This definitions covers Key Definitions within Purity & Formulations for GCSE Chemistry. Revise Purity & Formulations in Chemical Analysis for GCSE Chemistry with 22 exam-style questions and 12 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 6 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Pure substance (chemistry): A substance that contains only ONE type of element or compound. It has a sharp, fixed melting point and boiling point.
Formulation: A mixture that has been carefully designed so that each component is present in a measured quantity to give the product specific, desirable properties.
Melting point: The temperature at which a solid changes to a liquid at constant pressure. For a pure substance this is a fixed, sharp temperature.
Boiling point: The temperature at which a liquid changes to a gas at constant pressure.
Melting point depression: The lowering of a substance's melting point when impurities are present.
Practice questions for Purity & Formulations
In chemistry, what does it mean for a substance to be described as 'pure'?
Explain why the presence of impurities in a substance lowers its melting point and causes it to melt over a range of temperatures.