group 7

Question 1

how does boiling point change as you go down the group?

Answer 1

increase as you go down as their is more van der waals forces which require more energy to break

Question 2

when do halogens displace each other?

Answer 2

A halogen will displace another if its halide is further down the group

Question 3

what colours are formed when chlorine,bromine,iodine react

Answer 3

KCL KBR KI
Cl2 n/a orange brown
Br2 n/a n/a brown
I2 n/a n/a n/a

Question 4

how is bleach formed

Answer 4

disproportionation reaction

2NaOH + Cl2 -> NaClO + NaCl + H2O

Question 5

how does adding chlorine to water kill bacteria?

Answer 5

H2O + Cl2 -> 2H+ + Cl- + CLO-
However you must be careful as under sunlight this reaction doesnt make CLO-
it makes:
2H2O + Cl2 -> 4H+ +2Cl- +O2

Question 6

advantages and disadvantages of adding chlorine to drinking water?

Answer 6

kills bacteria
long lasting reduces bacteria build up later on
reduces growth of algae

is toxic

Question 7

what is the trend for halide ions as reducing agents

Answer 7

as you go down radius increases,more shielding electrons less attracted to nucleus so can be removed easier

Question 8

how to identify Cl-,Br-,I-

Answer 8

Add silver nitrate (AgNO3)
white precipitate = Cl-
cream precipitate = Br-
yellow precipitate = I-

Cl- dissolves indilute nh3
Br- dissolves in conc NH3
I- remains insoloble

Question 9

testing for group 2 ions

Answer 9

dip nichrome wire into hcl
dip into sample
put in blue flame

Dark red is ca2+
red is sr2+
green is ba2+

Question 10

how to test for sufate?

Answer 10

add acidified barium chloride BaCl2

white precipitate means it its sulfate

Question 11

testing for chlorides?

Answer 11

add excess NaOH
white precipitate = MgCl2
redissolves =AlCl2