4B: elements of group 7

Question 1

describe the nature & colour of F2.

Answer 1

highly reactive, pale yellow gas

Question 2

describe the nature & colour of Cl2.

Answer 2

pale green gas, poisonous in high reactions

Question 3

describe the nature & colour of Br2.

Answer 3

red liquid, dense brown / orange poisonous fumes

Question 4

describe the nature & colour of I2.

Answer 4

grey solid, sublimes in purple gas

Question 5

what is the definition of electronegativity?

Answer 5

relevant tendency of an atom in a molecule to attract e- in a covalent bond to itself

Question 6

what is the trend of electronegativity down group 7? why?

Answer 6

electronegativity decreases down the group
- increasing atomic radii as higher number of shells
- nucleus less able to attract bonding pair of e-

Question 7

what is the trend of melting / boiling point down group 7? why?

Answer 7

increases down the group
- more e- & stronger london forces & therefore more energy needed to overcome

Question 8

explain the reactivity of group 7 down the group.

Answer 8

reactivity decreases down the group
- atoms get bigger with more shielding -> less easily attract 1 e-

Question 9

describe the oxidising strength down group 7.

Answer 9

oxidising strength decreases down group 7 & will displace a halogen with lower oxidising power from 1 of its compounds

Question 10

what colour will be shown in the solution if KBr is reacted with Cl2? explain why.

Answer 10

yellow
- Cl displaces Br

Question 11

what colour will be shown in the solution if KI is reacted with Cl2? explain why.

Answer 11

brown
- Cl displaces I

Question 12

what colour will be shown in the solution if KI is reacted with Br2? explain why.

Answer 12

brown
- Br displaces I

Question 13

what colour will be shown in the organic layer if KBr is reacted with Cl2? explain why.

Answer 13

yellow
- Cl displaces Br

Question 14

what colour will be shown in the organic layer if KI is reacted with Cl2? explain why.

Answer 14

purple
- Cl displaces I

Question 15

what colour will be shown in the organic layer if KI is reacted with Br2? explain why.

Answer 15

purple
- Br displaces I

Question 16

which halogens will oxidise iron from 2+ to 3+?

Answer 16

Cl & Br

Question 17

which halogen will reduce iron from 3+ to 2+?

Answer 17

I

Question 18

state the disproportionation reaction of Cl which forms bleach.

Answer 18

Cl2 (g) + H2O (l) -> HClO (aq) + HCl (aq)

Question 19

if indicator is used in the disproportionation reaction of Cl, what will the observations be?

Answer 19

solution turns red & turns colourless as HClO bleaches the colour

Question 20

what conditions will halogens react with cold dilute NaOH? what observations will they be?

Answer 20

in aqueous solutions
- colour fades to colourless

Question 21

what happens when halogens are reacted with hot dilute NaOH?

Answer 21

disproportionation occurs

Question 22

what are the products of Cl2 reacting with cold dilute NaOH?

Answer 22

NaCl (aq) + NaClO (aq) + H2O (l)

Question 23

what are the products of Cl reacting with hot dilute NaOH?

Answer 23

5 NaCl (aq) + NaClO3 (aq) + 3 H2O (l)

Question 24

what are the reaction type of conc. sulfuric acid with group 1 halides (Cl & F) ? why?

Answer 24

acid-base
- sulfuric acid is not strong enough to oxidise Cl & F

Question 25

what will be observed when conc. sulfuric acid reacts with group 1 halides (Cl & F)?

Answer 25

white steamy fumes of HF / HCl

Question 26

describe & explain the trend down group 7 as reducing agents.

Answer 26

increasing strength down the group
- greater tendency to donate e- as outer e- is easier to give away

Question 27

what is the colour of S?

Answer 27

yellow

Question 28

how could H2S be distinguished?

Answer 28

bad egg smell

Question 29

how could halides be tested?

Answer 29

1) add nitric acid to remove any present carbonate
2) add silver nitrate

Question 30

which halogen does not form a precipitate with silver nitrate test?

Answer 30

F

Question 31

what will be formed when a hydrogen halide reacts with water?

Answer 31

H3O+ + (halide)-
[acidic solution]

Question 32

what will be formed & observed when hydrogen halides react with ammonia?

Answer 32

forms ammonium halides (white smoke)