This deep dive covers What Makes a Substance Pure? 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 2 of 13 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
🔬 What Makes a Substance Pure?
In everyday language, "pure" means natural or without additives — "pure orange juice" or "pure wool".
In chemistry, a pure substance contains only ONE type of element or compound. Nothing else. Not even a tiny trace of another substance.
Examples of Pure Substances
- Elements: Pure copper (Cu), pure gold (Au), pure oxygen (O₂)
- Compounds: Pure water (H₂O), pure sodium chloride (NaCl), pure carbon dioxide (CO₂)
Examples of Impure Substances (Mixtures)
- Tap water: Contains dissolved salts, chlorine, fluoride
- Air: Mixture of nitrogen (78%), oxygen (21%), other gases
- Brass: Mixture of copper and zinc
- Orange juice: Mixture of water, sugars, acids, vitamins
Quick Check: Is distilled water a pure substance in the chemical sense?
Yes — distilled water contains only H₂O molecules. It is a pure compound.
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.