Using matter: minerals and quick revision

4.1 Matter at work

Elements, compounds and mixtures fill our daily world. Air is a mixture of gases, water is a compound of hydrogen and oxygen, and iron and aluminium are elements used to build bridges, buildings and vehicles. Chemists study how elements combine to make medicines and vaccines, and how compounds can be used to make fertilisers that improve crop production.

Engineers and material scientists use mixtures and compounds to design materials with useful properties. Stainless steel is an alloy developed to be stronger and more durable than pure iron, and wood, steel and concrete are all mixtures used in construction. This is the practical value of knowing whether a material is an element, a compound or a mixture: the classification points to how it behaves and how it can be used.

4.2 Graphene aerogel

One remarkable modern material is graphene aerogel, made from carbon. It is described as the lightest material known, so light that a blade of grass can hold a piece of it. It is highly porous, which gives it a large absorbing capacity. Because of this, it could serve as a cleaner for the environment, soaking up oil spills at sea and on land, and it is also being studied for special coatings on buildings and for energy-saving devices.

4.3 Minerals

Most rocks are mixtures of minerals, which can be seen with the eyes or with a magnifying glass or microscope. Some minerals are native minerals, pure elements that occur in nature: gold, silver and copper are metals, while sulfur and carbon are non-metals. Most minerals are compounds made of more than one element. Quartz, calcite, mica, pyroxene and olivine are common examples.

Many useful materials come from minerals. Cement comes from calcite, quartz, alumina and iron oxide, and talc, a mineral, is used to make talcum powder. Understanding minerals therefore connects the chemistry of elements and compounds with the materials of everyday life.

4.4 Matter and what is not matter

If something has mass and occupies space, it is matter. Elements and compounds are its building blocks, and mixtures are combinations of them. Light, heat and electricity are real parts of our world, and thoughts and emotions matter to us, but they are not made of matter. Keeping the distinction clear helps when classifying the things around us.

4.5 Dhokra art

The Dhokra art of Bihar and Odisha uses metals to create figures inspired by nature. A design is first shaped in beeswax, then encased in clay to form a mould. Once the clay sets, the wax is melted away and a hollow space remains, which is filled with molten brass or bronze. The metal gives the figure strength and a shiny golden colour, and the figures often take animals, people and nature as subjects.

4.6 Common mistakes to avoid

• Treating a mixture as a compound: in a mixture the components keep their properties and can be separated physically.
• Thinking a compound can be separated by a magnet or by evaporation: the elements inside a compound are joined chemically.
• Reading pure on a packet as scientific purity: in science, a pure substance has only one kind of particle.
• Saying air is a compound: air is a uniform mixture of gases.
• Calling water an element: water is a compound of hydrogen and oxygen.
• Believing the components of a mixture lose their properties: they keep their own properties.
• Assuming every mineral is a compound: native minerals are pure elements such as gold, silver, copper, sulfur and carbon.
• Forgetting that light, heat and electricity are not matter, even though they are real.