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Chapter: 03. Elements Compounds And Mixtures

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EXERCISE FOR REVISION (Page 7-8)

A. Tick (✓) the correct options.
Substances that contain the same kind of particles (atoms or molecules) are called ______ substances.
(a) pure
A/An ______ is a pure substance made up of only one kind of atoms that cannot be split into two or more simpler substances by any physical or chemical method.
(a) element
Elements that show some properties of metals and some of non-metals are called
(b) metalloids
Which of the following elements is not present in glucose?
(​c​) sulphur
Which of the following is not correct about a compound?
(b) Its constituents can only be separated by physical methods.
B. Assertion-Reason based Question.
Assertion: Most elements are metals. ​Reason: Metals are mostly solid at room temperature.
(b) Both A and R are true but R is not the correct explanation of the assertion.
C. Write the symbols of the following.
Copper
Cu
Iron
Fe
Fluorine
F
Aluminium
Al
Potassium
K
Magnesium
Mg
Hydrogen
H
Carbon
C
Gold
Au
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IN-TEXT ACTIVITY QUESTIONS (Part 1)

Activity 2 (Page 8-9)
Q: What type of mixture is an emulsion?
An emulsion is a heterogeneous liquid-in-liquid mixture composed of two or more immiscible liquids that cannot be mixed completely.
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EXERCISE FOR REVISION (Page 40)

A. Tick (✓) the correct options.
Generally, energy is __________ during the formation of a mixture.
(d) neither released nor absorbed
Oil in water is an example of a ______________ mixture.
(​c​) heterogeneous liquid in liquid
Which of the following is not an example of a homogeneous mixture?
(​c​) oil in water
Which of the following is not an example of a heterogeneous mixture?
(b) salt and water
Which of the following is not an example of a solid in a solid mixture?
(a) ice cream
Which of the following is not an example of a mixture?
(b) water
Which of the following is not correct about a mixture?
(​c​) The components undergo a chemical change.
B. Assertion-Reason based Questions.
Assertion: Brass is an alloy. ​Reason: Brass is a homogeneous mixture of copper and zinc.
(a) Both A and R are true and R is the correct explanation of the assertion.
Assertion: The components of a mixture can be separated by simple physical methods. ​Reason: It is because they do not combine chemically.
(a) Both A and R are true and R is the correct explanation of the assertion.
⁠

IN-TEXT ACTIVITY QUESTIONS (Part 2)

Activity ① (Page 40)
Q: List any four examples of compound.
Water (
math
⁠
), Carbon dioxide (
math
⁠
), Common Salt (
math
⁠
), and Glucose (
math
⁠
).
Activity 4 (Page 41)
Q: What happens to ammonium chloride when it gets heated?
On heating, solid ammonium chloride undergoes sublimation and directly changes into its gaseous state (vapour) without passing through the liquid state.
Activity 5 (Page 42)
Q: Explain the process of evaporation.
Evaporation is the process during which a liquid changes into its vapour state at a temperature below its boiling point. It is used to separate solid solutes from homogeneous solid-liquid mixtures.
Activity 2 (Page 44)
Q: Write the use of separating funnel.
A separating funnel is used to separate the components of a heterogeneous liquid-liquid mixture consisting of two immiscible liquids that have different densities.
Activity 8 (Page 45)
Q: Is chromatography possible for materials that are insoluble in water?
Yes, chromatography is possible for water-insoluble materials, provided a different suitable solvent (like ethanol, acetone, or ether) in which the materials can dissolve is used as the mobile phase.
⁠

EXERCISE FOR REVISION (Page 45-46)

A. Tick (✓) the correct options.
When a solid directly changes into its gaseous state on heating, it is called
(​c​) sublimation
Which of the following can be separated by using a separating funnel?
(d) kerosene and water
Which of the following is the principle on which chromatography is based?
(​c​) Substances have different solubilities in a solvent and interact differently with mobile and stationary phase.
B. Assertion-Reason based Question.
Assertion: Petrol and diesel can be obtained from crude oil by simple distillation. ​Reason: Components of crude oil have different boiling points.
(d) A is false but R is true. (Note: Petrol and diesel are obtained by fractional distillation, not simple distillation.)
Complete the flowchart for Revision
Complete the missing terms in the flowchart based on the chapter content:
Classification of Matter: Matter is classified into Pure Substances (which are further split into Elements and Compounds) and Impure Substances or Mixtures (which are split into Homogeneous Mixtures and Heterogeneous Mixtures).
Separation of Solids from a mixture of solids: Hand-picking, Winnowing, Sieving, Magnetic separation, Gravitation, Sublimation.
Separation of Solids from a mixture of solid and liquid: Sedimentation and decantation, Filtration, Evaporation, Crystallisation, Distillation, Centrifugation.
Separation of Liquids from a mixture of liquids: Fractional distillation (for miscible liquids) and Using a separating funnel (for immiscible liquids).
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COMPETENCY BASED DISCUSSION: SEPARATION OF COMPONENTS OF MIXTURE

A. Short Answer Questions:
What are mixtures? Give two characteristics of mixtures.
A mixture is an impure substance formed when two or more pure substances (elements or compounds or both) are physically mixed together in any proportion without undergoing any chemical change, such that they retain their individual properties.
Two characteristics of mixtures are:
(i) They do not have a fixed composition; their components can be present in any proportion.
(ii) They do not have fixed melting and boiling points, as these depend on the proportion of their components.
Define evaporation. Why is distillation better than evaporation?
Evaporation is the process during which a liquid changes into its vapour state at a temperature below its boiling point.
Distillation is better than evaporation because evaporation only recovers the solid solute while the liquid solvent escapes into the air as vapour. Distillation recovers both the solid solute and the liquid solvent by condensing the evaporated liquid vapour back into a pure liquid (distillate).
What is the principle of centrifugation? How is cream separated from milk by using it?
The principle of centrifugation is based on separating insoluble particles from a liquid according to their densities by rotating the mixture at a very high speed. Under high-speed rotation, the heavier (denser) particles are forced to the bottom, while the lighter (less dense) particles float on top.
Cream is separated from milk by spinning milk at high speed in a centrifuge machine. Since cream is lighter than the rest of the milk components, it floats to the top and can then be easily separated.
What is the need for the separation of components of a mixture?
We need to separate the components of a mixture to:
(i) Remove undesirable and harmful substances.
(ii) Obtain useful individual components.
(iii) Get a pure sample of a substance.
Differentiate between homogeneous and heterogeneous mixtures.
Homogeneous Mixture: A mixture in which the constituent components are mixed uniformly throughout, such that they cannot be seen separately (e.g., salt dissolved in water, air, brass).
Heterogeneous Mixture: A mixture in which the components are not mixed uniformly and can be seen separately with the naked eye or a magnifying glass (e.g., oil in water, soil, sand and sawdust).
Give any two characteristics of compounds.
Two characteristics of compounds are:
(i) They are composed of two or more elements chemically combined in a fixed proportion by mass.
(ii) The physical and chemical properties of a compound are entirely different from the properties of its constituent elements.
B. Long Answer Questions:
What is distillation? How is it different from fractional distillation?
Distillation is a method used to obtain a pure liquid from a solution by boiling the solution to convert the liquid into vapour, and then cooling and condensing the vapour back into liquid form using a condenser. It is typically used for solid-liquid mixtures or miscible liquid mixtures where the components have a large boiling point difference (25 °C or more).
Fractional Distillation is different because it is used to separate miscible liquids that have a small boiling point difference (less than 25 °C). It utilizes a fractionating column filled with glass beads, which provides a large surface area for repeated evaporation and condensation cycles, ensuring complete separation of the liquids.
What are immiscible liquids? How do we separate oil from a mixture of oil and water?
Immiscible liquids are liquids that do not dissolve completely in each other and form separate, distinct layers when mixed (e.g., oil and water).
We separate oil from oil and water using a separating funnel as follows:
(i) Pour the mixture into a separating funnel and let it stand undisturbed for some time.
(ii) Two distinct layers will form: water (being denser) forms the lower layer, and oil (being lighter) forms the upper layer.
(iii) Place a beaker below the funnel and open the stopcock to allow the lower water layer to drain out.
(iv) Close the stopcock immediately when the separating boundary of the oil layer reaches the stopcock.
(v) Place another beaker and drain the remaining oil, separating the two liquids completely.
Describe the process of separation of ammonium chloride from a mixture of ammonium chloride and common salt.
This mixture is separated using the process of sublimation:
(i) Place the mixture of ammonium chloride and common salt (sodium chloride) in a china dish.
(ii) Block the nozzle of a glass funnel with a cotton plug and invert it over the china dish.
(iii) Heat the china dish gently using a Bunsen burner.
(iv) Ammonium chloride is a sublimable solid, so on heating, it directly changes from solid to vapour.
(v) The vapours of ammonium chloride rise and condense on the cool inner walls of the inverted funnel as a solid (deposition), which can be scraped off. Non-sublimable common salt remains behind in the china dish.
What is chromatography and on what principle does it work? How are the pigments in ink separated by this process?
Chromatography is a technique used to separate and identify different dissolved components present in a mixture in very small quantities based on their adsorption on an appropriate stationary material.
Principle: It works on the principle that different components in a mixture have different solubilities in a given solvent (mobile phase) and thus travel at different speeds and adsorb differently onto a stationary phase (like chromatography paper).
Separation of ink pigments (Paper Chromatography):
(i) Draw a reference line with a pencil about 3 cm from the bottom edge of a strip of Whatmann filter paper.
(ii) Put a small spot of ink from a marker pen at the centre of this line and let it dry.
(iii) Suspend the paper vertically in a chromatographic jar containing water (the level of water must be below the pencil mark).
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