chapter 8

Question 1

why are group 2 elements reducing agents?

Answer 1

• they donate their 2 outer shell electrons (sub-shell)

- the group 2 element is a reducing agent because it has reduced another species

Question 2

group 2 reactions w/ water

Answer 2

• form an alkaline hydroxide and hydrogen gas, general from M(OH)2
• reactivity increases down the group

Question 3

trend in ionisation energy

Answer 3

ionisation energies decrease down the group because attraction between the nucleus and outer electrons decreases as a result of increasing atomic radius & shielding

Question 4

solubility of group 2 hydroxides

Answer 4

• increases down the group (in water), so the resulting solutions are more alkaline
• Mg(OH)2 very slightly soluble in water
• Ba(OH)2 much more soluble

Question 5

trend in halogen bp

Answer 5

• down the group- more electrons
• stronger London forces
• more energy required to break the intermolecular forces
• bp increases

Question 6

halogen-halide displacement reactions

Answer 6

• reactivity decreases down the group
• a solution of halogen is added to aq solutions of other halides. if the halogen added is more reactive than the halide;
• a reaction takes place, displacing the halide from solution
• solution changes colour
• cl displaces br- and I-
• br displaces I-
• I does not react

Question 7

trend in reactivity (halogens)

Answer 7

• atomic radius increases
• shielding increases
• less nuclear attraction to capture an electron from another species
• reactivity decreases

Question 8

disproportionation

Answer 8

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

Question 9

benefits and risks of chlorine use

Answer 9

+kills bacteria, eg typhoid & cholera

• respiratory irritant
• chlorine can react w/ organic hydrocarbons to form chlorinated hydrocarbons- carcinogenic

Question 10

carbonate test

Answer 10

1) Add dilute HNO3
2) bubbles– could be a carbonate
3) bubble gas through limewater - cloudy= positive result

Question 11

sulfate test

Answer 11

BaSO4 = v insoluble
-add aq barium chloride or nitrate (if also doing halide test)
white precipitate= positive result

Question 12

halide tests

Answer 12

Ag+ aq + X- aq–> AgX s
1) add aq AgNO3
2) predicates into diff colours chloride- white, bromide- cream & iodide- yellow
3)add aq NH3 to test solubility, Cl- soluble in dilute NH3
Br- soluble in conc
I- insoluble

Question 13

sequence of tests

Answer 13

1) carbonate
2) sulfate
3) halide

Question 14

test fro ammonium ion, NH4+

Answer 14

1) add aq NaOH
2) ammonia gas produced (may not see bubbles bc v soluble in water)
3) mixture warmed and gas is released
4) test gas w/ moist pH paper- alkaline = will turn the paper blue