- (a) Filtration
- (b) Sedimentation
- (c) Decantation
- (d) Centrifugation
Answer:
(d) Centrifugation
- (a) Common salt
- (b) Juice
- (c) Carbon dioxide
- (d) Pure silver
Answer:
(b) Juice
- (a) Heterogeneous mixture
- (b) Compound
- (c) Homogeneous mixture
- (d) Suspension
Answer:
(c) Homogeneous mixture
- (a) Separating funnel
- (b) Filter paper
- (c) Centrifuge machine
- (d) Sieve
Answer:
(a) Separating funnel
- (a) Pure substance
- (b) Mixture
- (c) Colloid
- (d) Suspension
Answer:
(a) Pure substance
If false, correct the statement.
This statement is true. Oil and water are immiscible liquids, meaning they do not mix with each other to form a homogeneous solution. This occurs because oil is nonpolar while water is polar, and the difference in their chemical nature prevents them from dissolving in one another. When oil and water are mixed together, they form a heterogeneous mixture where the two liquids remain as separate phases with a distinct boundary between them. This immiscibility is due to the principle that like dissolves like, where polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.
This statement is false. A compound can be broken down into simpler substances through chemical methods. Compounds are pure substances formed when two or more elements combine chemically in a fixed ratio. The chemical bonds holding the elements together can be broken by applying chemical reactions, heat, or electricity. For example, water (a compound) can be decomposed into hydrogen and oxygen gases by passing electric current through it, a process called electrolysis. Similarly, copper sulfate can be decomposed by heating to produce copper oxide, sulfur dioxide, and oxygen. This ability to decompose into simpler substances is a defining characteristic that distinguishes compounds from elements.
This statement is false. The correct statement is that liquid-solid colloids are called gels. A gel is a colloidal system where a solid is dispersed as the dispersed phase in a liquid as the dispersion medium. Common examples of gels include gelatin, jelly, and agar. Liquid-liquid colloids, where a liquid is dispersed in another liquid, are called emulsions. Examples of emulsions include milk, mayonnaise, and cream. Understanding the correct classification of colloids is important because different types of colloids have different properties and applications based on the nature of their dispersed phase and dispersion medium.
This statement is true. Buttermilk is a heterogeneous mixture because it contains suspended particles of fat and milk solids dispersed throughout the liquid phase. These particles are visible under a microscope and do not dissolve uniformly in the liquid, meaning the composition and properties vary from one part of the mixture to another. The particles can be separated from the liquid by physical methods such as centrifugation or filtration. This heterogeneous nature is why buttermilk appears slightly opaque and why it exhibits the Tyndall effect when light passes through it, making the path of light visible due to scattering by the suspended particles.
This statement is false. Aspirin is a compound, not a mixture. Although aspirin does contain carbon, hydrogen, and oxygen in fixed proportions, the presence of elements in fixed proportions is a characteristic of compounds. In aspirin, these elements are chemically bonded together in a specific arrangement to form the aspirin molecule (acetylsalicylic acid). The key distinction is that in a compound, the constituent elements are chemically combined through covalent bonds in a definite ratio that cannot be altered without breaking the chemical bonds. In contrast, a mixture is a physical combination of two or more substances where the components retain their individual properties and can be present in variable proportions. The fixed ratio of elements in aspirin, combined with the fact that it has distinct chemical properties different from its individual elements, confirms that aspirin is a pure compound rather than a mixture.
| A | B |
|---|---|
| Element | Pure substance |
| Compound | Made up of molecules |
| Colloid | Intermediate mixture |
| Suspension | Settles down on standing |
| Mixture | Impure substance |
Correction made:
Original matching “Compound – made up of atoms” was scientifically inaccurate. Compounds are made up of molecules or ions.
Answer: homogeneous
Answer: camphor or dry ice
Answer: fractional distillation
Answer: fractional distillation
Answer: solubility and adsorption
| Absorption | Adsorption |
|---|---|
| Substance enters bulk of another substance | Substance accumulates only on surface |
| Entire material involved | Surface phenomenon |
| Example: sponge absorbing water | Example: charcoal adsorbing gases |
Answer:
Direct conversion of solid into vapour without becoming liquid is called sublimation.
Examples:
- Camphor
- Naphthalene
- Dry ice
The Dettol-water mixture becomes turbid because Dettol forms an emulsion in water. Dettol is an oily liquid that does not dissolve in water due to the difference in their polarities. When Dettol is mixed with water, the oil particles disperse throughout the water as a colloidal system, creating an emulsion where oil droplets are suspended in the water phase. These suspended oil particles scatter light in all directions through a phenomenon called the Tyndall effect. This scattering of light by the colloidal particles makes the mixture appear cloudy or turbid rather than clear and transparent. The turbidity increases with the concentration of Dettol because more oil particles are present to scatter the light.
(i) Miscible liquids
- Distillation apparatus
- Fractionating column
(ii) Immiscible liquids
- Separating funnel
| Mixture | Components |
|---|---|
| Ice cream | Milk, cream, sugar |
| Lemonade | Lemon juice, sugar, water |
| Air | Nitrogen, oxygen, gases |
| Soil | Sand, clay, minerals |
Given:
- Ice
- Milk
- Iron
- Hydrochloric acid
- Mercury
- Brick
- Water
Pure Substances:
- Ice
- Iron
- Mercury
- Water
Correction made:
Hydrochloric acid solution and brick are not pure substances.
Oxygen is an element. An element is a pure substance composed of only one type of atom, characterized by a specific atomic number. Oxygen atoms all have eight protons in their nucleus, which defines oxygen as a distinct element. Although oxygen can exist in different forms such as diatomic oxygen (O₂), which is the common form in the atmosphere, or ozone (O₃), which is a different allotrope, all these forms contain only oxygen atoms and no other elements. This is why oxygen is classified as an element rather than a compound, which would require a combination of two or more different elements chemically bonded together.
22-carat gold is not pure gold; it is an alloy and therefore an impure substance or mixture. Pure gold is defined as 24-carat gold, which contains 99.9% or higher gold content. In contrast, 22-carat gold contains approximately 91.67% gold by mass, with the remaining 8.33% consisting of other metals such as copper, silver, or other alloys added to increase durability and hardness. These added metals are mixed with gold in a fixed proportion to create an alloy with improved mechanical properties suitable for jewelry making. Since 22-carat gold contains more than one element and is a physical mixture of gold with other metals, it is classified as an impure substance rather than a pure substance.
To separate a mixture of sawdust, naphthalene, and iron filings, a multi-step separation process is required because each component has different physical properties. In step one, a magnet is used to remove iron filings from the mixture since iron is ferromagnetic and will be attracted to the magnet while sawdust and naphthalene remain unaffected. In step two, the remaining mixture of sawdust and naphthalene is heated gently. Naphthalene is a volatile solid that sublimes when heated, converting directly from solid to gas without passing through the liquid state, and can be collected by condensation. In step three, sawdust remains behind as a solid residue after naphthalene has sublimed away. This sequential use of magnetic separation, sublimation, and heating effectively separates all three components based on their distinct physical properties.
| Homogeneous Mixture | Heterogeneous Mixture |
|---|---|
| Uniform composition | Non-uniform composition |
| Single phase | Multiple phases |
| Components not visible | Components visible |
| Example: salt solution | Example: sand in water |
| Elements | Compounds |
|---|---|
| Made of only one kind of atom; some elements exist as molecules, such as O₂ | Made of two or more different elements chemically combined in a fixed ratio |
| Cannot be broken down into simpler substances by chemical methods | Can be broken down into simpler substances by chemical methods |
| Smallest particle may be an atom or molecule | Smallest particle may be a molecule or formula unit |
| Example: Copper (Cu), Oxygen (O₂) | Example: Water (H₂O), Carbon dioxide (CO₂) |
Brownian movement is the random, continuous, zig-zag motion exhibited by colloidal particles suspended in a fluid medium. This movement is caused by the unequal and random collisions of the medium's molecules with the colloidal particles from all directions. Since these molecular collisions are not perfectly balanced, the particles experience a net force that changes direction constantly, resulting in the characteristic random walk pattern. Tyndall effect is the phenomenon of scattering of light by colloidal particles suspended in a medium. When a beam of light passes through a colloidal solution, the path of the light becomes visible as a bright cone or track because the colloidal particles scatter the light in all directions. This effect can be observed when sunlight enters a dusty room, where the dust particles scatter the light and make the light beam visible. Both Brownian movement and Tyndall effect are important characteristics that help identify and distinguish colloidal solutions from true solutions and suspensions.
Step 1:
Take mixture in separating funnel.
Step 2:
Allow layers to settle.
- Oil forms top layer
- Salt solution forms bottom layer
Step 3:
Open tap to collect salt solution.
Step 4:
Evaporate water to obtain salt.
Air and Brass
Air:
Mixture of gases.
Brass:
Alloy of copper and zinc.
Hence brass is a mixture.
Iron and Sulphur
Without Heating
Iron and sulphur remain mixture.
On Heating
Chemical reaction occurs:
Iron sulphide formed.
Correction made:
Original text incorrectly mentioned “iron sulphate”.
Mixture or Compound
| Substance | Type |
|---|---|
| Sand + water | Mixture |
| Sand + iron filings | Mixture |
| Concrete | Mixture |
| Water + oil | Mixture |
| Salad | Mixture |
| Water | Compound |
| Carbon dioxide | Compound |
| Cement | Mixture |
| Alcohol | Compound |
Sugar, Starch and Wheat Flour in Water
Observation:
- Sugar dissolves completely.
- Wheat flour settles after some time.
Conclusion:
Some substances form solutions while others form suspensions.
# Test Yourself
Milk appears white because it is a colloidal dispersion containing suspended fat particles and protein molecules. These suspended particles scatter all colors of visible light equally in all directions through the Tyndall effect. Since all wavelengths of visible light are scattered uniformly without any preferential scattering of particular colors, the scattered light appears white to our eyes. The white appearance is due to the combined effect of all colors being scattered together. If milk were a true solution without suspended particles, it would be transparent. The opacity and white color of milk are direct consequences of its colloidal nature and the light-scattering properties of its dispersed phase.
Water absorbs longer wavelengths of light such as red and orange more strongly than shorter wavelengths. The shorter wavelengths, particularly blue light, are scattered more effectively by water molecules. When sunlight enters the ocean, the longer wavelengths are absorbed within the upper layers and converted to heat, while the blue wavelengths are scattered back towards our eyes. This scattered blue light is what we perceive when looking at the ocean, making it appear blue. The depth of water also plays a role, as deeper oceans appear darker blue because more light is absorbed before reaching greater depths.
The Sun appears yellow due to the scattering of light by Earth's atmosphere. When sunlight passes through the atmosphere, shorter wavelengths such as blue and violet light are scattered more effectively by atmospheric molecules and particles through a process called Rayleigh scattering. This scattering removes a significant portion of the blue and violet wavelengths from the direct beam of sunlight reaching our eyes. The remaining light that reaches us is enriched in longer wavelengths, particularly yellow, orange, and red. The combination of the scattered shorter wavelengths and the transmitted longer wavelengths results in the Sun appearing yellowish-white to our eyes. This effect is more pronounced when the Sun is near the horizon, where the light must travel through a greater thickness of atmosphere, causing even more blue light to be scattered away and making the Sun appear more orange or red.
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