2.4 Properties of Period 3 Elements and their Oxides

Question 1

Appearance and physical properties of sodium?

Answer 1

Metallic, shiny, conducts electricity (worst

conductor out of the metals)

Question 2

Reaction of sodium with water

Answer 2

Vigorous reaction, floats on water, fizzes, melts due to -ΔH of the reaction.

Question 3

Reaction of sodium with oxygen

Answer 3

Bright yellow flame, forms white powder of Na2O

Question 4

Appearance and physical properties of magnesium?

Answer 4

Metallic, shiny, conducts electricity (between Na and Al in terms of how well it does).

Question 5

Reaction of Mg in cold water

Answer 5

Very slow reaction. pH = 10 as Mg(OH)2 is sparingly soluble

Question 6

Reaction of Mg with steam

Answer 6

Much faster

Question 7

Reaction of Mg with Oxygen

Answer 7

Bright white flame, forms white powder of MgO

Question 8

Appearance and physical properties of aluminium?

Answer 8

Metallic, shiny, best conductor of electricity in period 3

Question 9

Reaction of Al with water

Answer 9

None

Question 10

Reaction of Al with Oxygen

Answer 10

Heat and lower into jar of O2 → bright flame, forms white powder.

Question 11

Why is aluminium considered unreactive even though the metal itself is reactive?

Answer 11

Covered by Al2O3 from where oxygen has oxidised the surface of the Al. Al2O3 is unreactive. Makes it useful for saucepans, window frames etc. If Al2O3 is scratched off, Al reacts rapidly with air to form a new coat.

Question 12

Appearance and physical properties of silicon?

Answer 12

Semimetal (metalloid), semiconductor (conducts electricity to an extent and in certain conditions)

Question 13

Reaction of silicon with oxygen

Answer 13

White powder produced when strongly heated

Question 14

Appearance and physical properties of phosphorus?

Answer 14

Non-metal, low m.p. And b.p., does not conduct electricity. Red Phosphorus as a crystal structure White Phosphorus as P4

Question 15

Reaction of phosphorus in excess oxygen

Answer 15

Red P needs to be heated significantly first, white P ignites spontaneously in air Phosphorus pentoxide (white crystalline solid) formed

Question 16

Reaction of P in limited oxygen

Answer 16

Incomplete combustion: colourless liquid phosphorus trioxide is formed.

Question 17

Appearance and physical properties of sulfur?

Answer 17

Non-metal, low mp and bp, does not conduct

electricity.

Question 18

Reaction of sulfur with O2

Answer 18

Need to heat and lower into a jar of oxygen. Colourless gas sulfur dioxide formed. Some SO3 also formed.

Question 19

What is the trend in melting points for period 3 oxides (state highest and lowest and why and draw graph)?

Answer 19

Highest is MgO, lowest is SO2 ; increases along group for metals for Na2O and MgO due to stronger ionic bonding, but Al2O3 is lower due to the covalent character of the bonding. Decreases with size for simple molecular molecules.

Question 20

Which period 3 oxides are basic?

Answer 20

Na2O and MgO

Question 21

Reaction of Na oxide with water

Answer 21

Na2O + H2O → 2Na+ + 2OH- ; pH = 14

Question 22

Reaction of Mg oxide with water

Answer 22

MgO + H2O → Mg2+ + 2OH- ⇌ Mg(OH)2 ; pH = 9-10 as Mg(OH)2 is sparingly soluble

Question 23

What are the products if Na2O and MgO are reacted with acid?

Answer 23

Salt and water

Question 24

Is aluminium oxide basic or acidic?

Answer 24

It is amphoteric; can act as either an acid or a base

Question 25

Is Aluminium oxide in water

Answer 25

no

Question 26

Reaction of aluminium oxide with NaOH

Answer 26

Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 ; sodium aluminate is formed

Question 27

Is silicon dioxide soluble in water

Answer 27

no

Question 28

In what conditions will silicon dioxide act as an acid?

Answer 28

Reacts as a weak acid with a strong base (e.g. hot, conc NaOH)

Question 29

Reaction of silicon dioxide with hot, conc NaOH

Answer 29

SiO2 + 2NaOH → H2O + Na2SiO3 - sodium silicate

Question 30

How is silicon dioxide used in the production of Fe?

Answer 30

SiO2 + CaO → CaSiO3 - calcium silicate

Question 31

Reaction of Phosphorus pentoxide with water? pH?

Answer 31

P4O10 + 6H2O → 4H3PO4 ; pH = 1-2

Question 32

Reaction of SO2 with water? pH?

Answer 32

SO2 + H2O → H2SO3 ; weak acid → pH = 2-3

Question 33

Reaction of SO3 with water? pH?

Answer 33

SO3 + H2O → H2SO4 ; strong acid → pH = 0-1

Question 34

Reaction of SO2 with NaOH?

Answer 34

SO2 + NaOH → NaHSO3 | NaHSO3 + NaOH → Na2SO3 + H2O

Question 35

Uses of MgO

Answer 35

Additive for cattle feed

Question 36

How useful is Al2O3 ?

Answer 36

Oxide layer on Aluminium makes it very useful as it is unreactive and returns quickly if it is scratched off

Question 37

Uses of SO2

Answer 37

Reactant in contact process (making H2SO4 )

Question 38

Would Lithium oxide or sodium oxide have a higher melting point? Why?

Answer 38

Li2O has a higher m.p., since Li+ is a smaller ion than Na+ , so the O2- and Li+ charge centres are closer together and there is a greater electrostatic force of attraction between the oppositely charged ions.