Group 7

Question 1

List 2 properties of halogens?

Answer 1

• Low melting and boiling points
• Exist as diatomic molecules

Question 2

What is the trend in reactivity down group 7?

Answer 2

Reactivity decreases because atomic radius and electron shielding increases so the ability to gain an electron decreases.

Question 3

What is the trend in oxidising ability down the group?

Answer 3

Decreases down the group (Cl strongest and I the weakest), because Cl has the fewest occupied shells it has the greatest attraction between outer electrons and nucleus thus easier to gain electrons

Question 4

What is the trend in reducing ability down the group?

Answer 4

Decreases down the group (Cl weakest I strongest) because outer electrons are furthest from the nucleus, weaker force of attraction thus easiest to be oxidised

Question 5

When a more reactive halogen displaces a less reactive halide, what is this reaction called?

Answer 5

Displacement reaction

Question 6

What is the colour of chlorine in water?

Answer 6

Pale green

Question 7

What is the colour of bromine in water?

Answer 7

Orange

Question 8

What is the colour of iodine?

Answer 8

Brown

Question 9

What is the colour of chlorine in cylohexane?

Answer 9

Pale green

Question 10

What is the colour of bromine in cylohexane?

Answer 10

Orange

Question 11

What is the colour of bromine in cylohexane?

Answer 11

Orange

Question 12

What is the colour of iodine in cylohexane?

Answer 12

Violet

Question 13

Out of the 3 halide ions which one can be oxidised by chlorine?

Answer 13

Br- and I- ions

Question 14

Write the equation for chlorine displacing bromide ions?

Answer 14

Cl2 + 2Br -> 2Cl- + Br2

Question 15

Write the equation for Cl2 oxidising 2I-.

Answer 15

Cl2 + 2I- -> 2Cl- + I2

Question 16

Out of the 3 halides which one can be oxidised by bromine?

Answer 16

I- ions

Question 17

Write the equation for bromine displacing iodide ions.

Answer 17

Br2 + 2I- -> 2Br- + I2

Question 18

Define disproportionation

Answer 18

The oxidation and reduction of the same element in a redox reaction

Question 19

What is the equation for the reaction of Cl2 with water?

Answer 19

Cl2 + H2O -> HClO + HCL

Question 20

What type of reaction is the reaction of chlorine with water?

Answer 20

Disproportionation, chlorine is both oxidised and reduced

Question 21

What acts as a weak bleach in this reaction?

Answer 21

HClO (chloric acid)

Question 22

What kills the bacteria in this reaction?

Answer 22

ClO- (chlorate ions) and chloric acid

Question 23

Is chlorine soluble in water?

Answer 23

Insoluble in water but can dissolve in sodium hydroxide

Question 24

How do you test for carbonates?

Answer 24

• Add dilute acid to a solution containing carbonate ions
• Will cause fizzing/effervescence due to the production of CO2 (limewater confirms the production of CO2)

Question 25

How do you test for sulphates?

Answer 25

- Firstly add dilute HCl to remove any impurities (carbonates) - Add barium chloride which contains barium ions and a white precipitate should form

Question 26

How do you test for halides?

Answer 26

- Firstly add dilute nitric acid to get rid of any impurities (carbonates or sulfite) - Add silver nitrate to form a precipitate

Question 27

What colour are the precipitates for each halide ion?

Answer 27

Cl- is a white precipitate Br- is a cream precipitate I- is a yellow precipitate

Question 28

Why is it important to carry out the carbonate test before the sulfate test?

Answer 28

If you carry out a sulfate test on a carbonate you will get a white precipitate too, only proceed to the sulfate test once you know there is no carbonate present

Question 29

What are the products formed when chlorine reacts with sodium hydroxide?

Answer 29

NaClO, NaCl and H2O

Question 30

How do you test for ammonium compounds?

Answer 30

- Add sodium hydroxide - Gently heat and gas will be produced - Use damp red litmus paper should turn blue

Question 31

What is the equation for another disproportionate reaction that is found in household bleach?

Answer 31

Cl2 + NaOH -> NaClO + NaCl + H2O

Question 32

Explain why, if you are testing a mixture, it is important to use dilute nitric acid instead of sulfuric and hydrochloric acid, for the carbonate test?

Answer 32

If sulfuric acid is used, sulfate ions will show up in the sulfate test with Ba2+ and if HCl is used chloride ions will show up in the halide test with Ag+

Question 33

Explain why group 7 has an increase in boiling point down the group

Answer 33

- Has van der Waals' forces - As you go down the group the number of electrons increase so the energy needed to break these forces increases

Question 34

At stage 1 the student bubbled some chlorine through an aqueous solution of potassium iodide. What would the student see at stage 1?

Answer 34

Goes brown

Question 35

Halogens have van der Waals’ forces between their molecules. (i) Describe how van der Waals’ forces arise.

Answer 35

- Uneven distribution of electrons - Creates an instantaneous dipole - Causes an induced dipole in neighbouring molecules