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Solutions for Chemistry, Class 7, ICSE
Write the symbols of helium, silver, krypton, antimony, barium.
Helium (He)
Silver (Ag)
Krypton (Kr)
Antimony (Sb)
Barium (Ba)
Write the names of the following elements
Na, C, Kr, U, Ra, Fe, Co
Na — Sodium
C — Carbon
Kr — Krypton
U — Uranium
Ra — Radium
Fe — Iron
Co — Cobalt
Define:
(a) Elements
(b) Compounds
(a) An element is a pure substance that cannot be converted further into anything simpler than itself by any physical or chemical process. It is made up of only one kind of atoms.
(b) A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.
Name the main metal present in the following:
(a) Haemoglobin
(b) Chalk
(c) Chlorophyll
(d) Chocolate wrappers
(a) Iron
(b) Calcium
(c) Magnesium
(d) Aluminium
Give four examples of non-metallic elements.
Hydrogen(H), Chlorine(Cl), Sulphur(S), Phosphorus(P)
What do you understand by:
(a) Metalloids
(b) Noble gases
Give two examples of each.
(a) Metalloids are those elements that show some properties of metals and some properties of non-metals. They are hard solids. Examples — Boron(B), Silicon(Si).
(b) Noble gases or inert gases are those elements that do not react chemically with other elements or compounds and they are found in air in traces. Examples — Helium(He), Neon(Ne).
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.
| Elements | Compounds |
|---|---|
| Iron | plaster of paris |
| Copper | chalk |
| aluminium | common salt |
| carbon | calcium oxide |
| silver | cane sugar, silica |
| uranium | sodium sulphate, potassium carbonate, carbon dioxide |
State four differences between compounds and mixtures.
| Compounds | Mixtures |
|---|---|
| A compound is a pure substance. | A mixture is an impure substance. |
| Compounds are always homogeneous. | Mixtures may be homogeneous or heterogeneous. |
| Formation of a compound involves a change in energy. | Formation of a mixture does not involve any change in energy. |
| Components of compounds can be separated only by complex chemical processes. | Components of mixtures can be separated by simple physical methods of separation. |
What are the characteristic properties of a pure substance? Why do we need them?
The characteristic properties of a pure substance are:
We need pure substances to:
Give two examples for each of the following:
(a) Solid + Solid mixture
(b) Solid + Liquid mixture
(c) Liquid + Liquid mixture
(a) Sand and sugar, Brass
(b) Sand and water, salt in water
(c) Oil in water, Alcohol and water
Define:
(a) Evaporation
(b) Filtration
(c) Sublimation
(d) Distillation
(e) Miscible liquids
(f) Immiscible liquids
(a) Evaporation is the process of converting a liquid into its vapour state either by exposing it to air or by heating.
(b) The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called filtration.
(c) The process in which a solid substance directly changes into its vapour state on heating without passing through its liquid state is called sublimation.
(d) Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
(e) Liquids which dissolve in each other completely in all proportions are called miscible liquids.
(f) Liquids which do not dissolve in each other are called immiscible liquids.
Name the process by which the components of following mixtures can be separated.
(a) Iron and sulphur
(b) Ammonium chloride and sand
(c) Common salt from sea water
(d) Chaff and grain
(e) Water and mustard oil
(f) Sugar and water
(g) Cream from milk
(a) Magnetic separation
(b) Sublimation
(c) Evaporation
(d) Winnowing
(e) Separating funnel
(f) Crystallization
(g) Centrifugation
How will you separate a mixture of common salt, chalk powder and powdered camphor? Explain.
On heating the mixture, camphor will evaporates as it is a sublime substance. Its vapours can be collected which will solidify on cooling. Common salt and chalk powder mixture is then mixed in water. Common salt gets dissolved in water while chalk powder does not. Then by filtration, chalk powder is removed from the solution as it gets deposited in filter paper. The filtrate contains water and common salt. Common salt can be separated from water by evaporation process.
How is distillation more advantageous than evaporation?
Distillation is more advantageous than evaporation because both the components of the solid-liquid mixtures are obtained in distillation process but in evaporation process only solid is obtained.
(a) What is chromatography?
(b) Why is it named so?
(c) What are the advantages of chromatography?
(d) Name the simplest type of chromatography?
(e) On what principle is this method based?
(f) What is meant by stationary phase and mobile phase in chromatography?
(a) The process of separating different dissolved constituents of a mixture by their adsorption(particles getting adhered to a surface) on an appropriate material is called chromatography.
(b) The word chromatography means colour writing. It is named so because earlier it was used to separate mixtures containing coloured components only.
(c) The advantages of chromatography are:
(d) Paper chromatography.
(e) Chromatography separates the components of a mixture on the basis of differences between two phases, one of which is stationary while the other is mobile.
(f) The stationary phase is made up of common adsorbents like filter paper, silica gel as they are stationary and the mobile phase is made up of common solvents like water, ethyl alcohol, acetic acid etc. which moves or spreads on the stationary phase.
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
(a) sublimation
(b) filtration
(c) sedimentation and decantation
(d) solvent extraction method
(e) magnetic separation
(f) by using a separating funnel
(g) fractional distillation
(a) This method is used for solid mixtures in which one of the components can sublime on heating. It is used to separate a mixture of common salt and ammonium chloride.
(b) This method is used for separating the components of a heterogeneous solid-liquid mixture in which solids are insoluble in liquids. A mixture of chalk and water can be separated by this method.
(c) This method is used when the solid component is insoluble and heavier than the liquid component. A mixture of sand and water can be separated by this method.
(d) This method is used when one component is soluble in a particular liquid while the other component is insoluble. A mixture of sand and salt can be separated by this method.
(e) This method is used when one of the components of the mixture is magnetic in nature. A mixture of iron and sulphur can be separated by this method.
(f) It is used to separate components of liquid-liquid heterogeneous mixture when one of the liquid components is heavier than the other. Kerosene oil and water can be separated by this method.
(g) It is used to separate components of homogeneous liquid-liquid mixture on the basis of their difference in boiling points. A mixture of water and alcohol can be separated by this method.
Fill in the blanks
(a) ............... are made up of same kind of atoms.
(b) ............... and ............... are pure substances.
(c) In a ..............., the substances are not combined chemically.
(d) Clay is separated from water by a method called ............... .
(e) ............... is a process to obtain a very pure form of a solid dissolved in a liquid.
(f) Camphor and ammonium chloride can ............... .
(a) Elements
(b) Elements, compounds
(c) mixture
(d) filtration
(e) Crystallization
(f) sublime
Give one word answers for the following:
(a) The solid particles which remain on the filter paper after the filtration.
(b) The liquid which evaporates and then condenses during the process of distillation.
(c) The process of transferring the clean liquid after the solid settles at the bottom of the container.
(d) The process by which two miscible liquids are separated.
(a) residue
(b) distillate
(c) decantation
(d) fractional distillation
Choose the most appropriate answer from the options given below:
A pure liquid is obtained from a solution by:
distillation
Reason — Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
Choose the most appropriate answer from the options given below:
Components of crude petroleum can be separated by:
fractional distillation
Reason — Petrol, kerosene, diesel etc. are obtained from crude petroleum by fractional distillation as they have different boiling points.
Choose the most appropriate answer from the options given below:
Example of a homogeneous mixture is:
tap water
Reason — Tap water is a homogeneous mixture because it contains small amounts of dissolved salts and air in it that we cannot see.
Choose the most appropriate answer from the options given below:
In chromatography, the filter paper is:
stationary phase
Reason — The stationary phase in the process of chromatography is made of common adsorbents like filter paper.
Choose the most appropriate answer from the options given below:
A set of mixtures is:
ink, honey, ice cream, milk
Reason — They are homogeneous mixtures where constituents are uniformly distributed throughout its volume and cannot be recognized separately.