2.3 Halogens

Question 1

give the state of fluorine at room temp

Answer 1

• very pale yellow gas
• highly reactive

Question 2

what is chlorine at room temp

Answer 2

• greenish reactive gas
• poisonous in high concentrations

Question 3

what is bromine in its natural state

Answer 3

• red liquid
• gives off brown/orange poisonous fumes

Question 4

what is iodine in its natural state?

Answer 4

• shiny grey solid sublimes to purple gas

Question 5

what happens to melting point and boiling point down group 7?

Answer 5

• increases
• molecules become larger, vdw forces between molecules become larger
• more energy required to break the forces

Question 6

what happens to electronegativity down group 7?

Answer 6

• electronegativity decreases
• atomic radii increasees due to increasing number of shells
• nuclei less able to attract the bonding pair of electrons

Question 7

what happens to oxidising strength down the group ?

Answer 7

• decreases
• less able to accept electrons

Question 8

which halogens displaces which

Answer 8

• chlorine can displace bromide and iodide ions
• bromine will displace iodide ions

Question 9

if the colour of the test tube is very pale green which halogen is present

Answer 9

• chlorine

Question 10

if the colour of the solution is yellow which halogen is present

Answer 10

bromine

Question 11

if the colour of the solution is brown which halogen is present

Answer 11

iodine

Question 12

what are the halogen displacement reactions?

Answer 12

Cl2 + 2Br- > 2Cl- +Br2 ( yellow solution )
Cl2 + 2I- > 2Cl- + I2 ( brown solution )
Br2 + 2I- > 2Br- + I2 ( brown solution )

Question 13

what reaction is used to test for the presence of halide ions?

Answer 13

• halide ions with silver nitrate

Question 14

why is nitric acid added to the solution

Answer 14

• reacts with any carbonates present to prevent formation of Ag2CO3, masking the desired observations

Question 15

what are the observations for silver nitrate with halide ions?

Answer 15

• chloride produces white precipitate
• bromie produces cream precipitate
• iodine produces pale yellow precipitate

Ag+(aq) + X- > AgX(s)

Question 16

what happens if the colours of the silver nitrate test look similar?

Answer 16

• add ammonia solution

Question 17

what happens if silver chloride is dissolved in dilute ammonia?

Answer 17

• it forms a complex ion
• colourless solution

Question 18

what happens if silver bromide dissolves in concentrated ammonia?

Answer 18

• forms a complex ion
• colourless solution

Question 19

finish the equation :
AgX(s) + 2NH3(aq) >

Answer 19

[ Ag ( NH3 ) 2 ] + (aq) + X-(aq)

Question 20

what happens to the reducing power down group 7?

Answer 20

• reducing power increases
• reducing agents donate electrons
• as the ions get bigger, it is easier for the outer electrons to be given away

Question 21

explain why no redox reactions occur with F- and Cl- and H2SO4

Answer 21

• they are not strong enough reducing agents to reduce the S in H2SO4
• only acid base reactions occur

Question 22

give the general equations between H2SO4 and Cl and F ions

Answer 22

NaX(s) + H2SO4(l) > NaHSO4(s) + HX(g)

• white steamy fumes of HX are given off

Question 23

give the equations for Br- reacting with H2SO4

Answer 23

• NaBr(s) + H2SO4(l) > NaHSO4(s) + HBr(g)
• 2Br- + H2SO4 + 2H+ > Br2 + SO2 +2H20

Question 24

what is meant by disproportionation

Answer 24

• name for a reaction where an element simultaneously oxidises and reduces

Question 25

give the reaction for chlorine with water

Answer 25

Cl2 + H2O >< HCLO + HCL

Question 26

give equation for reaction of chlorine with water in present of bright sunlight

Answer 26

2Cl2 + 2H2O > 4H+ + 4CL- + O2

Question 27

why is chlorine used in water treatment

Answer 27

• the benefits to health of water treatment by chlorine outweight its toxic effects