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Dalal Class-8 Elements Compounds & Mixtures New Simplified ICSE Chemistry

Dalal Class-8 Elements Compounds & Mixtures New Simplified ICSE Chemistry Solutions. Chapter-3 . We Provide Step by Step Solutions of Exercise/Lesson -3 The Elements Compounds & Mixtures with Objective Type , Fill in the blanks , Give reason and Figure base Questions of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-8.

Dalal Class-8 Elements Compounds & Mixtures New Simplified ICSE Chemistry Solutions.


Execise-3

Question 1.

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Represent with the help of a simple chart how matter is classified into pure or impure substances & further into elements, compounds & mixtures, with elements further segmented.
Answer 1:

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Question 2.
Define the terms elements, compounds & mixtures with a view to show their basic difference.
Answer 2:

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 – Hydrogen, Carbon, Oxygen

Compounds –

It is a combination of two or more elements.

It is a pure substance.

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Through chemical reactions, they can be broken down into metals.

Example – Water, Carbon dioxide

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 – Chalk powder, Washing Soda

.Question 3.

‘An atom is the basic unit of an element’. Draw a diagram of an atom – divisible as seen today.
Answer 3:
‘An atom is the basic unit of an element’.

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Question 4.
‘The modern periodic table consists of elements arranged according to their increasing atomic numbers’. With reference to elements with atomic numbers 1 to 20 only in the periodic table – differentiate them into – metallic elements, metalloids, non-metals & noble gases.
Answer 4:
Names and symbols of metal, non-metals, metalloids and noble – gases out of 1st 20 elements.

Metal Symbol Non-metal Symbol
Lithium Li Hydrogen H
Beryllium Be Carbon C
Sodium Na Nitrogen N
Magnesium Mg Oxygen O
Aluminium Al Fluorine F
Potassium K Phosphorus P
Calcium Ca Sulphur D
Chlorine Cl
Metalloids Symbol Noble Gases Symbols
Boron B Helium He
Silicon Si Neon Ne
Argon Ar

Question 5.
Elements are broadly classified into metals & non-metals. State six general differences in physical properties of metals & non-metals. State two metals & two non-metals which contradict with the general physical properties – giving reasons. State one difference in property between metalloids & noble gases.
Answer 5:

Properties of Metals:

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

Properties of Non-Metals:

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

Metals which contradict general properties of metals:

  • Zinc is a metal but it is not malleable and not ductile.
  • Mercury is a metal but it is liquid even at room temperature while other metals are generally solid.

Non-metals which contradict general properties of non-metals:

  • Iodine is lustrous while non-metals are not lustrous.
  • Graphite is a good conductor of electricity, while non-metals are bad conductors of electricity.

Question 6.
With reference to elements – define the term ‘molecule’. Give two examples each of a monoatomic, diatomic & polyatomic molecule.
Answer 6:

The smallest particle of any substance which can exist independently and retain the physical and chemical properties of the substance, made up of one or different elements is a molecule.

Monoatomic molecule : Metals –He Ne Ar etc.

Diatomic molecule : Cl2, Br2, N2.
Polyatomic molecule : O3, S8.

Question 7.
Define the term ‘compound’. In the compound carbon dioxide – the elements carbon & oxygen are combined in a fixed ratio. Explain.
Answer 7:

A compound is a combination of two or more different elements which are combined chemically in a fixed ratio.

It has two or more types of atoms, like monatomic, diatomic or polyatomic.

It can be broken down into elements chemically like it is combined.

It is a pure substance.

The properties of the compound are different from that of elements it is made of.

Carbon & Oxygen are combined in a fixed ratio because carbon is combustible and Oxygen is a supports combustion, but carbon dioxide has neither of these properties.

Question 8.
State five different characteristics of compounds. Give three differences between elements & compounds with relevant examples.
Answer 8:
Five characteristics of a compound :

  1. Elements in a compound are in fixed proportion.
  2. Compounds have a definite set of properties.
  3. Compounds can be broken down chemically only.
  4. Particles of compounds are of one kind only.
  5. They are homogenous i.e. identical.

Three differences between elements and compounds :

Elements Compounds
They have only one kind of atom, like Fe, Au, Co, Ag They may or may not have one kind of atom.
They have properties different from compounds they make. Example – Hydrogen & oxygen are combustible, but water is not. They have properties different from elements that they are made of. Example – Hydrogen and Oxygen are gases, but they make up water which is liquid.
They cannot be broken down further, they are the basic unit. They can be broken down, but only chemically.

Question 9.
Explain the term ‘mixture’. Differentiate between homogenous & heterogenous mixtures. State why brass is considered as a homogenous mixture while a mixture of iron & sulphur – heterogenous. Give an example of two liquids which form (a) homogenous (b) heterogenous – mixtures.
Answer 4:
Mixture : Mixture is a substance formed by two or more substances like elements or compounds or both in a fixed proportion.

Difference between homogenous & heterogenous mixtures :

Homogeneous Mixtures Heterogeneous mixtures
The elements and compounds are uniformly mixed. The elements and compounds are not uniformly mixed.
The properties of the mixture are the same in all compositions. The properties differ at different compositions.
Copper and Zinc are two solids which make brass, which is solid. The elements cannot be distinguished. In the mixture of Iron and Sulphur, iron can be easily separated using a magnet, the composition is not uniform.
Example of liquids – Salt and Water Example of liquids – Air, Milk

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Question 10.
Compare the properties of iron [II] sulphide with iron – sulphur mixture, considering iron [II] sulphide as a compound & particles of iron & sulphur mixed together as an example of a mixture.
Answer 10:

Iron [II] Sulphide Iron – Sulphur
It is a solid in black colour. Iron and sulphur can be seen separately.
They cannot be separated using a magnet. When the magnet is brought close to the mixture, Iron gets attracted to the magnet.
On adding dilute HCl, Hydrogen gas evolves. On adding dilute HCl, Cl2 evolves.

Question 11.
State any one method – to separate the following mixtures –

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