2-2 group 7

Question 1

Properties of halogens - fluorine

Answer 1

F2
pale yellow
gas
1s2 2s2 2p5

Question 2

Properties of halogens - chlorine

Answer 2

Cl2
green gas but pale green in solution
[Ne] 3s2 3p5

Question 3

Properties of halogens - bromine

Answer 3

Br2
brown liquid but orange in solution
[Ar] 3d10 4s2 4p5

Question 4

Properties of halogens - iodine

Answer 4

grey solid but brown in solution
[Kr] 4d10 5s2 5p5

Question 5

Boiling points

Answer 5

The boiling points of the halogens increase down the group.
as you go down group there are larger molecules which have more electrons - more potential temporary dipoles - more potential induced dipoles - stronger van der walls forces - higher boiling points

Question 6

Electronegativity

Answer 6

as you go down group there are larger molecules with more electron shells - more shielding - less attraction between nucleus and outer electron shell - lower ability to gain electrons - lower electronegativity as you descend group.
Since Electronegativity decreases down the group. the strength of halogens as oxidising agents (how easily its reduced (gain electrons)) decreases
the strength of halogens as reducing agents (how easily its oxidised (lose electrons)) increases

Question 7

Displacement reactions

Answer 7

The relative oxidising strengths of the halogens can be seen in their
displacement reactions with the halide ions. A halogen will displace a halide from solution if the halide is below it in the periodic table (e.g. chlorine can displace bromide ions, but chloride ions are displaced by fluorine). You can see this if you add a few drops of an aqueous halogen to a solution containing halide ions. A colour change is seen if there’s a reaction:

Question 8

Displacement reactions - eg

Answer 8

Question 9

Chlorine and water treatment

Answer 9

When you mix chlorine with water, it undergoes disproportionation.
You end up with a mixture of chloride ions and chlorate(I) ions (HCl chlorine ox state = -1 & HClO chlorine ox state = +1 )

HClO is used in cleaning swimming pools. The top reaction in the photo abouve involves bubbling chlorine gas through water. The problem with this method of water steralisation is that the bottom reaction also occurs in the presence of sunlight producing extra HCl and shifts the position of equilibrium of the anbove reaction to the left resulting in less HClO being produced.

The prefered reaction used to clean swimming pools is:
NaClO + H2O ⇌ NaOH + HClO

Question 10

Disproportionation

Answer 10

A reaction in which chlorine is oxidised and reduced at the sams time

Question 11

Bleach production

Answer 11

If you mix chlorine gas with cold, dilute sodium hydroxide solution at room temperature, you get sodium chlorate(I) solution(NaCIO(). This just happens to be common household bleach (which kills bacteria). In this reaction chlorine is both oxidised and reduced. This is called disproportionation.

Question 12

advantages of using chlorine for water sterilization

Answer 12

kills bacteria - e.g. cholera, typhoid, dysentery
prevents growth of algae - less eutrophication

Question 13

volatility

Answer 13

How readily a substance turns into a gas

Question 14

disadvantages of using chlorine for water sterilization

Answer 14

chlorine is toxic - needs care to handle and transport

chlorine reacts with organic matter to form carcinogenic compounds

Question 15

difficulties with adding silver nitrate test

Answer 15

difficult to identify cream ppt vs yellow ppt in isolation

mixture would be difficult to identify

Question 16

test for halide ions - addding silver nitrate

Answer 16

Add HNO3 (Nitric Acid) to remove soluble carbonates (CO3 2-) & Hydroxides (OH-) so no false positives

add silver nitrate to an aqueous solution of the metal halide
* Fluorine - AgF is formed but is soluble so no ppt is observed
* chlorine - AgCl white ppt
* bromine - AgBr cream ppt
* iodine - AgI yellow ppt

add excess dilute NH3:
* chlorine - AgCl white ppt will dissolve and disappear
* bromine - AgBr cream ppt will remain and not dissolve
* iodine - AgI yellow ppt will remain and not dissolve

add excess conc NH3:
* bromine - AgBr cream ppt will dissolve and disappear
* iodine - AgI yellow ppt will remain and not dissolve

Question 17

how does the radius of a halogen atom compare to the radius of the equivalent halide

Answer 17

outer shell electrons are held in the same shell

same amount of shielding from inner electrons

BUT more electrons and therefore more electron repulsion within the shell means halides are bigger than the equivalent halogens

Question 18

why cant silver nitrate by acidified with HCl

Answer 18

HCl contains Cl- ions

this would give a false positive

Question 19

What is the test for chlorine gas

Answer 19

damp blue litmus paper turns red (HCl) then bleaches white (HOCl)

Question 20

redox reactions with sulphuric acid: fluorides and chlorides

Answer 20

sulfuric acid is a moderately strong oxiding agent
BUT
fluorides and chlorides are poor reducing agents

acid base reaction - not redox

Thus there is no further reaction with hydrogen chlorides and hydrogen fluorides once the initial base reaction is complete:

Question 21

redox reactions with sulphuric acid : Bromides

Answer 21

produces bromide and sulphur dioxide - (choking gas formed)

this is because bromide (-1 to 0) is a strong enough reductant to reduce sulphur in H2SO4 from oxidation state +6 to +4

observation = br2 - brown fumes

H2SO4 + 2Br- + 2H+ ——> Br2 + SO2 + 2H2O

Question 22

redox reactions with sulphuric acid : iodide

Answer 22

this reeaction produces iodine, sulfur dioxide (ox state 4) / sulfur (ox state 0) / hydrogen sulfide (ox state -2)

this occurs because iodide is a much stronger reducing agent than bromide and so causes larger changes in the oxidation state of sulphur

H2SO4 + 2I- + 2H+ ——> I2 + SO2 + 2H2O
H2SO4 + 6I- + 6H+ ——> 3I2 + S + 4H2O
H2SO4 + 8I- + 8H+ ——> 4I2 + H2S + 4H2O

Question 23

observations of H2S (g) hydrogen sulfide

Answer 23

rotten egg smell

Question 24

observations of hydrogen halide gas i.e. HF, HCl, HBr etc.

Answer 24

steamy/misty fumes

Question 25

observations of S(s)

Answer 25

yellow solid

Question 26

observations of SO2 (g)

Answer 26

choking gas