Inorganic 1 - group 7 halogens

Question 1

what is the trend in boiling point down group 7? why?

Answer 1

MP and BP increases as you go dow the group = atom size increases due to more occupied electron shells = stronger van der waals forces of attraction between molecules = more energy needed to break them.

Question 2

what is the trend in electronegativity down group 7?

Answer 2

• decreases
• more occupied electron shells as you go down
• greater atomic radius
• outer electron further away from nucleus
• lower force of attraction between the nucleus and electron pair in the covalent bond/

Question 3

what do you use to test for halide ions?

Answer 3

Acidified AgNO3

Question 4

why do you add HNO3 instead of HCL?

Answer 4

• ## to remove CO3- (carbonate) / OH-HCl has Cl- ions = giving false positive result

Question 5

result and equation for F- test?

Answer 5

Ag+ + F- —-> AgF(aq)
no ppt

Question 6

result and equation for Cl- test?

Answer 6

Ag+ + Cl- ——> AgCl(s)
white ppt

Question 7

result and equation for Br- test?

Answer 7

Ag+ + Br- ——> AgBr(s)
cream ppt

Question 8

result and equation for I- test?

Answer 8

Ag+ + I- ——> AgI(s)
pale yellow ppt

Question 9

what happens (+ equations) to each of the silver halide ppts when dilute/conc NH3 are added?

Answer 9

AgCl - dissolves in dilute and conc NH3

AgCl(s) + 2NH3 (aq) —> Ag(NH3)2 + Cl-

AgBr - only dissolves in conc NH3

AgBr(s) + 2NH3 (aq) —> Ag(NH3)2 + Br-

AgI - will not dissolve in either

Question 10

what is the trend in oxidising ability down the group? why?

Answer 10

• decreases down group (F best I worst)
• F= fewest occupied shells = greatest force of attraction between outer shell electron and nucleus.
• easiest to reduce and gain electron = best oxidising agent

Question 11

write the equation for Cl2 oxidising I-

Answer 11

Cl2 + 2I- —> 2Cl- + I2

Question 12

what is the trend in reducing abilities of halides down the group? why?

Answer 12

increases down group ( F- worst and I- best)
- I- has most occupied electron shells
- outer electrons are further from the nucleus = weakest force of attraction between outer shell electron and nucleus
- easiest to be oxidised and lose electrons

Question 13

what products are formed when I- reduces H2SO4? write all 4 equations?

Answer 13

H2SO4 + 2I- —> SO4 (2-) + 2HI
H2SO4 + 2H+ + 2I- —-> SO2 + I2 + 2H2O
H2SO4 + 6H+ + 6I- —->S + 3I2 4H2O
H2SO4 + 8H+ + 8I- —-> H2S + 4I2 + 4H2O

Question 14

What are the products for Br- + H2SO4?

Answer 14

HBr and SO2

Question 15

does Cl- reduce H2SO4?

Answer 15

No, not a powerful enough reducing agent, only HCl is formed.

Question 16

why is chlorine added to water? why is it safe?

Answer 16

Forms ClO- ions = which oxidise (kills) all microorganisms in the water
Little remains after it has done its job = health benefits outweighs the risks of using it.

Question 17

what are the potential risks of adding chlorine to drinking water?

Answer 17

• Cl is toxic and damages the respiratory system in large quantities
• can form carcinogens with hydrocarbons

Question 18

why is ozone not used to purify water in the UK?

Answer 18

• more expensive than Cl
  -evaporates from water more quickly

Question 19

what is the equation of the reaction of Cl2 with water?

Answer 19

Cl2 (g) + H2O (l) —-> HClO (aq) + HCl (aq)

Question 20

what type of reaction is the reaction with Chlorine and water?

Answer 20

disproportionation - Cl both oxidised and reduced

Question 21

what are the two forms of chlorate ion?

Answer 21

ClO- is chlorate (I)
ClO3- chlorate (V)

Question 22

what is the equation for making bleach?

Answer 22

Cl2 + 2NaOH —> NaCl + NaClO + H2O

NaClO = bleach

Question 23

give the equation of chlorine and water in the presence of UV?

Answer 23

2Cl2 + 2H2O —-> 4HCl + O2(g)

Question 24

what is desalination?

Answer 24

• converts salt water into clean potable water
• reverse osmosis
• vacuum distillation at low pressure and temperature

Question 25

what are the advantages and disadvantages of desalination?

Answer 25

+ safe drinking water produced in places where it may not be available
- uses lots of energy
- reverse osmosis = low efficiency
- can disturb marine ecosystems