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Stainless steel contains chromium and nickel, brass is copper and zinc, and bronze is copper and tin. Free notes with key terms and 14 questions answered.
Common Alloys and Their Properties is part of Using materials (chemistry only) in GCSE AQA Higher Chemistry.
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Stainless steel contains chromium and nickel, brass is copper and zinc, and bronze is copper and tin. Free notes with key terms and 14 questions answered.
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Use this lesson to stay inside Using materials (chemistry only) while connecting the detail back to the wider Topic 10: Using resources topic.
Read the core explanations from Common Alloys and Their Properties before testing yourself from memory.
Look around you right now. That spoon in your kitchen? It's not pure iron. Your bike frame? Not pure aluminium. The coins in your pocket? Definitely not pure copper. Here's the thing that catches most students off guard: most metals in everyday use are alloys, not pure metals.
Pure metals have a problem. They're often too soft, too weak, or too reactive for real-world jobs. Iron rusts. Pure gold bends like butter. Aluminium corrodes. But mix them with other elements, and suddenly you get materials that can build skyscrapers, survive space missions, and last for decades.
Copper was one of the first metals humans used, but pure copper has limitations. It's soft and not particularly strong. Ancient metalworkers discovered that mixing copper with other metals created superior materials.
Bronze revolutionised human civilisation so much that we named an entire historical period after it. It's harder than pure copper and doesn't corrode as easily. Brass, meanwhile, looks like gold but costs far less, making it perfect for decorative applications and musical instruments like trumpets and saxophones.
Gold jewellery is often made as an alloy with other metals to make it harder and more durable.
Adding other metals makes gold harder and more durable.
Worked example: Calculating Gold Percentage in Jewellery
Why are gold alloys harder than pure gold? [2 marks]
Answer: 37.5% gold
The other metals in gold alloys aren't just fillers. Copper gives gold a reddish tint (rose gold), while white gold is usually made by alloying gold with metals such as nickel or palladium. These additions also make the jewellery much more resistant to scratching and bending.
Steel isn't just one alloy - it's a whole family. All steels are alloys of iron containing specific amounts of carbon and other metals. But here's where it gets interesting: tiny changes in carbon content create dramatically different materials.
Think of carbon atoms like tiny reinforcement bars in the iron structure. A few carbon atoms make the steel stronger. Too many, and the steel becomes brittle - strong but likely to snap under stress.
But the steel story doesn't end with carbon. Add chromium and nickel, and you get stainless steel - hard and resistant to corrosion. This is why your kitchen sink doesn't rust, even though it's made of iron-based steel.
Pure aluminium has one amazing property: it's incredibly light. But it also has a problem - it's not particularly strong. Aluminium alloys solve this by mixing aluminium with small amounts of other metals like copper, magnesium, or silicon.
The result? Materials that are still low density but much stronger. This combination of lightness and strength makes aluminium alloys perfect for aircraft, where every kilogram matters. A Boeing 747 is about 80% aluminium alloy.
Examiners love testing alloys because they combine chemistry knowledge with real-world applications. Here's how to nail these questions every time.
Remember the examiner's favourite trick: they'll give you a scenario and ask you to suggest the best alloy. Always justify your choice by linking the alloy's properties to the job requirements. 'Bronze for ship propellers because it's corrosion resistant in seawater' wins more marks than just 'bronze'.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Stainless steel is iron-based steel with chromium and nickel added, which makes it hard and resistant to corrosion. This is why a kitchen sink made of stainless steel does not rust.
Brass, an alloy of copper and zinc, is used in musical instruments such as trumpets and saxophones and for decorative items. It has a golden appearance and resists corrosion, and it looks like gold but costs far less.
Bronze, an alloy of copper and tin, is used for sculptures, ship propellers and musical instruments. It is harder than pure copper and does not corrode as easily, which is why it suits ship propellers in seawater.
Rose gold is gold alloyed with copper, which gives it a reddish tint, while white gold is usually made by alloying gold with metals such as nickel or palladium. These added metals also make the jewellery much more resistant to scratching and bending.
High carbon steel contains 0.6-1.5% carbon, which makes it strong but brittle, and it is used for cutting tools and springs. Too many carbon atoms make steel likely to snap under stress, so it is not used where shaping is needed.
Low carbon steel contains less than 0.3% carbon, which makes it softer and more easily shaped, so it is used for car bodies and construction. It is less brittle than high carbon steel, which contains 0.6-1.5% carbon.
High carbon steel contains 0.6-1.5% carbon, making it strong but brittle, so it is used for cutting tools and springs. Low carbon steel contains less than 0.3% carbon, making it softer and more easily shaped, so it is used for car bodies and construction.
Most metals in everyday use are alloys because pure metals are often too soft, too weak or too reactive for real-world jobs. An alloy is a mixture of a metal with one or more other elements, usually other metals or carbon, that has different properties from the pure metal.
9 carat gold is 37.5% gold. Since 24 carat is 100% gold, the percentage is 9 × 100 ÷ 24 = 900 ÷ 24 = 37.5%. The other metals in the alloy make the gold harder and more durable.
The percentage of gold in jewellery = carat ÷ 24 × 100, because 24 carat is 100% gold. For 9 carat gold, 9 × 100 ÷ 24 = 900 ÷ 24 = 37.5% gold.
24 carat gold means 100% pure gold, which is the definition of the carat system. Lower carat values contain other metals that make the gold harder and more durable, for example 9 carat gold is 37.5% gold.
Stainless steel does not rust because chromium and nickel are added to the iron, making it hard and resistant to corrosion. This is why a kitchen sink made of iron-based stainless steel does not rust.
Aluminium is mixed with small amounts of other metals such as copper, magnesium or silicon because pure aluminium is light but not particularly strong. The resulting aluminium alloys are still low density but much stronger, which makes them perfect for aircraft: a Boeing 747 is about 80% aluminium alloy.
Gold jewellery is made as an alloy because pure gold is too soft and bends easily. Adding other metals makes gold harder and more durable, and the added metals can also change its colour, such as copper giving rose gold a reddish tint.