If metal A is more reactive than metal B, which is more stable? Which metal’s compounds are more stable? Explain briefly.
Metal B is more stable. Metal A compounds are more stable. (e.g. K is very unstable, high tendency to lose e- to become K+ (K+ ion is very stable, low tendency to gain electron to become unstable); but Cu is more stable, so Cu2+ is more unstable and will have a larger tendency to become Cu to be stable)
Are more reactive metals easier or more difficult to extract from their compounds? Why?
More difficult. Reactive (Unstable) metals have stable compounds, and they have a low tendency to convert into an unstable compound by gaining an electron.
- Name the metals that only can be extracted by electrolysis
- Name the metals that can only be extracted by electrolysis or heating with C/replacements of C.
- Name the metals that can be only extracted by electrolysis, heating with C/replacements of C, or heating alone.
- Name the metals that can be extracted by physical separation.
Electrolysis: (5) K, Na, Ca, Mg, Al (11223)
Heating with C: (5) Zn, Fe, Sn, Pb, Cu (Zn, Fe, tin in the middle, pencil, Cu)
Heating alone: (2) Hg, Ag
Physical separation: (2) Pt, Au
Why are other methods not suitable for extracting K/Na/Ca/Mg/Al from their oxides?
Their oxides are too unreactive/stable.
What will happen when CuO and C are mixed together?
NOTHING!! PLS remember it is HEATING with metal oxides! No heat, no reaction!!
Alternatives of Carbon in heating metal oxide with carbon & their products after reacting
CO (g)/ H2 (g) -> form Metal + CO2 and Metal + H2O respectively
Can town gas be used for metal extraction of Cu, Pb, Zn, Sn & Fe?
Yes, as it contains H2 and CO gas.
If the metal ore is not an oxide:
- PbS / CuCO3, Fe2(CO3)3 , how do we convert it to its metal form? Include the equations.
By heating it in air to convert into metal oxide, then heating with carbon to convert into metal.
2PbS + 3O2 —> 2PbO + 2SO2
2CuCO3 —> 2CuO + 2CO2
**Fe2(CO3)3 —> Fe2O3 + 3O2
=> MCO3/M2(CO3)3 decomposes to form MO and M2O3 respectively during heating
What is the purpose of C in heating of metal oxides with carbon?
Act as a reducing agent to reduce the metal oxides upon heating (carbon reduction)
Why is it necessary to make the combustion tube inclined when heating CuO with town gas? (3 marks)
- CuO reacts with H2(g) in town gas to form H2O(g) (1)
- To prevent cracking (1) caused by flowing back of condensed H2O to the hot middle part of the test tube (1)
- check 2021 dse LQ6(a)(i) if want
—> (btw h2o will condense to become colder liquid so that’s why if it goes back to the heating area the temperature change will cause cracking!)
- Why pass town gas through test tube for some time before igniting the set up of heating CuO and town gas? (1 mark)
- Why continue pass town gas over copper until it cools? (2 marks)
- Igniting a mixture of town gas and air is explosive so the air in test tube must be flushed out. (1)
- Hot copper reacts easily with O2 in air to reform CuO (1)
It prevents re entering of air for Cu to be re-oxidised. (1)
Why is town gas burned away in the experiment of heating CuO and town gas? (3 marks)
- To prevent the escape of town gas (1)
- as town gas contains CO(g) that is toxic (1)
- and H2(g) that is explosive/flammable. (1)
- Two observable changes of CuO + Town gas reaction?
- How to prove metal formed?
- Black solid changes to reddish brown solid(1)
- Colorless liquid is formed(1)
- The metal obtained should be able to conduct electricity.
Color of Ag2O, HgO, CuO
Ag2O: black or brown
HgO: red
CuO: black
Can electrolysis of liquid caesium chloride be used to extract caesium? (caesium is an alkali metal)
No. Molten caesium chloride!
A certain amount of Ag2O, silver oxide, is heated in a test tube. What would the graph of “mass of contents of test tube” vs “time” look like and why?
It would be decreasing but will not reach zero.
O2 leaves the test tube but Ag remains.
Reaction of metals with air:
Observation when K, Na, Ca, Mg, Al, Zn, Fe is heated in air & Pb, Cu, Hg & Ag, Pt, Au
- K: lilac flame, white powder is formed
- Na: golden yellow flame, white powder is formed
- Ca: brick red flame, white powder is formed
- Mg: bright white flame, white powder is formed
- Al: white flame, white powder is formed
- Zn: white-blue flame, powder is formed (hot=yellow powder, cold=white powder)
- Fe: yellow sparks, black powder is formed
- Pb: powder is formed (hot= orange powder, cold= yellow powder)
- Cu: black powder is formed (CuO)
- Hg: Red powder is formed (HgO)
Why do shiny reactive metals tarnish on exposure to air? What protective measures for metals are done for storage of these metals?
As they react readily with O2 in air to form a full oxide layer. They are usually stored in paraffin oil (unreactive hydrocarbons) which prevents them from reacting with O2 and water in air.
