Period 3

Question 1

Na reaction with water

Answer 1

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

Question 2

Mg reaction with water

Answer 2

Magnesium reacts very slowly with cold water to form the hydroxide but reacts more readily with steam to form the oxide
Mg (s) + H2O (g)->MgO (s) + H2 (g)

Question 3

Na reaction with oxygen

Answer 3

burns with a yellow flame to produce a white solid

4 Na (s) + O2 (g)->2 Na2O (s)

Question 4

Mg reaction with oxygen

Answer 4

burn with a white flame to give white solid smoke

2Mg (s) + O2 (g)-> 2MgO (s)

Question 5

Al reaction with oxygen

Answer 5

burn with a white flame to give white solid smoke

4Al + 3O2 (g)-> 2Al2O3 (s)

Question 6

Si reaction with oxygen

Answer 6

burn with a white flame to give white solid smoke

Si + O2 (g)-> SiO2 (s)

Question 7

P reaction with oxygen

Answer 7

burn with a white flame to give white solid smoke

P4 + 5O2 (g)-> P4O10 (s)

Question 8

S reaction with oxygen

Answer 8

burns with a blue flame to form an acidic choking gas

S+ O2 (g)-> SO2 (g)

Question 9

Al2O3

Answer 9

ionic but does show some covalent character.

electronegativity difference being less big or alternatively by the small aluminium ion with a high charge being able to get close to the oxide ion and distorting the oxide charge cloud.

Question 10

Aluminium oxide corrosion

Answer 10

Aluminium metal is protected from corrosion in moist air by a thin layer of aluminium oxide. The high lattice strength of aluminium oxide and its insolubility in water make this layer impermeable to air and water.

Question 11

Na2O reaction with water

Answer 11

Na2O (s) + H2O (l)->2Na+ (aq) + 2OH- (aq) pH 13 (This is a vigorous exothermic reaction)
The ionic oxides are basic as the oxide ions accept protons to become hydroxide ions in this reaction (acting as a bronsted lowry base)

Question 12

MgO reaction with water

Answer 12

MgO (s) + H2O (l)->Mg(OH)2 (s) pH 9

Mg(OH)2 is only slightly soluble in water as its lattice is stronger sofewerfreeOH- ionsareproducedandsolowerpH

Question 13

Al2O3 and SiO2 in water

Answer 13

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

Question 14

Acid treatment

Answer 14

MgO is better than NaOH for treating acid in rivers and the stomach as it is only sparingly soluble and weakly alkaline so using an excess would not make the water excessively alkaline

Question 15

P4O10 reaction with water

Answer 15

P4O10 (s) + 6 H2O (l) -? 4 H3PO4(aq) 
pH 0 (this is a vigorous exothermic reaction

Question 16

SO2 reaction with water

Answer 16

SO2 (g) + H2O (l) ->H2SO3 (aq)

pH 3 (weak acid)

SO2 + H2O ->H+ + HSO3-

Question 17

SO3 reaction with water

Answer 17

SO3 (g) + H2O (l) ->H2SO4 (aq)

pH 0

SO3 + H2O ->H+ + HSO4-

Question 18

Acid-base behaviour

Answer 18

The trend is the ionic metal oxides show basic behaviour and the non-metal covalent oxides show acidic behaviour. The slightly intermediate nature of the bonding in aluminium oxide is reflected in its amphoteric behaviour: it can act as both a base and an acid

Question 19

Basic reactions with acids

Answer 19

acid+base->salt+water

Question 20

Amphoteric oxides

Answer 20

Base
Al2O3 + 6H+ -> 2Al3+ + 3H2O

Acid
Al2O3 (s)+ 2NaOH (aq) + 3H2O (l) -> 2NaAl(OH)4 (aq)

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

Question 21

SiO2

Answer 21

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

iant covalent structure with very strong bonds. This stops SiO2 dissolving or reacting with water and weak solutions of alkali. It will, however, react with very concentrated NaOH