🛡️

Content Protected

Screenshots and recording are not allowed.

Click anywhere or refocus to continue

Class 9  »  Chemistry  »  Is Matter Around Us Pure

Pure Substances vs Mixtures - UNSOLVED PRACTICE SET

Class 9

Chapter: Is Matter Around Us Pure | Topic: Pure Substances vs Mixtures

Unsolved Paper
Study Material.
Class 9

PURE SUBSTANCES VS MIXTURES - UNSOLVED PRACTICE SET

Topic: Pure Substances vs Mixtures

Time: 40 mins | Marks: 30 | Difficulty: Medium

Multiple Choice Questions

Q1. Which of the following is a pure substance?

  1. Air
  2. Seawater
  3. Distilled water
  4. Milk

Q2. A sample of matter has a fixed melting point of 0°C and a fixed boiling point of 100°C. It is most likely to be:

  1. A mixture of two liquids
  2. A pure substance
  3. A colloidal solution
  4.  A suspension

Q3. Which statement correctly distinguishes a pure substance from a mixture?

  1. Pure substances can be separated by physical methods, while mixtures cannot
  2. Mixtures have variable composition, while pure substances have fixed composition
  3. Pure substances are always solids, while mixtures are always liquids
  4. Mixtures have fixed melting points, while pure substances do not

Q4. Brass is an example of

  1. A pure substance
  2. A homogeneous mixture
  3. A heterogeneous mixture
  4. A compound

Q5. Which of the following pairs contains one pure substance and one mixture?

  1. Water and sugar
  2. Gold and 22-carat gold
  3. Sodium chloride and distilled water
  4. Oxygen and nitrogen

Q6. A student observes that a given sample does not have a sharp melting point but melts over a range of temperatures. This indicates that the sample is:

  1. A pure element
  2. A pure compound
  3. A mixture
  4. Either an element or a compound

Short Answer Questions

Q7. Define a pure substance. Give two examples — one from your daily life and one from the laboratory.

Q8. Why does a mixture not have a fixed melting point or boiling point? Explain with reasoning.

Q9. Your mother prepares a cup of tea by adding sugar, milk, and tea leaves to water. Is the final tea a pure substance or a mixture? Justify your answer with two reasons.

Q10. Differentiate between a pure substance and a mixture on the basis of composition and energy change during formation.

Q11. A chemistry teacher gives you two samples — Sample A melts sharply at 80°C, and Sample B melts over a range of 75°C to 85°C. Identify which is a pure substance and which is a mixture. Explain your reasoning.

Q12. "All pure substances are homogeneous, but not all homogeneous substances are pure." Do you agree with this statement? Justify your answer with suitable examples.

Long Answer Questions

Q13. Explain the concept of a pure substance with suitable examples. How would you experimentally distinguish between a pure substance and a mixture using the melting point test? Describe the expected observations and conclusions.

Q14. A student claims that distilled water and tap water are both pure substances. Another student disagrees. Who is correct? Present a detailed argument supporting your answer, including the composition of both types of water and how they differ at the molecular level.

Q15. "The purity of a substance is crucial in scientific experiments and industrial processes." Discuss this statement by giving three real-life examples where the use of impure substances led to problems or where pure substances were essential for success.

Numerical / Application-Based Problems

Q16. A chemist has a 200 g sample of an unknown material. She finds that 150 g of it melts at exactly 327°C (the melting point of lead), while the remaining 50 g remains solid even at 400°C.

(a) Is the sample a pure substance or a mixture? Give a reason.

(b) Calculate the percentage by mass of each component in the sample.

(c) Suggest one physical method to separate the two components.

Q17. In a school science fair, three students — Ravi, Priya, and Arjun — present three different samples:

Ravi's sample: Melts at exactly 1083°C (copper's melting point)

Priya's sample: Melts between 900°C and 1100°C

Arjun's sample: Melts at exactly 961°C (silver's melting point)

(a) Identify which samples are pure substances and which is a mixture.

(b) If Priya's sample contains copper and silver, what type of mixture is it likely to be?

(c) Calculate the approximate percentage of copper in Priya's sample if the melting point depression follows a linear relationship (assume pure copper = 1083°C, pure silver = 961°C, and the observed range midpoint is 1000°C).

Q18. A goldsmith has 10 g of 18-carat gold jewellery. Pure gold is 24 carats.

(a) Calculate the mass of pure gold in the jewellery.

(b) Calculate the mass of other metals (alloying elements) present.

(c) Is 18-carat gold a pure substance or a mixture? Justify your answer based on your calculations.

(d) Why do goldsmiths prefer 18-carat gold over 24-carat gold for making jewellery?


Total: 30 Marks | Time: 40 mins

Explore more topics in Is Matter Around Us Pure

Homogeneous and Heterogeneous Mixtures Solutions Solute Solvent Concentration Suspensions and Colloids Tyndall Effect Separation Techniques Evaporation Filtration Distillation Chromatography and Centrifugation Elements and Compounds Differences Mixtures vs Compounds