Topic 11 - Obtaining and Using Metals Flashcards
4.1 - What happens to metal atoms when they react with water and acids?
The most reactive metals ( K, Na, Ca ) react with cold water to form hydrogen + metal hydroxide. They react violently with dilute acids.
Fairly reactive metals ( Mg, Al, Zn, Fe ) react slowly or not at all with cold water but react with steam to form hydrogen + metal oxide. They react with acids to form hydrogen and a salt solution.
Non reactive metals ( Cu, Ag, Au ) don’t react with cold water or steam or acids.
Reactions with acids with lots of effervescence means the metal is highly reactive.
The easier the metal loses electrons, the higher the reactivity of that metal.
Comparing the reactivity of metals are done with a displacement reaction, the more reactive metal gradually forms the solution while the less reactive metal coats the surface of the solution.
4.2 - What are redox reactions?
Displacement reactions are also redox reactions.
E.g. Zinc + copper sulfate
Zn –> Zn 2+ + 2e - This is oxidation as electrons are lost.
Cu 2+ + 2e –> Cu - This is reduction as electrons are gained.
When one substance is oxidised and another is oxidised, it is a redox reaction.
4.3 - What are the relative reactivity of different metals?
Metals react depending on how easy it forms positive ions.
Metals are arranged in their order of reactivity :
Potassium
Sodium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Hydrogen
Copper
Silver
Gold
A more reactive metal, displaces a less reactive element in water and acids.
4.4 - What metals are found uncombined and what are found combined in the Earth’s crust?
Very unreactive metals are found in their natural states as uncombined elements.
Reactive metals react with other elements to form compounds in rocks. The process of obtaining an element from a compound is called extraction.
4.5 - How do you explain oxidation and reduction in terms of oxygen?
Oxidation is gain of oxygen.
Reduction is loss of oxygen.
4.6 - What type of reaction happens when metals are extracted from ores?
Reduction reactions take place, where one substance is oxidised and the other is reduced. This is a redox reaction.
E.g - Aluminium oxide is reduced to produce Aluminium by electrolysis.
In electrolysis Al3+ ions are attracted to the cathode where they gain electrons to form aluminium. The O 2- ions are attracted to the anode where they lose electrons to form oxygen.
In high temperatures, the O 2- reacts with graphite anode to form CO2.
4.7 - How is the method of extraction of a metal relative to its position in the reactivity series and its cost?
Metals below carbon in the reactivity series is heated and carbon displaces copper to produce pure copper. Profit is made when the ore contains a lot of the desired metal.
Metals more reactive than carbon is extracted through electrolysis. This is done by passing electricity through a molten ionic compound in order to decompose it into its ions. Electrolysis is used to only extract very reactive metals that can’t be obtained by heating it with carbon.
4.8 - How are biological methods used to extract metals?
Copper ores are running out, so copper with smaller amounts of copper are extracted.
Bioleaching uses bacteria grown on low grade ore to produce a solution of cooper ions which is a leachate. Copper is extracted from this leachate by displacement with scrap iron, then purified by electrolysis.
Phytoextraction involves growing plant which absorb metal compounds, these plants are then burnt and the metal compound is extracted.
4.8 - Evaluate these biological methods used to extract metals
Advantages - Both methods don’t release harmful gases, less damage to the landscape unlike mining and conserves supplies of high grade ores.
Bioleaching doesn’t require high temperatures and phytoextraction can extract metals from contaminated soils.
Disadvantages - Very slow.
Bioleaching can produce toxic substances and sulfuric acid which damage the environment.
Phytoextraction is more expensive than mining ores and growing plants depend on the weather.
4.9 - How is the position of a metal in the reactivity series related to its resistance to corrosion?
Corrosion is the oxidising of a metal when it reacts with oxygen and gains oxygen. This is rusting.
The more reactive a metal is, the quicker it corrodes. ( Gold is used in jewellery as it doesn’t corrode as it isn’t reactive ).
Some reactive metals like aluminium, are very reactive and should corrode quickly, however they don’t as its surface reacts with oxygen and rusts, forming a protective oxide layer ( tarnish ) which prevents further oxidation and reaction.
4.10 - What are the advantages and disadvantages of recycling metals?
Advantages - Natural metal ores reserves last longer.
Reduction in mining of ores so less damage, noise and dust to the landscape.
Less pollution produced. ( Like reactions of sulfur with carbon )
Many metals need less energy to recycle than to extract from ores.
Less waste metal in landfill sites.
Disadvantages - Cost and energy used in collecting, transporting and sorting metals. Sometimes it is more expensive, needs more energy to recycle a metal rather than extract it.
4.11 - What are life cycle assessments?
Life cycle assessments ( LCA ) are carried out to work the environmental impact of a product.
It helps people decide whether it is worthwhile to manufacture or recycle a product.
LCA’s compare the effect of using different materials for one product.
4.12 - What are the factors to consider in a life cycle assessment of a product?
What raw materials are needed?
How are the raw materials processed?
How much energy for the manufacture and packaging?
What is this energy’s source?
What is the product used for?
How will the product be disposed?
