Pure Substances & Mixtures · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Pure Substances and Mixtures

Science · Matter & Materials · ages 11-13
Name ______________________   Date ____________

  1. Which of these is a formulation, a mixture made on purpose with a precise recipe?

    • Rainwater
    • A paracetamol tablet
    • Seawater

  2. Which of these has one exact, fixed melting point?

    • A block of pure ice
    • A cup of salty water
    • A bowl of mixed nuts

  3. A pure substance melts over a range of temperatures.

    Circle one:   True   False

  4. Bronze is made by mixing copper and tin in a set ratio to make a metal harder than either one alone. What is bronze an example of?

    • A formulation
    • A pure element
    • A single compound

  5. A scientist heats a white powder and watches it melt gradually between 118°C and 124°C, not at one exact point. What does this tell her?

    110112114116118120122124126128130melting range
    • The powder is a pure compound
    • The thermometer is broken
    • The powder is a mixture or an impure sample

  6. Salt is stirred into water. At the particle level, what happens to the salt and water particles?

    • They join together into new bonds, making a compound
    • They mix together but stay as separate substances, not bonded
    • They disappear completely

  7. A student boils a clear liquid. The thermometer reads exactly 100°C the whole time it boils, then the liquid runs out. What can the student conclude?

    • The liquid is likely pure water
    • The liquid is definitely impure
    • The liquid is definitely a mixture

  8. Adding salt to water lowers its freezing point and raises its boiling point compared to pure water. What does this show about impurities?

    • Impurities only change the colour of a substance
    • Impurities have no effect on melting or boiling points
    • Impurities shift and spread out the melting and boiling points
LightMySky · lightmysky.comW1-mt_MBTVB-E-S7-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Pure Substances and Mixtures W1-mt_MBTVB-E-S7-s1

  1. A paracetamol tablet · A tablet mixes the drug with fillers in a precise, measured recipe. Rainwater and seawater are natural mixtures, not designed formulations.
  2. A block of pure ice · Pure ice is a pure substance, so it melts at one sharp temperature, 0°C.
  3. False · A pure substance melts at one exact, sharp temperature, not a range.
  4. A formulation · Bronze is an alloy: a formulation, a mixture made deliberately with a precise composition for a purpose.
  5. The powder is a mixture or an impure sample · Melting across a range, rather than at one sharp temperature, is the sign of a mixture or an impure sample.
  6. They mix together but stay as separate substances, not bonded · In a mixture, particles sit alongside each other without forming new bonds, unlike in a compound.
  7. The liquid is likely pure water · Boiling steadily at one exact, fixed temperature, matching water's known boiling point, is the sign of a pure substance.
  8. Impurities shift and spread out the melting and boiling points · Impurities shift and widen the melting and boiling points, which is why salty water needs a lower temperature to freeze and a higher one to boil.
Worksheet · LightMySky