2.3 Group 7

Question 1

Describe Fluorine

Answer 1

very pale yellow gas. It is highly reactive

Question 2

Describe chlorine

Answer 2

greenish, reactive gas, poisonous in high concentrations

Question 3

Describe Bromine

Answer 3

red liquid, that gives off dense brown/orange poisonous fumes

Question 4

Describe Iodine

Answer 4

shiny grey solid sublimes to purple gas.

Question 5

What happens to melting and boiling points as you go down group 7?

Answer 5

Increases

Question 6

What is the trend of electronegativity as you go down group 7?

Answer 6

Decreases

Question 7

What happens to oxidising strength as you go down group 7?

Answer 7

Decreases

Question 8

What colour is chlorine in solution?

Answer 8

Very pale green (often colourless)

Question 9

What colour is bromine in solution ?

Answer 9

Yellow solution

Question 10

What colour is Iodine in solution?

Answer 10

Brown (something black solid present)

Question 11

How do you identify halide ions?

Answer 11

Solution made acidic with nitric acid and then silver nitrate solution is added dropwise

Question 12

Why is nitric acid added to the halide solution?

Answer 12

The role of nitric acid is to react with any carbonates present to prevent formation of the precipitate Ag2CO3. This would mask the desired observations

Question 13

Halide ion test for fluorine

Answer 13

No precipitate

Question 14

Halide ion test for chlorides

Answer 14

White precipitate

Question 15

Halide ion test for bromides

Answer 15

Cream precipitate

Question 16

This question is about elements in Group 7 of the Periodic Table and their compounds.

(a) Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values.

Suggest, with reasons, the order of melting points for these three substances.(6)

Answer 16

SrCl2> ICl > Br>
If wrong can award 1 for one in the correct ‘position’
2
SrCl2 strong ionic bonds / (strong electrostatic attraction between opposite ions)
1
Lattice so many strong bonds to overcome
1
ICl has dipole-dipole between molecules – weaker than ionic bonds
1
Br2 has van der Waals forces between molecules – much weaker
Accept London / dispersion / induced dipole forces

Question 17

Halide ion test for iodide

Answer 17

Pale yellow precipitate

Question 18

How can you help differentiate between silver chloride, silver bromide and silver iodide in the halide ion test?

Answer 18

The silver halide precipitates can be treated with ammonia solution.

Silver chloride ions dissolve in dilute ammonia to form a colourless solution.

Silver bromide ions dissolve in concentrated ammonia to form a colourless solution.

Silver iodide doesn’t react with ammonia, it is insoluble.

Question 19

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

Answer 19

The reducing power of the halides increases down group 7 They have a greater tendency to donate electrons.
This is because as the ions get bigger it is easier for the outer electrons to be given away as the pull from the nucleus on them becomes smaller.

Question 20

What happens when F- and Cl- react with H2SO4?

Answer 20

F- and Cl- ions are not strong enough reducing agents to reduce the S in H2SO4. No redox reactions occur. Only acid-base reactions occur.

Question 21

Write the equation for the reaction of NaF and H2SO4 and what are the observations?

Answer 21

NaF (s) + H2SO4(l)—>NaHSO4(s) + HF(g)

Observations: White steamy fumes of HF are evolved.

Question 22

Write the equation for the reaction of NaCl and H2SO4 and what are the observations?

Answer 22

NaCl(s) + H2SO4(l)—>NaHSO4(s) + HCl(g)

Observations: White steamy fumes of HCl are evolved

Question 23

Write the 2 steps and the observations of the reaction between NaBr and H2SO4 ?

Answer 23

Acids-base step:NaBr(s) + H2SO4(l) —> NaHSO4(s) + HBr(g) Redox step:2HBr+H2SO4 —> Br2(g) + SO2(g) + 2H2O(l)

Observations: White steamy fumes of HBr are evolved.
Red fumes of bromine are also evolved and a colourless, acidic gas SO2

Question 24

Write the 2 half equations for the between reaction NaBr and H2SO4?

Answer 24

Ox 1⁄2 equation 2Br- —>Br2 + 2e-

Re 1⁄2 equation H2SO4 +2H+ +2e- —> SO2 +2H2O

Question 25

What is the role of H2SO4 in both steps in the reaction with NaBr?

Answer 25

Note the H2SO4 plays the role of acid in the first step producing HBr and then acts as an oxidising agent in the second redox step.

Question 26

What are the 4 reactions when NaI reacts with H2SO4?

Answer 26

NaI(s) + H2SO4(l) —> NaHSO4(s) + HI(g) 2HI+H2SO4 —> I2(s) + SO2(g) + 2H2O(l) 6HI+H2SO4 —> 3I2 +S(s)+4H2O(l) 8 HI + H2SO4 —> 4 I2(s) + H2S(g) + 4 H2O(l)

Question 27

What do you observe when NaI reacts with H2SO4?

Answer 27

Observations: White steamy fumes of HI are evolved. Black solid and purple fumes of Iodine are also evolved A colourless, acidic gas SO2 A yellow solid of sulfur H2S (Hydrogen sulfide), a gas with a bad egg smell,

Question 28

Define disproportionation.

Answer 28

Disproportionation is the name for a reaction where an element simultaneously oxidises and reduces.

Question 29

What is the reaction with Chlorine with water?

Answer 29

Chlorine with water: | Cl2 (g) + H2O (l) ⇌ HClO (aq) + HCl (aq)

Question 30

What is the reaction of chlorine and water under the presence of UV?

Answer 30

Reaction with water in sunlight If the chlorine is bubbled through water in the presence of bright sunlight a different reaction occurs. 2Cl2 + 2H2O —> 4H+ + 4Cl- + O2 The same reaction occurs to an equilibrium mixture of chlorine water when standing in sunlight. The greenish colour of chlorine water fades as the Cl2 reacts and a colourless gas (O2) is produced.

Question 31

What is the use of chlorine?

Answer 31

Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in swimming pools. The benefits to health of water treatment by chlorine outweigh its toxic effects.

Question 32

What do you observe when Cl2, Br2 and I2 in aqueous solutions react with Cold Sodium Hydroxide ?

Answer 32

The colour of the halogen solution will fade to colourless.

Question 33

What is the equation for the reaction between chlorine and sodium hydroxide? What is the use for the products?

Answer 33

Cl2 (aq) + 2 NaOH (aq) —> NaCl (aq) + NaClO (aq) + H2O (l) | The mixture of NaCl and NaClO is used as bleach and to disinfect/ kill bacteria.

Question 34

What is the Formula for sodium chlorate(I)

Answer 34

NaClO

Question 35

What is the formula for sodium chlorate(V) ?

Answer 35

NaClO3

Question 36

What is the formula for potassium sulfate(VI) ?

Answer 36

K2SO4

Question 37

What is the formula for potassium sulfate(IV) ?

Answer 37

K2SO3