inorganic chem; group 7

Question 1

Characteristics of group 7 elements

Answer 1

Fluorine — pale yellow gas
Chlorine — pale green gas
Bromine — brown/orange liquid
Iodine — grey solid

Question 2

What is the boiling point trend for Group 7?

Answer 2

Increases down the group

Question 3

Explain the boiling point trend in Group 7?

Answer 3

Increasing size & relative mass — VDWs also increase

Question 4

What is the physical state of Group 7?

Answer 4

Gas at the top to solid at the bottom

Question 5

Define electronegativity

Answer 5

It’s the ability for an atom to attract electrons towards itself in a covalent bond

Question 6

What is the electronegativity trend in Group 7?

Answer 6

Decreases down the group

Question 7

Explain the electronegativity trend in Group 7?

Answer 7

Atoms are larger
Distance between positive nucleus & e- increases
More shielding

Question 8

More reactive halogens will … less reactive halide ions

Answer 8

Displace

Question 9

Displacement reactions of halogens

Answer 9

Question 10

Oxidation trend in Group 7 & how is it shown?

Answer 10

Halogens are less oxidising as we go down the group — shown by reactions of halogens with halide ions

Question 11

In what condition would a halogen displace a halide in solution?

Answer 11

If the halide is lower in the periodic table

Question 12

How is bleach made?

Answer 12

By mixing chlorine & sodium hydroxide, forming a sodium chlorate (I) solution — disproportionation reaction

Question 13

Uses of sodium chlorate

Answer 13

• Treating water
• Bleaching paper & fabrics
• Cleaning agents (bleach)

Question 14

Define disproportionation reaction

Answer 14

A disproportionation reaction is one in which a single substance is both oxidised and reduced

Question 15

Examples of a disproportionation reaction & its equation

Answer 15

Making bleach:
2NaOH (aq) + Cl2 (g) → NaClO (aq) + NaCl (aq) + H2O (l)

Water sterilisation:
H2O (l) + Cl2 (g) → 2H⁺ (aq) + Cl⁻ (aq) + ClO⁻ (aq)

Question 16

How is water sterilised?

Answer 16

By adding chlorine — produces chlorate (I) ions (ClO-) which kills bacteria

Question 17

What decomposes chlorinated water & write its question

Answer 17

Sunlight
2H2O (l) + Cl2 (g) → 4H⁺ (aq) + 2Cl⁻ (aq) + O2 (g)

Question 18

Advantages of chlorinating drinking water

Answer 18

• Destroys microorganisms that cause disease
• Long lasting — reduces bacteria build up further down supply
• Reduces growth of algae

Question 19

Disadvantages of chlorinating drinking water

Answer 19

• Chlorine gas is toxic — irritates the respiratory system
• Liquid chlorine causes severe chemical burns to the skin
• Chlorine can react with organic compounds, forming chloroalkanes — linked with cancer

Question 20

What are halides in terms of oxidation & reduction?

Answer 20

Reducing agents — as halide ions lose e- in reactions

Question 21

Why is I⁻ a more powerful reducing agent than F⁻?

Answer 21

As its outer e- is lost more readily due to the ionic radius increase down the group

Question 22

What tests prove that halides are reducing agents?

Answer 22

• Reaction with sulfuric acid
• Reaction with silver nitrate solution

Question 23

Process of testing halide ions with silver nitrate solution

Answer 23

1. Add dilute nitric acid (HNO3) then silver nitrate solution (AgNO3)
2. Colour of precipitate tells you the halide ion

Question 24

What is the colour of the propitiates formed by halides reacting with silver nitrate solution?

Answer 24

Cl ions — white
I ions — yellow
Br ions — cream

Question 25

Why is nitric acid added when testing for halides using silver nitrate?

Answer 25

So it reacts with any anions other than halides (e.g. carbonates) — can give a false result

Question 26

What is the further test of halide ions with silver nitrate?

Answer 26

Add ammonia (NH3) solution to precipitates: - Cl — white ppt dissolves in dilute NH3 - Br — cream ppt dissolves in conc NH3 - I — yellow ppt insoluble in conc NH3

Question 27

Test for Group 2 ions (cations)

Answer 27

1. Dip the nichrome wire in conc hydrochloric acid 2. Dip into sample 3. Place the loop into the blue Bunsen flame & observe the colour

Question 28

What is the colour shown by Group 2 ions in the flame test?

Answer 28

Calcium (Ca2+) — dark red Strontium (Sr2+) — red Barium (Ba2+) — green

Question 29

Why are flame tests used & how?

Answer 29

Used to identify Group 2 ions in a solid sample Can be made into solutions & sprayed on the Bunsen too

Question 30

Disadvantage of using flame tests

Answer 30

Difficult to use if sample is insoluble

Question 31

What ions are tested with litmus paper?

Answer 31

Ammonium compounds & hydroxides

Question 32

How are ammonium compounds tested?

Answer 32

1. Add NaOH & gently heat 2. +ve result: ammonia gas produced OR 1. Use damp red litmus 2. Ammonia will dissolve in water & litmus turns blue

Question 33

How are hydroxides tested?

Answer 33

Are alkaline — so red litmus paper turns blue Further test needed — as red litmus turns blue for any alkali

Question 34

What is used to test carbonates & sulfates?

Answer 34

Hydrochloric acid & barium chloride

Question 35

Process of testing for carbonates

Answer 35

HCl reacts with carbonates to make CO2 gas When bubbled through limewater it turns cloudy

Question 36

Process of testing for sulfates

Answer 36

1. Add HCl to remove any carbonates — can precipitate out giving false result 2. Add barium chloride 3. +ve result: white ppt

Question 37

What is the specific order of tests to prevent false positives?

Answer 37

1. Test for carbonates 2. Test for sulfates 3. Test for halides