3.1.3 & 3.1.4- The halogens & Qualitative analysis

Question 1

How do the halogens look like and what is their electronic configuration

Answer 1

all have s2 p5

Question 2

What happens to the boiling point as you go down group 7.

Answer 2

Increase, as the London forces increase due to the size of the atom.

Question 3

what type of molecules do the halogen exits as ?

Answer 3

Diatomic (br2, cl2 etc)

Question 4

Explain the term electronegativity and explain what happens to electronegativity as we go down the group.

Answer 4

Question 5

What do you think will happen between chlorine, bromine and iodine ?

Answer 5

Chlorine displaces them all since its the most reactive.
Bromine displaces only iodine and Iodine displaces none.

• Remember this is because reactivity decreases as we go down group 7.

Question 6

Fill this table out with the equations and the colours
This is the aq and organic layer

Answer 6

Aq layer - colour of the least reactive solution
Organic layer - colour of the least reactive solution

Question 7

KCL, KBR and KI in a column(group) and do their waters in a period and fill out the table.

Answer 7

aq is always the colour of the least reactive solution

Question 8

Why do we use nitric acids and then silver nitrate ?

Answer 8

To remove any interfering ions e.g carbonates which give a white ppt

Question 9

How do we test for halide ions ?

Answer 9

Add dilute nitric acid (HNO₃) and silver nitrate (AgNO₃)

Question 10

Write out the reaction of silver nitrate and the halide ion and their reuslts.

Answer 10

Question 11

What test do we do after if the colours look to similar ?

Answer 11

The ammonia test.

Question 12

How do we create bleach ? - what is the equation for this ?
- what type of reaction is this ?
- Uses of one of the products of this reaction

Answer 12

By mixing chlorine and cold sodium hydroxide which forms sodium chlorate(I) + sodium chloride + water
- Used as bleach to disinfect or kill bacteria.

Question 13

What happens if hot sodium hydroxide is used ?

Answer 13

Sodium chlorate (V) is produced

Question 14

Uses of chlorine

Answer 14

• Kill bacteria
• Treat drinking water

Question 15

The reaction of chlorine and water.
- One of its reactants with water.

Answer 15

Rember when you clean the bath and it starts to bur your eye’s its because H3O+ is produced

Question 16

Risk of using chlorine

Answer 16

• Its toxic

Question 17

How do we test for CO₃2- ?

Answer 17

Add a few drops of dilute hydrochloric aciid.
- If carbonate ions are present, the acid will react with them to produce carbon dioxide gas. This reaction will be seen as effervescence (bubbling).
- Then to test for CO₂ we do the limewater test.

Or
CO₃ 2- + 2H⁺ -> CO₂ + H²O (then test for CO₂ )

Question 18

How do we test for Carbon dioxide ?

Answer 18

We do the lime water test.
- We buble gas through lime water.
- Lime water turns milky.

• If carbon dioxide is present, the limewater will turn milky or cloudy as it reacts with the gas to form calcium carbonate (CaCO₃), a white precipitate which makes the limewater milky.

Question 19

How do we test for sulfate ions ?

Answer 19

Question 20

Which order are anions tested in and why are they tested in this order.

Answer 20

• To prevent any false positives
• We do carbonate ions first as they produce a white ppt with barium chloride which is obviously the same colour ppt that sulfate ions produce in barium chloride.
• We do sulfate before halides because sliver ions can form a ppt (Ag₂SO₄) with sulfate ions also which gives a false positive.
• By adding barium chloride (BaCl₂) in the presence of dilute nitric acid, you precipitate out barium sulfate (BaSO₄) if sulfate ions are present.
  This ensures that sulfate ions are removed before you proceed to the halide test.
• And then we do carbonate test before halide test as carbonates form a white ppt with sliver ions (the whole reason why we use nitric acid)

Question 21

Why do we use dilute nitric acid instead of dilute HCL

Answer 21

HCl introduces chloride ions (Cl⁻) into the solution, which could interfere in the halide test if you’re testing for chlorides (Cl⁻) in the next step.

Question 22

How do we test for ammonium ions NH4+

Answer 22

Test for ammonium ion NH4+ by the reaction with warm NaOH(aq), forming NH3 gas.
- Red litmus paper turns blue

Question 23

How do we test for hydroxide ions ?

Answer 23

Hydroxides are alkaline so red litmus paper will turn blue,

Question 24

Type of forces in halogens

Answer 24

London forces or for ms sake say van der wals forces

Question 25

Type of bonding in halogens

Answer 25

Covalent don’t get bonding and forces mixed up.

Question 26

Remember that fluorine is colourless in them reaction deyaa