Reactivity, Redox and Electrolysis Flashcards
Order of reactivity
Please Stop Calling Me A Careless Zebra, Instead Learn How Copper Saves Gold
Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, (Carbon), Zinc, Iron, Lead, (Hydrogen), Copper, Silver, Gold
Conditions for iron rusting + equation
When oxygen and water are present
4Fe + 3O2 + nH2O -> 2[Fe2O3] . nH2O
Barrier methods:
Prevents iron rusting by stopping water and oxygen from directly contacting the iron
Using grease, oil, paint, plastic etc.
Galvanising:
Zinc coating on SURFACE stops water and oxygen from directly contacting the iron
Even if barrier is broken, the more reactive zinc corrodes before the iron
During the process, the zinc loses electrons to form zinc ions
Sacrificial protection:
Zinc blocks are attached to iron boat hulls etc. to act as sacrificial anodes
Zinc is more reactive than iron, so oxygen in the air reacts with the zinc to form a layer of zinc oxide instead of iron oxide
Oxidation
Gains O
Loses H
Loses e-
Oxidising/Reducing agent
A substance that gives/takes oxygen or removes/gives electrons (it is itself reduced/oxidised)
Reduction
Loses O
Gains H
Gains e-
Where and in what nature are most metals found
Where and in what nature are unreactive metals found e.g. gold
In the earth’s crust combined with other elements (known as ore)
In the earth’s crust as an uncombined element (found native)
Extraction of metals less reactive than carbon
Displacement reaction via carbon
e.g. zinc oxide + carbon -> zinc + carbon dioxide
Extraction of metals more reactive than carbon
Electrolysis
Uses of aluminium
Aircrafts and cans - low density, resists corrosion
Power cables - conducts electricity, ductile
Pots and pans - low density, strong (when alloyed), good conductor of elec. and heat
Uses of copper
Electrical wires - very good conductor of electricity, ductile
Pots and pans - very good conductor of heat, very unreactive, malleable
Water pipes - unreactive, malleable
Surfaces in hospitals - antimicrobial properties, malleable
Uses of iron
Buildings - strong
Saucepans - Conducts heat, high melting point, malleable
Uses of types of steel
Mild steel (0.25% carbon): Nails, car bodies, ship building
High-carbon steel (0.6-1.2% carbon): Cutting tools, masonry nails
Stainless steel (Chromium and nickel): Cutlery, utensils, kitchen sinks
Alloys and examples
An alloy is a mixture of a metal with, usually, other metals or carbon
E.g. brass (copper and zinc), steel (iron and carbon)
Why are alloys harder than pure metals
In an alloy, the different atoms have slightly different-sized atoms;
This breaks up the regular lattice arrangement;
Making it more difficult for the layers of ions to slide over each other;
Electrolysis definition
The decomposition of a substance into its elements via pathway of electricity
Molten electrolysis
Solid ionic compound is heated and becomes molten
Graphite electrodes attached to a power source are placed in the molten compound
Positive ions from the compound are attracted to the cathode (negative electrode)
Negative ions from the compound are attracted to the anode (positive electrode)
E.g. PbBr2 (l) -> Pb (l) + Br2 (g)
Cathode: [Pb2+] + 2[e-] -> Pb
Anode: 2[Br-] -> Br2 + 2[e-]
Why is graphite used as a material for electrodes
It is inert - does not interfere with the electrolysis
Cryolite usage
Lowers operating temperature (decreases melting point of Al2O3)
Makes extraction of aluminium more economically feasible
Aqueous electrolysis
Solid ionic compound is dissolved in water (can conduct electricity)
Graphite electrodes connected to a power source are placed in the solution
This causes H2O to dissociate: H2O ⇌ [H+] + [OH–]
Unreactive metals and hydrogen ions are attracted to the cathode (negative electrode)
Halogens and hydroxide ions are attracted to the anode (positive electrode)
Residue remains in the aqueous solution
E.g. NaCl: Na is more reactive than hydrogen so H2 formed at cathode
Cl is a halogen so Cl2 formed at anode
Residual solution: Na, OH -> NaOH (aq)
CHUM
Cathode: Hydrogen or Unreactive Metal (Cu, Ag, Au)
2[H+] + 2[e-] -> H2
[Mx+] + x[e-] -> M
Reduction reaction
ACHOO
Anode: Choose Halogen Or Oxygen
2[X-] -> X2 + 2[e-]
4[OH-] -> O2 + 2[H2O] + 4[e-]
Oxidation reaction
Sodium chloride observations
Cathode: Bubbles of gas given off (H2)
Anode: Green gas given off (Cl2)
Solution stays colourless
Litmus/Universal Indicator: Blue (NAOH residue is alkali)
Copper sulfate observations
Cathode: Brown layer formed (Cu)
Anode: Bubbles of gas given off (O2)
Solution goes from blue to colourless
Litmus/Universal Indicator: Red (H2SO4 residue is acidic)
Dilute sulfuric acid observations
Cathode: Bubbles of gas given off (H2)
Anode: Bubbles of gas given off (O2)
Solution stays colourless
Litmus/Universal Indicator: Red (Concentrated H2SO4 is highly acidic)
Twice the vol. of hydrogen gas is produced compared to oxygen
