---
title: "Pure Substances & Mixtures"
description: "Distinguish between pure substances and mixtures, identify formulations as useful mixtures with precise compositions, and use melting and boiling points to test for purity"
canonical: https://lightmysky.com/learn/science/pure-substances-and-mixtures-mt_MBTVB-E-S7
source: https://lightmysky.com/learn/science/pure-substances-and-mixtures-mt_MBTVB-E-S7.md
retrieved: 2026-10-19
---

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# Pure Substances & Mixtures

Distinguish between pure substances and mixtures, identify formulations as useful mixtures with precise compositions, and use melting and boiling points to test for purity

Subject: Science · Area: Matter & Materials · Ages 11 to 13
Page: https://lightmysky.com/learn/science/pure-substances-and-mixtures-mt_MBTVB-E-S7

## Ready when they can

- Explains why a pure substance has a sharp, fixed melting point but a mixture melts over a range
- Identifies common formulations (medicines, alloys, paints, fuels) as deliberate mixtures
- Explains what impurities do to melting and boiling points
- Distinguishes mixtures from compounds at the particle level

## Lesson: Pure Substances and Mixtures

You already know that atoms can bond into compounds, like water, or stay mixed without bonding. A pure substance is just one substance: one element or one compound, with nothing else in it. A mixture has two or more substances mixed together, but they aren't bonded, so you can still separate them apart.

Melting point is one of the best clues for spotting a pure substance. A pure substance melts at one exact, fixed temperature: pure ice always melts right at 0°C. A mixture is messier. It starts softening at a lower temperature and doesn't finish melting until several degrees higher, because the extra particles get in the way of the neat pattern a pure substance needs.

*(drawing: Pure ice melts at one sharp point, 0°C. A salty ice mixture softens gradually across a range instead.)*

**Example.** Formulations are mixtures made on purpose, with an exact recipe. A paracetamol tablet mixes the drug with fillers in a precise amount, so every tablet works the same way. Bronze mixes copper and tin in a set ratio to make a metal harder than either one alone. Paints and fuels are formulations too, each ingredient measured for the job it does.

**Tip.** To test if a sample is pure, measure its melting or boiling point. Impurities usually lower the melting point and raise the boiling point, spreading both into a range instead of one sharp value. If your sample melts or boils exactly at the known value, all at once, it's pure.

**Recap.** A pure substance melts and boils at one sharp temperature; a mixture, including formulations, melts and boils across a range.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Salt Water vs Fresh Water](https://lightmysky.com/learn/science/salt-water-vs-fresh-water-mt_LsY4-T2fU7)
- [Dissolving & Solutions](https://lightmysky.com/learn/science/dissolving-and-solutions-mt_Mf-T-fYRLX)
- [Atoms, Elements & Compounds](https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI)

## Opens up

- [Paper Chromatography and the Rf Value](https://lightmysky.com/learn/science/paper-chromatography-and-the-rf-value-mt_BAcCcz11ls)
- [Choosing How to Separate Mixtures](https://lightmysky.com/learn/science/choosing-how-to-separate-mixtures-mt_U_tJvy3cbB)