Uses of metals
Most metals in everyday use are alloyAn alloy is a mixture of two or more elements, at least one of which is a metal.. An alloy is a mixtureTwo or more substances that are not joined together. The substances can be elements, compounds, or both. of two or more elementA substance made of one type of atom only., where at least one element is a metalShiny element that is a good conductor of electricity and heat, and which forms basic oxides.. Many alloys are mixtures of two or more metals.
Copper alloys
Bronze was the first alloy to be made by humans, around 6000 years ago. Bronze is an alloy of copper and tin. Nowadays, bronze is used to make statues, bells and coins.
Brass is an alloy of copper and zinc, and is used to make musical instruments, door knobs, locks and taps.
Gold
Gold is a very soft and malleableCapable of being hammered or pressed into a new shape without being likely to break or return to the original shape. metal. It is also very unreactiveA substance is unreactive or inert if it does not easily take part in chemical reactions., so it resists corrosionWhen chemicals in the water dissolve minerals in the rocks, causing them to break up (also called solution). and stays shiny. The visors on space helmets are coated with a layer of gold. This is thin enough for the astronaut to see through but thick enough to reflect sunlight.
The gold used for jewellery is gold alloyed with other metals, often silver, copper and zinc. This makes the jewellery much stronger while keeping its ability to stay shiny. The proportion of gold in the alloy is measured in carats, with 24 carat gold being pure gold. The percentage of gold in different gold alloys is summarised in the table below.
| Carat of gold | Percentage of gold in the alloy |
| 24 | 100% |
| 18 | 75% |
| 12 | 50% |
| 9 | 37.5% |
| Carat of gold | 24 |
|---|---|
| Percentage of gold in the alloy | 100% |
| Carat of gold | 18 |
|---|---|
| Percentage of gold in the alloy | 75% |
| Carat of gold | 12 |
|---|---|
| Percentage of gold in the alloy | 50% |
| Carat of gold | 9 |
|---|---|
| Percentage of gold in the alloy | 37.5% |
Question
A piece of gold jewellery is made from 14 carat gold. Calculate the percentage of gold in this alloy.
(14 梅 24) x 100 = 58%
Alloy steels
alloy steelAlloy produced by mixing iron with one or more other metals. are alloys of iron that contain specific amounts of carbon (a non-metal) and certain metal elements. Different steels have different propertiesThe characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point., depending on their composition. The table shows three common examples.
| Alloy steel | Elements in addition to iron | Properties |
| High carbon steel | Carbon | Strong, brittle |
| Low carbon steel | Carbon | Softer, more easily shaped |
| Stainless steel | Chromium and nickel | Hard, resistant to rusting |
| Alloy steel | High carbon steel |
|---|---|
| Elements in addition to iron | Carbon |
| Properties | Strong, brittle |
| Alloy steel | Low carbon steel |
|---|---|
| Elements in addition to iron | Carbon |
| Properties | Softer, more easily shaped |
| Alloy steel | Stainless steel |
|---|---|
| Elements in addition to iron | Chromium and nickel |
| Properties | Hard, resistant to rusting |
High carbon steels are used for construction because of their strength. Low carbon steels are used for making car body panels because they are malleable. Stainless steel is used for cutlery because it does not rust.
Question
Explain why stainless steel is used to make washing machines and dishwashers.
Washing machines and dishwashers contain water. This would cause other steels to rust, but stainless steel does not rust.
Aluminium and magnalium
Aluminium does not react with water. Its surface is protected by a natural layer of aluminium oxide that allows the metal to resist corrosion. Aluminium foil is used in the home for wrapping and storing food because it does not react to substances in food. It is malleableCapable of being hammered or pressed into a new shape without being likely to break or return to the original shape., so it is easily folded into shape around the food.
Aluminium has a low densityA measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3)., so pieces of aluminium are relatively lightweight. Magnalium is an alloy of aluminium and magnesium. It is stronger than aluminium alone but still has a low density. It is used to make aircraft parts.
Question
Suggest an explanation for why aluminium is used to make overhead electricity cables.
Aluminium is a good electrical conductorA material which allows charge to move easily through it.. Its low density prevents the wires from sagging too much or breaking under their own weight.