AQA · Chemistry · 8462
GCSE Chemistry (AQA): Purity & Formulations
Topic 7 — Organic Chemistry. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Purity & Formulations (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 8.01 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_8.01.
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Why is salt water not classed as a pure substance?
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It is a mixture of two different compounds (water and sodium chloride), so it contains more than one substance.
What is analytical chemistry concerned with?
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The instruments and methods used to separate, identify and quantify substances.
In a formulation, the different components are always present in the same ?.
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proportions
What effect do impurities have on the boiling point of a substance?
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They raise it — e.g. salt water boils at about 100.5 °C rather than 100 °C.
What is a formulation?
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A mixture made to a specific formula, containing precise amounts of components so it has a particular function.
How can melting and boiling points be used to identify an unknown pure substance?
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Measure them in the lab and compare with published values in a data book to find the matching chemical.
What distinguishes a physical test from a chemical test when identifying a substance?
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A physical test measures physical properties such as boiling point; a chemical test involves reacting the substance with another chemical.
How do impure substances melt and boil compared to pure ones?
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They melt and boil over a range of temperatures rather than at a specific temperature.
What effect do impurities have on the melting point of a substance?
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They lower it — e.g. salt water melts at about −2 °C rather than 0 °C.
Why does each component of a formulation matter?
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Each one contributes a different property — e.g. in paint, one gives colour and another helps it stick to the wall.
What is a pure substance in chemistry?
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A substance containing only one type of element or compound, not mixed with anything else.
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