Group 7

Question 1

What are some properties of halogens?

Answer 1

Boiling points increase down the group due to the increasing strength of the temporary dipole dipole interactions as size and relative mass of the molecule increases

Electronegativity decreases down the group as larger atoms attract electrons less than smaller ones as the outer electron is further from the nucleus

Question 2

What is the trend in displacement with halogens?

Answer 2

They’re oxidising agents as they gain an electron and they become less oxidising down the group , (they get bigger) their relative strength (oxidation) can be seen through their reactions with halides . The general trend is a halogen will displace a halide if the halide is below it in the periodic table .(KCl, KBr, KI etc)

Question 3

How does one make bleach

Answer 3

Mix chlorine gas with cold diliuted sodium hydroxide : (disproportionation reaction)
2NaOH(aq)+Cl2(g)->NaClO(aq)+NaCl(aq)+H2O(l)

Question 4

What is the reaction with chlorine and water ?

Answer 4

It’s a disproportionate reaction and reversible:

Cl2(g)+H2O(l)->2H+(aq) +Cl-(aq)+ClO-(aq)

Question 5

What is the UV reaction with chlorine

Answer 5

Chlorine decomposes water to form chloride ions and oxygen(reversible)
Cl2(g)+H2O(l)-> 2H+ (aq) + 2Cl-(aq) + 1/2 O2(g)

Question 6

What does chlorate do to water?

Answer 6

Chlorate1 ions kill bacteria so adding chlorine to water will make it safe to drink however it is toxic.
Kills disease causing bacteria, prevents growth of algae,eliminates bad taste and odours and discolouration
Chlorine can cause: respiratory issues, severe chemical burns .
Most of the compounds that are used to treat water with chlorine are very dangerous eg chloromethane are also carcinogens

Question 7

How are halide ions formed?

Answer 7

In a redox reaction , its reduced . As you go down the group, its easier for Halide ions to lose electrons as shielding happens but this means the reducing power also decreases

Question 8

What reactions do halides have with sulphuric acid?

Answer 8

All halides react with concentrated sulphuric acid to produce a hydrogen halide:
E.g.
NaX + H2SO4->NaHSO4+ HX
X being the halide .
Some halides are strong enough reducing agents that they can reduce H2SO4 to just water and sulfur dioxide such as iodine :
2HX+H2SO4->X2+SO2+2H2O

Question 9

What’s the test for halides?

Answer 9

Silver nitrate (dilute nitric acid before to make all impurities soluble) a white precipitate forms with chlorine, a cream one with bromine and a yellow one with iodine