topic 4B

Question 1

reactivity of group 7 halogens

Answer 1

reactivity increases down the group

Question 2

trend in melting and boiling point

Answer 2

• increases down the group
• as molecules become larger they have more electrons so larger London forces between molecules

Question 3

trend in electronegativity

Answer 3

• electronegativity of the elements decreases
• atomic radii increases down the group due to increasing shells
• hence nucleus less able to attract the bonding pair of electrons

Question 4

trend in reactivity

Answer 4

reactivity decreases down the group
- as atoms get bigger, they less easily attract and accept electrons

Question 5

oxidation reactions of halide ions by halogens

Answer 5

• a halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power

Question 6

oxidation strength down the group

Answer 6

decreases

Question 7

colour of chlorine in solution

Answer 7

very pale green (often colourless)

Question 8

colour of bromine in solution

Answer 8

yellow solution

Question 9

colour of iodine in solution

Answer 9

brown solution (sometimes black solid)

Question 10

colour of organic solvent layer - chlorine

Answer 10

colourless

Question 11

colour of organic solvent layer - bromine

Answer 11

yellow

Question 12

colour of organic solvent layer - iodine

Answer 12

purple

Question 13

reaction of chlorine with water

Answer 13

Cl2 + H2O –> HClO + HCl

Question 14

what happens if universal indicator is added to solution

Answer 14

First turns red due to acidity of both reaction products.
Then goes colourless as the HClO bleaches the colour.

Question 15

what is chlorine used for in water

Answer 15

Used to kill bacteria
Used in swimming pools

Question 16

reactions of halogens with cold dilute NaOH solution

Answer 16

Cl2, Br2, I2
colour goes colourless
Cl2 + 2NaOH -> NaCl + NaClO + H2O
products used as bleach

Question 17

reaction of halogens with hot dilute NaOH

Answer 17

3Cl2 + 6NaOH -> 5NaCl + NaCLO3 + 3H2O

(same products for other halogens)

Question 18

Fluoride reaction with H2SO4 & observation

Answer 18

NaF + H2SO4 -> NaHSO4 + HF
observation: white steamy fumes of HF

Question 19

Chlorine reaction with H2SO4 & observation

Answer 19

NaCl + H2SO4 -> NaHSO4 + HCl
observation: white steamy fumes of HCl

Question 20

Bromine reaction with H2SO4

Answer 20

acid-base step: NaBr+ H2SO4 -> NaHSO4 + HBr

redox step: 2HBr + H2SO4 -> Br2 + SO2 + 2H2O

Question 21

Bromine reaction with H2SO4 oxidation and redox half equation

Answer 21

ox: 2Br- –> Br2 + 2e-
red: H2SO4 + 2H+ + 2e- –> SO2 + 2H2O

Question 22

Bromine reaction with H2SO4 observation

Answer 22

white steamy fumes of HBr are evolved
red fumes of Bromine also evolve and colourless acidic gas SO2

Question 23

Iodine reaction with H2SO4

Answer 23

strongest reducing agent
NaI+ H2SO4 -> NaHSO4 + HI
2HI + H2SO4 -> I2 + SO2 + 2H2O
6HI + H2SO4 -> 3 I2 + S + 4 H2O
8HI + H2SO4 -> 4 I2 + H2S + 4 H2O

Question 24

Iodine reaction with H2SO4 - observation

Answer 24

white steamy fumes
black solide and purple fumes of Iodine
colourless acidic gas SO2
yellow solid - sulphur
H2S, gas with bad egg smell

Question 25

Iodine reaction with H2SO4 - reduction products

Answer 25

sulfur dioxide sulfur hydrogen sulfide

Question 26

reaction of fluoride ions with silver nitrate

Answer 26

no precipitate

Question 27

reaction of chloride ions with silver

Answer 27

white precipitate Ag+ + Cl- -> AgCl

Question 28

reaction of bromide ions with silver nitrate

Answer 28

cream precipitate Ag+ + Br- -> AgBr

Question 29

reaction of iodide ions with silver nitrate

Answer 29

pale yellow precipitate Ag+ + I- -> AgI

Question 30

effect of light on silver halides

Answer 30

precipitates darken forming silvereff

Question 31

effect of ammonia on silver halides

Question 34

producing hydrogen halide

Answer 34

made by the reaction of solid sodium halide salts with phosphoric acid white steamy fumese

Question 35

test for presence of carbonate, CO3 2- and

Answer 35

bubble gas through lime-water to test for CO2 add any dilute acid and observe effervescence

Question 36

testing for presence of sulfate

Answer 36

acidified BaCl2 used as reagent white precipitate forms

Question 37

test for ammonium

Answer 37

react with NaOH forming NH3 ammonia gas can be identified by its smell or turning damp red litmus paper blue