ICSE Solutions for Chapter 3 Elements, Compounds and Mixtures Class 7 Chemistry Selina Publisher
Exercise- I
1. Write the symbols of helium, silver, krypton, antimony, barium.
Answer
2. Write the names of following elements Na, C, Kr, U, Ra, Fe, Co.
Answer
|
Symbol |
Element |
|
Na |
Sodium |
|
C |
Carbon |
|
Kr |
Krypton |
|
U |
Uranium |
|
Ra |
Radium |
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Fe |
Iron |
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Co |
Cobalt |
3. Define:
1. Elements
2. Compounds
Answer
1. Elements: An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.
2. Compounds: A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.
4. Name the main metal present in the following :
Answer
|
(a) Haemoglobin |
Iron |
|
(b) Chalk |
Calcium |
|
(c) Chlorophyll |
Magnesium |
|
(d) Chocolate wrappers |
Aluminium |
5. Give four examples of non - metallic elements.
Answer
Examples: Hydrogen, oxygen, nitrogen, carbon, chlorine, sulphur, phosphorus, etc.
6. What do you understand by:
1. Metalloids
2. Noble Gas
Answer
1. Metalloids: Metalloids are those substances which have some properties of metals and some of non-metals e.g. boron, silicon.
2. Noble gases: Noble gases are those which do not react chemically with other elements or compounds e.g. helium, neon, etc.
7. Select elements and compounds from the following list: Iron, plaster of paris, chalk, common salt, copper, aluminium, calcium oxide, cane sugar, carbon, silica, sodium sulphate, uranium, potassium carbonate, silver, carbon dioxide.
Answer
|
Element |
Compounds |
|
Iron |
Plaster of paris |
|
Copper |
Chalk |
|
Aluminium |
Common salt |
|
Carbon |
Calcium oxide |
|
Uranium |
Cane sugar |
|
Silver |
Silica |
|
Sodium sulphate |
|
|
Potassium carbonate |
|
|
Carbon dioxide |
Exercise- II
1. State four difference between compounds and mixtures.
Answer
|
Compound |
Mixture |
|
1. A compound is a pure substance. |
1. A mixture is an impure substance. |
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2. Compounds are always homogeneous. |
2. Mixtures may be homogeneous or heterogeneous |
|
3. A compound has a fixed composition, i.e., it is formed when two or more pure substances chemically combine in a definite ratio by mass. |
3. A mixture has no fixed composition, i.e., it is formed by mixing two or more substances in any ratio with any chemical reaction. |
|
4. Formation of a compound involves change in energy. |
4. Formation of a mixture does not involve any change in energy. |
|
5. Compounds have specific set of properties. |
5. Mixtures do not have any specific set of properties. |
|
6. Components of compounds can be separated only by complex chemical processes. |
6. Components of mixtures can be separated by simple physical methods. |
2. What are the characteristic properties of a pure substance? Why do we need them?
Answer
Pure substance: Pure substances have a definite set of properties such as boiling point, melting point, density, etc. They are all homogeneous i.e., their composition is uniform throughout the bulk. Both elements and compounds are pure substances.
Pure substances are needed to:
- Manufacture medicines.
- To prepare chemicals in industry.
- For scientific purposes.
- To maintain the good health of human beings.
3. Give two examples for each of the following :
(a) Solid + Solid mixture
(b) Solid + Liquid mixture
(c) Liquid + Liquid mixture
Answer
(a) Solid + Solid mixture
- Sand and sugar,
- Sand and stone,
- sand and sugar.
(b) Solid + Liquid mixture:
- Sand and water,
- Charcoal and water.
(c) Liquid + Liquid mixture :
- Oil in water,
- Alcohol and water.
4. Define:
1. Evaporation
2. Filtration
3. Sublimation
4. Distillation
5. Miscible Liquids
6. Immiscible Liquids
Answer
- Evaporation: Is the process ~of converting a liquid into its vapours state either by exposing it to air or by heating.
- Filtration: The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.
- Sublimation: The process in which a solid changes directly into its vapours on heating is called sublimation.
- Distillation : Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
- Miscible liquids : Homogeneous liquid-liquid mixtures are called miscible liquids.
- Immiscible liquids : Heterogeneous liquid-liquid mixtures are called immiscible liquids.
5. Name the process by which the components of following mixtures can be separated.
i. Iron and sulphur
ii. Ammonium chloride and sand
iii. Common salt from sea water
iv. Chaff and grain
v. Water and mustard oil
vi. Sugar and water
vii. Cream from milk
Answer
i. Magnetic separation.
ii. Sublimation.
iii. Evaporation.
iv. Winnowing separates chaff (lighter) from heavier grains in two different heaps.
v. Mustard oil and water is liquid-liquid immiscible mixture and is separated by separating funnel. Water being the heavier forms the lower layer.
vi. By evaporation in this process of converting a liquid into its vapour state by heating. Liquid is heated and water evaporate and sugar is obtained.
vii. Centrifugation.
Answer
Camphor with sublimation. Chalk powder by Alteration then the residual left is common salt.
7. How is distillation more advantageous than evaporation?
Answer
The advantage of distillation is that both components of the solid and liquid mixture are obtained. Whereas in evaporation only solid is obtained.
8. i. What is chromatography?
ii. Why is it named so?
iii. What are the advantages of chromatography?
iv. Name the simplest type of chromatography?
v. On what principle is this method based?
vi. What is meant by stationary phase and mobile phase in chromatography?
Answer
i. The process of separating different dissolved constituents of a mixture by their absorption on an appropriate material is called chromatography.
ii. It is named so, because earlier it was used to separate mixtures containing coloured components only but these days this technique is applied to colourless substances too.
iii. Advantages of chromatography:
- A very small quantity of the substance can be separated.
- Components with very similar physical and chemical properties can be separated.
- It identifies the different constituents of a mixture.
- It also helps in quantitative estimation of components of a mixture.
iv. The simplest type of chromatography is “Paper chromatography”.
v. Chromatography is based on differential affinities of compounds towards two phases i.e. stationary and mobile phase.
vi. The filter paper acts as “stationary phase” while the solvent act as “mobile phase”.
9. On what principle are the following methods of separation based? Give one example of a mixture for each of the methods mentioned in which they are used
Answer
i. Sublimation: Change of solid into vapours directly on heating and change of vapours into solid again on cooling. Example: Salt from ammonium chloride.
ii. Filtration: The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called Alteration. These filters allow liquids to pass through them but not solids. The insoluble solid left on the filter is called the residue, while the liquid which passes through the filter is called the filtrate. Mixtures like chalk and water, clay and water, tea and tea leaves, sawdust and water, etc., are separated by this method.
iii. Sedimentation and decantation: The settling down of suspended, insoluble, heavy, solid particles in a solid- liquid mixture when left undisturbed is called sedimentation.
The solid which settles at the bottom is called sediment while the clear liquid above it is called supernatant liquid. The process of pouring out the clear liquid, without disturbing the sediment, is called decantation.
Example: A mixture of sand and water.
iv. Solvent extraction method: This method is used when one of the solid components is soluble in a liquid.
Example: A mixture of sand and salt can be separated by this method. Salt gets dissolved in water while sand settles down in the container. The salt solution is then decanted. Salt is separated from the solution by evaporation. In this way, they can be separated.
v. Magnetic separation: This method is used when one of the components of the mixture is iron. Iron gets attracted towards a magnet and hence can be separated. Mixtures of iron and sulphur, iron and sand, etc., can be separated by moving a magnet over them. Iron gets attached to the magnet and is separated.
vi. By using a separating funnel: It is a simple device used to separate the components of a liquid-liquid heterogeneous mixture.
Example: Kerosene oil and water. The mixture is placed in a separating funnel and allowed to stand for sometime. The components form two clear layers. Water being heavier forms the lower layer and oil being lighter forms the upper layer. When the stopper of the funnel is opened, the heavier liquid trickles out slowly and is collected in a vessel. The stopper is closed when the bottom layer is entirely removed the funnel. In this way, the two liquids are separated.
vii. Fractional distillation: The process of distillation is used for separating the components of a homogeneous liquid-liquid mixture, like water and alcohol. This is based on the fact that alcohol boils at a lower temperature than water. The vapour of alcohol are collected and cooled while water is left behind in the original vessel. Thus, two liquids having different boiling points can be separated by distillation provided that difference in their boiling points must be 25°C or more.
Objective Type Questions
1. Fill in the blanks:
i. ______ are made up of same kind of atoms.
ii. ______ and ______ are pure substances.
iii. In a _______ the substances are not combined chemically.
iv. Clay is separated from water by the method called ______
v. _______ is a process to obtain a very pure form of a solid dissolved in a liquid.
vi. Camphor and ammonium chloride can _______
Answer
i. Elements
ii. Elements, compounds
iii. mixture
iv. loading and decantation
v. crystallisation
vi. sublimate.
2. Give one word answers for the following :
a. The solid particles which remain on the filter paper after the filtration residue.
b. The liquid which evaporates and then condenses during the process of distillation distillate.
c. The process of transferring the clean liquid after the solid settles at the bottom of the container decantation.
d. The process by which two miscible liquids are separated fractional distillation.
Answer
a. residue.
b. distillate
c. decantation
d. fractional distillation
Multiple Choice Questions
Select the correct alterative from the choices given for the following statements:
1. A pure liquid is obtained from a solution by :
a. evaporation
b. distillation
c. Alteration
d. crystallisation
Answer
b. distillation
2. Components of crude petroleum can be separated by :
a. distillation
b. evaporation
c. filtration
d. fractional distillation
Answer
d. fractional distillation
3. Example of a homogeneous mixture is :
a. tap water
b. distilled water
c. sand and water
d. water and oil
Answer
a. tap water
4. In chromatography the filter paper is :
a. stationary phase
b. mobile phase
c. mixture
d. none of the above
Answer
a. stationary phase
5. A set of mixture is :
a. ink, honey, icecream, milk
b. tapwater, gold, common salt, alloy
c. milk, brass, silver, honey
d. butter, petroleum, tapwater, iron
Answer
a. ink, honey, icecream, milk
Additional Questions
Check Your Progress 1
1. Fill in the blanks.
a. A pure substance has definite _____ and constant _____
b. Mixtures can be _____
c. Use of a ______ to separate the components of a mixture of solids is based on the difference in the size of the components.
d. _____ is used when the constituents of a mixture of solids have difference in their weights.
e. Iodine, camphor, naphthalene, ammonium chloride and dry ice are some substances that _____
Answer
a. composition , properties.
b. heterogeneous or homogenous.
c. sieve
d. winnowing
e. sublimate
Check Your Progress 2
1. Filtration is a method used to separate fine particles of solid from a liquid.
Answer
Filtration is a method used to separate fine particles of insoluble solid from a liquid.
2. Loading is basically speeding up ______
Answer
sedimentation.
3. Name the techniques used to separate a solid from its solution.
Answer
Sedimentation and Decantation
4. A separating funnel can be used for separating a mixture of immiscible liquids. True or false ?
Answer
True
5. During centrifugation, solid particles of the mixture move towards the bottom. True or false ?
Answer
True
Exercise- III
A. Tick the most appropriate answer.
1. The constituents of a mixture are present in a fixed ratio
a. a fixed ratio
b. a variable ratio,
c. the ratio of 2 : 1
d. none of these
Answer
b. a variable ratio,
2. Solutions are
a. heterogeneous mixtures.
b. compounds,
c. homogeneous mixtures.
d. elements.
Answer
c. homogeneous mixtures.
3. The methods of separating components of a given mixture are based on the
a. physical properties and state of the components.
b. colour of the components only.
c. state of the components.
d. none of these.
Answer
a. physical properties and state of the components.
4. Winnowing is the method used to separate
a. chaff from grain.
b. stones from rice.
c. oil from water.
d. salt from sand.
Answer
a. chaff from grain.
5. During filtration the substance left behind on the filter paper is called
a. distillate,
b. filtrate
c. sublimate.
d. residue.
Answer
d. residue.
6. Loading is a process in which
a. impurities become heavy and sink to the bottom.
b. impurities float on the top.
c. impurities vaporize.
d. none of these
Answer
a. impurities become heavy and sink to the bottom
7. Fractional distillation is used to separate liquids having an appreciable difference in their
a. size and shape
b. solubility
c. boiling points.
d. none of these
Answer
c. boiling points
8. The different constituents of an ink are separated by
a. handpicking.
b. paper chromatography
c. filtration.
d. magnetic separation.
Answer
b. paper chromatography
B. Fill in the blanks.
a. A _____ substance has only one kind of matter.
b. The composition and properties of a _____ mixture is uniform throughout.
c. An ______ is a homogeneous mixture of two or more metals.
d. Chalk powder dissolved in water is an example of a ______
e. An ______ is formed when one liquid is dispersed as tiny droplets throughout another liquid.
f. Immiscible liquids are separated by using a _____
Answer
a. pure
b. homogenous
c. alloy
d. suspension
e. emulsion
f. separating funnel
C. Write true or false for each statement. Rewrite the false statements correctly.
1. All pure substances have characteristic melting and boiling points.
Answer
True
2. Milk is an emulsion.
Answer
True
3. A heterogeneous mixture has a uniform composition throughout the mixture.
Answer
False. A heterogeneous mixture has a non-uniform composition throughout the mixture.
4. The constituents of a mixture can only be separated by chemical means.
Answer
False. The constituents of a mixture can be separated by chemical means and physical means.
5. Handpicking can be used as a separation technique if the particle size of the constituents of the mixture is the same.
Answer
False. Handpicking can be used as a separation technique if the particle size of the constituents of the mixture is the not the same.
D. Match the columns.
|
1. to separate grain from chaff |
a. filtration |
|
2. to separate sawdust |
b. sedimentation and decantation |
|
3. to separate iodine from sodium chloride |
c. winnowing |
|
4. to separate iron fillings from sand |
d. sublimation |
|
5. it is used to separate sand and water |
e. magnetic separation |
Answer
|
1. to separate grain from chaff |
c. winnowing |
|
2. to separate sawdust |
a. filtration |
|
3. to separate iodine from sodium chloride |
d. sublimation |
|
4. to separate iron fillings from sand |
e. magnetic separation |
|
5. it is used to separate sand and water |
b. sedimentation and decantation |
E. Differentiate between the following.
1. solution and suspension
|
Solution |
Suspension |
|
1. It is an example of homogeneous mixture. |
1. It is an example of heterogeneous mixture. |
|
2. It is formed when a solid dissolves in liquid. |
2. It is formed when an insoluble solid is added |
|
3. For example – sugar dissolved in water. |
3. For example – chalk dissolved in water. |
2. Supernatant liquid and Fill rate
|
Solution |
Suspension |
|
1. It is an example of homogeneous mixture. |
1. It is an example of heterogeneous mixture. |
|
2. It is formed when a solid dissolves in liquid. |
2. It is formed when an insoluble solid is added |
|
3. For example – sugar dissolved in water. |
3. For example – chalk dissolved in water. |
3. Filter Paper
|
Filter paper |
Alum |
|
1. It is a special paper fitted in funnel during filtration. |
1. It is a solid which is used to load suspended mud particles in water. |
|
2. It does not dissolve in water. |
2. It dissolves easily in water |
|
3. It does not speeds up – loading. |
3. It speeds up loading. |
F. Write short answers.
1. Is food that we eat a mixture ?
Answer
Yes food that we eat is a mixture of carbohydrates, proteins, fats, minerals and vitamins.
2. Name two methods by which solid-solid mixtures can be separated.
Answer
- Winnowing
- Hand Picking
3. How can you separate iron metal from non-magnetic impurities ?
Answer
We can separate iron metal from non-magnetic impurities by the method of magnetic separation.
4. Name the technique that you use if only the solid component of a solution is required.
Answer
Evaporation.
5. Name the substance you will add to speed up sedimentation.
Answer
Alum
6. Name the different types of chromatographic techniques.
Answer
- Paper Chromatography
- Column Chromatography
- Thin Layer Chromatography
- Gas Chromatography.
G. Answer in detail.
1. What is the difference between a pure substance and a mixture ?
Answer
- A pure substance consists of only one kind of matter, that is, all the particles are same. It has a definite composition and constant properties. It cannot be split into simpler substances by physical means. All pure substances have characteristic melting and boiling points. A pure substance is either a compound or an element.
- A Mixture contains two or more substances in any proportion which can be separated by physical methods. Mixtures are generally of two types Homogeneous and Heterogeneous.
In a mixture, the constituents can be present in any ratio. They do not have
characteristic melting and boiling points. In a mixture each constituent retain its original properties. These can be separated by physical means.
- Homogeneous Mixtures : The composition of these mixtures is uniform throughout the mixture. Besides the properties of the mixture are the same in all the parts of the mixture, e.g. sugar dissolved in water.
- Heterogeneous Mixtures : A heterogeneous mixture composition is not uniform throughout the mixture. The properties of the mixture are different in different parts of mixture e.g. chalk dissolved in water.
- Centrifugation : It is a technique used to speed up sedimentation of fine particles suspended in a solid-liquid mixture.
- Principle : The principle of centrifugation is that an object, when spun at high speed, experiences an outward force away from the centre of rotation.