Classification of Matter

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

1. CSCA Chemistry December 2025 Past Paper
   Which of the following substances is a pure substance? ( )
   • A. Hydrochloric acid solution
   • B. A mixture of ice and water
   • C. Air
   • D. Saturated sodium chloride solution
   Show answer & solution

   Answer: B

   Answer: B A pure substance contains only one substance. A mixture of ice and water has a solid and a liquid phase, but both are H₂O, so it is a pure substance. Hydrochloric acid, air and saturated salt solution all contain several components and are mixtures.
   See it in the full CSCA Chemistry December 2025 Past Paper
2. CSCA Chemistry April 2026 Past Paper
   Which of the following changes is a chemical change? ( )
   • A. Complete combustion of carbon
   • B. Crushing paper
   • C. Freezing of water
   • D. Evaporation of alcohol
   Show answer & solution

   Answer: A

   Answer: A Carbon undergoes complete combustion to form carbon dioxide - a new substance is produced, so it is a chemical change; the others are physical changes.
   Take the full CSCA Chemistry April 2026 Past Paper — timed & graded
3. CSCA Chemistry March 2026 Past Paper
   Which everyday phenomenon involves a chemical change？
   • A．Refrigerator cooling
   • B．Rusting of an iron pot
   • C．Glass breaking
   • D．Evaporation of alcohol
   Show answer & solution

   Answer: B

   Chemical change produces new substances. A/C/D are physical. B: Iron rusting = $\mathrm { Fe } + \mathrm { O } _ { 2 } + \mathrm { H } _ { 2 } \mathrm { O } \rightarrow \mathrm { Fe } _ { 2 } \mathrm { O } _ { 3 } \cdot \times \mathrm { H } _ { 2 } \mathrm { O }$. Answer: B．
   Take the full CSCA Chemistry March 2026 Past Paper — timed & graded