Metals Flashcards
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
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
3
Q
What is the process called in which some ores can be converted into an oxide by heating in air?
A
Roasting
4
Q
How do you remove the oxygen from the metal?
A
- 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
- A reaction that separates a metal from the oxygen in its oxide is called a Reduction Reaction
- In a reduction reaction, the substance that reduces the metal (and is oxidised) is called the reducing agent
- The most common type of reduction reaction uses carbon as a reducing agent to separate the oxygen from the metal
5
Q
What are the three methods of the extraction of metals?
A
- Native metals
- Smelting/reduction (usually with carbon) (Zinc, Iron, Tin)
- 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
6
Q
Describe the properties of iron
A
- Moderatley reactive
- Most commonly used metal
- Ships, bridges, iron nails, cars
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
8
Q
What are the raw materials in the Extraction of Iron?
A
- Haematite (iron ore)
- Coke
- Air
- Coke and air react together to form the reducing agent, carbon monoxide - Limestone: removes silicon dioxide (sand), an acidic impurity form haematite, to from a waste material called “molten slag”
- All happens in a blast furnace
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
10
Q
Describe reduction
A
- 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
11
Q
Describe the process of Aluminium extraction
A
- Impure bauxite is mined from the ground
- Pure bauxite (white powder, aluminium oxide) is separated from the other rocks
- Another mineral called cryolite is mined and purified
- Cryolite is heated until it melts
- Bauxite is dissolved in the liquid cryolite
- Electricity is passed through the molten mixture
- Aluminium metal collects at one electrode and oxygen gas bubbles are given off at the other
- Oxygen then reacts with the carbon anode to form carbon dioxide gradually wearing away the anode
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
13
Q
Why are the electrodes made of graphite?
A
They are a good conductor of electricity
14
Q
What are the negative impacts of using electrolysis?
A
- Electrolysis uses a lot of electricity which is expensive
- Energy is also needed to heat the electrolyte mixture to 900 degrees, which is also expensive
- 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
15
Q
What properties do Aluminium and Iron have in common?
A
- They are both dense and lustrous
- They both have high melting points (Iron: 1538 degrees and Aluminium: 660 degrees)
- They both have a high tensile strength, they are strong and hard to break
- But both malleable
- They are both good conductors of electricity and heat energy
16
Q
Describe cast iron and its uses
A
- 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
- Cast iron is very impure with iron, carbon (4%) and silicon
- It is very hard but brittle
- It is used for manhole covers, guttering and drainpipes and cylinder blocks in car engines and some cooking pans
17
Q
Describe mild steel and its uses
A
- 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
- 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 - It is used for making car bodies, girders (for construction) , wire, nails, ship building and bridges
18
Q
Describe wrought iron and its uses
A
- Almost pure iron
2. It is malleable so is used to make ornamentals gates and railings
