Chapter 8 - Reactivity Trends

Question 1

Describe the trends in group 2 down the group

Answer 1

• increase in atomic radii
• decrease in first ionisation energies
• Be has the highest melting/boiling point. Then generally increases down the group

Question 2

What are the group 2?

Answer 2

• alkaline earth metals
• metals/react with water to make alkaline solution/ reactive so not found in native form
• REDUCING AGENT - reduces another species

Question 3

Complete the sentence:
Reactivity…………… Down the group as the ionisation energy… …………. down the group. As well the solubility…………… down the group.

Answer 3

• increase
• decrease
• increase

Question 4

Describe the trends in boiling point of the halogens down the group

Answer 4

• more electrons
• stronger London forces
• more energy required to break intermolecular force
• boiling point increases

Question 5

What happens during the halogen-halide Displacement reaction?

Answer 5

• shows that reaction decreases down the group
• chlorine has clearly reacted with Br^- and I^-
• bromide has reacted with only I^-
• iodine has not reacted at all

Question 6

Describe fluorine

Answer 6

pale, yellow gas reacting with any substance

Question 7

Describe astatine

Answer 7

Extremely rare as radioactive, decays rapidly, never been seen

Question 8

Describe the trends in reactivity of the halogens

Answer 8

• atomic radius increase
• more inner shells so shielding increase
• less nuclear attraction to catch an election from another species
• reactivity decrease

Question 9

Describe the reaction of water and chlorine

Answer 9

•Used in water purification •chlorine is added to water where a disproportional reaction takes place

Question 10

What are the benefits of Chlorine use?

Answer 10

• Water purification- kills bacteria

* if not used water would be compromised and disease breakout causing mass illness

Question 11

What are the risks of chlorine use?

Answer 11

• Toxic gas - respirational irritated can be fatal

* Chlorinated hydrocarbon suspected to cause cancer

Question 12

What does disproportionation mean?

Answer 12

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

Question 13

What is the sequence of tests to find an organic compound?

Answer 13

• carbonate
• sulfate
• halides

Question 14

What do you do there is a mixture of ions?

Answer 14

You carry out the same tests but with the same solution. What this does it removes step-by-step the different organic compounds

Question 15

Define what reducing agent means

Answer 15

A reagent that reduces ( adds electron to) another species

Question 16

Define oxidising agent

Answer 16

A reagent the oxidise (takes electrons from) another species

Question 17

Halogen-halide displacement reaction:
•Cl2(aq)+ Cl^-(aq) ->
•Cl2 (aq) + 2Br^-(aq) -> 
•Cl2 (aq) + 2I^-(aq) ->
 •Br2 (aq) + 2Cl^-(aq) ->
•Br2 (aq) + 2Br^- (aq) ->
•Br2 (aq) + 2I^-(aq) ->
•iodine ......... react with any of these ions

Answer 17

• no reaction
• 2Cl^- (aq) + Br2(aq) turns orange
• 2Cl^- (aq) + I2 (aq) turns violet
• no reaction
• no reaction
• 2Br^- + I2 (aq) turn violet
• doesn’t

Question 18

The three reaction in the displacement reaction:
Solution in water (colour):
•Cl2 = 
•Br2 =
•I2 =
solution in cyclohexane (colour):
•Cl2 =
•Br2 =
•I2 =

Answer 18

• pale green
• orange
• brown
• pale green
• orange
• violet

Question 19

What are the three tests for anions?

Answer 19

• Carbonate test (gases)
• Sulfate test (precipitates)
• Halide test (precipitates)

Question 20

Describe the carbonate test

Answer 20

Carbonates react with acid to form carbon dioxide gas

1) add dilute nitric acid to solid or solution
2) if you see bubbles, the compound could be a carbonate
3) to prove that gas is carbon dioxide get the bubbles to go through limewater. A white precipitative of calcium carbonate should form if carbon dioxide is present

Question 21

Describe the sulfate test

Answer 21

You use barium as if a sulfate is present a barium sulfate should form as it is very insoluble in water. A white precipitate should form.

Question 22

Describe the halide test

Answer 22

They are very soluble in water but silver halides are insoluble. Aqueous silver ions react with aqueous halide ions to form precipitates of silver halides
1) add an silver nitrate to an aqueous solution of a halide
2)silver halide precipitates are different colours • Silver chloride is white • Silver bromide is cream-coloured • Silver iodide is yellow
3) add aqueous ammonia to test solubility
•Chloride is soluble in dilute ammonia • bromide is soluble in concentrated ammonia • iodide is insoluble in concentrated ammonia

Question 23

What is the test used for cations?

Answer 23

•test for ammonium ions

Question 24

Describe the test for ammonium ions

Answer 24

When heated together, aqueous ammonium ions and aqueous hydroxide ions react from ammonia gas.

1) Aqueous sodium hydroxide is added to a solution of ammonia ions. Gently warm.
2) ammonia gas is produced. You may be able to smell it. Test with pH indicator paper, it should turn blue

Question 25

Why are group 2 elements called reducing agents?

Answer 25

In a redox reaction, they lose electrons (oxidation) which is donated to the other reactant, reducing it

Question 26

What chemical is added to the solution during a displacement reaction and why?

Answer 26

Cyclohexane - the non-polar halogens dissolve more readily with this than water and so the colour change is clearer to see

Question 27

What colour can be observed when bromide ions are added to chlorine?

Answer 27

Orange - Br2 is formed

Question 28

What colour can be observed when iodide ions are added to chlorine?

Answer 28

Violet - I2 is formed

Question 29

What colour can be observed when chloride ions are added to bromine?

Answer 29

No reaction

Question 30

What is a disproportionation reaction?

Answer 30

A chemical reaction in which an element is both oxidised and reduced