Group VII, The Halogens

Question 1

As you go down group 7 what happens to the atomic radius?

Answer 1

Increases

Question 2

As you go down the group what happens to the electronegativity?

Answer 2

Decreases

Question 3

As you go down group 7 what happens to the melting and boiling points?

Answer 3

Increases
This is because the number of electrons increases and so the van der waals forces between atoms get stronger and so requires more energy to break the intermolecular forces between atoms.

Question 4

As you go down the group what happens to the 1st ionisation energy?

Answer 4

Decreases

Question 5

With dilute NH₃ is Cl⁻ soluble or insoluble?

Answer 5

soluble

Question 6

With dilute NH₃ is Br₂ soluble or insoluble?

Answer 6

Insoluble

Question 7

Does AgI react with NH₃ and if not, why not?

Answer 7

It is too insoluble

Question 8

With concentrated NH₃ is Cl⁻ soluble or insoluble?

Answer 8

Soluble

Question 9

With concentrated NH₃ is Br⁻ soluble or insoluble?

Answer 9

Soluble

Question 10

What is the first step before adding AgNO₃ for testing for halide ions and why?

Answer 10

Add nitric acid to remove carbonate ions

Question 11

What type of ion does Br⁻ ions form when reacted with concentrated ammonia?

Answer 11

complex ion

Question 12

What type of ion does Cl- ions turn in to when reacted with dilute NH₃?

Answer 12

complex ion

Question 13

What happens to the reducing power of halides as you move down the group?

Answer 13

They become stronger reducing agents as it is easier to lose electrons from an outer shell which is further away from the nucleus as the attraction is weaker.

Question 14

K₂SO₃

Answer 14

potassium sulphate(IV)

Question 15

K₂SO₄

Answer 15

potassium sulphate(VI)

Question 16

NaClO

Answer 16

Sodium chlorate(I)

Question 17

NaCLO₃

Answer 17

Sodium chlorate(V)

Question 18

Define disproportionation?

Answer 18

Disproportionation is the name for a reaction where an element simultaneously oxidises and reduces.
i.e CL₂ +H₂O = HClO + HCl

Question 19

What are uses for the Chlorate(I) ion?

Answer 19

Water disinfection and its uses as an antibacterial substance

Question 20

If universal indicator is added to the products of Cl₂ and H₂O what is the observation and why does it happen?

Answer 20

The solution will first turn red due the the acidity of the chloric(I) acid and the hydrochloric acid and then the chloric(I) acid bleaches it colourless.

Question 21

What are the products of Cl₂ and H₂O in bright sunlight?

Answer 21

HCl and O₂

Question 22

What happens to the reactivity as you move down the group 7?

Answer 22

The reactivity decreases as you move down the group

Question 23

What happens to the reactivity as you move down the group 7
?

Answer 23

The reactivity decreases as you move down the group

Question 24

When iodine has been displaced what colour does the solution turn?

Answer 24

Brown

Question 25

When Bromine has been displaced what colour does the solution turn?

Answer 25

Yellow

Question 26

What happens when F⁻ and Cl⁻ halide salts are reacted with sulphuric acid?

Answer 26

NaF + H₂SO₄ = NaHSO₄ + HF
NaCl + H₂SO₄ = NaHSO₄ + HCl

The observations for both of these reactions are white steamy fumes.
Redox reactions do not occur as the F⁻ and Cl⁻ are not strong enough to reduce the S

Question 27

What happens when Br- halide salts are reacted with sulphuric acid?

Answer 27

NaBr + H₂SO₄ = NaHSO₄ + HBr
2HBr + H₂SO₄ = Br₂ + SO₂ + 2H₂O

The observations for this reaction is the white steamy fumes of HBr and then the brown fumes of Br2 and there is a colourless SO2 gas formed.

Question 28

What is the trend in the number of products that form as you move down the group Ⅶ when reacting with H₂SO₄?

Answer 28

The number of products increases and progressively get more aggressive (smell and colour)

Question 29

What happens when I- halide salts are reacted with sulphuric acid?

Answer 29

NaI + H₂SO₄ = NaHSO₄ + HI
2HI + H₂SO₄ = I₂ + SO₂ + 2H₂O
6HI + H₂SO₄ = 3I₂ + S + 4H₂O
8HI + H₂SO₄ = 4I₂ + H₂S + 4H₂O

The observations for this reaction is that white steamy fumes of HI are formed and purple/black fumes of I₂ are formed, some yellow solid of S is formed and the colourless gas SO₂ is formed and some H₂S is formed which has a bad egg smell.