Elements, compounds and mixtures Edexcel International GCSE Science (Double Award) revision
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In plain words
An element is one kind of atom and nothing else, like gold. A compound is different atoms chemically joined into something new, like water. A mixture is just things stirred together, like sand and salt, which you can pull apart again without any chemistry.
Three things to know
- Element: only one kind of atom. Compound: two or more elements chemically joined in fixed proportions. Mixture: substances not chemically joined, which can be separated by physical methods.
- A compound has different properties from the elements in it. Sodium is a reactive metal, chlorine a poisonous gas; sodium chloride is table salt.
- A pure substance melts and boils at fixed, sharp temperatures. An impure one melts over a range, at a lower temperature.
Tips and tricks
- "Chemically joined" (or "chemically bonded") are the words that separate a compound from a mixture. Use them.
- Pure, in chemistry, means one substance only. A pure substance has one sharp melting point; a mixture melts over a range.
It lands in your notebook with its questions as flashcards.
Elements, compounds and mixtures: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which is an element?
Copper contains only copper atoms.
Which is a mixture?
Air is several gases that are not chemically joined.
Which is a compound?
Carbon and oxygen are chemically bonded in fixed proportions.
How does an impurity affect the melting point of a solid?
Impure substances do not have sharp melting points.
How can the parts of a mixture be separated?
Nothing is chemically joined, so no reaction is needed.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Elements, compounds and mixtures
Edexcel International GCSE Science (Double Award) 4SD0 · 8 marks · papermunch.org
Name ______________________________ Date ______________
State the difference between a compound and a mixture.[2]
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In a compound the elements are chemically bonded in fixed proportions; in a mixture the substances are not bonded and can be in any proportions.
Describe how the melting point of a solid shows whether it is pure.[2]
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A pure solid melts sharply at one temperature. An impure solid melts over a range of temperatures, below the true melting point.
Classify each as an element, a compound or a mixture: air, water, oxygen, sodium chloride.[4]
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Air: mixture. Water: compound. Oxygen: element. Sodium chloride: compound.
Answers: Elements, compounds and mixtures
- 1. In a compound the elements are chemically bonded in fixed proportions; in a mixture the substances are not bonded and can be in any proportions.
- 2. A pure solid melts sharply at one temperature. An impure solid melts over a range of temperatures, below the true melting point.
- 3. Air: mixture. Water: compound. Oxygen: element. Sodium chloride: compound.