Halogens

Question 1

Explain the trend in boiling points of the halogens

Answer 1

1. more electrons down group so stronger van der waals forces between molecules. 2. also size of atom gets larger so molecule size increases so stronger van der waals forces between molecules

Question 2

What is the physical state of At₂ at room temperature and explain why

Answer 2

solid; At₂ is the larges group 7 molecule so has the strongest vdw forces between molecules

Question 3

Which halogen is the best at accepting electrons/best oxidising agent? and explain

Answer 3

F. Atoms are the smallest in group 7 with the least shielding so most able to capture external electrons

Question 4

What is he general rule for a halogen displacement?

Answer 4

A more reactive halogen can displace a less reactive halogen from a solution

Question 5

What is the colour change when KBr reacts with Cl₂? explain your answer

Answer 5

from colourless to orange. chorine displaces bromide ions because it is more reactive. Bromine solution is orange

Question 6

What you would observe when KI reacts with Cl₂? explain your answer

Answer 6

black ppt formed. chlorine displaces iodide ions because it is more reactive. Iodine ppt is black

Question 7

What you would observe when KI reacts with Br₂? explain your answer

Answer 7

black ppt formed. Bromine displaces iodide ions because Br₂ more reactive. I₂ is a black ppt

Question 8

Explain why would you add nitric acid (HNO₃) to a solution before testing for halides

Answer 8

HNO₃ gets rid of CO₃^2- which would form the same colour ppt as some halides

Question 9

What is the colour change when you add silver nitrate (AgNO₃) to a solution containing Cl^- ions?

Answer 9

colourless to white

Question 10

What is the colour change when you add silver nitrate (AgNO3) to a solution containing Br- ions?

Answer 10

colourless to cream

Question 11

What is the colour change when you add silver nitrate (AgNO3) to a solution containing I- ions?

Answer 11

colourless to yellow

Question 12

What is the ionic equation for silver nitrate with chloride ions?

Answer 12

Ag+ + Cl^- ———> AgCl

Question 13

Explain the trend in oxidising power of the halogens

Answer 13

1. decreases down the group.
2. atoms get larger so more electrons so more shielding
3. so ability to attract external electrons decreases

Question 14

Which reactioin with the halides is not a redox equation? hence deduce the type of reaction it is. and what the observation is

Answer 14

NaX with H₂SO₄ forming HX

e.g.

NaCl + H₂SO₄ ——> NaHSO₄ + HCl

therefore neutralisation (acid-base)

in all cases you would see steamy white fumes

Question 15

For the reduction of H2SO4 reacting with HI what are all the main product we are looking for and write the half equations

Answer 15

SO₂ & S & H₂S

2H+ + 2e- + H2SO4 —–> SO2 + 2H2O

6H⁺ + 6e^- + H₂SO_{4 <span>—–</span><span>> <span>S + 4H</span></span>2O}

8H+ + 8e- + H2SO4 —–> H2S + 4H2O

Question 16

For the reduction of H₂SO₄ reacting with HBr (that HI can also do) what is the main product we are looking for and write the half equation

Answer 16

SO₂

2H⁺ + 2e^- + H₂SO₄ —–> SO₂ + 2H₂O

Question 17

What happens when universal indicator paper is added to a solution of chlorine?

Answer 17

1. UI turns red because both HCl and HClO are acids
2. UI bleeches because the ClO- ion is a bleach

Question 18

What is chlorine used for?

Answer 18

1. water treament
2. used to make bleach