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Z Chemistry GCSE > Metals > Flashcards

Metals Flashcards

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1
Q

What is a native metal?

A
  • When a metal exists naturally as the uncombined element
  • Very unreactive metals (e.g. gold and rarely silver and copper)
  • Most metals that are unreactive do not tend to form compounds with other elements. Unreactive metals such as gold are found uncombined
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2
Q

What is an ore?

A
  • Most metals do react with other elements to form compounds, which can be found naturally in the Earth’s crust
  • If a compound contains enough of the metal to make it worthwhile extracting, the compound is called a metal ore
  • There are limited amounts of metal ores and they are finite resources
  • The more reactive a metal is, the harder it is to extract it from a compound
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3
Q

What is the process called in which some ores can be converted into an oxide by heating in air?

A

Roasting

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4
Q

How do you remove the oxygen from the metal?

A
  1. Lots of common metals, like iron and aluminium, react with oxygen to from oxides and these oxides are often the ores that the metals need to be extracted from
  2. A reaction that separates a metal from the oxygen in its oxide is called a Reduction Reaction
  3. In a reduction reaction, the substance that reduces the metal (and is oxidised) is called the reducing agent
  4. The most common type of reduction reaction uses carbon as a reducing agent to separate the oxygen from the metal
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5
Q

What are the three methods of the extraction of metals?

A
  1. Native metals
  2. Smelting/reduction (usually with carbon) (Zinc, Iron, Tin)
  3. Electrolysis (VERY expensive) with stable ores (aluminium-potassium)
    E.G. Carbon may use reduction but for cooper wire it needs to be very pure so will use electrolysis
    Sometimes two methods are needed
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6
Q

Describe the properties of iron

A
  • Moderatley reactive
  • Most commonly used metal
  • Ships, bridges, iron nails, cars
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7
Q

What is an iron ore called?

A

A haematite: it contains Fe and Fe2O3 and can be extracted by reduction with carbon in a blast furnace

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8
Q

What are the raw materials in the Extraction of Iron?

A
  1. Haematite (iron ore)
  2. Coke
  3. Air
    - Coke and air react together to form the reducing agent, carbon monoxide
  4. Limestone: removes silicon dioxide (sand), an acidic impurity form haematite, to from a waste material called “molten slag”
    - All happens in a blast furnace
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9
Q

How is molten slag formed and what are the uses of molten slag?

A
  • Chemical name: Calcium silicate
  • Floats so is less dense and can be scraped off
  • When cooled it is a solid, and is used for building, road-building and fertiliser
    1. The limestone is decomposed by the heat into calcium oxide and CO2
    2. The calcium oxide then reacts with the sand to form calcium silicate, or slag, which is molten and can be tapped off
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10
Q

Describe reduction

A
  1. The ore is heated with carbon monoxide

2. Only metals that are less reactive than carbon can be extracted by a reduction reaction with carbon

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11
Q

Describe the process of Aluminium extraction

A
  1. Impure bauxite is mined from the ground
  2. Pure bauxite (white powder, aluminium oxide) is separated from the other rocks
  3. Another mineral called cryolite is mined and purified
  4. Cryolite is heated until it melts
  5. Bauxite is dissolved in the liquid cryolite
  6. Electricity is passed through the molten mixture
  7. Aluminium metal collects at one electrode and oxygen gas bubbles are given off at the other
  8. Oxygen then reacts with the carbon anode to form carbon dioxide gradually wearing away the anode
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12
Q

Why is the molten cryolite used in Aluminium extraction?

A
  • The molten cryolite as a solvent is used to decrease the required operating temperature
  • Aluminium oxide has a very high melting point of over 2000 degrees, so melting it would be very expensive
  • Cryolite (a less common ore of aluminium) brings the temperature down to about 900 degrees which makes it much cheaper and easier
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13
Q

Why are the electrodes made of graphite?

A

They are a good conductor of electricity

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14
Q

What are the negative impacts of using electrolysis?

A
  1. Electrolysis uses a lot of electricity which is expensive
  2. Energy is also needed to heat the electrolyte mixture to 900 degrees, which is also expensive
  3. As the anode wears away it needs replacing which costs money as well
    - However now aluminium now comes out as a reasonably cheap and widely-used metal. A hundred years ago it was a very rare metal, simply because it was so hard to extract
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15
Q

What properties do Aluminium and Iron have in common?

A
  1. They are both dense and lustrous
  2. They both have high melting points (Iron: 1538 degrees and Aluminium: 660 degrees)
  3. They both have a high tensile strength, they are strong and hard to break
  4. But both malleable
  5. They are both good conductors of electricity and heat energy
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16
Q

Describe cast iron and its uses

A
  1. When molten iron is cooled it is called pig iron and if the pig iron is remelted and cooled under controlled conditions it is called cast iron
  2. Cast iron is very impure with iron, carbon (4%) and silicon
  3. It is very hard but brittle
  4. It is used for manhole covers, guttering and drainpipes and cylinder blocks in car engines and some cooking pans
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17
Q

Describe mild steel and its uses

A
  1. Iron containing about 0.25% carbon and this small amount of carbon increases the hardness and strength of the carbon but it can still be hammered easily into sheets and welded together
  2. Steel is an alloy made of iron, carbon and (usually) some other metals
    - Steel has more useful properties than iron e.g. it is harder than pure iron but can still be hammered easily into sheets and welded together
  3. It is used for making car bodies, girders (for construction) , wire, nails, ship building and bridges
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18
Q

Describe wrought iron and its uses

A
  1. Almost pure iron

2. It is malleable so is used to make ornamentals gates and railings

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19
Q

What is the main problem with iron?

A

Corrodes easily (rusts)

20
Q

Describe high-carbon steel and its uses

A
  1. 0.25-1.5% carbon
  2. Increasing the carbon content makes the iron harder but at the same time it gets more brittle
  3. It is used for cutting tools and masonry nails
21
Q

Describe stainless steel and its uses

A
  1. Alloy of iron with chromium and nickel, which form strong oxide layers and these protect the iron and so stainless steel is very resistant to corrosion
  2. It is therefore used for cutlery (knives and forks), kitchen sinks, saucepans and major uses for it in the brewing, dairy and chemical industries.
22
Q

Describe Aluminium and its uses

A
  1. Passive oxide layer means that it does not corrode easily and so is useful for products that come into contact with water e.g. used in drinks cans
  2. Less dense than iron so is lighter, this makes it useful when the weight of the metal is important, e.g. in bicycle frames and aeroplanes
  3. Pure aluminium is not very strong, but can be strengthened by adding other elements such as silicon, copper or magnesium (aluminium alloy)
  4. Aluminium’s uses depend on (its):
    - Low density
    - Strength (when alloyed)
    - Ability to conduct electricity and heat
    - Its appearance
    - Its ability to resist corrosion
23
Q

How are methods of extraction linked to the order of reactivity?

A
  1. Only metals that are less reactive than carbon can be extracted by a reduction reaction with carbon, this is done by heating the ore with carbon monoxide
  2. This is because more reactive elements form compounds more readily. Carbon is more reactive than iron, so carbon ‘steals’ oxygen from the iron oxide. I can also remove oxygen from zinc oxide and tin oxide
    - CARBON IS PLACED UNDER ALUMINIUM AND ABOVE ZINC IN THE REACTIVITY SERIES
  3. Carbon can only take oxygen away from metals which are less reactive that carbon itself
24
Q

How are metals, above carbon, extracted?

A
  1. Very reactive metals form very stable ores, and so it is difficult to get the metal out of its compound
  2. So metals that are more reactive than carbon (they come higher in the reactivity series)have to be extracted using electrolysis
  3. Electrolysis uses electricity to separate the metal from the other elements in the compound
25
Q

What is the manufacture of ammonia usually referred to?

A

The Haber process

26
Q

What are the raw materials in the manufacture of ammonia and where do they come from?

A
  1. Nitrogen, from the air

2. Hydrogen, from natural gas or the cracking of hydrocarbons

27
Q

What conditions are needed for the manufacture of ammonia by the Haber process?

A
  1. Temperature of about 450 degrees Celsius
  2. Pressure of about 200 atmospheres
  3. Iron catalyst
28
Q

What sort of reaction is the Haber process? What si the equation?

A
  • The reaction is reversible
  • Not all of the hydrogen and nitrogen will convert to ammonia
  • The reaction reaches a dynamic equilibrium
  • N2 (g) + 3H2 (g) (reversible reaction arrow) 2NH3 (g) (+heat)
29
Q

What does the cooling of the reaction mixture do in the Haber process?

A

Liquefies the ammonia produced and allows the unused hydrogen and nitrogen to be recirculated

30
Q

Why was that temperature chosen for the Haber process?

A
  • about 450 degrees Celsius (relatively high)
    1. If the temperature was lower the yield would increase but the rate of reaction would decrease and shift to the RHS (rate too slow)
    2. If the temperature was higher the yield would decrease but the rate of reaction would increase and shift to the LHS (too little yield)
31
Q

Why was that pressure chose for the Haber process?

A
  • about 200-250 atmospheres (relatively high)
    1. Higher pressure would be too expensive and potentially dangerous
    2. Lower pressure would decrease the yield and decrease the rate of reaction, shift to the LHS
32
Q

Why was that catalyst chosen for the Haber process?

A
  • It provides an alternative route with a lower activation energy
  • Allows rate of reaction to increase with a lower temperature (cheaper than using a higher temperature because does not get used up)
33
Q

Why did they choose to remove the ammonia in the Haber process?

A

-Will increase the yield because it shifts the equilibrium to the RHS (not affect on the rate)

34
Q

What is the forward reaction in the Haber process?

A

Exothermic, negative deltaH (-92 KJ/mol)

35
Q

What are the uses of ammonia?

A
  1. Used to make nitric acid: as ammonia is used in the Ostwald process to make nitric acid (HNO3)
  2. Fertiliser: as if you react ammonia with nitric acid, you get ammonium nitrate which is a good fertiliser because it has nitrogen from two sources, the ammonia and the nitric acid (kind of a double dose). Plants need nitrogen to make proteins
    - Ammonium nitrate is a much more effect fertiliser than organic alternatives (e.g. pig poo), so it helps farmers produce crops from land that otherwise would not have been fertile enough
  3. Making nylon
36
Q

What raw materials are used in the manufacture of sulphuric acid? (the contact process)

A
  1. Sulphur from oil refineries

2. Air (oxygen from the air) is used

37
Q

What is stage 1 in the contact process?

A
  • Oxidation
  • S + O2 —> SO2
  • Done by burning sulphur in air or roasting sulphur ores
38
Q

What is stage 2 in the contact process?

A
  • Oxidation
  • 2SO2 + O2 (reversible reaction arrow) 2SO3
  • Exothermic, -deltaH, -196KJ/mol
39
Q

What is stage 3 in the contact process?

A
  • Sulphur trioxide is dissolved in concentrated sulphuric acid to from liquid oleum
  • SO3 + H2SO4 –> H2S2O7
  • Oleum is then diluted with measured amounts of water to form concentrated sulphuric acid
  • H2S2O7 + H2O –> 2H2SO4
40
Q

Why is it ok to use sulphuric acid in the contact process?

A

Fore very 1 mole of H2SO4 used, 2 moles of H2SO4 are formed

41
Q

What conditions are used in stage 2 of the contact process?

A
  1. Temperature: about 450 (400-450) degrees Celsius
  2. Pressure: about 2 atmospheres
  3. Catalyst: Vanadium (V) oxide (V2O5)
42
Q

Why is that temperature chosen in stage 2 of the contact process?

A
  • Relatively low so that it shifts to the exothermic reaction 1. If temperature too high then would decrease yield. because then shift to LHS
    2. If temperature too low then rate of reaction would be too slow
43
Q

Why is that pressure chosen in stage 2 of the contact process?

A
  • Relatively high as less gaseous molecules on the RHS
    1. If pressure too high would be too expensive and potentially dangerous
    2. If pressure too low yield would be too low as then shift to LHS
44
Q

Why is a catalyst used in stage 2 of the contact process?

A

Increases rate of reaction by providing an alternative route with a lower activation energy and does not affect yield

45
Q

What are the uses of sulphuric acid?

A
  1. Fertilisers: Sulphuric acid is mostly used to make phosphate fertilisers. Farmers use them to improve the amount of nutrients in the soil, and this increases plant growth
  2. Detergents: used for cleaning just about anything and everything
  3. Paints: sulphuric acid is used to make titanium dioxide, which is a white pigment that is used in paints and for drawing white lines on tennis courts

Z Chemistry GCSE (16 decks)

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