Section 3 - Period 3 Elements

Question 1

Is Na or Mg more reactive?

Answer 1

Sodium - it takes less energy to lose one electron than to lose two.

Question 2

How does sodium react with cold water?

Answer 2

• vigorously
• forms alkaline solution
• forms a molten ball on surface
• fizzes and produces H₂ gas

Question 3

Complete the equation:

2Na_(s) + 2H₂O_(l) –>

Answer 3

2NaOH_(aq) + H_2(g)

Question 4

What is the pH of NaOH?

Answer 4

Strongly alkaline - pH 12-14

Question 5

How does magnesium react with cold water?

Answer 5

• Very slowly
• Alkaline solution is formed
• Thin coating of magnesium hydroxide forms on surface of metal

Question 6

What is the pH of magnesium hydroxide and why?

Answer 6

Weakly alkaline - pH 9-10

It is not very soluble in water so very few hydroxide ions are produced.

Question 7

Complete the equation:

Mg_(s) + 2H₂O_(l) –>

Answer 7

Mg(OH)_2(aq) + H_2(g)

Question 8

What is a faster way to react magnesium with water and what does it produce?

Answer 8

React it with steam

Magnesium Oxide

Question 9

Complete the equation:

Mg_(s) + H₂O_{(g) –>}

Answer 9

MgO_(s) + H_2(g)

Question 10

What do period 3 elements form when they react with oxygen?

Answer 10

Oxides

Question 11

What is the general pattern for oxidation states of elements in oxides? (and what is the exception?)

Answer 11

Usually oxidised to their highest oxidation state (the same as their group numbers).

Sulfur is the exception - it forms SO₂ which has an oxidation state of +4. A catalyst and high temp are needed to create SO₃.

Question 12

Give the equation for:

Sodium and Oxygen

Answer 12

2Na_(s) + 1/2O_2(g) –> Na₂O_(s)

Question 13

Give the equation for:

Magnesium and Oxygen

Answer 13

Mg_(s) + 1/2O_(g) –> MgO_(s)

Question 14

Give the equation for:

Aluminium and Oxygen

Answer 14

2Al_(s) + 3/2O_2(g) –> Al₂O_3(s)

Question 15

Give the equation for:

Silicon and Oxygen

Answer 15

Si_(s) + O_2(g) –> SiO_2(s)

Question 16

Give the equation for:

Phosphorous and Oxygen

Answer 16

P_4(s) +5O_2(g) –> P₄O_10(s)

Question 17

Give the equation for:

Sulfur and Oxygen

Answer 17

S_(s) + O_2(g) –> SO_2(g)

Question 18

How does Na react in air?

Answer 18

Vigorously

Question 19

How does Mg react in air?

Answer 19

Vigorously

Question 20

How does Al react in air?

Answer 20

Slow (faster if powdered)

Question 21

How does Si react with air?

Answer 21

Slowly

Question 22

How does P react in air?

Answer 22

Spontaneously combusts

Question 23

How does S react in air?

Answer 23

Burns steadily

Question 24

What does the graph of period 3 oxides mpts look like?

Answer 24

(ignore chlorine)

Question 25

Why do the metal oxides (sodium, magnesium and aluminium) have high mpts?

Answer 25

They form giant ionic lattices

Strong forces of attraction between each ion

A lot of energy required to break the bonds

Question 26

Why does MgO have a higher mpt than Na₂O?

Answer 26

Mg forms 2+ ions so it bonds more strongly than the 1+ Na ions.

Question 27

Why does Al₂O₃ have a lower mpt?

Answer 27

The highly charged Al³⁺ ions distort the oxygen’s electron cloud making the bonds partially covalent.

Question 28

Why does SiO₂ have the highest non-metal oxide mpt?

Answer 28

It has a giant macromolecular structure

The strong covalent bonds must be broken

This requires a lot of energy

Question 29

Why do the phosphorous and sulfur oxides have relatively low mpts?

Answer 29

They form simple molecular structures

Weak intermolecular forces (dipole-dipole and VdWs) are easy to break

Question 30

How do you determine if an oxide is acidic or alkaline?

Answer 30

Ionic oxides are alkaline, covalent oxides are acidic.

Question 31

Why do ionic oxides form alkaline solutions when dissolved in water?

Answer 31

The oxide ions (O^2-) accept protons from the water molecules to form hydroxide ions.

Question 32

Give the equation for the reaction of:

sodium oxide with water

Answer 32

Na₂O_(s) + H₂O –> 2NaOH_(aq)

Question 33

Give the equation for the reaction of:

magnesium oxide and water

Answer 33

MgO_(s) + H₂O_(l) –> Mg(OH)_2(aq)

Question 34

What type of solutions do the simple covalent oxides of phosphorus and sulfur form?

Answer 34

Strong acidic

Question 35

Give the equation for the reaction of:

phosphorus (V) oxide and water

Answer 35

P₄O_10(s) + 6H₂O_(l) –> 4H₃PO_4(aq)

Question 36

Give the equation for the reaction of:

sulfur dioxide and water

Answer 36

SO_2(g) + H₂O_(l) –> H₂SO_3(aq)

Question 37

Give the equation for the reaction of:

sulfur trioxide and water

Answer 37

SO_3(l) + H₂O_(l) –> H₂SO_4(aq)

Question 38

Give the equation for the disassociation of phosphoric (V) acid:

Answer 38

H₃PO_4(aq) –> 3H⁺_(aq) + PO₄^3-_(aq)

Question 39

Give the equation for the disassociation of sulfurous acid:

Answer 39

H₂SO_3(aq) –> 2H⁺_(aq) + SO₃^2-_(aq)

Question 40

Give the equation for the disassociation of sulfuric acid:

Answer 40

H₂SO_4(aq) –> 2H+_(aq) + SO₄^2-_(aq)

Question 41

What happens when you react silicon dioxide with water?

Answer 41

Nothing - it is insoluble in water

Question 42

Is silicon dioxide classed as acidic or basic?

Answer 42

acidic - it reacts with bases.

Question 43

What happens when you react aluminium oxide with water?

Answer 43

Nothing - it is insoluble

Question 44

Is aluminium oxide classed as acidic or basic?

Answer 44

Both - it is amphoteric

Due to its partially ionic and partially covalent bonding

Question 45

Give the equation of the neutralisation reaction between sodium oxide and hydrochloric acid:

Answer 45

Na₂O_(s) + 2HCl_(aq) –> 2NaCl_(aq) + H₂O_(l)

Question 46

Give the equation of the neutralisation reaction between magnesium oxide and sulfuric acid:

Answer 46

MgO_(s) + H₂SO_4(aq) –> MgSO_4(aq) + H₂O_(l)

Question 47

Give the equation of the neutralisation reaction between silicon dioxide and sodium hydroxide:

Answer 47

SiO_2(s) + 2NaOH_(aq) –> Na₂SiO_3(aq) + H₂O_(l)

Question 48

Give the equation of the neutralisation reaction between phosphorous oxide and sodium hydroxide:

Answer 48

P₄O_10(s) + 12NaOH_(aq) –> 4Na₃PO_4(aq) + 6H₂O_(l)

Question 49

Give the equation of the neutralisation reaction between sulfur dioxide and sodium hydroxide:

Answer 49

SO_2(g) + 2NaOH_(aq) –> Na₂SO_3(aq) + H₂O_(l)

Question 50

Give the equation of the neutralisation reaction between sulfur trioxide and sodium hydroxide:

Answer 50

SO_3(g) +2NaOH_(aq) –> Na₂SO_4(aq) + H₂O_(l)

Question 51

Give the equation of the neutralisation reaction between aluminium oxide and sulfuric acid:

(aluminium oxide as a base)

Answer 51

Al₂O_3(s) + 3H₂SO_4(aq) –> Al₂(SO₄)_3(aq) + 3H₂O_(l)

Question 52

Give the equation of the neutralisation reaction between aluminium oxide and sodium hydroxide:

(aluminium oxide as an acid)

Answer 52

Al₂O_3(s) + 2NaOH_(aq) + 3H₂O_(l) –> 2NaAl(OH)_4(aq)