Elements, Compound Mixtures Class-7 Dalal Simplified ICSE Chemistry Solutions Chapter-3

Elements, Compound & Mixtures Class-7 Dalal Simplified ICSE Chemistry Solutions Chapter-3 Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-3. We Provide Step by Step Solutions of Exercise/Lesson -3  Question and Answers of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-7.

Elements, Compound & Mixtures Class-7 Dalal Simplified ICSE Chemistry Solutions Chapter-3

Board	ICSE
Class	7th
Subject	Chemistry
Book Name	Dalal New Simplified
Chapter-3	Elements, Compound & Mixtures
Unit-1	Elements, Compound & Mixtures
Topic	Solution of exercise questions
Session	2023-24

Exercise – 1

Elements, Compound & Mixtures Class-7 Dalal Simplified ICSE Chemistry Solutions Chapter-3

Question 1. Differentiate between the terms elements, compounds and mixtures with suitable examples.

Answer 1: Element – It is the basic unit of matter, which cannot be broken down into substances by any way but can be combined to form new substances. It is a pure substance. It classifies into metals, non-metals, metalloids and noble gases.

Example -Chlorine, Nickle, Gold

Compounds – It is a combination of two or more elements. It is a pure substance. Through chemical reactions, they can be broken down into metals.

Example – Sugar, petroleum

Mixtures – It is a combination of two or more elements or compounds or both.The substances combined in a mixture are in a particular ratio.

Example – Milk, Alloy

Question 2. State which element exists in the highest percentage in –

(a) earth’s crust

(b) atmosphere

(c) human body.
Answer 2:
(a) Oxygen (O) — 46.1%
(b) Nitrogen (N) — 78%
(c) Oxygen (O) — 65%

Question 3.Elements are mainly classified into metals and non-metals. State six properties of metals which differ from non-metals.

Answer 3: Properties of Metals:

• They are lustrous, i.e. they shine.
• They are ductile, i.e. they can be drawn into wires.
• They are good conductors of heat and electricity.
• They have high density.
• They have high melting and boiling points.

• They are malleable, i.e. they can be drawn into sheets.

Properties of Non-Metals:

• They are non-lustrous, hence they do not shine.
• They are non-ductile,  cannot be drawn into wires.
• They are bad conductors of heat and electricity.
• They have low density.
• They have low melting and boiling points.

• They are non-malleable, therefore they cannot be beaten into sheets.

Question 4. Give the symbols of the following elements – and state in each case whether they are metals, non-metals, metalloids or noble gases.

(a) Potassium

(b) Carbon

(c) Oxygen

(d) Mercury

(e) Fluorine

(f) Neon

(g) Sulphur

(h) Zinc

(i) Boron

(j) Copper

(k) Calcium

(l) Xenon

(m) Arsenic

(n) Mercury

(o) Chlorine

(p) Silicon

(q) Neon

(r) Lead

(s) Antimony

(t)Sodium

(u) Iodine

(v) Platinum

(w) Radon

(x) Phosphorus

(y) Bromine

(z) Aluminum

Answer 4:

Name	Symbols	Metals /Non-metals /Noble gases /Metalloids
(a) Potassium	K	Metal
(b) Carbon	C	Non-metal
(c) Oxygen	O	Non-metal
(d) Mercury	Hg	Metal
(e) Fluorine	F	Non-metal
(f) Neon	Ne	Noble Gas
(g) Sulphur	S	Non-metal
(h) Zinc	Zn	Metal
(i) Boron	b	Metalloid
(j) Copper	Cu	Metal
(k) Calcium	Ca	Metal
(l) Xenon	Xe	Noble Gas
(m) Arsenic	As	Metalloid
(n) Mercury	Hg	Metal
(o) Chlorine	Cl	Non-metal
(p) Silicon	Si	Metalloid
(q) Neon	Ne	Noble Gas
(r) Lead	Pb	Metal
(s) Antimony	Sb	Metalloid
(t) Sodium	Na	Metal
(u) Iodine	I	Non-metal
(v) Platinum	Pt	Metal
(w) Radon	Rn	Noble Gas
(x) Phosphorus	P	Non-metal
(y) Bromine	Br	Non-metal
(z) Aluminum	Al	Metal

Question 5. State what is meant by the term ‘activity series of metals’. State the most reactive and the least reactive metal from the following – Zn, Ag, Na, Fe, Cu, Pb.

Answer 5: Activity series of metals:- Activity series is a series of arrangement of metals in decreasing order of their reactivity. The most reactive metal is Na. while The least reactive metals from above option is Ag,

Question 6. Give three reasons why – carbon dioxide is considered a compound, while carbon – an element.

Answer 6: Carbon (C)  is an element and Carbon dioxide C0₂ constitutes of carbon and oxygen which are both independent elements combined together in a fixed ratio to form carbon dioxide C0₂. Carbon (C) is combustible and oxygen (O) supports combustion, but carbon dioxide C0₂ extinguishes fire.

Question 7. State what information is provided by the formula of calcium hydroxide – Ca(OH)₂

Answer 7: Compound :- Calcium hydroxide

Formula :- Ca(OH)₂

Information provide by formula :-

1. atom of calcium,
2. atoms of oxygen and hydrogen

Question 8: Four atoms of hydrogen combine with one atom of carbon to give methane [CH4]. State the valency of carbon.

Answer 8: Methane is formed by the combination of four hydrogen atoms and one carbon atom where valency of hydrogen is 1 and valency of carbon is 4.

Question 9. Write the symbols of the following elements and radicals along with their valencies.

(a) Sodium

(b) Magnesium

(c) Chlorine [Chloride]

(d) Nitrate

(e) Sulphite

(f) Aluminium

(g) Zinc

(h) Sulphur [Sulphide]

(i) Bromine [Bromide]

(j) Sulphate

(k) Hydroxide

(l) Calcium

(m) Carbonate

(n) Potassium

(o) Phosphate

(p) Iodine [Iodide]

Valency list: (i) 1+ (ii) +2, (iii) +3, (iv) -1, (v) -2-(vi) -3

Answer: 

Name	Symbols	Radicals
(a) Sodium	Na	Na1+
(b) Magnesium	Mg	Mg2+
(c) Chlorine	Cl	Cl1-
(d) Nitrate	NO3	NO31-
(e) Sulphite	SO3	SO32-
(f) Aluminium	Al	Al3+
(g) Zinc	Zn	Zn2+
(h) Sulphur	S	S2-
(i) Bromine	Br	Br1-
(j) Sulphate	SO4	SO42-
(k) Hydroxide	OH	OH1-
(l) Calcium	Ca	Ca2+
(m) Carbonate	CO3	CO32-
(n) Potassium	K	K1+
(o) Phosphate	PO4	PO43-
(p) Iodine	I	I1-

 

Question 10. Write the chemical formula:

Question: (a) magnesium oxide

Answer: (a) MgO

Question: (b) Sodium bromide

Answer: (b) NaBr

Question: (c) calcium sulphide

Answer: (c) CaS

Question: (d) magnesium sulphate

Answer: (d) Mg SO₄

Question: (e) aluminium chloride

Answer: (e) AIC₄

Question: (f) zinc oxide

Answer: (f) ZnO

Question: (g) calcium carbonate.

Answer: (g) CaCO₃

Question 11. Give the formulas of the following acids:

Question: (a) hydrochloric

Answer: (a) Hydrochloric — HCI

Question: (b) nitric

Answer: (b) Nitric —HNO₃

Question: (c) sulphuric

Answer: (c) Sulphuric —H₂SO₄

Question: (d) carbonic — acid.

Answer: (d) Carbonic acid —H₂CO₃

Question 12. Give the formulas of the following gases:

(a) hydrogen chloride

Answer: (a) hydrogen chloride — HCI

(b) ammonia

Answer: (b) ammonia — NH₃
(c) carbon monoxide

Answer: (c) carbon monoxide— CO
(d) nitric oxide

Answer: (d) nitric oxide— NO
(e) nitrous oxide

Answer: (e) nitrous oxide — N₂O
(f) nitrogen dioxide

Answer: (f) nitrogen dioxide — NO₂
(g) nitrogen

Answer: (g) nitrogen – N₂
(h) sulphur dioxide
Answer: (h) sulphur dioxide— SO₂

Question 13. Explain the term mixture. Differentiate between a homogenous and a heterogeneous mixture with one example of each in the

(a) solid-solid

(b) solid-liquid

(c) liquid-liquid state of the mixture.

Answer 13: Substances made up of two or more elements / compounds or both, mixed together in any proportion are called mixtures.

Examples – Air, Smoke, milk and sugar

Homogeneous Mixture	Heterogeneous mixture
The constituents are uniformly mixed in a homogeneous mixture.	The constituents are not mixed uniformly in a heterogeneous mixture.
The properties and composition are uniform throughout the mixture.	The properties and composition vary throughout the mixture.
Example – (i) Solid-solid – Alloys (ii) Solid-liquid – Sugar solution, (iii) Liquid-liquid – Alcohol & Water	Examples – (i) Solid-solid – Iron & Sulphur (ii) Solid-liquid – Sand & Water (iii) Liquid-liquid – Oil & Water

Question 14. State four differences between – elements, compounds and mixtures with suitable examples.

Answer 14: State four differences between – elements, compounds and mixtures with suitable examples:-

 Elements:- 1. Pure substance made up of one kind of atoms only. e.g. Iron [Fe], Sulphur [S]

2. Elements i.e. atoms of one kind are present on their own. e.g. Iron and sulphur exist on their own as elements iron and sulphur.

3. Elements have a definite set of properties. Elements classified into metal and non-metals each with its own properties.

4. Elements occur on their own or as compounds and can be separated by chemical and physical methods.

Example: Metals – Iron, copper, silver, gold.

Compounds:- 1. Pure substance made up of two or more elements, e.g. Iron sulphide [FeS]

2. Components in a compound present in a definite proportion. e.g. Iron and sulphur are chemically combined in a fixed ratio in iron sulphide.

3. Compounds have a definite set of properties.

4. Elements in a compound are chemically combined and can be separated by chemical methods only.

Example:  Iron sulphide, copper oxide, water, Sodium chloride, copper, sulphate.

Mixtures:- 1. Impure substance made up of two or more elements or compounds, e.g. Iron sulphur mixture.

2. Components in a mixture present in any proportion. e.g. Iron and sulphur are mixed in any ratio in the mixture of iron and sulphur.

3. Mixture does not have a definite set of properties. Components of a mixture do retain their original properties.

4. Components in a mixture are chemically mixed and can be separated by physical methods only.

Example: Iron + sulphur, copper + silver, air, brass. Sodium chloride + water, copper sulphate + water.

Question 15: State the correct technique for separation of the following mixtures.

Question: (a)  a sublimable solid and a non-sublimable solid.

Answer: (a) Sublimation

Question: (b) a liquid component from soluble impurities in the liquid component.

Answer: (b) Evaporation

Question: (c) a lighter liquid from a heavier liquid.

Answer: (c) Separating funnel

Question: (d) a low boiling point liquid from a high boiling point liquid.

Answer: (d) Fractional distillation

Question: (e) solid constituents in a liquid constituent by adsorption.

Answer: (e) Chromatography

Question 16. Give – (a) The principle involved in separation of the mixture (b) The technique of separation for each of the following mixtures.

(1) Naphthalene and sodium chloride
(2) Common salt from a solution of common salt in water
(3) Pure water from impure water
(4) Kerosene and water
(5) Methyl alcohol and water
(6)Dyes of an ink

Answer 16: (1) By Sublimation

Principle – The process of conversion of solid directly into gaseous state and back to solid without passing through the liquid state.

Sublimable solid changes into vapour on heating and the non-sublimable solid is left behind, and they are separated.

Technique – Naphthalene and sodium chloride are heated in a dish and a funnel is kept over it, after some time naphthalene evaporates and turns into vapour which is seen on the walls of the funnel. Sodium chloride is left behind, and the mixture is separated.

 

(2) By Evaporation

Principle – Evaporation is the process of conversion of liquid component to its gaseous state by heating.

Technique – In a salt solution, water evaporates on heating and salt crystals are left behind in the dish.

(3) By Distillation

Principle – The process of separating two liquids by heating and converting into vapour in a distillation flask and its condensation of the vapour back into the liquid.

Technique – the mixture is kept in a distillation flask and the flask is heated. The liquid or the pure water vaporises and the impurities are left behind in the flask.

(4) By Separating funnel

Principle – The method used to separate two immiscible liquids, out of which one is heavy and the other is light.

Technique – The mixture of kerosene and water is kept in a funnel. The heavier liquid that is water settles down in the funnel and removed by opening the tap at the bottom. The lighter liquid, i.e. kerosene remains in the funnel.

(5) By Fractional Distillation

Principle – The process of separating two miscible liquids with different boiling points.

Technique – The mixture of alcohol and water is kept in a distillation flask and heated slowly, the liquid which has a lower boiling point evaporates and collects in the receiver after condensation in the Leibigs condenser,

The fractionating column separates the vapours of other liquid to condense, keeping the two separated.

(6) By Chromatography

Principle – It is a method of separating the various components of a mixture by their difference in rate of flow over an absorbent medium.

Technique – Ink spots contain different solid constituents. It is kept on the filter paper. The lower end of filter paper is dipped in the solvent and hung. The solvent flows over the ink spot and the dyes separate out.

– : End of Elements, Compound & Mixtures Class-7 Dalal Simplified Solutions :–

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