AS - group 7

Question 1

What colour is fluorine?

Answer 1

pale yellow gas

Question 2

what colour is chlorine?

Answer 2

yellow green gas

Question 3

what colour is bromine?

Answer 3

dark red liquid

Question 4

what colour is iodine?

Answer 4

shiny grey-black solid

Question 5

What happens to the melting points of group 7 and why?

Answer 5

They increase as molecules get larger they have more electrons, so have stronger van der Waals so more energy is required to overcome

Question 6

What happens to the electronegativity and why?

Answer 6

decrease as outer electrons are further from the nucleus and there is more shielding so less attraction

Question 7

What ions would fluorine displace?

Answer 7

Cl-, Br-, I-

Question 8

What ions would chlorine displace?

Answer 8

Br-, I-

Question 9

What ions would bromine displace?

Answer 9

I-

Question 10

What ions would iodine displace?

Answer 10

none

Question 11

What colour would the solution turn if chlorine, bromine or iodine were present?

Answer 11

chlorine - yellow
bromine - orange
iodine - brown

Question 12

E.g. ionic equation between chlorine and sodium bromide.

Answer 12

Cl2(aq) + 2Br-(aq) –> 2Cl- (aq) + Br2(aq)

Question 13

what are example half equations for the displacement between chlorine and sodium bromide?

Answer 13

oxidation -
2Br- > Br2 + 2e-
reduction -
Cl2 + 2e- > 2Cl-

Question 14

What is the strongest oxidising agent and why?

Answer 14

F2
-most likely to gain an e-
-smallest atomic radius
-less shielding
-more attraction between e- and nucleus

Question 15

what is the strongest reducing agent and why?

Answer 15

iodide
-lose e- most easily
-largest atomic radius
-more shielding
-less attraction between e- and nucleus

Question 16

How do you test for halides?

Answer 16

acidify with nitric acid and then add silver nitrate

Question 17

When testing for halides, why do you acidify with nitric acid?

Answer 17

It reacts with any carbonates to prevent the formation of Ag2CO3, which would give a false result

Question 18

What is the general equation for the test for halides, where X is the halide?

Answer 18

AgNO3 (aq) + NaX (aq) > AqX (s) + NaNO3 (aq)

Question 19

What are the results when only silver nitrate has been added?

Answer 19

chloride > white ppt
bromide > cream ppt
iodide > yellow ppt

Question 20

What are the results when dilute NH3 has been added?

Answer 20

chloride > colourless as soluble
bromide > cream, NVC
iodide > yellow, NVC

Question 21

What are the results when conc. NH3 is added?

Answer 21

chloride > NVC, still colourless
bromide > soluble, colourless
iodide > NVC

Question 22

What are the observations and their causes when potassium chloride reacts with conc. sulfuric acid?

Answer 22

misty fumes > displacement of CL-
Universal indicator goes red/orange

Question 23

what is the equation when KCl reacts with H2SO4? Is it a redox and why?

Answer 23

H2SO4 + KCl > HCL + KHSO4
not a REDOX as oxidation states of halide and sulfur stay the same

Question 24

What are the observations and their causes when potassium bromide reacts with conc. sulfuric acid?

Answer 24

misty fumes > displacement of Br-
brown vapour > oxidation of Br-
colourless gas > reduction of H2SO4
potassium dichromate paper goes green > SO2 made

Question 25

What are the equations when KBr reacts with H2SO4?

Answer 25

H2SO4 + KBr > HBr + KHSO4 HBr - reducing agent 2HBr + H2SO4 > SO2 + Br2 + 2H2O

Question 26

What are the observations and their causes when potassium iodide reacts with conc. sulfuric acid?

Answer 26

misty fumes > displacement of I- purple vapour > oxidation of I- colourless gas > reduction of H2SO4 yellow solid - sulfur bad egg smell > H2S potassium dichromate paper goes green > SO2

Question 27

What are the equations when KI reacts with H2SO4?

Answer 27

H2SO4 + KI > HI + KHSO4 2HI + H2SO4 > SO2 + I2 + 2H2O 8HI + H2SO4 > H2S + 4I2 + 4H20 6HI + H2SO4 > S + 3I2 + 4H2O

Question 28

Why is chlorine used in swimming pools?

Answer 28

to kill bacteria

Question 29

What is the equation when chlorine is added to swimming pools?

Answer 29

Cl2 (g) + H2O <> HOCl (aq) + HCl (aq)

Question 30

When chlorine is added to the swimming pools, has it been oxidised or reduced?

Answer 30

both, it undergoes disproportionation

Question 31

What is the equation when chlorine is added in sunlight?

Answer 31

2Cl2 (g) + 2H2O (l) > 4HCl (aq) + O2 (g)

Question 32

What is added due to the fact in sunlight, chlorine is rapidly lost? what is the equation?

Answer 32

solid sodium chlorate (I) NaClO (s) + H2O <> Na+ (aq) + OH- (aq) + HClO (aq)

Question 33

why are swimming pools kept slightly acidic?

Answer 33

In alkaline solution, eqm moves to the left and HClO is removed as ClO- ions

Question 34

what is the equation when chlorine reacts with cold, dilute NaOH?

Answer 34

Cl2 (g) + 2NaOH (aq) > NaClO (aq) + NaCl (aq) + H2O (l)

Question 35

what is the ionic equation when chlorine reacts with cold, dilute NaOH?

Answer 35

Cl2 (g) + 2OH- > ClO- (aq) + Cl- (aq) + H2O (l)

Question 36

why is chlorine used in pools even though it can be toxic?

Answer 36

the health benefits outweigh the risks.