the layer impermeable to air and water

Question 19

What happens to the covalent character of period 3 oxides across the period

Answer 19

Covalent character increases

Question 20

What happens to the ionic character of period 3 oxides across the period

Answer 20

Decreases

Question 21

How do metal ionic oxides react with water

Answer 21

They form hydroxides which are alkaline

Question 22

Why are ionic oxides basic

Answer 22

The oxide ions accept protons to become hydroxide ions in the reaction

Question 23

Reaction between Na2O and water and the pH of the products

Answer 23

Na2O (s) + H2O (l) → 2NaOH (aq)
pH 14

Question 23

Reaction between MgO and water and its pH

Answer 23

MgO (s) + H2O (l) → Mg(OH)2 (aq)
pH 10

Question 24

Reaction between Al2O3 and water and its pH

Answer 24

No reaction. Aluminium oxide does not dissolve in the water due to the high strength of its ionic lattice.
pH 7

Question 25

Reaction between SiO2 and water and the pH

Answer 25

No reaction. It is insoluble in water due to its macromolecular structure.
pH 7

Question 26

Reaction between p4O10 and water and its pH

Answer 26

P4O10 (s) + 6H2O (l) → 4H3PO4 (aq)
pH 2

Question 27

Reaction between SO2 and water and its pH

Answer 27

SO2 (g) + H2O (l) → H2SO3 (aq)
pH 1

Question 28

Reaction between SO3 and water and its pH

Answer 28

SO3 (g) + H2O (l) → H2SO4 (aq)
pH 1

Question 29

Reaction between basic oxides (Na2O, MgO) and acid

Answer 29

Na2O (s) + 2HCl (aq) → 2NaCl (aq) + H2O (l)
MgO (s) + 2HCl (aq) → MgCl2 (aq) + H2O (l)

acid + base → salt + water

Question 30

Nature of the period 3 oxides

Answer 30

Ionic metal oxides are basic
Non-metal covalent oxides are acidic
Aluminium oxide can act as both base and acid so is amphoteric

Question 31

Reactions of aluminium oxide with acid

Answer 31

Al2O3 (s) + 3H2SO4 (aq) → Al2(SO4)3 (aq) + 3H2O (l)

Al2O3 + 6H+ → 2Al3+ + 3H2O

Question 32

Reactions of aluminium oxide with alkalis

Answer 32

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

Al2O3 (s) + 2NaOH (aq) + 3H2O (l) → 2NaAl(OH)4 (aq)

Question 33

What does SiO2 react with and not with

Answer 33

With : hot, concentrated NaOH
Not with : water, weak alkalis

Question 34

Reaction of SiO2 with hot concentrated NaOH

Answer 34

SiO2 (s) + 2NaOH (aq) → Na2SiO3 (aq) + H2O (l)

SiO3 = SiO3 2- ion

Question 35

Reaction of P4O10 with alkali (NaOH)

Answer 35

P4O10 (s) + 12NaOH → 4Na3PO4 + 6H2O (l)

PO4 = PO4 3- ion

Question 36

Reaction of SO2 with alkali

Answer 36

SO2 (g) + 2NaOH (aq) → Na2SO3 (aq) + H2O (l)

Question 37

Reaction of SO3 with alkali

Answer 37

SO3 (g) + 2NaOH (aq) → Na2SO4 (aq) + H2O (l)