Exploring Mixtures and their Separation — Class 9 MCQs with Answers

Exploring Mixtures and their Separation — important questions & MCQs with answers (Class 9 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   A homogeneous mixture is also called a:

   AElementBSuspensionCCompoundDSolution
   Show answerHide answer

   Answer: Solution

   Explanation: A mixture with the same composition throughout, like sugar dissolved in water, is called a solution; suspensions and colloids are not uniform enough to earn that name.

2. Q2 of 6Easy

   Which of these is an element?

   AIronBAirCWaterDBrass
   Show answerHide answer

   Answer: Iron

   Explanation: Iron is a pure element made of only one type of atom. Water is a compound of hydrogen and oxygen, while air and brass are mixtures of several substances.

3. Q3 of 6Medium

   Distillation separates two liquids when their:

   

   ABoiling points differ significantlyBDensities differ greatlyCColours differDParticles differ in size
   Show answerHide answer

   Answer: Boiling points differ significantly

   Explanation: Distillation works by heating a mixture until the liquid with the lower boiling point vaporises first, then condensing it separately — it needs a real gap in boiling point, not just differing densities or colours.

4. Q4 of 6Medium

   Assertion (A): The particles in a colloid do not settle down over time. Reason (R): Milk and vanishing creams are oil-in-water emulsions.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
   Show answerHide answer

   Answer: Both A and R are true but R is not the correct explanation of A

   Explanation: Both statements are true. Colloid particles stay uniformly spread through the mixture, so they do not settle; the type of emulsion milk is has nothing to do with this, so R does not explain A.

5. Q5 of 6Hard

   Which of the following can be decomposed by chemical means?

   AIronBOxygenCGoldDWater
   Show answerHide answer

   Answer: Water

   Explanation: Water is a compound, and compounds can be broken down chemically — electrolysis splits H₂O into hydrogen and oxygen gas. Elements like iron, oxygen and gold cannot be decomposed further by chemical means.

6. Q6 of 6Hard

   Assertion (A): A saturated solution of compound B, made with 287 g of B in 100 g of water at 60 °C, is cooled to 40 °C, where the solubility of B is 241 g per 100 g of water. About 46 g of B separates out as crystals. Reason (R): The solubility of a solid in a liquid generally decreases as the temperature rises.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
   Show answerHide answer

   Answer: A is true but R is false

   Explanation: A is true: 287 g − 241 g = 46 g of B can no longer stay dissolved. R is false: the solubility of a solid in a liquid generally increases with temperature, which is why cooling makes crystals form.

Exploring Mixtures and their Separation notes: key concepts (Class 9 Science)

A pure substance has a fixed composition, while a mixture does not. This chapter separates mixtures from pure substances, distinguishes elements from compounds, classifies solutions, colloids and suspensions, and covers the standard separation techniques.

Pure substance

A substance made of only one kind of particle with a fixed composition throughout, such as an element or a compound.

Mixture

A material containing two or more substances mixed in any proportion, each keeping its own properties.

Homogeneous and heterogeneous mixtures

A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has visibly distinct parts.

Element

A pure substance made of only one kind of atom, which cannot be broken into simpler substances by chemical means.

Compound

A pure substance formed when elements combine chemically in a fixed ratio, with properties entirely different from its constituents.

Mixture versus compound

In a mixture the components keep their properties and can be separated physically; in a compound they do not and cannot.

Solution

A homogeneous mixture of solute and solvent whose particles are smaller than 1 nm, so it does not scatter light and never settles.

Concentration of a solution

The amount of solute in a given amount of solution, commonly expressed as mass percentage.

Saturated and unsaturated solutions

A saturated solution can dissolve no more solute at that temperature; raising the temperature usually allows more to dissolve.

Suspension

A heterogeneous mixture whose particles are large enough to be seen, to scatter light and to settle on standing.

Colloid

A heterogeneous mixture that appears uniform but whose particles are large enough to scatter light, and which does not settle.

Tyndall effect

The scattering of a light beam by colloidal particles, making its path visible — the standard test distinguishing a colloid from a solution.

Separation by physical means

Techniques exploiting differences in physical properties: evaporation, centrifugation, decantation, sublimation and magnetic separation.

Distillation and fractional distillation

Distillation separates a solvent from a solution by boiling and condensing; fractional distillation separates miscible liquids whose boiling points differ by less than 25 K.

Chromatography

A technique separating substances dissolved in the same solvent, used to separate dyes in ink or pigments in a leaf.