8 Reactivity Trends

Question 1

Are group 2 elements reducing agents or oxidising agents?

Answer 1

Reducing agents
In reactions a group 2 element is oxidised as it loses 2 electrons causing another species to gain these 2 electrons and be reduced

Question 2

How do group 2 elements react with oxygen?

Answer 2

React with oxygen to form a metal oxide
e.g. 2Mg (s) + O2 (g) –> 2MgO (s)
Redox reaction

Question 3

How do group 2 elements react with water?

Answer 3

Group 2 elements react with water to form an alkaline hydroxide and hydrogen gas
Reactions with water become more vigorous down the group
Redox reactions

Question 4

How do group 2 elements react with dilute acids?

Answer 4

Metal + acid –> salt + hydrogen
Ex: Mg (s) + 2HCl (aq) –> MgCl2 (aq) + H2 (g)
Redox reaction

Question 5

What is the trend in reactivity of the group 2 elements?Explain why

Answer 5

Reactivity increases down Group 2 and stronger reducing agents
Ionisation energies decrease down the group because the attraction between the nucleus and the outer electrons decreases as a result of increasing atomic radius and increasing shielding

Question 6

What are the reactions of group 2 oxides with water?

Answer 6

Oxides of Group 2 elements react with water, releasing hydroxide ions and forming alkaline solutions of the metal hydroxide
CaO (s) + H2O (l) –> Ca2+ (aq) + 2OH- (aq)

Question 7

Describe the solubility of the hydroxides in water

Answer 7

Group 2 hydroxides are only slightly soluble - once saturated metal and hydroxide ions form a solid precipitate
Ca2+ (aq) + 2OH- (aq) –> Ca (OH)2 (s)
Solubility increases down the group, so the resulting solutions contain more OH- (aq) ions and are more alkaline

Question 8

What is the experiment to show the trend of the solubility of the hydroxides in water?

Answer 8

• Add a spatula of each Group 2 oxide to water in a test tube
• Shake the mixture (saturated solution of metal hydroxide with some undissolved white solid at the bottom)
• Measure the pH of each solutions and the alkalinity will increase down the group

Question 9

How are group 2 compounds as bases used in agriculture?

Answer 9

Calcium hydroxide is added to fields to increase the pH of acidic soils which neutralises the acid
Ca(OH)2 (s) + 2H+ (aq) –> Ca2+ (aq) + 2H2O (l)

Question 10

How are group 2 compounds as bases used in medicine?

Answer 10

Group 2 bases used as antacids for treating acid indigestion
The magnesium hydroxide and calcium carbonate in the tablets neutralise the HCl in the stomach
Mg(OH)2 (s) + 2HCl (aq) –> MgCl2 (aq) + 2H2O (l)
CaCO3 (s) + 2HCl (aq) –> CaCL2 (aq) + H2O (l) + CO2 (g)

Question 11

How do halogens exist at room temperature and pressure?

Answer 11

Diatomic molecules, X2
Gas at top of the group and solid at the bottom
As a solid state the halogens form lattices with simple molecular structures

Question 12

Explain the trend in boiling points of the five halogens - fluorine to astatine

Answer 12

Down the group:
More electrons
Stronger London forces
More energy required to break the intermolecular forces
Boiling point increases

Question 13

State the appearance and state of the 5 halogens

Answer 13

Fluorine - pale yellow gas
Chlorine - pale green gas
Bromine - red-brown liquid
Iodine - shiny grey-black solid
Astatine - never been seen

Question 14

Are the halogens oxidising or reducing agents?

Answer 14

oxidising agent

Question 15

What experiment can you do to show the reactivity of the halogens down the group?

Answer 15

Halogen-halide displacement reactions
Reactivity of the halogens decreases down the group

Question 16

Why is cyclohexane added to the halogen-halide solution?

Answer 16

Non-polar halogens dissolve more readily in cyclohexane than in water as it is a non-polar solvent
In cyclohexane their colours are easier to tell apart

Question 17

What are the original colours of the halogens in water and in cyclohexane?

Answer 17

Chlorine: Both pale green
Bromine: Both orange
Iodine: Brown, violet

Question 18

What are the is the colour change and equation for Br- and Cl2?

Answer 18

Orange
Cl2 (aq) + 2Br- (aq) –> 2Cl- (aq) + Br2 (aq)

Question 19

What are the is the colour change and equation for I- and Cl2?

Answer 19

Violet
Cl2 (aq) + 2I- (aq) –> 2Cl- (aq) + I2 (aq)

Question 20

What are the is the colour change and equation for I- and Br2?

Answer 20

Violet
Br2 (aq) + 2I- (aq) –> 2Br- (aq) + I2 (aq)

Question 21

Describe the trend in reactivity for the halogens down the group

Answer 21

Atomic radius increases
More inner shells so shielding increases
Less nuclear attraction to capture an electron from another species
Reactivity decreases

Question 22

What is the stronger oxidising agent of the halogens?

Answer 22

Fluorine
Become weaker oxidising agents down the group

Question 23

Define a disproportionation reaction

Answer 23

A redox reactions in which the same element is both oxidised and reduced

Cl2(aq) + H2O (l) –> HClO(aq) + HCl (aq)

Question 24

What is the reaction of chlorine with cold dilute aqueous sodium hydroxide?

Answer 24

Cl2(aq) +2NaOH (aq) –> NaClO (aq) + NaCl (aq) + H2O (l)