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GCSE Chemistry 2 > Obtaining and Using Metals - Topic 4 > Flashcards

Obtaining and Using Metals - Topic 4 Flashcards

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1
Q

Important uses of metals:

A
  • main use of iron is construction - strong and cheap
  • aluminium is used in pylon wires because it is a good conductor of electricity and it has a low density (unlike the transition metals)
  • aluminium is used to make saucepans because it is a good conductor of heat and does not react with the food due to a protective layer of aluminium oxide. on its surface
    • this protective layer also makes it a good material for window frames as it will not corrode
  • copper is used for electrical wire as it is a good conductor of electricity
  • copper is used to make hot water pipes and boilers as it is an unreactive metal
  • gold and copper are often used to make jewellery as they are unreactive and have an attractive appearance (most other metals are silver in their appearance and reactive metals will quickly tarnish and lose their shine)
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2
Q

Difference between rusting and corrosion:

A
  • only iron rusts, other metals corrode
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3
Q

What should you react metals that don’t react with water with?

A
  • metals that don’t react with cold water can be tested steam
  • reactive metals react very vigorously with steam therefore steam should only be used with those that show a low/no rate of reaction with cold water
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4
Q

What will the most reactive metals react with?

A
  • The most reactive metals will react with cold water:
    • Products are a metal hydroxide (forming an alkaline solution) andhydrogen gas
    • E.g. with potassium: 2K + 2H2 O -> 2KOH + H2
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5
Q

What will fairly reactive metals react with?

A

fairly reactive metals react with acids: acid + metal → salt + hydrogen

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6
Q

What do almost all metals react with?

A

almost all metals react with oxygen: metal + oxygen -> metal oxide, though more reactive metals will react with oxygen more quickly

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7
Q

What is the only metal that doesn’t react with water, steam or acids?

A

only metal that does not react with any of the above is gold, because it is extremely unreactive

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8
Q

How can you deduce the relative reactivity of some metals?

A
  • deduce the relative reactivity of some metals by seeing if they react with water (i.e. VERY reactive), acid (reactive), and oxygen (not that reactive)
  • for these reactions, you can see if they have taken place by looking for bubbles (if hydrogen is produced)
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9
Q

How can you see if one metal is more reactive than another?

A
  • You can see if one metal is more reactive than another by using displacement
    reactions
  • Easily seen when a salt of the less reactive metal is in the solution:
    • More reactive metal gradually disappears as it forms a solution
    • Less reactive metal coats the surface of the more reactive metal
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10
Q

What takes place in displacement reactions?

A
  • More reactive metals form a cation (+) as they displace the less reactive metal, losing electrons and therefore being oxidised (Oxidation Is Loss of electrons), it forms an ion as it replaces the less reactive metal in the salt solution
  • Less reactive metals form atoms from negative ions as they are displaced, gaining electrons and therefore being reduced (Reduction Is Gain of electrons), it forms an atom as it is replaced in the salt solution
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11
Q

What allows a displacement reaction to take place?

A

for a displacement react to occur the element must be more reactive than the element in the compound it wants to displace

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12
Q

Displacement:

A

a chemical reaction in which a more reactive element displaces a less reactive element from its compound

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13
Q

What happens when aluminium and iron (III) oxide react together?

A
  • when these 2 substances react (rect violently) there is a bright yellow flame and pure iron is formed
  • Al2O3 is formed
  • v. exothermic
  • Al more reactive than Fe so displaces Fe in Fe2O3
  • Al oxidised and Fe is reduced
  • displacement and redox reaction
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14
Q

What happens when copper and silver nitrate react together?

A
  • v. exothermic
  • high activation E so takes some time for reaction to start
  • rapid reaction
  • bright yellow flame
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15
Q

Redox reaction:

A

a reaction in which oxidation and both reduction occur simultaneously

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16
Q

The reactivity series:

A
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17
Q

Reactivity series:

A
  • a series in which metals are arranged in order of their reactivity
  • can be used to predict products from reactions
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18
Q

What is shown when a metal reacts with water and a dilute acid?

A

these reactions show the relative tendency of metal atoms to form cations

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19
Q

What is the reactivity of a metal related to?

A

reactivity of a metal is related to its tendency to form positive ions- more reactive metals can form positive ions more easily

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20
Q

Where are most metals extracted from?

A

most metals extracted from ores found in the Earth’s crust

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21
Q

How are unreactive metals found?

A

unreactive metals are found in the Earth’s crust as the uncombined elements

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22
Q

Ore:

A

rock that contains enough of the desired metal in it to make it economical to extract

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23
Q

What does the reactivity of a metal determine?

A

the reactivity of a metal determines how it can be extracted from its ore

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24
Q

How are the most unreactive metals found?

A
  • most unreactive metals found natively as the free, uncombined element
  • these metals are most resistant to oxidation and just need to be separated from the rock by a physical method
  • other metals have to be extracted from their ores by chemical extractions
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25
Q

Which metals were among the first to be discovered and why?

A
  • copper, silver, gold and platinum
  • as they exist natively in the environment so do not have to react with anything to gain pure sample of metal
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26
Q

Explain why metals like aluminium and calcium were not discovered until the 19th C:

A

exist in ore and does not occur natively

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27
Q

Oxidation:

A

reaction involving gain of oxygen, loss of electrons

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28
Q

Reduction:

A

reaction involving loss of oxygen, gain of electrons

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29
Q

Oxidising agents:

A
  • substance that cause other substances to be oxidised i.e. provide oxygen to the other substance
  • when an oxidising agent oxidises something - it loses electrons i.e. is positive
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30
Q

Reducing agents:

A
  • substances that cause another substance to be reduced i.e. to remove oxygen from the other substance
  • when a reducing agent reduces something it loses electrons i.e. is positive
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31
Q

How can metals be extracted?

A

metals can be extracted by reduction through carbon and by electrolysis

32
Q

How expensive is carbon and how accessible is it?

A

carbon is cheap and is easily obtained

33
Q

What metals can carbon be used to reduce?

A

zinc, iron, tin and lead

34
Q

Reduction with carbon:

A
  • process used to extract metals from their oxides when the metal is less reactive than carbon
  • the metal oxide is heated with carbon so that carbon reduces the metallic element
35
Q

How does carbon reduce metals?

A
  • Metals less reactive than carbon:
    • Can be extracted from their oxides by reduction with carbon
    • Reduction involves the loss of oxygen, so are reducing the ores to remove the oxygen to obtain the pure metal
36
Q

What is carbon said to be?

A
  • reducing agent - substance that takes oxygen or gives electrons (it itself is oxidised)
37
Q

Extraction of iron by heating it with carbon:

A
  • Iron oxide loses oxygen, and is therefore reduced
  • The carbon gains oxygen, and is therefore oxidised
  • 2Fe2O3(s)+3C(s)->4Fe(l)+3CO2(g)
  • For iron, this is carried out at high temperatures in a blast furnace
38
Q

Method for extracting copper from copper oxide using reduction by carbon:

A
  1. Collect an ignition tube filled with copper oxide and carbon powders
  2. Attach test tube clips at the top of the tube and heat it using the hottest Bunsen flame for at least 5 mins
  3. After 5 mins empty the mixture on to a ceramic mat and check for any signs of copper
39
Q

Safety for extracting copper from copper oxide using reduction by carbon:

A
  • have the tube at a 45 degrees angle when heating
  • do not point the mouth of the tube at anybody
  • gently shake the tube to allow trapped air pockets to escape
40
Q

Extracting copper from copper oxide: What did the copper oxide and carbon mixture look like?

A

black powder

41
Q

Extracting copper from copper oxide: How could you tell if there was copper present at the end?

A

if there was a brown/orange colour

42
Q

Extracting copper from copper oxide: Write a word equation for the reaction. Copper oxide has the formula of CuO. Bearing this in mind write a symbol equation as well:

A

Cu + C —> Cu + CO

43
Q

Extracting copper from copper oxide: Explain why this reaction works:

A

carbon more reactive than copper so displaces it in the compound of oxygen

44
Q

When can a metal be extracted by carbon?

A

can only be extracted by reduction of carbon if metal is less reactive so that carbon displaces the metal from the ore

45
Q

Electrolysis:

A
  • the splitting of an ionic compound using electricity
  • the electric current is passed through a substance causing chemical reactions at the electrodes which leads to the decomposition of the materials
  • electrolysis is used for metal extraction if the metal is more reactive than carbon
46
Q

When is electrolysis used?

A

If more reactive than carbon, electrolysis can be used (metals less reactive than carbon can also be extracted this way)

47
Q

What other metals can be extracted by electrolysis?

A

Metals that react with carbon can be extracted by electrolysis as well

48
Q

Why is electrolysis expensive?

A

Electrolysis is expensive due to the use of large amounts of energy to melt the compounds and to produce the electrical current (so you wouldn’t extract a metal using electrolysis if it could be done more cheaply using carbon)

49
Q

How does electrolysis work?

A
  • compounds that contain a metal and a non-metal are ionic compounds
  • the metal ion is positive - cation
  • the non-metal is negative - anion
  • the metal compound is melted by heating it and an electric current is passed through via 2 electrodes
  • the positive electrode is called the anode
  • the negative electrode is called the cathode
  • the positive ions (cations) are attracted to the negative electrode (cathode)
  • the electrode is negative because it has surplus of electrons
  • here, the metal ions gain electrons to make the metal
  • the negative ions (anions) are attracted to the positive electrode (the anode)
  • here, the non-metal element is made by losing electrons
50
Q

Electrolysis diagram:

A
51
Q

How is aluminium extracted?

A
  • aluminium is a reactive metal that is more reactive than carbon and has to be extracted by electrolysis
  • aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode (anode)
  • aluminium is mixed with a substance called cryolite and melted
  • electrodes are inserted into the mixture and a large current is passed through it
52
Q

In aluminium oxide what is the symbol of the cation?

A

Al³⁺

53
Q

In aluminium oxide what is the symbol of the anion?

A

O²⁻

54
Q

Extraction of aluminium using electrolysis: At what electrode is the aluminium produced at?

A

cathode

55
Q

Extraction of aluminium using electrolysis: Write a half equation for the reaction that takes place at the cathode and what type of reaction takes place there:

A
  • Al³⁺ + 3e⁻ ——> Al
  • reduction
56
Q

Extraction of aluminium using electrolysis: What substance is made at the anode?

A

oxygen

57
Q

Extraction of aluminium using electrolysis: Write a half equation for the reaction at the anode and what reaction takes place there:

A

2O²⁻ ——> O₂ + 4e⁻

58
Q

Extraction of aluminium using electrolysis: What is usually melted for other reactive metals that need to be extracted by electrolysis?

A
  • for other reactive metals that need to be extracted using electrolysis
  • it is usually the chloride that is melted
59
Q

What is phytomining/phytoextraction?

A
  • some plants absorb metal compounds through their roots
  • a plant is chosen that will absorb the desired metal from the soil without dying (these plants are called (hyperaccumulaters)
  • the plans are grown and then concentrate the desired metal/compound into their shoots and leaves
  • after harvesting, these plants are burned
  • the ash contains metals compounds from which the metal can be extracted
60
Q

Advantages of phytomining/phytoextraction compared to traditional methods:

A
  • allows metal to be extracted from poor quality sources
  • can generate electricity by burning plant
  • less environmental damage (no hole in ground)
  • cheap and less wasteful
  • carbon neutral-ish
61
Q

Disadvantages of phytomining/phytoextraction compared to traditional methods:

A
  • slow process
  • space intensive
  • inefficient = small amounts of metal from plant extracted
  • farming costs - irrigation
  • plant habitat incompatibility
62
Q

What is bacterial extraction/bioleaching?

A
  • some bacteria absorb metal compounds
  • uses bacteria to produce leachate solutions that contain metal compounds
  • scrap iron can be used to obtain the metal from the leachate
63
Q

Example of bacterial extraction/bioleaching:

A

bacteria can be used to convert insoluble copper sulphide into soluble copper sulphate which can be dissolved in water and extracted from the solution

64
Q

Advantages of bacterial extraction/bioleaching compared to traditional methods:

A
  • less environmental damage
    • no large mine
    • don’t need acids or cyanides (harmful chemicals)
  • cheap
    • don’t need as much hazard protection
    • not using heavy machinery
  • v. small carbon footprint
    • not using expensive machinery
  • sustainable and can extract from soil that has very little of desired material
65
Q

Disadvantages of bacterial extraction/bioleaching compared to traditional methods:

A
  • low yield
  • v. slow
  • not v. profitable
66
Q

How is a metal’s relative resistance to oxidation related to its position in the reactivity series?

A
  • Relative resistance to oxidation is the same as relative resistance to losing electrons / forming positive metal ions
  • less reactive a metal is, the more resistant it is to oxidation, because for a metal to react, it forms a positive metal ion by losing electrons (loss of electrons=oxidation)
67
Q

What is the Earth’s population doing at an alarming rate?

A

consuming the planet’s resources at an alarming rate

68
Q

Economic and environmental benefits of recycling:

A
  • saves energy as it requires less energy to melt and remould metals than it does to extract new metals from their ores
  • mining ores is bad for the environment as large quarries are created, which produce noise pollution and dust - habitat destruction
  • recycling allows for waste metals to be reused, saving money, helping the environment and the supply of valuable raw materials (meaning metal ores will last longer)
  • reduces volume of waste → less landfill sites needed
  • can be cheaper e.g. lower cost for recycling Al than extracting Al
  • recycling can preserve both environment and the supply of valuable raw materials
  • less waste separated
  • less CO2 produced
  • conserves reserves
69
Q

Why might some metals be more expensive?

A

more expensive to extract as they have smaller reserves left

70
Q

What problems might arise from recycling pure metals from their alloys?

A

alloying metals makes them harder to separate and recycle

71
Q

What does a life-cycle assessment involve?

A

involves the consideration of the effect on the environment of obtaining the raw materials, manufacturing the product, using the product and disposing of the product when it is no longer useful

72
Q

Key features of a life-cycle assessment:

A
  • the main equipment for energy input
  • the environmental impact and sustainability of making the materials from natural resources
  • the environmental impact of making the product from the material
  • the environmental impact of using the product
  • the environmental impact of disposing the product by incineration, landfill or recycling
73
Q

What can easily be quantified in a life-cycle assessment?

A

Use of water, resources, energy sources and production of some wastes can be fairly easily quantified

74
Q

What is less straight-forward in life-cycle assessments?

A
  • Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LTA (life time assessment) is not a purely objective process
  • Selective or abbreviated LTAs can be devised to evaluate a product but these can be misused e.g. in support of claims for advertising purposes
75
Q

A building company is considering making window frames from aluminium or wood. Create life-cycle assessments for these 2 possibilities and decide which would be better for the environment:

A

Aluminium

  • bauxite —> mined from ground
  • extracted using electrolysis
    • lots of electricity/energy needed
  • Al windows will last longer than wood windows
  • disposal —> can be recycled but needs some energy input
    • if dumped will not rot

Wood

  • trees can be replaced —> sustainable resource
  • low E costs for processing
    • needs to sawed and painted
  • will not last as long as Al
  • disposal —> could be recycled if wood is not rotten
    • if dumped wood will rot

Conclusion

  • therefore wood would be better for the environment but its use might depend on other factors
    • e.g. weight, strength, cost etc.

GCSE Chemistry 2 (29 decks)

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