Unit Test: The Amazing World of Solutes, Solvents, and Solutions - Class 8 PDF Download

Time: 1 hour

M.M. 30

Attempt all questions.

• Question numbers 1 to 5 carry 1 mark each.
• Question numbers 6 to 8 carry 2 marks each.
• Question numbers 9 to 11 carry 3 marks each.
• Question numbers 12 & 13 carry 5 marks each.
• 1-mark questions include MCQs.

Q1: A solution is defined as (1 Mark)
(i) any mixture of two solids
(ii) a uniform mixture in which components are evenly distributed
(iii) a non-uniform mixture where components settle
(iv) only liquids mixed with liquids

Q2: In the solution of salt in water, salt is the ______ and water is the ______. (1 Mark)
(i) solvent, solute
(ii) solute, solvent
(iii) suspension, colloid
(iv) liquid, solid

Q3: When no more solute can dissolve in a solution at a given temperature, the solution is (1 Mark)
(i) dilute
(ii) concentrated
(iii) saturated
(iv) supersaturated at all temperatures

Q4: Generally, the solubility of most solids in liquids ______ with increase in temperature, while the solubility of gases in liquids ______. (1 Mark)
(i) decreases, increases
(ii) increases, decreases
(iii) unchanged, unchanged
(iv) decreases, decreases

Q5: Density is defined as (1 Mark)
(i) mass × volume
(ii) volume/mass
(iii) mass/volume
(iv) weight/area

Q6: State the difference between a saturated and an unsaturated solution with one example from class activities. (2 Marks)

Q7: Give one reason why air is considered a solution. Identify the solvent in air. (2 Marks)

Q8: Explain why oxygen dissolves more in cold water than in hot water. How is this important for aquatic life? (2 Marks)

Q9: In an experiment, baking soda is added to water at 20 °C until some remains undissolved. On heating to 50 °C, the undissolved part disappears. Explain what this shows about solubility and the status of the solution at the higher temperature. (3 Marks)

Q10: Define concentration in simple terms. Which is more concentrated and why: (a) 2 spoons of salt in 100 mL water or (b) 4 spoons of salt in 50 mL water? (3 Marks)

Q11: A student mixes sawdust in water and notices it floats, while sand sinks. Use density ideas to explain both observations. (3 Marks)

Q12: Measurement and density applications. (5 Marks)
(a) Describe how to measure 50 mL of water accurately in a measuring cylinder (mention meniscus and eye position).
(b) A stone has mass 16.400 g. Using water displacement, its volume increases from 50 mL to 55 mL after immersion. Calculate its density.
(c) Predict qualitatively how heating a liquid generally affects its density and why.

Q13: (a) Give one everyday example showing that solutions can be formed from gases too; identify solute and solvent.
(b) An unpeeled orange floats while a peeled one sinks. Explain.
(c) A 2 L bottle currently holds 500 mL of water. How much more water can it hold? If filled completely, what mass of water would it contain approximately at room temperature? (5 Marks)