Group 7

Question 1

What are group 7 elements called?

Answer 1

Halogens

Question 2

What is the trend in electronegativity for group 7? Why?

Answer 2

Decrease
> atoms get bigger
> outer e- get further away

Question 3

What is the trend in boiling point for group 7? Why?

Answer 3

Increase
> weak vdw
> get stronger as Ar increases

Question 4

What is the trend in oxidising ability for group 7? Why?

Answer 4

Decrease
> atoms get bigger
> decreased attraction to outer e-
> harder to gain e-

Question 5

What is the displacement of halides reaction?

Answer 5

More reactive/better oxidising agent displaces other halogen from aqueous solution

Question 6

What is the trend in reducing ability for group 7? Why

Answer 6

Increase
> atoms get bigger
> less attraction to outer e-
> easier to lose e-

Question 7

What is produced when sodium halides (s) react with concentrated H2SO4?

Answer 7

NaHSO4 (s) + HX (g)

Question 8

What observations are made due to hydrogen halide gas?

Answer 8

White steamy fumes

Question 9

Why is the reaction of F/Cl with H2SO4 not a redox reaction?

Answer 9

Oxidation states don’t change
Not strong enough reducing agents

Question 10

What is the second reaction of Br with H2SO4?

Answer 10

HBr (g) + H2SO4 (l) –> Br2 (g) + SO2 (g) + 2H2O (l)

Question 11

What is observed from the second reaction of Br with H2SO4?

Answer 11

Orange fumes (Br2)
Acidic choking gas (SO2)

Question 12

What are the products of the second reaction of I with H2SO4?

Answer 12

I2 (s) + H2) (l)
+ SO2 (g) or S (s) or H2S (g)

Question 13

What is observed from the second reaction of I with H2SO4?

Answer 13

Black solid + purple fumes (I2)
Acidic choking gas (SO2)
Yellow solid (S)
Egg-smelling gas (H2S)

Question 14

Why do Br and I have second reaction with H2SO4?

Answer 14

They are good reducing agents (for sulfur)

Question 15

What compound is used to identify halide ions? Why?

Answer 15

Silver nitrate solution
> AgNO3 (aq)
> silver halides form different coloured ppt

Question 16

What colours are the silver halides?

Answer 16

F = no ppt
Cl = white
Br = cream
I = pale yellow

Question 17

Why must AgNO3 be acidified when testing for halides?

Answer 17

To react with carbonates
> could mask desired observations

Question 18

Why is ammonia solution added when testing for halides?

Answer 18

To distinguish halides of colours are similar
> AgCl = dissolves in dilute
> AgBr = dissolves in concentrated
> AgI = insoluble

Question 19

What is the reaction of chlorine with water?

Answer 19

Cl2 + H2O –> ClO- + Cl- + 2H+
> chlorate (I)
> chloride

Question 20

What type of reaction is chlorine + water? Why?

Answer 20

Disproportionation
> Cl is oxidised and reduced

Question 21

What is produced when chlorine discomposes in water?

Answer 21

HCl (Cl- + H+) + O2

Question 22

What condition is needed for chlorine to decompose in water?

Answer 22

UV light/sunlight

Question 23

Why is chlorine used in water treatment?

Answer 23

To kill bacteria
> outweighs toxicity

Question 24

What is the reaction of chlorine with cold, dilute aqueous NaOH?

Answer 24

Cl2 (aq) + NaOH (aq) –> NaCl (aq) + NaClO (aq) + H2O (l)

Question 25

What is the use of the solution formed when chlorine reacts with NaOH?

Answer 25

Used as bleach
> disinfect
> kill bacteria