Group 7

Question 1

What colour is chlorine at RTP?

Answer 1

Green

Question 2

What colour is bromine at RTP?

Answer 2

Brown

Question 3

What colour is iodine at RTP?

Answer 3

Grey

Question 4

What state is chlorine at RTP?

Answer 4

Gas

Question 5

What state is bromine at RTP?

Answer 5

Liquid

Question 6

What state is iodine at RTP?

Answer 6

Solid

Question 7

What is the trend in boiling points down the group?

Answer 7

Boiling points increase down the group

Question 8

Why do boiling points increase down the group? (extended answer)

Answer 8

• further down the group halogen MOLECULES contain more electrons
• the electron cloud can become more unevenly distributed
• larger dipoles can be induced in neighbouring molecules
• attraction between larger dipoles means stronger London forces
• stronger London forces require more energy to be overcome

Question 9

Why do boiling points increase down the group? (short answer)

Answer 9

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

Question 10

Why are Cl-Cl bonds the strongest?

Answer 10

• the covalent bonds are formed by a shared pair of electrons being attracted to the nuclei of the bonded atoms
• the closer electrons are to the nucleus the stronger the attraction
• chlorine is the smallest atom
• smaller atoms have a higher nuclear charge

Question 11

Why are halide ions larger than their atoms?

Answer 11

• an additional electron has been added
• this leads to greater repulsion between the electrons
• meaning ions are smaller

Question 12

What can be added to a halide solution to test for which halide ion is present?

Answer 12

An organic solvent, such as cyclohexane or hexane

Question 13

When cyclohexane is added to a solution containing chloride ions, what would be seen?

Answer 13

Two layers form, the top one pale green

Question 14

When cyclohexane is added to a solution containing bromide ions, what would be seen?

Answer 14

Two layers form, the top one orange

Question 15

When cyclohexane is added to a solution containing iodide ions, what would be seen?

Answer 15

Two layers form, the top one violet

Question 16

When the mixture of halide solution and hexane is shaken why does the colour of the top layer become more vivid?

Answer 16

• halogens are much more soluble in the organic layer
• shaking assists the movement of the halogens into the organic layer
• as their concentration increases, the colour becomes more vivid

Question 17

What is the colour of Cl2 in water?

Answer 17

Pale green

Question 18

What is the colour of l2 in water?

Answer 18

Brown

Question 19

What is the colour of Br2 in water?

Answer 19

Orange

Question 20

Which halogen is the most powerful oxidising agent?

Answer 20

Fluorine

Question 21

Which halogen is the least powerful oxidising agent?

Answer 21

Astatine

Question 22

What is the trend in reactivity down the group?

Answer 22

Reactivity decreases

Question 23

Why does reactivity decrease down the group?

Answer 23

• halogens react by gaining an electron
• no. shells increases down the group
• shielding increases
• atomic radius increases
• attraction of the nucleus to electrons decreases

Question 24

Does chlorine react with Br-, I-, or both?

Answer 24

Both

Question 25

Does bromine react with Cl-, I-, or both?

Answer 25

I-

Question 26

Does iodine react with Cl-, Br-, or both?

Answer 26

Neither

Question 27

Define disproportionation reaction

Answer 27

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

Question 28

Write the word equation for the reaction between water and chlorine

Answer 28

Chlorine + water ---> Chloric(I) acid + hydrochloric acid

Question 29

Write the symbol equation for the reaction between water and chlorine

Answer 29

Cl2 (g) + H2O (l) ---> HClO(aq) + HCl (aq)

Question 30

How is the reaction between chlorine and water used?

Answer 30

To purify water, the chloric (I) acid produced kills bacteria in drinking water

Question 31

When universal indicator is added to a solution of chlorine in water what colour does it first turn?

Answer 31

Red

Question 32

Why does universal indicator first turn red when added to a solution of chlorine in water?

Answer 32

The acids in the solution release H+ ions

Question 33

After a while what happens to colour of the indicator in a solution of chlorine in water?

Answer 33

Colourless

Question 34

Why does the universal indicator turn colourless after a while of being in a solution of chlorine in water?

Answer 34

The ClO- ions bleach the solution

Question 35

Give the word equation for the reaction of chlorine with COLD DILUTE sodium hydroxide

Answer 35

Chlorine + Sodium hydroxide ---> sodium chorate (I) + sodium chlorine + water

Question 36

Give the symbol equation for the reaction of chlorine with COLD DILUTE sodium hydroxide

Answer 36

Cl2(g) + NaOH (aq) ---> NaClO (aq) + NaCl + H2O

Question 37

What is sodium chlorate (I) used for?

Answer 37

A household bleach

Question 38

Why is sodium chlorate (I) a more effective bleach than chloric(I) acid?

Answer 38

It is more stable/decomposes less readily and so stays reactive for longer