CHAPTER 8: Reactivity Trends

Question 1

What type of reaction is most common for Group 2 and Group 7 elements?

Answer 1

REDOX reactions

Question 2

What name is given to GROUP 2 elements?

Answer 2

Alkaline metals

Question 3

Group 2 elements are “reducing agents’ WHY?

Answer 3

They become OXIDISED and lose 2 electrons, meaning another element receives these electrons and becomes reduced.

Question 4

When group 2 elements react with OXYGEN what is formed?

give general formula product

Answer 4

a METAL OXID

general formula = _O

Question 5

When group 2 elements react with water what is formed? (give general formula of product)

Answer 5

an ALKALINE HYDROXIDE and hydrogen gas

general formula = _(OH)2

Question 6

What is the reactivity trend of Group 2?

why?

Answer 6

Increases down the group.
Because the ionisation energies decrease down the group as the atomic radius increases and shielding increases so nuclear attraction for outer electron decreases.

Question 7

What happens when OXIDES of group 2 elements react with water?

Answer 7

Hydroxide ions are released forming alkaline solutions.

Question 8

What is the SOLUBILITY of HYDROXIDES trend of Group 2?

Answer 8

Solubility of group 2 hydroxides INCREASES down the group.

Question 9

How can you measure solubility of hydroxides?

Answer 9

measure the PH.

More soluble = more hydroxide ions released so more alkaline.

Question 10

How are group 2 compounds used in daily life?

Answer 10

AGRICULTURE = uses calcium hydroxide to increase the pH of acidic soils to form neutral water.

MEDICINE = used to neutralise acid indigestion.

Question 11

What is the name given to group 7 elements?

Answer 11

Halogens

Question 12

At room temperature in form do all halogens exist as?

Answer 12

DIATOMIC molecules

Question 13

What is the boiling point trend of halogens? WHY?

Answer 13

Increases down the group.

More electrons so therefore stronger London Forces so more energy required to overcome the intermolecular forces.

Question 14

What agent are halogens in a redox reaction?

Answer 14

OXIDISING agent

Question 15

What reaction shows the reactivity of halogens?

Answer 15

displacement reaction

Question 16

What happens during a halide displacement reaction?

Answer 16

You add a halogen solution to aqueous solutions of the other halides.
Whichever halogen is the more reactive will displace the halide from the solution and result in a colour change.

Question 17

What is used to help distinguish the colours better during a displacement reaction? identify the colours.

Answer 17

CYCLOHEXANE
pale green = chlorine
orange = bromine
violet = iodine

Question 18

What is the trend of reactivity of halogens? Why?

Answer 18

Decreases down the group because the atomic radius increases so more shielding therefore the nuclear attraction for an electron from another species is weaker

Question 19

What is a DISPROPORTIONATION reaction?

Answer 19

a redox reaction where the same element is BOTH oxidised and reduced.

Question 20

How are halogens used in daily life?

Answer 20

Chlorine is added to purify water.

It undergoes a disproportionation reaction and forms 2 acid products which kill the bacteria.

Question 21

What is the disadvantage and advantage of using chlorine to purify water?

Answer 21

Chlorine is very toxic and can cause respiratory irritant however the advantage of clean water and preventing waterborne diseases outweighs this.

Question 22

How can you test for carbonates?

Answer 22

React with acids and carbon dioxide gas should form.
-add dilute nitric acid and if u see bubbles, bubble the gas through lime water to see if it turns cloudy for the presence of CO2.

Question 23

Why does lime water turn cloudy with carbon dioxide?

Answer 23

Carbon dioxide reacts to forms a fine white precipitate of calcium carbonate

Question 24

How do you test for sulfates?

Answer 24

Most sulfates are soluble in water except BARIUM sulfate which is insoluble.

Add barium chloride/nitrate and a WHITE precipitate should form.

Question 25

Why shouldn’t you use barium CHLORIDE for the sulfate test if you’re going to carry out a halide test afterwards?

Answer 25

Because the chloride ions would be detected.

Question 26

How do you test for halide ions?

Answer 26

Halides are soluble in water except silver halides.

So aqueous silver nitrate is added and the solution should change colour.

Question 27

Identify the colours for chloride, bromide and iodide when reacted with aqueous silver nitrate.

Answer 27

Chloride = White
Bromide = Cream
Iodide = Yellow

Question 28

How else can you identify the halides if the colours aren’t very clear?

Answer 28

Add aqueous ammonia and test the solubility.

• Chlorine is soluble in DILUTE ammonia
• Bromide is soluble in CONC ammonia
• Iodide is insoluble in CONC ammonia

Question 29

What is the sequence order of the qualitative test to identify a compound?

Answer 29

1. Carbonate test - neither sulfate or halides produce gas with dilute acid.
   (If you do see bubbles continue adding dilute nitric acid so all carbonate ions are removed)
2. Sulfate test - barium carbonate can form a white precipitate so if u carry it out after carbonate test, you can be sure that the precipitate is not because of carbonate.
   (add EXCESS barium nitrate and filter out barium sulfate )
3. Halide test - silver carbonate and silver sulfate form white precipitates so it is important halide test is last.

Question 30

How can you test for ammonium ions?

Answer 30

Aqueous sodium hydroxide is added and if ammonium ions present, ammonia gas will be produced.
As ammonia is alkaline, you can test with litmus paper.