This topic summary covers Knowledge Organiser: Purity and Formulations 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 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Purity and Formulations
Key Definitions
- Pure substance: one type of element/compound only
- Formulation: designed mixture with measured component quantities
- Melting point depression: impurities lower melting point
- Boiling point elevation: impurities raise boiling point
Pure Substance Properties
- Sharp, fixed melting point
- Sharp, fixed boiling point
- Temperature constant during state change
- One spot on chromatogram
Effect of Impurities
- Lower the melting point
- Raise the boiling point
- Cause melting/boiling over a range
- Broader range = more impurities
Formulation Examples
- Paint: pigment + binder + solvent
- Medicines: active ingredient + binder + filler
- Petrol: hydrocarbons + octane improvers
- Alloys: e.g. steel = iron + carbon
Key Equations
- No calculation equations — descriptive topic
- Pure substance: melting point is sharp (single temperature, not a range)
- Impure substance: melts over a range; melting point is LOWER than pure form
Common Mistakes
- Saying impurities raise the melting point: Impurities LOWER the melting point and cause melting to occur over a range of temperatures — not at a sharp fixed point
- Confusing pure (chemistry) and pure (everyday): In chemistry, "pure" means a single element or compound — fruit juice is NOT pure in the chemistry sense
- Saying formulations are pure substances: Formulations are designed MIXTURES — they contain more than one component in specific proportions
- Forgetting that impurities also raise boiling point: Impurities lower melting point AND raise boiling point — examiners ask about both
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.
Quick recall flashcards
What is a formulation?
A mixture designed to have specific properties for a particular purpose, with each component in measured quantities
Give 3 examples of formulations
1) Paint (pigment + binder + solvent), 2) Medicine tablets (active ingredient + binder + filler), 3) Petrol (hydrocarbons + octane improvers + additives)