M3 ,, The Halogens

Question 1

Fluorine?

Answer 1

Fluorine (F2): very pale yellow gas. It is highly reactive

Question 2

Chlorine?

Answer 2

Chlorine : (Cl2) greenish, reactive gas, poisonous in high concentrations

Question 3

Bromine?

Answer 3

Bromine (Br2) : red liquid, that gives off dense brown/orange poisonous fumes

Question 4

Iodine?

Answer 4

Iodine (I2) : shiny grey solid sublimes to purple gas.

Question 5

G7 MP/BP trend?

Answer 5

Increase 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 the melting and boiling points

Question 6

Displacement of halogens?

Answer 6

A halogen that is more reactive will displace a halogen that has a lower reactivity from one of its compounds

Question 7

G7 reactivity?

Answer 7

The reactivity of the halogens decreases down the group as the atoms get bigger with more shielding so they less easily attract and accept electrons. They therefore form -1 ions less easily down the group

Question 8

Chlorine (aq) + potassium chloride (aq)?
And if solvent is added?

Answer 8

Very pale green solution
No reaction

Solvent added - colourless, no reaction

Question 9

Chlorine (aq) + potassium bromide (aq)?
W/organic solvent?

Answer 9

Yellow solution,
Cl displaced Br

W/solvent - yellow, cl has displaced br

Question 10

Chlorine (aq) + potassium iodide (aq)?
W/organic solvent?

Answer 10

Brown solution, cl has displaced I

W/organic solvent - purple, cl has displaced I

Question 11

Bromine (aq) + potassium bromide (aq) ?
W/organic solvent?

Answer 11

Yellow solution, no reaction

W/organic solvent - yellow, no reaction

Question 12

Bromine + potassium bromide ?
W/solvent?

Answer 12

Yellow solution, no reaction

W/organic solvent - yellow, no reaction

Question 13

Bromine + potassium iodide?
W/ organic solvent?

Answer 13

Brown solution. Br displaced I

W/solvent - purple, Br has displaced I

Question 14

Iodine + potassium chloride?
W/ organic solvent?

Answer 14

Brown solution, no reaction

W/solvent - purple, no reaction

Question 15

Iodine + potassium bromide?
W/solvent?

Answer 15

Brown solution, no reaction
W/solvent - purple, no reaction

Question 16

Iodine + potassium iodide ?
W/solvent?

Answer 16

Brown solution, no reaction
W/solvent - purple, no reaction

Question 17

Colour of halogens without organic solution?

Answer 17

Chlorine =very pale green solution (often colourless),
Bromine = yellow solution
Iodine = brown solution (sometimes black solid present

Question 18

Halogen with organic solvent?

Answer 18

Chlorine = colourless
Bromine = yellow
Iodine = purple

Question 19

Halogen reactivity explained?

Answer 19

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 20

Disproportionation reactions of chlorine?

Answer 20

Disproportionation is the name for a reaction where an element simultaneously oxidises and reduces.

If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products

Question 21

Chlorine uses?

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 risks of toxic effects and possible risks from formation of chlorinated hydrocarbons .

Question 22

Reaction of chlorine with cold dilute NaOH solution?

Answer 22

Cl2,(and Br2, I2) in aqueous solutions will react with cold sodium hydroxide. The chlorine is reacting by disproportionation. The colour of the halogen solution will fade to colourless
Cl2(aq) + 2NaOH(aq) —> NaCl(aq) + NaClO(aq) + H2O(l)
The mixture of NaCl and NaClO (sodium chlorate (I)) is used as Bleach and to disinfect/ kill bacteria

Question 23

The reactions of halide ions with silver nitrate?

Answer 23

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 24

What if precipitates look similar G7?

Answer 24

The silver halide precipitates can be treated with ammonia solution to help differentiate between them if the colours look similar