Properties of Period 3 elements and their oxides (A-level)

Question 1

What is the reaction of Na with cold water?

Answer 1

2NA(s) + 2H20(l) –> 2NaOH (aq) + H2(g)

Question 2

Reaction of Magnesium with water

Answer 2

Mg(s) + 2H2O(l) —> Mg(OH)2(s) + H2(g)

Question 3

Reaction of Magnesium with steam

Answer 3

Mg(s) + H20 —> MgO(s) + H2(g)

Question 4

Describe the reactions of elements in Period 3 (up to sulphur) with oxygen

Answer 4

Na - burns with yellow flame to produce a white solid
Mg, Al, Si and P - burn with white flame + white solid smoke
S - burns with Blue flame to form acidic choking gas

Question 5

Equation: Na with oxygen

Answer 5

4Na + O2 —> 2 Na2O

Question 6

Equation: Mg + O2

Answer 6

2Mg + O2 –> 2MgO

Question 7

Equation: Al + O2

Answer 7

4AL + 3O2 –> 2Al2O3

Question 8

Equation: Si + O

Answer 8

Si + O2 –> SiO2

Question 9

Equation: P + O2

Answer 9

4P + 5O2 —> P4O10

Question 10

Equation: S + O2

Answer 10

S(s) + O2 —> SO2(g)

Question 11

How can we stop elements such as sodium and phosphorus from coming into contact and reacting with air?

Answer 11

Storing under oil and phosphorus under water

Question 12

Describe the trend in melting points from Na-S

Answer 12

Ionic oxides - Na2O, MgO, Al2O3
- high melting points.
- ionic giant lattice structures:
-strong forces of attraction between oppositely charged ions : higher mp.
- increased charge on the cation makes the ionic
forces stronger going from Na to Al so increased melting points.

Macromolecular oxides - SiO2
- macromolecular:
- many very strong covalent bonds between atoms.
- High energy needed to break the many strong covalent bonds – very high mp

Simple molecular oxides: P4O10 (s), SO2 (g)
- weak intermolecular forces between molecules
(van der waals + permanent dipoles)
- lower mp’s.
- P4O10 is a bigger molecule and has more electrons than SO2 it will have larger van der waals forces between molecules and a higher melting point.

Question 13

Why do ionic oxides react with water?

Answer 13

They accept H+ ions to become OH- ions acting as a Bronsdted-lowry base

Question 14

Reaction + PH: sodium oxide with water

Answer 14

Na2O (s) + H2O (l) –> 2NaOH(aq)
pH 13
vigorous exothermic reaction

Question 15

Will Na20 react with acids or alkalis, depending on which what is it’s nature?

Answer 15

Acids
Acid + Alkali –> Salt + H20
Na20 –> BASIC

Question 16

Reaction + PH: Mg oxide with water

Answer 16

MgO (s) + H2O (l) –> Mg(OH)2(s)
pH 9
sparingly soluble

Question 17

Why does MgO oxide produce a lower pH when reacting with water compared to Na2O?

Answer 17

Mg(OH)2 (the product) is a slightly soluble in water as its lattice is stronger so fewer free OH- ions are produced and so lower pH

Question 18

Does Al203 react with water and explain answer?

Answer 18

No
high strength of the ionic lattice in Al2 O3 so gives neutral PH7

Question 19

What is the reaction of aliminium oxide with acids? (use. hcl as example)

Answer 19

Acts as a base
Al2O3 + 6H+ —> 2Al.3+ + 3H2O

Question 20

What is the reaction of aliminium oxide with alkalis?

Answer 20

Acts as a acid
Al2O3 (s) + 2OH-(aq) +3H20 —> 2Al(OH)4-(aq)

Question 21

Does SiO2 reacts with water?

Answer 21

no reaction
insoluble
due to many strong covalent bonds in macromolecular structure

Question 22

Reaction of SiO2 with alkalis?

Answer 22

SiO2 + 2OH- —> SiO3.2- + H20

Question 23

What does the reaction of simple mocleular acidic oxides with bases form?

Answer 23

Salt + H20

Question 24

Reaction and PH: P4O10 with water

Answer 24

P4O10 + 6H2O –» 4H3PO4
PH 0

Question 25

Reaction of P4O10 with alkalis

Answer 25

P4O10+ 12OH- —> 4PO4.3- + 6H2O

Question 26

Reaction of SO2 with alkalis

Answer 26

SO2(g) + 2OH- (aq) –> SO3.2- (aq) + H2O (l)

Question 27

Reaction of SO2 with water + PH

Answer 27

H2O(l) + SO2(g) —> H2SO3(aq)
PH 3

Question 28

Reaction of SO3 with water + PH

Answer 28

SO3 + H20 —> H2SO4
PH 0

Question 29

Reaction of SO3 with alkalis

Answer 29

SO3(g) + 2OH- (aq) —> SO4.2- (aq) + H2O (l)

Question 30

What do the products of Phosphorus oxide, Sulfur dioxide and Sulfur trioxide reacting with water have in common?

Answer 30

All products consist of a double bond between primary element and oxygen

Question 31

Reaction of acid and base make what?

Answer 31

Salt + Water

Question 32

True/False: Non-metal covalent oxides show acidic behaviour

Answer 32

TRUE

Question 33

True/False: Ionic metal oxides show acidc behaviuor

Answer 33

False

they show basic behaviour as they accept H+ ions ot become OH- ions