Topic 4 - extracting metals and equilibria Flashcards
What are the products when a metal reacts with cold water?
Metal hydroxide and hydrogen gas
What are the products when a metal reacts with steam?
Metal oxide and hydrogen gas
What are the products when a metal reacts with a dilute acid?
Salt and hydrogen
If a metal reacts with cold water, what does it suggest about the reactivity of this metal?
It is very reactive
A metal reacts with oxygen but not acid or cold water. What does this suggest about the reactivity of this metal?
Not very reactive, most metal react with oxygen
Name a metal which will not react with water, acid or oxygen
Gold
Describe an experiment that uses displacement to compare the reactivity of two metals
Add a solid metal to a salt solution (the salt must contain a different metal)
If the solid metal is more reactive, it will gradually disappear, displacing the metal that was in the salt solution
If nothing happens, the metal in the salt is more reactive and cannot be displaced
Why can a displacement reaction be called a redox reaction? Explain in terms of electron transfer
A redox reaction occurs when reduction and oxidation are taking place in the same reaction
In a displacement reaction, the more reactive metal atoms lose electrons to form ions (oxidation) and the less reactive metal ions gain electrons to form the element (reduction)
What is the reactivity of a metal related to its tendency to form?
Cations
Which metals are most easily oxidised?
The ones highest in the reactivity series.
Where are most metals extracted from?
From ores forums in the earth’s crust
What is an ore?
A rock which contains metals often chemically combined with other substances
Which metals are found in the earth’s crust as in combined elements?
Unreactive metals
Explain what oxidation means in terms of oxygen
Gain of oxygen
Explain what reduction means in terms of oxygen
Loss of oxygen
Most ores contain metals chemically combined with oxygen. What process must be carried out to extract the metal?
Reduction
Which two methods could be used to extract metals from their ores?
Reduction with carbon
Electrolysis
How would you extract iron from its ore?
Iron is less reactive than carbon so can be extracted by reduction with the carbon
Electrolysis could also be used, but this would use a lot of unnecessary energy
How can aluminium be extracted from its ore?
Aluminium is more reaction than carbon so electrolysis must be used
When the molten ore undergoes electrolysis, the metal forms at the cathode
When aluminium is extracted from aluminium oxide, why is it first dissolved in molten cryolite?
Aluminium oxide has a very high melting point. It is dissolved in molten cryolite to produce an electrolyte with a lower melting point, reducing energy usage and cost
How can plants be used as an alternative metal extraction method? How does it work?
Phytoextraction
Plants are grown in areas with metals in the soil. The plants take up metals through their root and concentrate them in their shoots and leaves. These plants are burned and the metals are removed from the ash
How can bacteria be used as an alternative metal extraction method? How does it work?
Bacteria extraction
Some bacteria absorb metal compounds. These bacteria produce solutions called leachates containing the metals. Scrap iron can be used to remove the metal from the leachate
What are the limitations of biological methods of extraction?
Only suitable for low grade ores with smaller quantities of metals
Slow processes
Require displacement of electrolysis for the final step
How is a metal’s relative resistance to oxidation related to its position in the reactivity series?
Metals lower in the reactivity series are less reactive. This means they are less likely to form their cations so are more resistant to oxidation
What are the advantages of recycling metals?
Prevents detrimental environmental impact of mining and extraction of new metals
Less waste produced so less landfill
Less energy required compared to electrolysis
More sustainable
The process provides employment
What is a life cycle assessment?
Analysis of the overall environmental impact that a product may have throughout its lifetime
What different factors does a life cycle assessment of a product consider?
Extraction and processing of raw materials Manufacturing Packaging and transportation Use of the product Disposal
What is a reversible reaction?
A reaction in which the products can react to form the original reactants
How can the direction of a reversible reaction be altered?
Changing the reaction conditions
What is meant by the term dynamic equilibrium?
When the rate of the forward reaction equals the rate of the backwards reaction. This means the concentration of reactants and products are constant even though compounds are continually reacting
What is a closed system?
A system where nothing is added or removed
All reactants and products remain in the reaction vessel
Why is equilibrium only reached if the reaction take solace in a close system?
It prevents any reactants and products escaping so that they are able to react continuously
What is the Haber process?
An industrial process used to produce ammonia (for making fertilisers)
Where are the sources of nitrogen and hydrogen for the Haber process?
Nitrogen: extracted from the air
Hydrogen: obtained from natural gas
Is the formation of ammonia a reversible reaction?
Yes, it will reach dynamic equilibrium in a closed system
What conditions are used for the Haber process?
450°C temperature
200 at, pressure
Iron catalyst
Explain the effect of changing the temperature of a reversible reaction if the forward reaction is endothermic
It favours the forward reaction so the yield of th products will increase
Explain the effect of increasing the pressure of a reversible gaseous reaction
It will favour the reaction that produces the least number of molecules
The concentration of the reactants are increased during a reversible reaction. What effect will this have on the equilibrium position?
It will shift to the right so the product yield will increase. This will reduce the effect of the increased concentration of the reactants
If there are equal gaseous molecules of the reactant and product in a reversible reaction, what effect will changing the pressure have on the equilibrium position?
No effect
