Reactivity trends

Question 1

what happens to reactivity down group 2?

Answer 1

reactivity increases

Question 2

what reactions do group 2 elements undergo? (and products)

Answer 2

redox with:
- oxygen (metal oxide)
- water (metal hydroxide + H2)
- acid (salt + H2)

Question 3

what happens to ionisation energy down group 2?

Answer 3

IE decreases

Question 4

what observations would be made when group 2 reacts with water?

Answer 4

• increase in pH (shown by indicator)
• solid precipitate once the solution becomes saturated (group 2 hydroxide are sparingly soluble)

Question 5

what happens to solubility down group 2 hydroxides? and what effect does this have on pH?

Answer 5

solubility increases which increases [OH-] so increases pH

Question 6

uses of group 2 compounds

Answer 6

• Ca(OH)2 used in agriculture (as lime) to increase pH of acidic soils (producing water)
• Mg(OH)2 or CaCO3 used in antacids (treating acid indigestion) by neurtalising HCl/stomach acid

Question 7

what happens to boiling point down group 7?

Answer 7

boiling point increases (more e-, stronger LDFs)

Question 8

chlorine state and colour (RTP)

Answer 8

pale green gas

Question 9

bromine state and colour (RTP)

Answer 9

red-brown liquid with orange vapour

Question 10

iodine state and colour (RTP)

Answer 10

solid grey-black crystals

Question 11

what reactions do halogens undergo?

Answer 11

• redox
• halogen-halide displacement

Question 12

what happens in halogen-halide displacement?

Answer 12

more reactive halogen displaces the halide from solution (causes colour change)

Question 13

reaction and colour change when I-(aq) is mixed with Cl2(aq)

Answer 13

2I- + Cl2 –> I2 + 2Cl-

pale green to violet

Question 14

colours of Cl2, Br2, I2 in water

Answer 14

Cl2 - pale green
Br2 - orange
I2 - brown

Question 15

colours of Cl2, Br2, I2 in cyclohexane

Answer 15

Cl2 - pale green
Br2 - orange
I2 - violet

Question 16

how can you tell apart solutions of iodine and bromine in water?

Answer 16

• add cyclohexane and shake mixture
• halogens will dissolve more readily
• colours will be more obvious

Question 17

fluorine state and colour

Answer 17

pale yellow gas

Question 18

disproportionation

Answer 18

redox reaction in which the same element is both oxidised and reduced

Question 19

two examples of disproportionation

Answer 19

• Cl2 + H2O
• Cl2 + NaOH

Question 20

how is Cl used in disinfectant and water sterilisation?

Answer 20

chlorate, ClO- ions kill bacteria

Question 21

how can you demonstrate ClO- acting as bleach?

Answer 21

• mix Cl2 + H2O
• add indicator
• indicator will turn red (HCl and HClO are acidic) then colour will disappear as it is bleached

Question 22

why would use dissolve NaOH in water before adding Cl2?

Answer 22

• Cl2 is sparingly soluble in water
• more Cl2 dissolves in the presence of NaOH
• Cl2 reacts with NaOH in a disproportionation reaction to form ClO-

Question 23

risks of chlorine use

Answer 23

• Cl2 reacts with organic hydrocarbons such as methane from decaying vegetation
• this forms chlorinated hydrocarbons which are suspected carcinogens

Question 24

benefits of chlorine use

Answer 24

• prevent outbreaks of waterborne diseases like typhoid and cholera

Question 25

write an equation of the reaction between sodium iodide in the solution of bromine in an organic solvent (and explain why this happens)

Answer 25

Br2 + 2I- --> 2Br- + I2 - bromine is more reactive than iodine - bromine displaces the iodine in solution