Topic 4- Extracting metals and equilibria Flashcards
Explain displacement reactions as redox reactions
- More reactive metals form a cation (+) as they displace the less reactive metal losing electrons and being oxidised– forms an ion as it replaces less reactive metal in salt solution
- Less reactive metals form atoms from negative ions as they’re displaced, gaining electrons and being reduced
- forms atom as it’s replaced in salt solution
Reactivity series of metals with water and dilute acid ?
- metals react with other substances, metal atoms form positive ions
- Reactivity of a metal is related to its tendency to form positive ions– more reactive metals form positive ions more easily
- Metals arranged in order of reactivity in reactivity series
Where are metals found?
- most metals extracted from ores found in Earth’s
crust, unreactive metals found in Earth’s crust as
uncombined elements - &, most metals found as compounds that require chemical reactions to extract the metal
How to extract metals less reactive than carbon?
- extracted from oxides by reduction w/ carbon
- reduction involves loss of oxygen, so ores reduced to remove the oxygen to obtain the pure metal
Method used to extract metal from its ore
- Can only be extracted by reduction of carbon if metal is less reactive so carbon can displace metal from ore
- If more reactive than carbon, use electrolysis, but electrolysis can be expensive, since requires a lot of energy
How to extract metal using carbon? e.g. Iron
- Iron oxide loses oxygen, and is reduced– carbon gains oxygen, and is oxidised.
- For iron, this is carried out at high temperatures in a blast furnace
How to extract metal via electrolysis e.g. aluminium
- Metals more reactive than carbon e.g aluminium are extracted by electrolysis of molten compounds.
- uses molten mixture of aluminium oxide and carbon as the electrodes
- aluminium has positive charge, so it forms at cathode and oxygen has a negative charge so it forms at anode
Describe Phytoextraction:
○ Some plants absorb metal compounds through their roots
○ concentrate these compounds into their shoots and leaves
○ plants burned to produce an ash that contains the metal
compounds
Describe bacterial extraction
- Some bacteria absorb metal compounds
○ Produce solutions called leachates which contain them
○ use scrap iron to obtain the metal from the leachate
how is a metals’ resistance to oxidation related to its
position in the reactivity series
- less reactive a metal is, the more resistant it is to oxidation, since to react metal forms a positive metal ion by losing electrons
Advantages of recycling metals
-Requires less energy to melt and remould metals than to extract new metals from their ores
- Mining ores is bad for the environment –quarries created, produce noise pollution and dust
- allows waste metals to be reused, saving money,
helping the environment and the supply of valuable raw materials
What is the life assessment of a product?
- stages carried out to assess environmental impact of products
Stages of a life time assessment
Extracting and processing raw materials
- Manufacturing and packaging
- Use and operation during its lifetime
- Disposal at end of its useful life, including transport and distribution at each stage
What is a reversible reaction?
- a chemical reactions, where products of the reaction can react to produce the original reactants
e. g. Haber process nitrogen + hydrogen ⇌ ammonia
Difference between equilibrium and dynamic equilibrium
equilibrium
-rate of forward reaction = rate of backward reaction
- concentration of reacting substances stay the same
dynamic equilibrium
- once forward and backward reaction reach equilibrium, they keep going
Describe formation of ammonia
- Nitrogen obtained from air and hydrogen from natural
gas or other sources. - purified gases passed over catalyst of iron at a 450 °C and high pressure – 200 atmospheres
- Some hydrogen and nitrogen reacts to form ammonia
- ammonia cooled and condensed to be used in fertilisers
- reaction is reversible so ammonia breaks down again into nitrogen and hydrogen.
- in Haber process optimum conditions used to produce ammonia as fast & economically as possible
Effect of changing conc. in equilibrium reaction
- system not at equilibrium so concentrations of substances will change until equilibrium is reached again.
- If conc. of reactants increases: equilibrium shifts towards products (right) so more product is produced until equilibrium reached again
- if conc. of products increases: equilibrium shifts towards reactants (left) so more reactant is produced until equilibrium is reached again
Effect of changing temp. in equilibrium reaction
- If temp. increased: equilibrium moves to the direction of the endothermic reaction e.g. if reaction is endothermic and temp. increases equilibrium shifts right to make more product
- If temperature decreased: equilibrium moves to the direction of exothermic reaction
- For the forwards being exo/endothermic and yield meaning the amount of product from the forwards reaction
What is Le chatelier’s principle
- if a change in pressure, temperature, or concentration of a reactant is applied to a system in equilibrium, equilibrium will shift to counteract the effect of the change
Difference between exothermic and endothermic reaction
endothermic
- heat is absorbed
exothermic
- heat is released
How to remember the charges of the anode and cathode in electrolysis
- Cathy the negative cathode
- And the anode is negative
General rule
What substances are formed at the cathode and what substances at the anode
- metal ions always have positive charges, so they will always go to the cathode — hydrogens will also since it has a positive charge
- at the anode are negatively charged ions, so non-metals except for hydrogen
