halogens

Question 1

what are halogens

Answer 1

group 17 the most reactive nonmetals
exist as diatomic molecules

Question 2

what are examples of halogens

Answer 2

Fluorine (F2): very pale yellow gas. It is highly reactive
Chlorine : (Cl2) greenish, reactive gas, poisonous in high concentrations
Bromine (Br2) : red liquid, that gives off dense brown/orange poisonous fumes
Iodine(I2) : shiny grey solid turns to purple gas

Question 3

what are trends in melting and boiling points down a group

Answer 3

increases down the group
As the molecules become larger they have more electrons and so have larger induced dipole-dipole forces
(London forces) between the molecules. As the intermolecular forces get larger more energy has to be put into break these intermolecular forces. This increases melting and boiling point

Question 4

what’s the electron configuration of group 17

Answer 4

All group 7 elements have the outer shell s2p5 electron configuration.
The will often react by gaining of one electron in redox reactions to form 1–ions

Question 5

why does the reactivity of halogens decreases down the group

Answer 5

because atoms get bigger with more shielding so they less easily attract and accept electrons. They therefor form -1 ions less easily down the group

Question 6

what is the halogen halide displacement reaction

Answer 6

a solution of each halogen is added to aqueous solutions of the other halides.

Question 7

what happens if the halogen is more reactive than the halide present

Answer 7

a reaction takes place, the halogen displacing the halide from the solution.
the solution changes colour

Question 8

how can you tell apart the solution of iodine and bromine in water when they appear a similar orange brown colour depending on the concentration

Answer 8

an organic non polar solvent such as cyclohexane can be added and the mixture shaken
The non polar halogens dissolve more readily in cyclohexane than in water
In cyclohexane their colours are much easier to tell apart with
Iodine being deep violet.

Question 9

what are the colours of halogen solutions in water

Answer 9

chlorine –> pale green
bromine –> orange
iodine –> brown

Question 10

what are the colours of halogens in cyclohexane

Answer 10

the top layers for :
chlorine—> pale green
bromine—> orange
iodine —> violet

Question 11

whats the reaction of chlorine with bromide ions

Answer 11

Cl2(aq) + 2NaBr(aq) —-> 2NaCl(aq) + Br2(aq)
Ionic equation
Cl2(aq) +2Br(aq) —-> 2Cl-(aq) + Br2(aq)
0 —–> -1 REDUCTION
-1 —–> 0 OXIDATION

Question 12

what are the results from the halogen displacement reaction

Answer 12

chlorine has clearly reacted with both Br- and I-
e.g Cl2(aq) + 2Br(aq) —-> 2Cl-(aq) + Br2(aq)
bromine has only reacted with I- only
e.g Br2(aq) + 2I- —-> 2Br-(aq) + I2(aq)
iodine has not reacted at all

Question 13

whats the reactivity between chlorine to bromine

Answer 13

chlorine most reactive than bromine than iodine is the least reactive

Question 14

Whats the explanation of reactivity

Answer 14

Chlorine is more reactive than bromine because it will
gain an electron and form a negative ion more easily than
bromine. The is because an atom of chlorine is smaller
than bromine and the outermost shell of chlorine is less
shielded than bromine so the electron to be gained is
attracted more strongly to the nucleus in chlorine than bromine

Question 15

what about fluorine

Answer 15

is a pale yellow gas reacting with almost any substance that comes into contact with the

Question 16

what about astatine

Answer 16

is extremely rare because its radioactive and decays rapidly
predicted to be least reactive halogen

Question 17

what is the strongest oxidising agent in the halogens

Answer 17

fluorine because its gaining electrons from other species more rapidly than the other halogens. The halogens become weaker oxidising agents down the group

Question 18

what is disproportionation

Answer 18

is a redox reaction in which the same element is both oxidised and reduced. The reaction of chlorine with water and with cold dilute sodium hydroxide are two examples of disproportionation reaction

Question 19

what happens during the reaction with chlorine and water

Answer 19

disproportionation reaction takes place

Question 20

show the reaction between chlorine and water

Answer 20

Cl2(aq) + H20(l)——> HCl(aq) + HCL (aq)
0 —–> -1 REDUCTION
0 —–> +1 OXIDATION

Question 21

what is chlorine used as

Answer 21

Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in
swimming pools. The benefits to health of water treatment by chlorine by its killing of bacteria outweigh its risk of toxic effects and possible risks from formation of chlorinated hydrocarbons

Question 22

the product of the reaction between water and chlorine should produce acids how can we prove this

Answer 22

If some universal indicator is added to the
solution it will first turn red due to the acidity
of both reaction products. It will then turn
colourless as the HClO bleaches the colour

Question 23

what is bacteria killed by from the water and chlorine reaction

Answer 23

chloric acids and chlorate ions ClO-

Question 24

what can chloric acid act as

Answer 24

a weak bleach

Question 25

what happens in the reaction between chlorine with dilute NaOH solution

Answer 25

Cl2,(and Br2, I2) in aqueous solutions will react with cold sodium hydroxide. The chlorine is reacting by disproportionation. The colour of halogen solution will fade to colourless

Question 26

show the reaction of chlorine with dilute NaOH solution

Answer 26

Cl2(aq) + 2NaOH(aq) —–> NaClO(aq) + NaCl(aq) +H2O
0 —–> -1 REDUCTION
0 —–> +1 OXIDATION

Question 27

what is the use of the products formed from chlorine with dilute NaOH solution

Answer 27

The mixture of NaCl and NaClO (sodium chlorate (I)) is used as Bleach and to disinfect/ kill bacteria

Question 28

what are the benefits of chlorine use

Answer 28

beneficial in ensuring our water is afe to drink and that bacteria is killed

Question 29

what are risks of chlorine use

Answer 29

chlorine is a respiratory irritant in small concentrations and large concentrations can be fatal

Question 30

what happens in the test for halides

Answer 30

This reaction is used as a test to identify which halide ion
is present. The test solution is made acidic with nitric
acid, and then Silver nitrate solution is added drop wise

Question 31

show the reaction of the test of halides

Answer 31

Ag+(aq) + X-(aq) —–> AgX(s)

Question 32

when chlorine bromine and iodine are used in the test of halides what percipitate is formed

Answer 32

Fluorides produce no precipitate
Chlorides produce a white precipitate
Ag+(aq) + Cl- (aq)  AgCl(s)
Bromides produce a cream precipitate
Ag+(aq) + Br- (aq)  AgBr(s)
Iodides produce a pale yellow precipitate
Ag+(aq) + I- (aq)  AgI(s)

Question 33

what is the role of nitric acid

Answer 33

The role of nitric acid is to react with any carbonates
present to prevent formation of the precipitate
Ag2CO3. This would mask the desired observations
2 HNO3 + Na2CO3 2NaNO3 + H2O + CO2

Question 34

how can we differentiate the colours of the silver halide percipitates

Answer 34

can be treated with ammonia
Silver chloride can be dissolves in dilute ammonia to form complex ion
AgCl(s) + 2NH3(aq) [Ag(NH3)2]+ (aq) + Cl- (aq)
colourless solution

Silver bromide dissolves in concentrated ammonia to form a complex ion
AgBr(s) + 2NH3(aq) [Ag(NH3)2]+ (aq) + Br- (aq)
Colourless solution

Silver iodide does not react with ammonia– it is too insoluble.

Question 35

Bromine is used to extract iodine from a solution containing iodide ions what’s the ionic equation for this reaction

Answer 35

Br2 + 2I^- —-> I2 + 2Br-

Question 36

Bromine can extracted by bubbling chlorine gas through concentrated solution containing bromide ions . Write the ionic equation

Answer 36

Cl2 + 2Br^- ——>2Cl + Br1