Class 9 Science · Original EZT practice
Exploring Mixtures and their Separation (Class 9 Science Chapter 5): summary and practice
Salt water, air, alloys - most of the matter around us is mixtures, and separating them is a core Class 9 skill. This chapter covers classifying mixtures, what makes a solution, how to express concentration, solubility and saturation, and the separation of homogeneous mixtures by crystallization and distillation. All questions are original EZT tutor practice following the chapter's own section order.
6 original worked examples, 6 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 22 October 2026:
1. Classifying mixtures and solutions
A mixture is homogeneous when its composition is uniform throughout, like salt water, and heterogeneous when it is not, like muddy water - a solution is simply a homogeneous mixture of a solute dissolved in a solvent.
2. Concentration of a solution
Concentration tells how much solute is present in a given amount of solution - one common measure is mass by mass percentage, which is (mass of solute / mass of solution) x 100, where the solution mass is solute plus solvent together.
3. Solubility and saturation
Solubility is the maximum amount of a solute that dissolves in a fixed amount of solvent at a given temperature - a solution holding that maximum is saturated, and temperature is the factor that most often changes solubility.
4. Separating homogeneous mixtures
Crystallization recovers a dissolved solid by evaporating the solvent away, while distillation boils the liquid off and condenses it back - so distillation can recover the liquid as well as the solid.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Tell solute from solvent
Choose the method: The solute dissolves; the solvent does the dissolving.
EZT practice question
In a salt-water solution, which is the solute and which is the solvent?
Show the worked solution
- A solution has two players - the substance that dissolves and the substance it dissolves into.
- Salt disappears into the water.
- So salt is the solute and water is the solvent.
Answer: Salt is the solute (it dissolves); water is the solvent (it does the dissolving).
Check: The solvent is usually the component present in the larger amount - here the water.
Watch for this: Do not call water the solute just because the mixture is named salt water - the naming order can mislead.
Now try it yourself
In sugar syrup, which is the solvent?
Check your answer
Water.
The sugar dissolves into the water.
Classify mixtures
Choose the method: Uniform throughout is homogeneous; not uniform is heterogeneous.
EZT practice question
Classify: (a) air, (b) muddy water, (c) sugar syrup.
Show the worked solution
- Air's gases are mixed uniformly - you cannot spot separate parts.
- Muddy water shows visible particles that settle - not uniform.
- Sugar syrup is uniform once the sugar has fully dissolved.
Answer: (a) homogeneous, (b) heterogeneous, (c) homogeneous.
Check: A solution like sugar syrup is always homogeneous - that is what makes it a solution.
Watch for this: Do not judge by transparency alone - the test is uniform composition, not clarity.
Now try it yourself
Is a mixture of sand and salt homogeneous or heterogeneous?
Check your answer
Heterogeneous.
The two solids stay visibly separate and unevenly mixed.
Compute mass by mass percentage
Choose the method: Solute over total solution, times 100.
EZT practice question
20 g of salt is dissolved in 180 g of water. Find the mass by mass percentage of the solution.
Show the worked solution
- Mass of solution = solute + solvent = 20 + 180 = 200 g.
- Mass by mass percentage = (mass of solute / mass of solution) x 100.
- = (20 / 200) x 100 = 10%.
Answer: 10%.
Check: The denominator is the whole solution (200 g), not the water alone - using 180 g would wrongly give about 11%.
Watch for this: Do not divide by the solvent mass - the formula needs the total solution mass.
Now try it yourself
Find the mass by mass percentage when 15 g of sugar dissolves in 100 g of water.
Check your answer
Solution = 115 g, so (15 / 115) x 100 = 13.04%, about 13%.
Solute 15 g over the full 115 g of solution.
Work backwards from a percentage
Choose the method: Solute = percentage x solution mass.
EZT practice question
A solution is 25% by mass. How many grams of solute are in 80 g of this solution?
Show the worked solution
- 25% by mass means 25 g of solute in every 100 g of solution.
- Scale to 80 g of solution: (25 / 100) x 80.
- = 20 g.
Answer: 20 g of solute.
Check: 20 g out of 80 g is exactly one quarter - that matches 25%.
Watch for this: Do not compute 25% of 100 g and stop - the question asks about 80 g of solution.
Now try it yourself
How much solute is in 50 g of a 10% solution?
Check your answer
5 g.
(10 / 100) x 50 = 5 g.
Test for saturation
Choose the method: Compare dissolved amount with the solubility limit.
EZT practice question
The solubility of a salt is 36 g per 100 g of water at a given temperature. A student dissolves 30 g in 100 g of water. Is the solution saturated?
Show the worked solution
- Saturation means the solution holds the maximum that can dissolve.
- Here the maximum is 36 g per 100 g of water.
- Only 30 g is dissolved, so 6 g more could still dissolve - the solution is unsaturated.
Answer: No - it is unsaturated, because 6 g more could still dissolve at that temperature.
Check: If the student stirred in 40 g, then 36 g would dissolve and 4 g would remain undissolved - that solution would be saturated.
Watch for this: Do not call a solution saturated just because it contains a lot of solute - compare with the solubility limit.
Now try it yourself
State one factor that changes a substance's solubility in water.
Check your answer
Temperature.
Most solids dissolve more as water warms.
Pick the right separation method
Choose the method: Need the liquid back? Distill, do not crystallize.
EZT practice question
Which method would you use to obtain pure water from salt water, and why not crystallization?
Show the worked solution
- The goal is to collect the water itself.
- Crystallization evaporates the water away and keeps only the salt crystals.
- Distillation boils the water off and then condenses the vapour - so the pure water is collected.
Answer: Distillation - the water is boiled off and condensed back as pure liquid. Crystallization only recovers the salt; the water is lost to evaporation.
Check: Reverse goal, reverse method: to obtain the salt as crystals, crystallization is the right choice.
Watch for this: Do not say evaporation when the liquid must be recovered - plain evaporation loses the vapour to the air.
Now try it yourself
Why is distillation better than evaporation when the liquid is needed?
Check your answer
Distillation condenses and collects the vapour.
The liquid is recovered instead of lost.
Try a mixed set
Choose a method or explanation before opening each answer.
1. Mass by mass percentage formula?
Show answer and reason
(Mass of solute / mass of solution) x 100.
The denominator is the whole solution, solute plus solvent.
2. Saturated solution?
Show answer and reason
One holding the maximum solute that can dissolve at that temperature.
No more solute will dissolve in it.
3. Solubility?
Show answer and reason
The maximum solute that dissolves in a fixed amount of solvent at a given temperature.
Usually stated per 100 g of water.
4. Crystallization vs distillation?
Show answer and reason
Crystallization recovers the solid; distillation can recover the liquid too.
Distillation condenses the vapour back to liquid.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Using a solubility of 36 g per 100 g of water, what happens when 40 g of salt is stirred into 100 g of water?
- Which method recovers salt from salt water as crystals?
- Is air a homogeneous or a heterogeneous mixture?
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Questions about this practice page
- What is the formula for mass by mass percentage?
- (Mass of solute / mass of solution) x 100. Remember the denominator is the whole solution, solute plus solvent.
- What is a saturated solution in the Class 9 mixtures chapter?
- One that already holds the maximum solute that can dissolve in that amount of solvent at that temperature - no more will dissolve.
- What is solubility?
- The maximum amount of a solute that dissolves in a fixed amount of solvent (usually 100 g of water) at a given temperature.
- Crystallization vs distillation?
- Crystallization recovers the dissolved solid by evaporating the solvent away; distillation boils the liquid off and condenses it, so it can recover the liquid too.
- Are these the NCERT exercise questions for Class 9 Science Chapter 5?
- No. EZT pages are original practice following the chapter's section order - use them to prepare for the textbook exercises, not as a substitute for your book.