Group 7 Halogen T Halide

Question 1

Describe and explain the trends in oxidising ability of the halogens

Answer 1

Decreases as you go down the group because:
-the size of the atom increases as you go down
-increase In shielding
-halogen gains electrons less easily as you go down

Question 2

Write equations and observations for the following reactions
NaCl,NaBr,NaI with halogens

Answer 2

NaCl: NVC with all (Cl2, Br2, I2)

NaBr:
-2Br- + Cl2 —> 2Cl- + Br2. = yellow/orange/brown solution
-NVC with Br2
- NVC with I2

NaI:
-2I- + Cl2 —> 2Cl- + I2. = brown solution and black ppt
-2I- + Br2 - > 2Br- + I2. = brown solution and black ppt

Question 3

Describe and explain the reducing ability of the halide ions

Answer 3

Increases as you go down the group
-increase in ionic radius /size
-more shielding
-ability to lose electrons is easier as u go down (weaker attraction net outer e- and nucleus)

Question 4

Write the acid base reactions for halide ions and what they produce

Answer 4

F- : 2NaF + H2SO4 —> Na2SO4 + 2HF.
Cl- : 2NaCl + H2SO4 —> NaSO4 + 2HCl.
Br- : 2NaBr + H2SO4 —> NaSO4 + 2HBr.
I-: 2NaI + H2SO4 –> Na2SO4 + 2HI.
^all these reactions produce misty fumes

Question 5

write the redox reaction for the reaction for Br⁻ with H₂SO₄ and what it produces

Answer 5

2e- + 2H+ + H₂SO₄ —> SO₂ + 2H₂O
2Br- —> Br2 + 2e-
2H+ + H2SO4 + 2Br —> Br2 + SO2 + H2O
SO2: produces choking gas
Br2: brown gas

Question 6

write the redox reactions for the reaction for I⁻ with H₂SO₄ and what it produces

Answer 6

2I- —>I2 + 2e-
I2: produces black solid and purple gas

8e- + 8H+ + H2SO4 —> H2S + 4H2O
8H⁺ + H₂SO₄ + 8I⁻ –> 4I₂ + H₂S + 4H₂O
H₂S: produces rotten egg smell

2e- + 2H+ + H2SO4 —> SO2 + 2H2O
2H+ + H2SO4 + 2I- –> 12 + SO2 + 2H2O
SO₂: produces choking gas

6e-+ 6H+ + H₂SO₄ —> S + 4H₂O
6H⁺ + H₂SO₄ + 6I⁻ –> 3I₂ + S + 4H₂O
S: produces a yellow solid

Question 7

describe the test for halide ions include observations

Answer 7

first react each halide with acidified silver nitrate.
Cl- + Ag+ –> AgCl = a white ppt
Br- + Ag+ –> AgBr = cream ppt
I- + Ag+ —> AgI = yellow ppt
then add ammonia
AgCl with dilute/ conc NH3 = dissolves
AgBr with dilute NH3 = slightly dissolves
with conc NH3 = fully dissolves
AgI with dilute /conc NH3 = NVC

Question 8

why must the sliver nitrate must be acidified

Answer 8

to remove any carbonates that would form ppt.

Question 9

why cant HCl be used to acidify silver nitrate

Answer 9

HCl cant be used as it contains Cl- ions and it would form a white ppt.

Question 10

write the equation for chlorine water

Answer 10

Cl2(g) + H2O(l) –> HCl(aq) + HClO(aq)

Question 11

write the equation for chlorine and water in bright sunlight

Answer 11

2Cl2 + 2H2O –>4HCl + O2
pale green —> colourless

Question 12

write the equation for chlorine with sodium hydroxide

Answer 12

Cl2 + 2NaOH –>H2O + NaCl + NaClO

Question 13

describe the boiling point in the halogen down the group

Answer 13

increases
-size of atom increases
-there are more van der waals forces between the molecules that need breaking

Question 14

what does each halogen colour appear at room temp

Answer 14

F2: pale yellow gas
Cl2: pale green gas
Br2: dark red/orange liquid
I2: dark purple/black solid

Question 15

what is an oxidising agent

Answer 15

electron acceptor

Question 16

what can halogen act as

Answer 16

oxidising agents

Question 17

what observation is made when iodine reacts with bromine ions and why

Answer 17

NVC
iodine isnt a strong enough oxidising agent to oxidise bromine

Question 18

what are the two methods of separating a ppt from a mixture and explain the filteration and drying process

Answer 18

-gravity filteration (with filter paper and funnel)
-reduced pressure filteration (with buchner funnel and water pump)
1.filter the precipitate from the solution using gravity or vacuum filteration
2.wash the residue with water to remove soluble impurities
3.dry to remove the water, either by pressing between two sheets of filter paper or in air.