Topic 4 - Extracting Metals And Equilibria Flashcards
Deduce the relative reactivity of some metals, by their reactions with water, acids and salt solutions
REACTION WITH WATER:
Potassium, sodium, calcium - reacts quickly with cold water
Magnesium - very slow
Aluminium - none
Zinc, iron - reacts with steam
Hydrogen - not a metal, metals less reactive than hydrogen do not react with water or dilute acids
Copper, silver, gold - no reaction with water or steam
REACTION WITH DILUTE ACIDS:
Potassium, sodium, calcium - violent reaction
Magnesium, aluminium, zinc, iron - reaction becoming less vigorous
Copper, silver, gold - no reaction with dilute acids
These reactions show the relative tendency of metal atoms to form cations
Explain products of metals reacting with water and acids
METAL WITH WATER:
HYDROGEN is produced if a metal reacts with water:
Metal + water —> metal hydroxide + hydrogen
In general, the more reactive the metal, the greater the rate of bubbling
METAL WITH ACIDS:
HYDROGEN is produced if a metal reacts with a dilute acid:
Metal + acid —> salt + hydrogen
- the rate of reaction is greater in warm acid than cold acid
- in general, the more reactive the metal, the greater the rate of bubbling
Explain DISPLACEMENT reactions and what can be observed
A displacement reaction is a redox reaction (reduction and oxidation taking place) .
A more reactive metal will displace a less reactive metal from its salts in solution. For example, magnesium is more reactive tan copper. It can displace copper from copper sulfate solution.
In this reaction, you observe:
- The colour of the solution fading as blue copper sulfate is replaced by colourless magnesium sulfate
- An orange-brown coating of copper forming on the surface of the magnesium
- An increase in temperature because the reaction is exothermic
Explain where metals are extracted from in the earth
- Most metals are extracted from ores found in the crust
- Unreactive metals are found in the earths crust as the unconfined elements
Describe oxidation
Oxidation is the loss of electrons and the gain of oxygen
Describe reduction
Reduction is the gain of electrons and the loss of oxygen
Explain why the method used to extract a metal from its ore is related to its position in the reactivity series and the cost of the extraction process
The method used to extract a metal from its ore is related to:
- the cost of the extraction process
- the metal’s position in the reactivity series
In principle all metal as can be extracted using electrolysis, but:
- electricity is needed, which is expensive
- reduction by heating with carbon can be used if a metal is less reactive than carbon
- chemical reactions may be needed to separate silver and gold from other metals
Evaluate alternative biological methods of metal extraction
BIOLEACHING:
- biological method of metal extraction that uses bacteria .
- copper can be extracted from copper sulfide, CuS in the following way:
> the bacteria oxidise sulfide ions S2-
> copper sulfide ores break down
> Cu2+ ions are released
The solution that the bacteria produce is called a leachate. This leachate contains:
- a high concentration of metal ions
Scrap iron can be used to obtain copper from the leachate
PHYTOEXTRACTION:
- uses plants
- Metal compounds absorbed by roots
- Plant concentrates metal compounds in its shoots and leaves
- Plants burned
- Ash contains metal compounds
Explain iron extraction
Iron is less reactive than carbon, so it’s produced by reducing iron oxide using carbon, this happens in a blast furnace. Inside it:
- Iron oxide is reduced by carbon:
Iron oxide + carbon —> iron + carbon monoxide - It is also reduced by carbon monoxide:
Iron oxide + carbon monoxide —> iron + carbon dioxide - Molten iron (iron in the liquid state) is produced
Explain how a metal’s relative resistance to oxidation is related to its position in the reactivity series
A metal’s relative tendency to form cations and its resistance to oxidation are both related to its position in the reactivity series. In general: the higher up a metal, the greater the tendency to form cations. the lower down a metal, the greater its resistance to oxidation.
Evaluate the disadvantages of extracting metals and advantages of recycling metals
Extracting metals from their ores:
- uses up limited resources
- uses a lot of energy
- damages the environment
Recycling reduces these disadvantages, used metal items are collected. Rather than throwing these away, these are taken apart. The metal is melted down to make new items.
Recycling metals means:
- metal ores will last longer
- less energy is needed
- fewer quarries and mines are needed
- less noise and dust are produced
- less land is needed
Explain disadvantages of recycling metals
- used metal items must be collected and transported to the recycling centre
- different metals must be removed from used items and sorted
Describe a life cycle assessment
A life cycle assessment (LCA) of a product is a ‘cradle to grave’ analysis of its impact on the environment. It includes these stages:
- Obtaining raw materials
- Manufacturing the product
- Using the product
- Disposing of the product
Describe data needed for an LCA
An LCA is likely to need data on these factors at most or all stages:
- the use of energy
- the release of waste materials
- transport and storage
An LCA is also likely to need data on:
- whether the raw materials needed are renewable or non renewable
- whether any of the product can be recycled or re used
- how the product is disposed of
Explain how reversible reactions are shown
Chemical reactions are REVERSIBLE. The direction of some reversible reactions can be altered by changing the reaction conditions.
These changes can be modelled using ⇌ the reversible symbol.
Eg// NH4Cl(s) ⇌ NH3(g) + HCl(g)
Explain what is meant by dynamic equilibrium
In a CLOSED SYSTEM, a container where no reacting substances can enter or leave, a reversible reaction can reach equilibrium.
At EQUILIBRIUM:
- rate of forward reaction = rate of backward reaction
- the concentrations of the reacting substances stay constant
A chemical equilibrium is a DYNAMIC equilibrium:
- the forward and backward reactions keep going - they do not stop at equilibrium
Describe the formation of ammonia as a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas)
Ammonium chloride decomposes when heated:
NH4Cl(s) —> NH3(g) + HCl(g)
Ammonia and hydrogen chloride combine when cool:
NH3(g) + HCl(g) —> NH4Cl(s)
This is a reversible reaction that can reach a dynamic equilibrium
Describe the Haber process and conditions required for it to take place
The haber process is a reversible reaction between nitrogen and hydrogen to form ammonia.
Conditions required:
- temperature 450 degrees
- pressure 200 atmospheres
- iron catalyst
Predict how the position of a dynamic equilibrium and rate of reaching equilibrium is affected by changes in:
temperature
pressure
concentration
TEMPERATURE INCREASED - moves in the direction of the endothermic reaction, rate increased
PRESSURE INCREASED - moves in the direction of the fewest molecules of gas, rate increased (if reaching gases are present)
CONCENTRATION OF A REACTING SUBSTANCE INCREASED - moves in the direction away from the reacting substance, rate increased
CATALYST ADDED - no change, rate increased
Describe aluminium extraction
Aluminium is more reactive than carbon. It is produced by reducing aluminium oxide in an electrolytic cell (electrolysis)
- Aluminium oxide is dissolved in molten cryolite. This reduces the temperature needed for electrolysis to happen, when an electric current passes through the mixture
- At the cathode, aluminium ions gain electrons and are reduced to aluminium atom:
Al3+ + 3e- —> Al
- At the anode, oxide ions lose electrons ad form oxygen gas:
2o2- —> O2 + 4e-
- Oxygen reacts with the graphite anodes, so these must be replaced every few weeks
