1
For a scientist a pure substance is one in which —
💡 Hint:
Milk is a mixture for a scientist.
Explanation:
A substance is pure when all the particles have the same chemical nature.
Class 9 · Science · Chapter 2 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Is Matter Around Us Pure?
Is Matter Around Us Pure?
How to use this page:
1. Read — 2.1 homogeneous · 2.2 torch · 2.3 saturated · 2.4 ink · 2.5 cream · 2.6 funnel · 2.7 chromatography · 2.8 distillation · 2.9 crystals · 2.10 iron-sulphur, diagram, worked example, board tip
2. Check — each lesson has its own questions; the number follows the lesson
3. Mastery ★ — all of that lesson correct. Redo the wrong ones
4. Use the solution, suspension and colloid memory picture — the torch path shows in a suspension and a colloid, and stays hidden in a solution.
In the Bihar book this is chapter 2. In the NCERT 2026-27 Exploration book, mixtures are chapter 5. Progress stays in this browser.
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- 1 A pure substance and a mixture — Activity 2.1
- 2 Solution, suspension, colloid — Activity 2.2
- 3 A saturated solution and percentage — Activity 2.3
- 4 Evaporation, cream and the funnel — Activities 2.4, 2.5, 2.6
- 5 Sublimation, colours and distillation — Activities 2.7, 2.8
- 6 Crystals and physical or chemical change — Activity 2.9
- 7 Elements, compounds and iron-sulphur — Activity 2.10
- Chapter winner — every lesson at mastery ★
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📄 PDF download — notes + answer key
A pure substance and a mixture — Activity 2.1
शुद्ध पदार्थ और मिश्रण — क्रियाकलाप 2.1 · Section 2.1 · homogeneous and heterogeneous
Pure on a packet and pure in science are not the same thingNotes
Packs of milk, ghee, butter, salt, spices, mineral water and juice say pure. For a buyer that means no adulteration. For a scientist, all the particles of a pure substance are chemically the same. Its properties do not change when the source changes.
Dissolved sodium chloride can be separated from water by evaporation. Sodium chloride itself is a substance. A physical method does not separate its elements. Sugar is the same kind of substance. A soft drink and soil are not single substances. Sea water, minerals and soil are mixtures.
A mixture contains more than one pure substance. The proportion can change. Merely mixing them does not create a new substance.
Activity 2.1 — one spatula and two spatulasActivity
Divide the class into groups A, B, C and D. Group A dissolves one spatula of copper sulphate in 50 mL of water. Group B dissolves two spatulas in the same 50 mL. Both mixtures are the same throughout. Such a mixture is homogeneous, or a solution. Salt water and sugar water are of this kind. Both solutions are copper sulphate, but the depth of colour differs. So a homogeneous mixture can have a variable composition.
Groups C and D mix copper sulphate with potassium permanganate or common salt in different amounts. Separate parts can be seen and the composition is not uniform. These are heterogeneous. Sodium chloride with iron filings, salt with sulphur, and oil with water are examples.
Worked exampleExample
Question: Soda water, wood, air, soil, vinegar and filtered tea — which will you call homogeneous?
Answer: Soda water, air, vinegar and filtered tea are homogeneous. Wood and soil are heterogeneous. Air is a homogeneous mixture of several gases.
10-second revision
- Pure = particles of one kind
- In 2.1 one and two spatulas are both homogeneous, the colour differs
- Oil-water and salt-sulphur are heterogeneous
Board tip · BSEBBoard tip
In the definitions of a substance and a mixture, write the sentence about separation by a physical method.
Board tip · CBSEBoard tip
Air is homogeneous and soil is heterogeneous. Do not put them in one class.
Check your understandingall correct = mastery ★
2
A homogeneous mixture always has one fixed proportion.
Explanation:
False — in Activity 2.1 both one and two spatulas are homogeneous, but the colour differs. The proportion can change.
3
A mixture of oil and water is called ______.
💡 Hint:
The parts look separate.
Explanation:
Heterogeneous.
4
Which of these is a homogeneous mixture?
💡 Hint:
A gas in a gas.
Explanation:
Air is homogeneous. Soil, wood and oil-water are heterogeneous.
5
Write two differences between a substance and a mixture.
Model answer (board format)
A substance has particles of one kind and a physical method does not split it into other substances. A mixture has more than one substance and the proportion can change.
Check your answer:
Solution, suspension, colloid — Activity 2.2
विलयन, निलंबन, कोलाइड — क्रियाकलाप 2.2 · Section 2.2 · Tyndall · 1 nm
Three mixtures, three kinds of particlesNotes
A solution is a homogeneous mixture of two or more substances. The part that dissolves the other, usually present in the larger amount, is the solvent. The part that dissolves, usually the smaller amount, is the solute. In sweet water, sugar is the solute and water is the solvent. Iodine in alcohol is tincture of iodine. In soda, carbon dioxide is the solute and water is the solvent. Air is a gas in a gas. Its main parts are about 21 percent oxygen and 78 percent nitrogen.
An alloy is a mixture of two or more metals, or of a metal and a non-metal. Physical methods do not separate the parts, yet it is a mixture, because the properties of the parts show and the composition can vary. Brass is about 30 percent zinc and 70 percent copper.
Particles of a solution are smaller than 1 nm. They are not visible, they do not scatter light, they do not filter and they do not settle. A suspension is heterogeneous. The particles are visible, they scatter light, they settle and they can be filtered. After they settle, the scattering stops. A colloid looks homogeneous but is heterogeneous, like milk. The particles are not visible, but they scatter light. This is the Tyndall effect. A colloid is stable and ordinary filtration does not separate it. Centrifugation, Activity 2.5, can separate colloidal particles.
Activity 2.2 — four groups and a torchActivity
Give group A a few crystals of copper sulphate. Give group B one spatula of copper sulphate. Give group C chalk powder or wheat flour. Give group D a few drops of milk or ink. Each group adds its sample to water and stirs with a glass rod.
Write whether the particles are visible. Send a torch beam through the beaker and look from the front. Is the path visible. Leave it unstirred for a few minutes. Do the particles settle, or does the mixture hold. Then filter. Is there a residue on the paper.
A and B get a solution. The depth of colour can differ. C gets a suspension. D gets a colloid. A dusty beam through a hole in a room, and sunlight in the mist of a dense forest, are also the Tyndall effect.
| Dispersed | Medium | Type | Example |
|---|---|---|---|
| Liquid | Gas | Aerosol | Fog, cloud |
| Solid | Gas | Aerosol | Smoke |
| Liquid | Liquid | Emulsion | Milk |
| Solid | Liquid | Sol | Milk of magnesia, mud |
Worked exampleExample
Question: A salt solution, milk, a copper sulphate solution and a starch solution — which will show the Tyndall effect?
Answer: Milk and starch solution are colloids, so they show Tyndall. The salt solution and the copper sulphate solution do not.
10-second revision
- The solvent is usually the larger amount, the solute the smaller
- Solution: under 1 nm, no Tyndall, stable
- In 2.2, C is the suspension and D is the colloid
Board tip · BSEBBoard tip
Do not call a sol a solution. A sol is a solid-liquid colloid, such as mud.
Board tip · CBSEBoard tip
Brass is a mixture, not a compound. About 70 percent copper and 30 percent zinc.
Check your understandingall correct = mastery ★
1
In tincture of iodine the solvent is —
💡 Hint:
Iodine is the solid solute.
Explanation:
Alcohol is the solvent and iodine is the solute.
2
The path of a torch is clearly visible in a copper sulphate solution.
Explanation:
False — particles of a solution are smaller than 1 nm and do not scatter light.
3
Group D, with milk or ink, makes a ______.
💡 Hint:
Chalk is the suspension.
Explanation:
A colloid.
4
When a suspension is left unstirred —
💡 Hint:
An unstable mixture.
Explanation:
The particles settle. After that the scattering of light also stops.
5
Write two differences among a sol, a solution and a suspension.
Model answer (board format)
A solution is homogeneous and its particles are smaller than 1 nm. A sol is a colloid of a solid in a liquid, it shows Tyndall and it stays stable. Particles of a suspension are visible, they settle and they can be filtered.
Check your answer:
6
Brass is called a mixture because —
💡 Hint:
About 70 percent copper.
Explanation:
Physical methods do not separate it, yet the proportion can change, so it is a mixture.
A saturated solution and percentage — Activity 2.3
संतृप्त विलयन और प्रतिशत — क्रियाकलाप 2.3 · Section 2.2.1 · 11.1 percent · the table
Concentrated and dilute are words of comparisonNotes
At a given temperature, a solution that has dissolved as much solute as it can is saturated. Less solute than that makes it unsaturated. The amount of solute in the saturated solution at that temperature is the solubility. Different substances have different solubilities in the same solvent at the same temperature. Cool a saturated solution slowly and some solute can come out as crystals.
Concentration is the amount of solute in a given amount of solution, or in a given amount of solvent. Two methods are used here. Mass percentage = (mass of solute / mass of solution) × 100. Mass by volume percentage = (mass of solute / volume of solution) × 100. Mass of solution = solute + solvent.
At 293 K, in 100 g of water for a saturated solution, the table gives potassium nitrate 32 g, sodium chloride 36 g, potassium chloride 35 g and ammonium chloride 37 g. At 313 K potassium nitrate is 62 g. At 353 K potassium chloride is 54 g, and at 293 K it is 35 g. The solubility of these salts rises with temperature. Common salt stays almost steady.
Activity 2.3 — when no more solute dissolvesActivity
Take about 50 mL of water in two beakers. Add salt to one and sugar or barium chloride to the other, stirring all the time. When no more solute dissolves, heat the beaker so that the temperature rises by about 5°C. Add solute again.
At the same temperature the amounts of salt and of sugar or barium chloride that dissolve are not equal. After heating, more solute dissolves. In Activity 2.2 as well, a few crystals in group A and one spatula in group B give different depths. A is dilute compared with B. Dilute and concentrated are not fixed numbers.
Worked exampleExample
Question: 40 g of salt is dissolved in 320 g of water. Find the mass percentage.
Formula: mass percentage = (mass of solute / mass of solution) × 100.
Substitution: solution = 40 g + 320 g = 360 g.
Percentage = (40 / 360) × 100 = 11.1%.
10-second revision
- Saturated: no more solute dissolves at that temperature
- 40 g + 320 g = 360 g, and 11.1 percent
- At 313 K, 50 g of water needs 31 g of potassium nitrate
Board tip · BSEBBoard tip
In the percentage use the mass of the solution, not only the water. 40/320 is wrong.
Board tip · CBSEBoard tip
The 25 K gap belongs to distillation. The 5°C belongs to the heating in Activity 2.3. Do not mix them.
Check your understandingall correct = mastery ★
1
The mass percentage of a solution of 40 g salt and 320 g water is —
💡 Hint:
First make 360 g.
Explanation:
(40/360) × 100 = 11.1%. 40/320 is not the percentage.
2
At the same temperature the solubilities of salt and sugar are equal.
Explanation:
False — Activity 2.3 shows that different substances have different solubilities.
3
At 313 K the solubility of potassium nitrate in 100 g of water is ______ g.
💡 Hint:
Half of that for 50 g of water.
Explanation:
62 g. So 31 g in 50 g of water.
4
At 293 K, 36 g of sodium chloride is dissolved in 100 g of water and the solution is saturated. Find the mass percentage.
Model answer (board format)
Mass of solution = 36 g + 100 g = 136 g. Percentage = (36/136) × 100 = 26.47%.
Check your answer:
5
In the table at 293 K the most soluble salt is —
💡 Hint:
37 g per 100 g of water.
Explanation:
Ammonium chloride is 37 g. Salt is 36 g, potassium chloride 35 g and potassium nitrate 32 g.
Evaporation, cream and the funnel — Activities 2.4, 2.5, 2.6
वाष्पन, क्रीम और कीप — क्रियाकलाप 2.4, 2.5, 2.6 · Sections 2.3.1 to 2.3.3
The parts can be studied only after they are separatedNotes
Most natural materials are not chemically pure. Heterogeneous mixtures are often separated by handpicking, filtration or sieving. Very small particles need a different technique.
Evaporation separates a volatile solvent from a non-volatile solute. In centrifugation, fast spinning sends denser particles to the bottom and lighter ones stay on top. Immiscible liquids form layers by density. The lower layer is drawn off through the stopcock.
Activities 2.4, 2.5 and 2.6 — ink, milk and keroseneActivity
2.4. Fill a beaker half with water. Place a watch glass on its mouth. Put a few drops of ink on the glass. Do not heat the ink directly. Heat the beaker. Evaporation takes place from the watch glass. Stop the flame when you see no further change. Water leaves and a coloured residue remains. Ink is a mixture of a dye in water.
2.5. Take full-cream milk in a test tube. Spin it in a centrifuge for two minutes. If there is no machine, use a kitchen churner. Ask a nearby dairy how cream is separated and how paneer is made. On churning, the cream rises. The same idea is used in blood and urine tests, in butter, and in a washing machine that squeezes wet clothes.
2.6. Pour a mixture of kerosene and water into a separating funnel. Let it stand until layers form. Open the stopcock and draw off the lower water carefully. Close it when the oil reaches the stopcock. The same principle separates oil and water, and removes lighter slag from molten iron in a furnace.
Worked exampleExample
Question: Butter from curd, leaves from tea, and oil from water — write a different method for each.
Answer: Butter from curd by centrifugation. Tea leaves by filtration, the residue on the paper and the filtrate as tea. Oil and water are immiscible, so a separating funnel.
10-second revision
- 2.4: ink is a mixture, water leaves, the dye stays
- 2.5: two minutes, dense at the bottom, cream on top
- 2.6: water below, close the stopcock as the oil arrives
Board tip · BSEBBoard tip
Centrifugation and the separating funnel are different. One spins, the other draws off a layer.
Board tip · CBSEBoard tip
The ink is not heated directly. Water in the beaker warms the watch glass.
Check your understandingall correct = mastery ★
1
The residue after heating ink on a watch glass shows that —
💡 Hint:
Activity 2.4.
Explanation:
Water evaporates and the dye stays. Ink is a mixture.
2
In centrifugation the lighter particles settle at the bottom.
Explanation:
False — denser particles go to the bottom and lighter ones stay on top.
3
Kerosene and water are separated with a ______ funnel.
💡 Hint:
The lower layer is water.
Explanation:
A separating funnel.
4
While making tea, where are the solvent, solute, soluble part, insoluble part, filtrate and residue?
Model answer (board format)
Water is the solvent. Sugar is the soluble solute. The tea leaf is insoluble. On filtering, the leaf is the residue and the tea in the cup is the filtrate.
Check your answer:
Sublimation, colours and distillation — Activities 2.7, 2.8
ऊर्ध्वपातन, रंग और आसवन — क्रियाकलाप 2.7, 2.8 · Sublimation after 2.6 · 2.7 · 2.8 · air
The gap in boiling points chooses the methodNotes
Ammonium chloride, camphor, naphthalene and anthracene become vapour directly on heating. Salt does not. So a mixture of salt and ammonium chloride is separated by sublimation. This comes after 2.6 and before 2.7. It has no activity number of its own.
Chromatography separates solutes that dissolve in the same solvent. Kroma in Greek means colour. The more soluble colour climbs the paper faster. Uses: colours, natural pigments, drugs from blood.
If two miscible liquids boil without decomposing and their boiling points differ enough, use distillation. If the difference is less than 25 K, use fractional distillation. Glass beads in the column cool the vapour again and again. The flow for air: raise the pressure and lower the temperature to get liquid air, then warm it slowly in the column. The table in the figure: oxygen boils at −183°C and is 20.9 percent, argon −186°C and 0.9 percent, nitrogen −196°C and 78.1 percent. Increasing boiling point: nitrogen, argon, oxygen. On cooling, oxygen becomes liquid first.
Activities 2.7 and 2.8 — a line at 3 cm and acetoneActivity
2.7. Take a thin strip of filter paper. Draw a pencil line about 3 cm above the lower edge. Put a small drop of water-soluble ink, from a sketch pen or a fountain pen, at the centre of the line. Let it dry. Hang the strip in a jar of water so that the ink drop is just above the water level. Water climbs the strip and carries the dye. Usually two or more colours separate.
2.8. Take a mixture of acetone and water in a distillation flask. Fit a thermometer. Heat slowly. Acetone becomes vapour first, condenses in the condenser and is collected outside. Water stays in the flask. The temperature at which the thermometer stays steady for a while is the boiling point of acetone. It is lower than the boiling point of water, so the two separate. If kerosene and petrol differ by more than 25°C and are miscible, simple distillation is enough.
Worked exampleExample
Question: Which gas becomes liquid first as air is cooled? Also write the order.
Answer: The higher boiling point becomes liquid first. The order is nitrogen −196°C, argon −186°C, oxygen −183°C. Oxygen becomes liquid first.
10-second revision
- Sublimation has no number; it sits between 2.6 and 2.7
- In 2.7 the line is about 3 cm up and the drop is above the water
- A gap below 25 K means fractional distillation
Board tip · BSEBBoard tip
The answer for camphor and salt is sublimation. Do not write distillation.
Board tip · CBSEBoard tip
Oxygen boils at −183°C and nitrogen at −196°C. Oxygen becomes liquid first.
Check your understandingall correct = mastery ★
1
The technique to separate camphor from salt is —
💡 Hint:
Camphor becomes vapour directly.
Explanation:
Sublimation. Salt does not leave as vapour.
2
In chromatography the more soluble colour climbs the paper more slowly.
Explanation:
False — the more soluble colour climbs faster.
3
The ink line is about ______ cm above the lower edge.
💡 Hint:
The drop stays above the water level.
Explanation:
3 cm.
4
When the boiling points differ by less than 25 K, the choice is —
💡 Hint:
Air and petroleum.
Explanation:
Fractional distillation. Simple distillation is for a sufficient gap.
5
Write the steps to obtain oxygen from air and the order of boiling points.
Model answer (board format)
Air is made liquid by raising the pressure and lowering the temperature. It is then warmed slowly in a fractionating column. The increasing order of boiling points is nitrogen −196°C, argon −186°C, oxygen −183°C. Oxygen becomes liquid first.
Check your answer:
6
In the distillation of acetone and water, the first to be collected is —
💡 Hint:
The one with the lower boiling point.
Explanation:
Acetone becomes vapour first. Water stays in the flask.
Crystals and physical or chemical change — Activity 2.9
क्रिस्टल और भौतिक-रासायनिक परिवर्तन — क्रियाकलाप 2.9 · Sections 2.3.8 and 2.4 · water works
A change of state is physical, burning is chemicalNotes
Colour, hardness, rigidity, fluidity, density, melting point and boiling point are physical properties. Ice, water and steam look different, but chemically they are the same water. A change of state is a physical change, because the composition does not change.
Oil burns and water puts a fire out. That is a chemical property. Burning makes a new substance. It is a chemical change, or a chemical reaction. A candle has both: melting of wax is physical and burning of wax is chemical.
Cutting a tree, melting butter, boiling water, dissolving salt and a fruit salad are physical. Rust on an almirah, water splitting into hydrogen and oxygen by electricity, and burning paper or wood are chemical.
Activity 2.9 — 5 g of impure copper sulphateActivity
Take about 5 g of impure copper sulphate in a china dish. Dissolve it in the minimum amount of water. Filter out the impurity. Evaporate water until the solution is saturated. Cover it with filter paper and leave it to cool slowly at room temperature for a day. Crystals of copper sulphate form in the dish. Separate them from the liquid.
Crystallisation is better than simple evaporation. Some solids break down when heated to dryness. Sugar can char. Some impurity stays dissolved and joins the solid on drying. Purification of sea salt and crystals of alum use this method.
The city water works in the figure runs: reservoir, a sedimentation tank where solids settle, a loading tank where suspended impurity is made to settle, a filtration tank with fine sand, coarse sand and gravel, then chlorine to kill bacteria, and on to the home.
Worked exampleExample
Question: Potassium chloride saturated at 353 K is cooled to 293 K. What is seen for 100 g of water?
Answer: The solubility is 54 g at 353 K and 35 g at 293 K. The difference, 54 g − 35 g = 19 g, separates as crystals, per 100 g of water.
10-second revision
- In 2.9, about 5 g, little water, cool slowly for a day
- Crystallisation keeps sugar from charring
- Melting wax is physical, burning wax is chemical
Board tip · BSEBBoard tip
Evaporation is also right for salt from sea water. If pure crystals are asked, write crystallisation.
Board tip · CBSEBoard tip
Cutting a tree is physical because the composition of the wood does not change. Rust is chemical.
Check your understandingall correct = mastery ★
1
Pure crystals from impure copper sulphate are obtained by —
💡 Hint:
Activity 2.9.
Explanation:
Crystallisation. About 5 g of sample, a saturated solution, slow cooling.
2
Ice becoming water is a chemical change.
Explanation:
False — the composition does not change, so it is physical.
3
At the water works, ______ is done at the end to kill bacteria.
💡 Hint:
After filtration.
Explanation:
Chlorination.
4
Which of these is a chemical change?
💡 Hint:
A new substance is formed.
Explanation:
Rust is chemical. Melting, dissolving and freezing are physical.
5
Why is crystallisation better than evaporation? Two reasons.
Model answer (board format)
Some solids, such as sugar, can char when heated to dryness. Dissolved impurity joins the solid after evaporation. Crystals from slow cooling give a purer solid.
Check your answer:
Elements, compounds and iron-sulphur — Activity 2.10
तत्त्व, यौगिक और लोहा-गंधक — क्रियाकलाप 2.10 · Section 2.5 · Activity 2.10 · group model
Acid, carbon disulphide and a red-hot flameCaution
Do Activity 2.10 under a teacher. Dilute sulphuric or hydrochloric acid and carbon disulphide are hazardous. The hydrogen from group I is combustible. Do not do its combustion test in class. After the mixture is red hot, let it cool. Do not taste it.
An element does not break down, a compound is a new substanceNotes
Robert Boyle used the word element in 1661. Lavoisier called an element a basic form that chemical reactions cannot break into simpler substances. More than 100 elements are known. Ninety-two are natural and the rest are made by people. Most are solid. Eleven elements are gases at room temperature. Two are liquids: mercury and bromine. Gallium and cesium become liquid a little above 303 K.
A metal shines, conducts heat and electricity, can be drawn into wire, can be beaten into a sheet and rings when hit. Mercury is the only metal that is liquid at room temperature. A non-metal is usually a poor conductor of heat and electricity and is not lustrous, sonorous or malleable. Boron, silicon and germanium are metalloids.
A compound is a chemical union of two or more elements in a fixed proportion. A mixture keeps the properties of its parts. A compound has new properties. A mixture separates by a physical method. A compound separates only by a chemical or electrochemical method.
Activity 2.10 and the matka at the endActivity
Give both groups 5 g of iron filings and 3 g of sulphur powder in a china dish. Group I only mixes and crushes. Group II mixes and heats strongly until red hot, then takes it off the flame and lets it cool.
Bring a magnet near. Look at the texture and the colour. Add carbon disulphide to one part, stir and filter. Add dilute sulphuric or hydrochloric acid to the other part. Do the same steps with iron and with sulphur separately.
The material of group I is a mixture. The magnet pulls the iron. The acid gives colourless, odourless hydrogen. The material of group II is the compound iron sulphide. The acid gives hydrogen sulphide, like rotten eggs. On heating, Fe and S join to give FeS.
Group model. After the numbered activities, use an earthen matka, pebbles and sand to build a small plant that cleans muddy water. It is a home form of the filter bed at the water works.
Worked exampleExample
Question: Which gas does dilute hydrochloric acid give from group I and from group II?
Answer: Group I gives hydrogen. The equation is Fe + 2HCl → FeCl2 + H2. Group II gives hydrogen sulphide. The equation is FeS + 2HCl → FeCl2 + H2S. The smell tells them apart: hydrogen has no smell, hydrogen sulphide smells of rotten eggs. Do not burn the hydrogen in class to check.
10-second revision
- An element does not break into simpler substances by a chemical reaction
- 2.10: 5 g iron, 3 g sulphur; I mixture, II compound
- Hydrogen has no smell; H2S smells of rotten eggs
Board tip · BSEBBoard tip
Write that a compound has a fixed proportion. A mixture can vary. Do not reverse the two in one sentence.
Board tip · CBSEBoard tip
Mercury is a metal and a liquid. Bromine is a non-metal and a liquid. Both are liquids, not one class.
Check your understandingall correct = mastery ★
1
The metal that is liquid at room temperature is —
💡 Hint:
Bromine is a non-metal.
Explanation:
Mercury is the only such metal. Bromine is a liquid non-metal.
2
The gas from group I with dilute acid smells of rotten eggs.
Explanation:
False — group I gives hydrogen, which has no smell. The rotten-egg gas is hydrogen sulphide from group II.
3
Heating iron and sulphur strongly makes the compound ______.
💡 Hint:
5 g and 3 g.
Explanation:
Iron sulphide, FeS.
4
Write any three of the four differences between a mixture and a compound. Add one iron-sulphur example.
Model answer (board format)
In a mixture no new substance forms, the proportion can change, the properties stay like the parts and separation is physical. In a compound the elements react, the proportion is fixed, the properties are new and separation is chemical. Iron that is only mixed is pulled by a magnet. FeS made by heating red hot is not pulled the same way and gives H2S with acid.
Check your answer:
❓ Full question bank — with answers and explanations — 67 questions
Pick a type. The 35 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual60 tried · 0 correctMultiple choiceMCQ140 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason50 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA120 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
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Multiple choice
0/14Pick one option. A wrong try brings a hint.
1
From a scientist’s view, a mixture is —
💡 Hint:
Milk contains fat and proteins.
Explanation:
Milk is a mixture. Pure salt and distilled water are substances.
2
A homogeneous mixture is —
💡 Hint:
Filtered tea too.
Explanation:
Vinegar is homogeneous. Soil, wood and oil-water are heterogeneous.
3
The size of particles of a solution is —
💡 Hint:
10^-9 metre.
Explanation:
Smaller than 1 nm. So no Tyndall effect.
4
The Tyndall effect is shown by —
💡 Hint:
A colloid.
Explanation:
Milk is a colloid and shows Tyndall. Solutions do not.
5
In soda water the solute is —
💡 Hint:
A gas in a liquid.
Explanation:
Carbon dioxide is the solute and water is the solvent.
6
(40/360) × 100 equals —
💡 Hint:
360 g of solution.
Explanation:
11.1%. This is the mass percentage of 40 g salt and 320 g water.
7
Butter is separated from curd by —
💡 Hint:
The principle of Activity 2.5.
Explanation:
Centrifugation.
8
For two immiscible liquids the right choice is —
💡 Hint:
Layers by density.
Explanation:
A separating funnel. Water is usually below.
9
Pigments from flower petals are separated by —
💡 Hint:
Solutes that dissolve in the same solvent.
Explanation:
Chromatography.
10
The gas that becomes liquid first as air is cooled is —
💡 Hint:
−183°C is the highest of these three.
Explanation:
Oxygen. The order is nitrogen, argon, oxygen.
11
A good check that a colourless liquid is pure water is —
💡 Hint:
A pure substance has a fixed boiling point.
Explanation:
Boiling at 100°C or 373 K is a sign of pure water.
12
Which of these is an element?
💡 Hint:
A metal.
Explanation:
Silver is an element. A salt solution, air and soil are mixtures.
13
Dilute acid on a mixture of iron and sulphur gives —
💡 Hint:
The compound gives H2S.
Explanation:
The mixture gives hydrogen. The compound gives H2S, like rotten eggs.
14
An example of a metalloid is —
💡 Hint:
Boron and germanium too.
Explanation:
Silicon is a metalloid.
True or false
0/81
Brass is a compound because copper does not separate by a physical method.
Explanation:
False — the proportion can change and the properties of the parts show, so it is a mixture.
2
Particles of a suspension keep scattering light the same way after they settle.
Explanation:
False — the scattering stops after they settle.
3
In mass percentage the mass of the solution is the sum of solute and solvent.
Explanation:
True — 40 g + 320 g = 360 g.
4
On the chromatography strip the ink drop should stay dipped in the water.
Explanation:
False — the drop should be just above the water level.
5
Drying sugar to purify it can be unsafe because it can char.
Explanation:
True — that is why crystallisation is better.
6
Getting hydrogen and oxygen by passing electricity through water is a physical change.
Explanation:
False — new substances are formed, so it is chemical.
7
Mercury and bromine are both elements that are liquid at room temperature.
Explanation:
True — mercury is a metal and bromine is a non-metal.
8
The gas from group II should be identified by burning it in class.
Explanation:
False — do not do the combustion test for hydrogen in class. Identification is by smell and properties. H2S smells of rotten eggs.
Fill in the blanks
0/81
Oxygen in air is about ______ percent.
💡 Hint:
Nitrogen is about 78.
Explanation:
About 21 percent. The figure gives oxygen as 20.9 percent.
2
The scattering of light is called the ______ effect.
💡 Hint:
A solution does not show it.
Explanation:
The Tyndall effect. Colloids and suspensions show it.
3
A saturated solution of KNO3 in 50 g of water at 313 K needs ______ g of solute.
💡 Hint:
Half of 62.
Explanation:
31 g. Because 100 g of water holds 62 g.
4
If there is no centrifuge, milk can be churned at home with a ______.
💡 Hint:
Ask a dairy too.
Explanation:
A churner. Two minutes is the time on the machine.
5
Fractions of petroleum are separated by ______ distillation.
💡 Hint:
Glass beads.
Explanation:
Fractional distillation. When the gap is less than 25 K.
6
The impure copper sulphate in the activity is about ______ g.
💡 Hint:
A china dish.
Explanation:
5 g. Then a little water and a day of cooling.
7
The iron filings are ______ g and the sulphur is 3 g.
💡 Hint:
Give the same to both groups.
Explanation:
5 g of iron and 3 g of sulphur.
8
The gas from the compound with dilute acid is ______.
💡 Hint:
The mixture gives hydrogen.
Explanation:
Hydrogen sulphide. The smell is like rotten eggs.
Match
0/21
Match the mixture with its separation.
Column B: A. Sublimation · B. Separating funnel · C. Chromatography · D. Evaporation
1. Salt dissolved in water
2. Camphor and salt
3. Oil and water
4. Colours in ink
Explanation:
The solution by evaporation, camphor by sublimation, oil by the funnel, colours by chromatography.
2
Match the word with its class.
Column B: A. Element · B. Mixture · C. Compound · D. A colloidal mixture
1. Silver
2. Air
3. Calcium carbonate
4. Blood
Explanation:
Silver is an element, air a mixture, calcium carbonate a compound and blood a colloidal mixture.
Assertion–reason
0/5Check both statements, then see whether the reason explains the assertion.
1
Assertion (A): Milk shows the Tyndall effect.
Reason (R): Particles of a colloid scatter light, but they are not seen separately.
Explanation:
Both are true and R explains A.
2
Assertion (A): The mass percentage of 40 g salt and 320 g water is 11.1.
Reason (R): Particles of a suspension stay on the filter paper.
Explanation:
Both are true, but R does not explain the percentage.
3
Assertion (A): Fractional distillation is used when boiling points differ by less than 25 K.
Reason (R): Acetone and water are immiscible, so they are separated with a funnel.
Explanation:
A is true. R is false — acetone and water are miscible and are separated by distillation.
4
Assertion (A): A mere mixture of iron and sulphur is not pulled by a magnet.
Reason (R): A mixture shows the properties of its components.
Explanation:
A is false. The iron in the mixture is pulled by a magnet. R is true.
5
Assertion (A): Crystallisation can be safer than evaporation for cleaning sea salt.
Reason (R): Some solids break or char on strong heating, and dissolved impurity joins them on drying.
Explanation:
Both are true and R is the correct reason.
Balance the equation
0/4These are chemical changes from this chapter: iron and sulphur, the gas from acid, and water split by electricity. A blank coefficient means 1.
1
Group II heats iron and sulphur red hot. Fill the coefficients of Fe + S → FeS (blank = 1).
Fe + S → FeS
Explanation: Fe + S → FeS
2
Dilute hydrochloric acid on the mixture of group I gives hydrogen. Balance Fe + HCl → FeCl2 + H2 (blank = 1).
Fe + HCl → FeCl2 + H2
Explanation: Fe + 2HCl → FeCl2 + H2
3
Dilute sulphuric acid on the compound gives hydrogen sulphide. Balance FeS + H2SO4 → FeSO4 + H2S (blank = 1).
FeS + H2SO4 → FeSO4 + H2S
Explanation: FeS + H2SO4 → FeSO4 + H2S
4
Passing electricity through water gives hydrogen and oxygen. This is a chemical change from this chapter. Balance H2O → H2 + O2 (blank = 1).
H2O → H2 + O2
Explanation: 2H2O → 2H2 + O2
Classify
0/21
Place each name as element, compound or mixture.
Sodium
Methane
Coal
Carbon dioxide
Explanation:
Sodium is an element. Methane and carbon dioxide are compounds. Coal is a mixture.
2
Place each change as physical or chemical.
Mixing iron filings and sand
Rusting of iron
Cooking of food
Freezing of water
Explanation:
Mixing and freezing are physical. Rust and cooking are chemical.
Very short answer
0/51
Define a substance in one line.
Model answer (board format)
A pure substance is one in which all the particles have the same chemical nature.
Check your answer:
2
What is the Tyndall effect?
Model answer (board format)
The Tyndall effect is the scattering of a beam of light by particles of a colloid or a suspension. The path is not seen in a solution.
Check your answer:
3
What is a saturated solution?
Model answer (board format)
A saturated solution is one that cannot dissolve any more solute at a given temperature.
Check your answer:
4
What is an element?
Model answer (board format)
An element is a basic form of matter that cannot be broken into simpler substances by a chemical reaction.
Check your answer:
5
How would you separate iron pins from sand?
Model answer (board format)
With a magnet. Iron is pulled by the magnet and sand is not.
Check your answer:
Short answer
0/41
36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find the mass percentage.
Model answer (board format)
Solution = 36 + 100 = 136 g. Percentage = (36/136) × 100 = 26.47%.
Check your answer:
2
Write three differences between a suspension and a colloid.
Model answer (board format)
Particles of a suspension are visible, they settle and they can be filtered. Particles of a colloid are not visible, they do not settle and ordinary filtration does not separate them, but they show the Tyndall effect.
Check your answer:
3
Small pieces of metal in engine oil, wheat from husk, and salt from salt water — write three methods.
Model answer (board format)
The metal pieces by filtration. Wheat by winnowing. Salt by evaporation, and by crystallisation if pure crystals are needed.
Check your answer:
4
Write the physical and the chemical change in a burning candle separately.
Model answer (board format)
Melting of wax is physical, because the wax stays wax. Burning of wax to new substances is chemical.
Check your answer:
Long answer
0/31
Write the method of Activity 2.2. Compare a solution, a suspension and a colloid on particle size, Tyndall effect and stability.
Model answer (board format)
Give A a few crystals, B one spatula of copper sulphate, C chalk or flour and D milk or ink. Stir in water, look at a torch from the front, let it stand and filter. Solution particles are under 1 nm, no Tyndall, stable. Suspension particles are visible, Tyndall until they settle, unstable, and they filter. A colloid is not visible, shows Tyndall, is stable and does not separate by ordinary filtration.
Check your answer:
2
Write the separation sequence with one example each: evaporation, centrifugation, separating funnel, sublimation, chromatography, distillation and crystallisation.
Model answer (board format)
Water of ink leaves by evaporation. Cream by centrifugation. Kerosene and water by the funnel. Camphor and salt by sublimation. Colours of ink by chromatography, the line 3 cm up. Acetone and water by distillation. Impure copper sulphate, about 5 g, by crystallisation. If boiling points differ by less than 25 K, use fractional distillation.
Check your answer:
3
What do the two groups do in Activity 2.10? Identify the mixture and the compound from the properties. Why is hydrogen not burnt?
Model answer (board format)
Both receive 5 g of iron filings and 3 g of sulphur. Group I only mixes. Group II heats red hot. The mixture is pulled by a magnet and gives odourless hydrogen with dilute acid. The compound FeS shows new properties and gives H2S, like rotten eggs, with acid. Hydrogen is combustible, so the combustion test is not done in class. A teacher must supervise.
Check your answer:
BSEB model paper · practice
0/6This model set is for practice. It is not a question from any year’s annual examination. Annual questions will be added only when a source page is available.
1
Which of these is a pure substance?
💡 Hint:
Ice is a pure form of water.
Explanation:
Ice is a pure substance. Air, milk and a brick are mixtures.
2
Iron pins and sand are separated by —
💡 Hint:
Iron is pulled.
Explanation:
A magnet.
3
In the figure the boiling point of oxygen is ______ °C.
💡 Hint:
This one becomes liquid first.
Explanation:
−183°C. Nitrogen is −196°C.
4
What mass of potassium nitrate is needed for a saturated solution in 50 g of water at 313 K? Show the steps.
Model answer (board format)
62 g dissolves in 100 g of water. In 50 g of water, (62/100) × 50 = 31 g.
Check your answer:
5
Model practice: red-hot iron and sulphur. Fill the coefficients of Fe + S → FeS (blank = 1).
Fe + S → FeS
Explanation: Fe + S → FeS
6
Write the order at the water works. Which layers would you put in the matka model at home? What is the job of chlorine?
Model answer (board format)
Reservoir, sedimentation tank, loading tank, a filter tank of sand and gravel, then chlorination and the home. In the matka, pebbles and sand are the filter layers. Chlorine kills bacteria.
Check your answer:
CBSE-style questions
0/6These are competency-based practice questions. They are not copies of a CBSE paper.
1
A student puts the ink drop on the paper and dips the strip so that the drop is under water. The colours do not separate. The most likely reason is —
💡 Hint:
Activity 2.7.
Explanation:
If the drop sits under the water the dye washes away. It should be just above the water level.
2
Potassium chloride saturated at 353 K cools to a room temperature of 293 K. For 100 g of water the crystals are about —
💡 Hint:
35 taken away from 54.
Explanation:
54 − 35 = 19 g of crystals.
3
Assertion (A): A starch solution shows Tyndall, a salt solution does not.
Reason (R): Starch is a colloid and a salt solution is a true solution.
Explanation:
Both are true and R is the correct reason.
4
Assertion (A): The gas from group II is odourless hydrogen.
Reason (R): The properties of a compound differ from those of its elements.
Explanation:
A is false. Group II gives hydrogen sulphide. R is true.
5
A lab has two beakers. One holds chalk in water, the other a blue copper sulphate solution. Without tasting, write three checks that show which is the suspension.
Model answer (board format)
If particles are visible, the torch path shows and the particles settle in a few minutes, it is the suspension. The blue liquid is a solution: particles are not seen, the path is not seen and it stays stable. On filtering, chalk stays on the paper.
Check your answer:
6
A report says that dissolving 40 g of salt in 320 g of water gives 40/320 × 100 = 12.5%. What is the mistake? Find the correct percentage.
Model answer (board format)
The mistake is that the percentage uses the mass of the solution, not only the water. The solution is 360 g. (40/360) × 100 = 11.1%.
Check your answer:
🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
Switch board with BSEB | CBSE above. The lessons follow the same NCERT chapter.
BSEB model · practiceBoard tip
This page has no verified annual-exam question, because no source page has been added. The model set below is practice in the board pattern.
🏛️ Model questions on one page →
The verified label will be used only when a source page for the question is available.
CBSE-style · competency-based
These are case and assertion-reason practice items. Do not treat them as past CBSE questions.
🔁 Spaced review — today’s questions
Wrong questions return soon; correct ones return after a few days.
🧠 What you learned + equation sheet
What you learned
- A substance is pure when all its particles are the same. A mixture has more than one substance in any proportion.
- A solution is homogeneous, its particles are smaller than 1 nm, it shows no Tyndall effect and it does not filter.
- A suspension is heterogeneous, its particles are visible, they settle and they can be filtered. A colloid shows the Tyndall effect and stays stable.
- Mass percentage = (mass of solute / mass of solution) × 100.
- The separation order is evaporation, centrifugation, separating funnel, sublimation, chromatography, distillation, crystallisation.
- A mixture keeps the properties of its parts. A compound has new properties and a fixed proportion.
| What | Keep this |
|---|---|
| Solution particles | smaller than 1 nm |
| Air | about 21 percent oxygen, 78 percent nitrogen |
| Brass | about 70 percent copper, 30 percent zinc |
| Fractional distillation | boiling points differ by less than 25 K |
| Example 2.1 | 40 g salt in 320 g water is 11.1 percent |
| Iron and sulphur | 5 g filings and 3 g sulphur |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.