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A mixture consists of two or more elements or compounds not chemically combined together. Free GCSE AQA notes with key terms and 10 questions answered.
What are mixtures and their properties is part of A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes in GCSE AQA Higher Chemistry.
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A mixture consists of two or more elements or compounds not chemically combined together. Free GCSE AQA notes with key terms and 10 questions answered.
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Use this lesson to stay inside A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes while connecting the detail back to the wider Topic 1: Atomic structure and the periodic table topic.
Read the core explanations from What are mixtures and their properties before testing yourself from memory.
Look around your kitchen right now. That cup of tea? It's a mixture. The air you're breathing? Also a mixture. But here's what's fascinating - even though these substances are mixed together, each one keeps its own identity completely unchanged.
This is the crucial difference between mixtures and compounds. In water ($H_2O$), hydrogen and oxygen are chemically bonded - they've lost their individual properties and created something entirely new. But in salt water, the salt stays salt and the water stays water. They're just hanging out together.
Here's the golden rule that defines every mixture: each substance keeps its own chemical properties. Think of it like a party where everyone keeps their own personality - the sugar in your tea is still sweet, the iron filings in sand are still magnetic, and the oxygen in air still supports combustion.
This is why you can separate mixtures using physical methods. Since nothing has chemically changed, you can use differences in physical properties to pull them apart again. Magnetic substances stay magnetic, soluble substances stay soluble, and dense substances stay dense.
Mixtures are everywhere, but they don't always look obvious. Air seems like one substance, but it's actually 78% nitrogen, 21% oxygen, and traces of other gases. Each gas keeps its own properties - oxygen still supports burning, nitrogen is still unreactive.
Some mixtures are clear and systematic to spot because you can see the different parts - like a salad or concrete. Others look uniform but are still mixtures - like brass (copper and zinc) or seawater (water, salt, and dissolved minerals).
Worked example: Identifying Mixtures vs Compounds
A student has four samples: pure water, salt water, carbon dioxide gas, and air. Which are mixtures?
Answer: Salt water and air are mixtures. Pure water and carbon dioxide are compounds.
Understanding that mixtures preserve individual properties is the key to separation techniques. Since each substance keeps its original characteristics, you can exploit these differences to separate them.
If one substance is magnetic and another isn't - use a magnet. If one dissolves in water and another doesn't - add water and filter. If one boils at a lower temperature - use distillation. The possibilities exist because the properties never changed in the first place.
Exam questions about mixtures often test whether you understand the fundamental difference between mixtures and compounds. The key phrase to remember is 'not chemically combined' - this appears in mark schemes repeatedly.
When describing separation methods, always explain why the method works by referring to the unchanged properties. For example: 'Iron filings can be separated using a magnet because iron remains magnetic in the mixture.'
Exam precision note: In What are mixtures and their properties - Mixtures - mixtures and how substances keep their own physical and chemical properties, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
In a mixture, the substances are together physically but not chemically bonded. That means each substance keeps its own chemical properties, so iron in a sulfur-and-iron mixture is still magnetic and sulfur still burns in air. Those unchanged properties are what make physical separation possible.
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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.
A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged; in salt water, the salt stays salt and the water stays water.
Air is a mixture of about 78% nitrogen, 21% oxygen and traces of other gases, with no chemical bonds between the different gases. Each gas keeps its own properties: oxygen still supports burning and nitrogen is still unreactive.
Chemical properties are the characteristics that determine how a substance reacts with other substances, such as flammability, reactivity with acids or the ability to support combustion. In a mixture, each substance keeps its chemical properties unchanged.
In a compound, elements are chemically bonded, such as hydrogen and oxygen in water (H₂O), creating a new substance. In a mixture, substances are together physically but not chemically combined, so each keeps its own properties; salt water and air are mixtures, while pure water and carbon dioxide are compounds.
Carbon dioxide (CO₂) is a compound, not a mixture, because carbon and oxygen are chemically bonded. Air, however, is a mixture of gases with no chemical bonds between them.
Salt water is a mixture, because the salt (NaCl) is dissolved in water (H₂O) with no chemical bonds between them, so the salt keeps its properties. Pure water itself is a compound, because hydrogen and oxygen are chemically bonded.
Brass is a mixture of copper and zinc. Some mixtures, like brass and seawater, look uniform, while others, like a salad or concrete, have parts that can clearly be seen.
Mixtures can be separated by physical methods because nothing has chemically changed, so each substance keeps its properties. Iron filings stay magnetic and can be separated with a magnet, soluble substances can be dissolved and filtered, and substances with lower boiling points can be distilled.
In an iron and sulfur mixture, the iron is still magnetic and the sulfur still burns in air, because they are not chemically bonded. These unchanged properties are what make physical separation, such as using a magnet, possible.
Physical separation is separating a mixture without changing the chemical identity of the substances, using differences in physical properties such as magnetism, solubility or boiling point.