Halogens - 4th

Question 1

what are halogens?

Answer 1

• group 7 elements
• covalently bonded
• simple, molecular structures
• all are diatomic
• colours get darker down the group
• MP/BP increases down the group

Question 2

state the formula, colour, state and extra points for the halogen fluorine.

Answer 2

• F2
• very pale yellow
• (g)
• none

Question 3

state the formula, colour, state and extra points for the halogen chlorine.

Answer 3

• Cl2
• pale green
• (g)
• none

Question 4

state the formula, colour, state and extra points for the halogen bromine.

Answer 4

• Br2
• brown
• (l)
• volatile, releases brown fumes

Question 5

state the formula, colour, state and extra points for the halogen iodine.

Answer 5

• I2
• dark grey
• (s)
• sublimes, releases purple fumes

Question 6

what happens when halogens react with metals?

Answer 6

• form ionic compounds
• e.g. sodium and chlorine
• outer shell electrons from metal are transferred to the halogen
• redox reaction - Na oxidised, Cl reduced
• Chlorine atom -> chloride ion
• Halogen -> halide

Question 7

why do halogens get less reactive down the group?

Answer 7

• all halogen atoms need to gain an electron to fill their outer shell
• this happens less easily as you move down the group as atoms have more electron shells, the extra electron is further from the nucleus so its attraction to the nucleus is weaker

Question 8

what is the chemical test for chlorine?

Answer 8

• damp blue litmus paper -> turns white
• chlorine acts as a bleaching agent, so it removes the colour from the paper.

Question 9

what are displacement reactions with halogens?

Answer 9

• more reactive halogens can displace less reactive halogens from their compounds
• e.g. chlorine replacing bromine from potassium bromide
• in this reaction, chlorine replaces bromine as chlorine is more reactive than bromine

Question 10

state the colour of the halogen Cl2(aq).

Answer 10

colourless

Question 11

state the colour of the halogen Br2(aq).

Answer 11

yellow

Question 12

state the colour of the halogen I2(aq).

Answer 12

brown

Question 13

state the colour of the salt KCl (aq).

Answer 13

colourless

Question 14

state the colour of the salt KBr (aq).

Answer 14

colourless

Question 15

state the colour of the salt KI(aq).

Answer 15

colourless

Question 16

what are the observations when halogen Br2 reacts with the salt KCl?

Answer 16

• no change
• stays yellow

Question 17

what are the observations when halogen I2 reacts with the salt KCl?

Answer 17

• no change
• stays brown

Question 18

what are the observations when halogen Cl2 reacts with the salt KBr?

Answer 18

• Cl2 + 2KBr -> Br2 + 2KCl
• chlorine displaces bromine
• colourless -> yellow

Question 19

what are the observations when halogen I2 reacts with the salt KBr?

Answer 19

• no change
• stays brown

Question 20

what are the observations when halogen Cl2 reacts with the salt KI?

Answer 20

• Cl2 + 2KI -> I2 + 2KCl
• chlorine displaces iodine
• colourless -> brown

Question 21

what are the observations when halogen Br2 reacts with the salt KI?

Answer 21

• Br2+ 2Kl -> I2 + 2KBr
• Bromine displaces iodine
• yellow -> brown

Question 22

why does displacement occur in three cells?

Answer 22

• because the halogen added is more reactive than the halogen present in the salt
• confirms the reactivity trend as:
  chlorine > bromine > iodine
• colour change is due to the halogens present, as salts are all colourless
• where no change occurred, the colour of the halogen initially present remains

Question 23

what type of reactions are all halogen displacement reactions?

Answer 23

• redox reactions
• the more reactive halogen atom steals an electron from the halide ion in the salt
• e.g. in the reaction between chlorine and potassium bromide:
• chlorine + potassium bromine -> bromine + potassium chloride
• the Cl atoms in Cl2 each take an electron from a Br- ion
• it is a redox reaction because Cl2 gains an electron = reduced
• Br- loses an electron = oxidised