chemistry - extracting metals & equilibria: obtaining & using metals (4.1 - 4.12)

4.1 deduce relative reactivity of some metals by their reactions with water

metal + water → metal hydroxide + hydrogen

only metals above carbon in reactivity series react with water

more reactive metal = more vigorous reaction

measure reaction by: observe flames/bubbles produced; measure temp. change

4.1 deduce relative reactivity of some metals by their reactions with acids

metal + acid → salt + hydrogen

only metals above hydrogen in reactivity series react with dilute acids

more reactive metal = more vigorous reaction

measure reaction by: observe flames/bubbles produced; measure temp. change

4.1 deduce relative reactivity of some metals by their reactions with salt solutions

displacement reactions in salt solutions of one of metals

more reactive metal displaces less reactive metal from its salt solution - more reactive slowly disappears from solution when it displaces less reactive

metal displaces another - more reactive than it

4.2 displacement reactions

more reactive element displaces less reactive element from compound

redox reaction: one substance oxidised, one reduced

e.g. Zn _(s) + CuSO_{4 (aq)} → Cu _(s) + ZnSO_{4 (aq)}

• Zn + Cu²⁺ → Cu + Zn²⁺

• Zn → Zn²⁺ + 2e^- (oxidation - loses electrons)

• Cu²⁺ + 2e^- → Cu (reduction - gains electrons)

spectator ions

ions that don’t change in reaction

e.g. sulfate ions in Zn _(s) + CuSO_{4 (aq)} → Cu _(s) + ZnSO_{4 (aq)}

4.3 reactivity series - order

potassium

sodium

calcium

magnesium

(carbon)

zinc

iron

(hydrogen)

copper

silver

gold

4.3 reactivity series - reaction with water

K, Na, Ca: + water → metal hydroxide + hydrogen

Mg, Al, Zn, Fe: + water → metal hydroxide + hydrogen; react very slowly/not at all with cold water

Mg, Al, Zn, Fe: + steam → metal oxide + hydrogen

Cu, Ag, Au: do not react with cold water/steam

4.3 reactivity series - reaction with dilute acid

K, Na: + acid → salt + hydrogen; react violently

Ca, Mg, Al, Zn, Fe: + acid → salt + hydrogen

Cu, Ag, Au: do not react with dilute acid

4.3 reactivity series - tendency of metal atoms to form cations

more reactive = loses electrons & forms cations more easily

4.4 where are metals found?

most metals extracted from ores in earth’s crust

unreactive metals found in earth’s crust as uncombined elements

4.5 oxidation & reduction - gain/loss of oxygen

oxidation: gain of oxygen

reduction: loss of oxygen

4.6 is extraction of metals oxidation/reduction?

extraction of metals involves reduction (gains electrons, loses oxygen) of ores

4.7 extracting metals from ores (position in reactivity series, cost of extraction process) - heating with carbon

metals compounds less reactive than carbon

e.g. extracting iron from ore containing iron oxide

• iron oxide heated with carbon

• carbon more reactive than iron - displaces it

• iron oxide + carbon → iron + carbon dioxide

4.7 extracting metals from ores (position in reactivity series, cost of extraction process) - electrolysis

metals compounds more reactive than carbon

expensive - requires lots of energy to keep metal oxides molten

e.g. extracting aluminium from ore containing aluminium oxide

• electricity passed through molten aluminium oxide (ionic compound)

• decomposes into its elements

• aluminium oxide → aluminium + oxygen

4.8 biological methods of metal extraction - bioleaching

bacteria grown on low grade ore produce solution containing copper ions (leachate)

copper extracted from leachate by displacement using scrap iron

copper purified by electrolysis

also used for metals like nickel, cobalt & zinc

4.8 biological methods of metal extraction - phytoextraction

plants grown that absorb metal compounds

plants burnt to form ash

metal extracted from ash

4.8 bioleaching advantages

no harmful gases produced

causes less damage to landscape than mining

conserves supplies of higher grade ores

does not require high temps.

4.8 bioleaching disadvantages

very slow

toxic substances & sulfuric acid produced in process - damage environment

4.8 phytoextraction advantages

no harmful gases produced

causes less damage to landscape than mining

conserved supplies of higher grade ores

can extract metals from contaminated soils

4.8 phytoextraction disadvantages

very slow

more expensive than mining some ores

growing plants depends on weather conditions

4.9 metal’s relative resistance to oxidation related to position in reactivity series

corrosion: metal reacts with oxygen - oxidised

metal more reactive = reacts with oxygen more readily = corrodes faster

4.10 advantages of recycling metals - economic implications

cheaper - many metals need less energy to recycle them than extract new metal from ore

4.10 advantages of recycling metals - preserving environment & supply of valuable raw materials

natural reserves of metal ores last longer

reduced need to mine ores - mining damages landscape, creates noise & dust pollution

produces less pollution

uses less energy - many metals need less energy to recycle them than extract new metal from ore

less waste metal in landfill sites

4.11 for life cycle assessment for product, consider effect on environment of:

obtaining raw materials

manufacturing product

using product

disposing product

4.12 evaluate data from life cycle assessment of product

helps people decide whether it’s worthwhile to manufacture & recycle product

used to compare effects of using diff. materials for same product