Chapter 10 Group 7, the halogens

Question 1

what is the trend in the boiling point?

Answer 1

increases as we go down group 7, due to the van der waals forces increasing as a result of increasing size and relative mass

physical state changes from as to solid
F2 - pale yellow gas
Cl2 - pale green gas
Br2 - brown/orange liquid
I2 - grey solid

Question 2

what is the trend in electronegativity?

Answer 2

decreases as we go down
electronegativity is the ability to attract electrons towards itself in a covalent bond.
The atom gets larger therefore the distance between the nucleus and electrons increases and there is more shielding

Question 3

what occurs in displacement reactions?

Answer 3

the more reactive halogens will displace the less reactive halide ions
Cl displaces Br ions, orange solution made (br2)
Cl / Br displaces I ions, brown solution made (I2)

Question 4

trend in reactivity

Answer 4

decreases as we go down
for a reaction to occur, an electron is gained.
atoms with a smaller radius attract electrons better than larger atoms

Question 5

how is bleach made

Answer 5

made via a disproportionation reaction
- mixing chlorine and sodium hydroxide will form sodium chlorate (I) solution
2NaOH(aq) + Cl2(g) -> NaClO (aq) + NaCl(aq) + H2O (l)

Question 6

what is a disproportionation reaction?

Answer 6

when an element has simultaneously been reduced and oxidised, such as chlorine in the formation of bleach

Question 7

how is water sterilised?

Answer 7

adding chlorine to water to kill the bacteria within the water
- produces chlorate (I) ions (ClO-) which kill bacteria.
- disproportionation reaction
H2O(g) + Cl2(g) -> 2H+ (aq) + Cl-(aq) + ClO- (aq)

Question 8

what effect does sunlight have on chlorinated water?

Answer 8

can decompose chlorinated water, however no ClO- is made
2H2O(l) + Cl2 (g) -> 4H+ (aq) + 2Cl- (aq) + O2(g)

Question 9

what are the advantages of chlorinating drinking water?

Answer 9

destroys microorganisms that cause disease
long lasting so reduces bacteria build up further down supply
reduces growth of algae that discolours water and gives it bad taste and smell

Question 10

disadvantages of chlorinating drinking water

Answer 10

chlorine gas is toxic and irritates the respiratory system
liquid chlorine causes severe chemical burns to the skin
chlorine can react with organic compounds in water to make chloroalkanes, which are linked to causing cancer

Question 11

what is the trend in reducing ability in halide ions?

Answer 11

as we go down the group the ionic radius increases, so there is more shielding and distance between the nucleus and outer electrons is larger. so an attractive force is weaker
therefore Iodine is a more powerful reducing agent than F

Question 12

what happens when chloride ions react with sulfuric acid

Answer 12

only reduces H2SO4
NaCl + H2SO4 -> NaHSO4 + HCl
a white misty fume is produced

Question 13

what happens when bromide ions react with sulfuric acid

Answer 13

can reduce H2SO4 and SO2
H2SO4 + NaBr -> NaHSO4 + HBr

H2SO4 + 2H+ + 2Br- -> Br2 + SO2 + H2O
an orange vapour is formed (Br2)

Question 14

what happens when iodide ions react with sulfuric acid

Answer 14

can reduce H2SO4, SO2, S to produce H2S
H2SO4 + NaI -> NaHSO4 + HI

H2SO4 + 2H+ + 2I- -> SO2 + I2 + H2O

H2SO4 + 6H+ + 6I- -> 3I2 + S + 4H2O
yellow solid of S is produced

H2SO4 + 8H+ + 8I- -> 4I2 + H2S + 4H2O
rotten egg smell of H2S produced