Notes
Common Solute–Solvent Examples
| Solute | Solvent | State of Solution | Type | Example |
|---|---|---|---|---|
| Sugar | Water | Liquid | Solid in liquid | Sugar solution (syrup) |
| Salt | Water | Liquid | Solid in liquid | Saline water |
| Sulphur | Carbon disulphide | Liquid | Solid in liquid | Sulphur solution |
| Iodine | Alcohol | Liquid | Solid in liquid | Tincture of iodine |
| Copper sulphate | Water | Liquid | Solid in liquid | Copper sulphate solution (blue) |
| Alcohol | Water | Liquid | Liquid in liquid | Alcoholic beverages |
| Oxygen | Water | Liquid | Gas in liquid | Oxygenated water (aquatic respiration) |
| Carbon dioxide | Water | Liquid | Gas in liquid | Soda water |
| Ammonia | Water | Liquid | Gas in liquid | Aqueous ammonia |
| Alloys (e.g., brass) | Other metals | Solid | Solid in solid | Brass (zinc in copper), steel |
| Air (O₂, CO₂, etc.) | Nitrogen | Gas | Gas in gas | Air |
Key Point:
- The solvent is usually the component present in larger quantity, and it determines the phase of the solution.
- These combinations help understand homogeneous mixtures in various physical states.
Common Suspension Examples
| Solute (Dispersed Particles) | Solvent (Dispersion Medium) | Type | Example | Observation |
|---|---|---|---|---|
| Mud | Water | Solid in liquid | Muddy water | Particles settle if left undisturbed |
| Chalk powder | Water | Solid in liquid | Chalk in water | Opaque mixture, settles on standing |
| Sand | Water | Solid in liquid | Sand in water | Clear separation seen over time |
| Flour | Water | Solid in liquid | Flour paste | Thick, cloudy, settles if undisturbed |
| Paint pigments | Oil or water | Solid in liquid | Wall paint before stirring | Needs shaking; particles settle in can |
| Medicines (e.g., antacids) | Water | Solid in liquid | Milk of magnesia | Must be shaken before use |
| Dust | Air | Solid in gas | Dusty air during storm | Visible dust particles suspended temporarily |
Key Characteristics of Suspensions:
- Heterogeneous – not uniform throughout
- Particles are visible (to naked eye or microscope)
- Tyndall effect may be seen (if particles are large enough)
- Particles settle on standing
- Can be separated by filtration
Common Colloid Examples
| Dispersed Phase (Solute) | Dispersion Medium (Solvent) | Type of Colloid | Common Name / Example | Appearance |
|---|---|---|---|---|
| Solid | Solid | Solid sol | Coloured glass, alloys with large particles | Transparent but light-scattering |
| Liquid | Solid | Gel | Jelly, butter, cheese | Soft and semi-solid |
| Gas | Solid | Solid foam | Pumice stone, foam rubber | Spongy and porous |
| Solid | Liquid | Sol (or colloidal sol) | Paint, muddy water (fine clay) | Colored or cloudy but stable |
| Liquid | Liquid | Emulsion | Milk, mayonnaise | Opaque and creamy |
| Gas | Liquid | Foam | Whipped cream, shaving foam | Bubbly, frothy |
| Solid | Gas | Aerosol | Smoke, automobile exhaust | Tiny particles suspended in air |
| Liquid | Gas | Aerosol | Mist, clouds, fog | Light-scattering droplets in air |
Key Characteristics of Colloids:
- Heterogeneous (but appear homogeneous to the naked eye)
- Particles do not settle on standing
- Show Tyndall effect
- Cannot be separated by filtration
- Particles size: Between true solution and suspension (1–1000 nm)
Comparison: Solution vs Suspension vs Colloid
| Property | Solution | Suspension | Colloid |
|---|---|---|---|
| Type of mixture | Homogeneous | Heterogeneous | Heterogeneous (appears uniform) |
| Particle size | < 1 nm | > 1000 nm | 1 – 1000 nm |
| Particle visibility | Not visible | Visible to naked eye | Not visible to naked eye, visible under microscope |
| Tyndall effect |  Not shown |
 May show (if particles large) |
Clearly shows |
| Stability | Stable; does not settle | Unstable; particles settle on standing | Stable; particles do not settle |
| Separation by filtration | Not possible |
Possible |
Not possible (ordinary filter) |
| Examples | Salt in water, sugar in tea | Sand in water, chalk in water | Milk, fog, paint |
Questions
1. What is meant by a substance?
Answer:
A substance is a form of matter that has a definite composition and distinct properties.
It can be either:
- Element (e.g., oxygen, gold)
- Compound (e.g., water, carbon dioxide)
2. List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
| Feature | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Appearance | Uniform throughout | Non-uniform |
| Visibility of components | Components not visible | Components are visibly distinct |
| Examples | Salt in water, air | Sand in water, salad |
| Separation | Difficult to separate by simple methods | Can often be separated by physical means like filtration |
3. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:
| Feature | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Uniformity | Uniform composition throughout | Composition is not uniform |
| Visibility | Components not visible separately | Components can be seen |
| Separation | Difficult to separate | Can be separated easily |
| Examples | Salt in water, air | Oil in water, sand in iron filings |
4. How are sol, solution, and suspension different from each other?
Answer:
| Property | Solution | Colloid (Sol) | Suspension |
|---|---|---|---|
| Particle Size | Very small (< 1 nm) | Medium (1–1000 nm) | Large (> 1000 nm) |
| Appearance | Transparent | Often appears cloudy | Opaque |
| Stability | Stable, particles don’t settle | Stable, particles don’t settle quickly | Unstable, particles settle over time |
| Filtration | Cannot be separated by filtration | Cannot be separated by filtration | Can be separated by filtration |
| Example | Salt in water | Milk, starch in water | Muddy water, sand in water |
5. To make a saturated solution, 36g of sodium chloride is dissolved in 100g of water at 293 K. Find its concentration at this temperature.
Answer:
Answer: \boxed{26.47\%}
6. Classify the following as chemical or physical changes.
Chemical Changes:
- Cutting of trees (irreversible, cellular structure is changed)
- Rusting of almirah (formation of new substance—iron oxide)
- Passing of electric current through water and the water breaking down into hydrogen and oxygen gases (electrolysis—new substances formed)
- Burning of paper and wood – This is a chemical change because it produces new substances (like ash, carbon dioxide, and smoke), and the change is irreversible.
Physical Changes:
- Melting of butter in a pan (only change of state, no new substance)
- Boiling of water to form steam (physical state change—water remains H₂O)
- Dissolving common salt in water (no new substance, reversible)
- Making a fruit salad with raw fruits (no new substance formed, physical mixing)
7. Try segregating the things around you as pure substances or mixtures.
Answer:
Pure Substances
(Fixed composition; cannot be separated by physical means)
- Distilled water
- Iron nails
- Sugar (sucrose)
- Oxygen gas
- Gold ring (if 24-carat)
Mixtures
Homogeneous Mixtures
(Appear uniform; components not visibly distinct)
- Saltwater
- Air
- Vinegar
- Tea (without milk)
Heterogeneous Mixtures
(Components can be seen separately)
- Salad
- Soil
- Milk and cereal
- Sandy water
Exercises
1. Which separation techniques will you apply for the separation of the followings?
Answer:
(a) Sodium chloride from its solution in water
Technique: Evaporation
Explanation: Water can be evaporated, leaving the solid sodium chloride behind.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride
Technique: Sublimation
Explanation: Ammonium chloride sublimates on heating, turning into vapors directly, which can then be cooled and collected separately.
(c) Small pieces of metal in the engine oil of a car
Technique: Filtration using a magnet or centrifugation (if magnetic), or filtration using a fine mesh
Explanation: A magnet can remove magnetic metal pieces, or centrifugation can be used to separate denser metal particles from oil.
(d) Different pigments from an extract of flower petals
Technique: Chromatography
Explanation: Chromatography separates different pigments based on their movement through a medium.
(e) Butter from curd
Technique: Churning
Explanation: Churning separates butter (fat) from curd by spinning, which causes the fat to separate.
(f) Oil from water
Technique: Separating funnel
Explanation: Oil and water are immiscible liquids and can be separated by a separating funnel based on their density difference.
(g) Tea leaves from tea
Technique: Filtration
Explanation: Tea leaves are separated from liquid tea using a strainer or filter.
(h) Iron pins from sand
Technique: Magnetic separation
Explanation: Iron pins are magnetic and can be removed using a magnet.
(i) Wheat grains from husk
Technique: Winnowing
Explanation: The lighter husk is separated from heavier wheat grains by blowing air (traditional winnowing method).
(j) Fine mud particles suspended in water
Technique: Centrifugation or sedimentation followed by decantation
Explanation: Fine mud settles down on standing (sedimentation), or can be quickly separated by spinning (centrifugation).
Small pieces of metal in the engine oil of a car – What is happening?
When a car engine runs, friction between moving parts can sometimes cause tiny metal fragments (like iron, steel, or aluminum shavings) to break off. These metal pieces mix with the engine oil, which is used to lubricate and cool the engine.
Why is this a problem?
- These metal particles are solid and not soluble in oil.
- If not removed, they can damage engine parts, clog oil filters, or reduce efficiency.
- That’s why modern engines use oil filters to trap these particles.
How do we separate these metal particles?
Separation Techniques:
- Filtration (Mechanical filters):
- The oil is passed through a fine mesh or filter paper that traps the metal particles.
- Common in most engine oil filter systems.
- Magnetic separation (if the metal is magnetic like iron or steel):
- A magnet can be used to attract and remove the particles from the oil.
- Some advanced oil filters use magnetic elements for extra protection.
- Centrifugation (in industrial setups):
- The oil is rapidly spun in a machine.
- Denser metal particles move outward and settle, separating from the lighter oil.
Summary:
- The metal pieces are insoluble solids in a liquid (oil).
- This is a classic example of a heterogeneous mixture.
- Separation depends on particle size, magnetism, and the density difference.
Small pieces of metal in the engine oil of a car – What is happening?
Why is this a problem?
Summary:
Different pigments from an extract of flower petals
When you crush flower petals and mix them with a solvent (like alcohol or water), the colored substances (pigments) dissolve into the liquid. These pigments are responsible for the flower’s color—like red, purple, blue, or yellow.
What are pigments?
- Pigments are colored compounds that absorb specific wavelengths of light.
- Flowers often contain multiple pigments like anthocyanins, chlorophyll, carotenoids, etc.
- These pigments may all be dissolved in the solvent but are chemically different, and they behave differently when separated.
How do we separate them?
- Chromatography is the method used here.
- It separates substances based on their solubility and rate of movement through a medium.
- A strip of filter paper is prepared.
- A drop of the flower pigment extract is placed near the bottom.
- The bottom of the paper is dipped in a suitable solvent (like alcohol or water).
- As the solvent rises up the paper, it carries the pigments with it.
- Different pigments move at different speeds, depending on their solubility and interaction with the paper.
You see distinct colored spots at different heights on the paper — each representing a different pigment from the flower.
- Some pigments are more soluble, so they travel farther.
- Others bind more to the paper and move slower.
Different pigments from an extract of flower petals
What are pigments?
How do we separate them?
- Churning is a manual or mechanical process used to separate butter from curd or cream.
- It involves stirring or shaking the curd.
- As a result, butter (fat) separates out from the liquid part (buttermilk).
- This works because fat globules are lighter and clump together during agitation.
Used in homes or traditional methods.
- Centrifugation uses a machine that spins at high speed to separate components of a mixture.
- It forces denser particles to the bottom and lighter ones to the top, due to centrifugal force.
- Used to separate:
- Cream from milk
- Blood components
- Fine solids from liquids
Key Differences
Aspect Churning Centrifugation Method Manual/mechanical stirring High-speed spinning Energy Low-tech Machine-powered Force Used Physical agitation Centrifugal force Where Used Traditional settings (e.g., making butter) Scientific & industrial applications
So:
They are not the same, but they are based on the same principle — separation due to density difference. Centrifugation is just a faster and more efficient version of what churning does.
So:2. Making Tea – Scientific Explanation Using Key Terms
- Boil water, which acts as the solvent in this process.
- Add tea leaves, which are insoluble in water. They do not dissolve but release flavor and color.
- Add sugar, which is a solute. It is soluble in water and dissolves completely, forming a solution.
- Add milk if desired. Stir well. The resulting mixture is a uniform solution of all soluble substances.
- Once the tea is ready, filter it using a strainer.
- The liquid that passes through the strainer is called the filtrate (this is the tea we drink).
- The residue left behind in the strainer is made up of the insoluble tea leaves.
3. Based on the solubility table:
(a) What mass of potassium nitrate would be needed to produce a saturated solution in 50g of water at 313 K?
Answer
At 313 K, 62 g of potassium nitrate dissolves in 100 g of water.
So, for 50 g water:
Answer:
31 grams of potassium nitrate.
(b) What would Pragya observe if a saturated solution of potassium chloride at 353 K is cooled to room temperature?
Answer:
At 353 K, solubility = 54 g/100 g water
At room temperature (assume ~293 K), solubility = 35 g/100 g water
Excess solute = 54 – 35 = 19 g
She will observe that some potassium chloride will settle down as crystals, because the solution becomes supersaturated and the excess solute precipitates out.
(c) Solubility of each salt at 293 K:
Answer:
- Potassium nitrate – 32 g
- Sodium chloride – 36 g
- Potassium chloride – 35 g
- Ammonium chloride – 37 g
Highest solubility: Ammonium chloride
(d) Effect of temperature on solubility:
Answer:
In general, solubility increases with temperature. Most solids dissolve more at higher temperatures (as seen with potassium nitrate, whose solubility increases drastically). However, some like sodium chloride show very little change.
4. Explain with examples:
(a) Saturated solution:
A solution that cannot dissolve more solute at a given temperature.
Example: Sugar solution that no longer dissolves more sugar.
(b) Pure substance:
A material with uniform and definite composition.
Example: Water (H₂O), Oxygen (O₂)
(c) Colloid:
A mixture where particles are evenly dispersed but do not settle down. Shows Tyndall effect.
Example: Milk
(d) Suspension:
A heterogeneous mixture with large particles that settle down on standing.
Example: Mud in water
5. Classify into homogeneous and heterogeneous mixtures:
| Homogeneous | Heterogeneous |
|---|---|
| Soda water | Wood |
| Air | Soil |
| Vinegar | |
| Filtered tea |
6. How to confirm if a colourless liquid is pure water?
Answer:
- Check boiling point: Pure water boils at 100°C at 1 atm pressure.
- Check freezing point: Pure water freezes at 0°C.
- Evaporation test: When evaporated, pure water leaves no residue.
- Electrical conductivity: Pure water is a poor conductor of electricity (impure water conducts better due to ions).
7. Which of the following materials fall in the category of a “pure substance”?
Answer:
Pure substances:
- (a) Ice – solid form of water (H₂O), a compound.
- (c) Iron – element.
- (d) Hydrochloric acid – compound (HCl in water).
- (e) Calcium oxide – compound (CaO).
- (f) Mercury – element.
Not pure substances (they are mixtures or composites):
- (b) Milk – colloidal mixture of fats and proteins in water.
- (g) Brick – man-made mixture of materials.
- (h) Wood – natural composite of cellulose, lignin, etc.
- (i) Air – mixture of gases.
8. Identify the solutions among the following mixtures.
Solutions (homogeneous mixtures):
- (b) Sea water – salt dissolved in water.
- (c) Air – gases evenly mixed.
- (e) Soda water – carbon dioxide dissolved in water.
Not solutions:
- (a) Soil – heterogeneous mixture.
- (d) Coal – complex mixture of carbon and other compounds.
9. Which of the following will show “Tyndall effect”?
The Tyndall effect is the scattering of light by colloidal particles.
Will show Tyndall effect:
- (b) Milk – colloid.
- (d) Starch solution – colloid.
Will NOT show Tyndall effect:
- (a) Salt solution – true solution (particles too small).
- (c) Copper sulphate solution – true solution.
10. Classify the following into elements, compounds, and mixtures.
| Substance | Category |
|---|---|
| (a) Sodium | Element |
| (b) Soil | Mixture |
| (c) Sugar solution | Mixture (solution) |
| (d) Silver | Element |
| (e) Calcium carbonate | Compound |
| (f) Tin | Element |
| (g) Silicon | Element |
| (h) Coal | Mixture |
| (i) Air | Mixture |
| (j) Soap | Compound (or mixture if impure) |
| (k) Methane | Compound |
| (l) Carbon dioxide | Compound |
| (m) Blood | Mixture (colloidal in nature) |
Coal — Not a compound
- Coal is a mixture, not a compound.
- It is naturally occurring and made up of carbon, volatile substances, moisture, and mineral matter.
- The composition varies from sample to sample, which is a key trait of mixtures.
- It does not have a fixed formula like a compound does.
Soap — Can be a compound or a mixture, depending on context
If you’re talking about pure soap:
- It’s typically a compound like sodium stearate (C₁₇H₃₅COONa), formed by the reaction of fat with caustic soda (saponification).
- In this pure chemical form, it has a fixed composition and specific chemical properties — so yes, it’s a compound.
If you’re talking about commercial soap (used at home):
- It’s usually a mixture of:
- Soap base (compound),
- Glycerin,
- Perfume,
- Color,
- Moisturizers, etc.
- So, in everyday use, soap is often a mixture.
11. Which of the following are chemical changes?
Chemical changes (irreversible and involve new substances):
- (a) Growth of a plant – complex biochemical reactions.
- (b) Rusting of iron – iron reacts with oxygen and moisture.
- (d) Cooking of food – new substances formed by heat.
- (e) Digestion of food – chemical breakdown by enzymes.
- (g) Burning of a candle – combustion reaction.
Not chemical changes (physical processes):
- (c) Mixing of iron filings and sand – no new substance formed.
- (f) Freezing of water – change of state only.