3.3 - Group 7

Question 1

Boiling point down group 7

Answer 1

increases because:
- more electrons
- stronger London forces
- intermolecular forces require more energy to overcome

Question 1

Appearance of group 7 elements at RTP

Answer 1

• F2: pale yellow gas
• Cl2: pale green gas
• Br2: red-brown liquid
• I2: shiny grey-black solid

Question 2

How do group 7 elements act in redox reactions?

Answer 2

oxidising agents
(become weaker ones down group)

Question 3

Colours of solutions of chlorine, bromine and iodine in water

Answer 3

chlorine: pale green
bromine: orange
iodine: brown

Question 4

Colours of solutions of chlorine, bromine and iodine in cyclohexane (top layer)

Answer 4

chlorine: pale green
bromine: orange
iodine: violet

Question 5

Trend in reactivity down group 7

Answer 5

decreases AND oxidising power decreases because:
- atomic radius increases
- shielding increases
- nuclear attraction decreases
- IE increases

Question 6

Products of chlorine and water (water treatment reaction)

Answer 6

HClO + HCl

Question 7

Equation for bleach formation and conditions

Answer 7

Cl2+ 2NaOH→ NaCl+ H2O + NaClO (bleach)
conditions: NaOH must be cold and dilute

Question 8

Benefits and drawbacks of using chlorine for water treatment

Answer 8

benefits:
- kills bacteria preventing disease e.g.cholera

drawbacks:
- can react with organic hydrocarbons to form chlorinated hydrocarbons which are carcinogens
- chlorine gas is toxic

Question 9

Apparatus to separate two liquid layers present at end of experiment

Answer 9

separating funnel

Question 10

Systematic name for e.g KClO4

Answer 10

use oxidation numbers
name: metal ____-ate (oxidation number of middle)
e.g potassium chlorate (VII)