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.

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:

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 4

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.

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:

  • 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:

  • 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

.

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 –

(a) Two solid mixtures one of which – directly changes into vapour on heating.
(b) Two solid mixtures one of which – dissolves in a – particular solvent and other does not
(c) A solid-liquid mixture containing – an insoluble solid in the liquid component
(d) A solid-liquid mixture containing – a soluble solid in the liquid component
(e) A liquid-liquid mixture containing – two immiscible ”’ liquids having different densities
(f) A liquid-liquid mixture containing – two miscible liquids having different boiling points.
(g) A liquid-gas mixture containing – a gas dissolved in a liquid component.
(h) A gas-gas mixture containing – two gases with different densities.
(i) A mixture of different solid constituents – in a liquid constituent.

Answer 11:

  1. Sublimation – Sublimable solid changes into vapour on heating and the non-sublimable solid is left behind, and they are separated.
  2. Solvent extraction – The soluble solid dissolves in the solvent and the insoluble solid is left behind, and they are separated.
  3. Filtration – insoluble solid is left behind in the filter.
  4. Evaporation – The soluble solid is left behind while the liquid evaporates.
  5. Separating funnel – Heavier liquid collects at the bottom layer, while the lighter liquid layers on the top in the funnel.
  6. Fractional distillation – The liquid with a high boiling point remains in a distillation flask while the other one collects in the receiver.
  7. Boiling – The gas escapes when the mixture is boiled, as the solubility of gas decreases with increase in temperature.
  8. Diffusion – Lighter gas diffuses faster than heavier gas, the porous partition separates them.
  9. Chromatography

Question 12.   (Dalal Class-8 Elements Compounds & Mixtures) 
Explain with diagrams the process used to – separate the following substances from the given mixtures.

(a) Ammonium chloride from a mixture of – ammonium chloride & potassium chloride.
(b) Iron from a mixture of – iron & copper
(c) Sulphur from a mixture of – sulphur & copper.
(d) Potassium nitrate from a mixture of – potassium nitrate & potassium chlorate.
(e) Lead carbonate [insoluble] from a mixture of – lead carbonate & water.
(f) Lead nitrate [soluble] from a mixture of – lead nitrate & water Le. lead nitrate solution.
(g) Carbon tetrachloride from a mixture of – carbon tetrachloride [heavier component] & water.
(h) Benzene from a mixture of – benezene [b.p. 80°C] & toluene [b.p. 110°C].
(i) Different dyes – in their liquid constituent ink.

Answer 12:

(a) By sublimation :

Ammonium Chloride from a mixture of ammonium chloride & potassium chloride

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 11
Here A is Ammonium Chloride and B is Potassium Chloride.
(b) By magnetic separation : By bringing a magnet near the mixture iron pieces can be separated which will cling to the magnet.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 12
Here A is Iron and B is Copper.
(c) By solvent extraction : Mixture of copper and sulphur is added to the beaker containing solvent carbon disulphide and stirred well. Sulphur dissolves. Put this mixture on filter paper in the funnel. Copper remains on filter paper and sulphur passes into the beaker as filtrate. Sulphur separates as carbon disulphide evaporates.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 12.1

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 13
Here A is for Copper and B is Sulphur.
(d) Potassium nitrate KNO3 is more-soluble than potassium chlorate KClO3.
On heating to get saturated solution and on cooling the saturated solution less soluble (KClO3) crystallise out. .More soluble KNO3 is filtered out from hot saturated solution and is recrystallised from hot water and dried.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 13.1
(e) Evaporation : Lead carbonate can be separated by evaporation. On evaporation, water evaporates leaving behind solid lead carbonate which has higher M.P.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 14
(f) Lead nitrate is separated from soluble lead nitrate solution by crystallisation.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 14.1
new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 15
(g) By separing funnel, heavier CCl4 carbon tetrachloride form the lower layer is separated when tap is opened and is collected in the flask. Water the lighter top layer remains in the funnel.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 15.1
(h) By fractional distillation, miscible low boiling point benzene (B.P. 80°C) evaporates on heating the mixture and condenses in and collects in flask ‘Y’ where as higher boiling pt. Toluene (B.P. 110°C) remains in flask ‘X’ after condensation.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 15.2
(i) By chromatography : Different dyes [solid constituents i.e. A, B, C, D] in ink which is the liquid constituent. By placing the ink spot containing different solid constituents [dyes] on the filter paper. Filter paper is hung with it’s lower end completely dipped in the solvent.

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 16
The solvent flows over the ink spot and the solid constituents [dyes ‘A’, ‘B’, ‘C’, ‘D’] separate out.


OBJECTIVE TYPE QUESTIONS

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

Question.1. 

Select the correct answer from A, B, C, D & E for each statement given below 

A: Gunpowder
B: Iodine
C: Boron
D: Helium
E: Bromine

  1. A diatomic molecule
  2. A metalloid
  3. A non-metal which is lustrous.
  4. A mixture consisting of elements & compounds.
  5. A noble gas

Answer-1

  1. A diatomic molecule E: Bromine
  2. A metalloid C: Boron
  3. A non-metal which is lustrous. B: Iodine
  4. A mixture consisting of elements & compounds. A: Gunpowder
  5. A noble gas D: Helium

Question-.2. 

Match the separation of components in List I with the most appropriate process in List II.

List I List II
1. Naphthalene from Naphthalene and Sodium Chloride A: Separating funnel
2. Cream from milk B: Sublimation
3. Kerosene oil from kerosene oil & water C: Boiling
4. Lead nitrate from an aqueous solution of lead nitrate D: Centrifugation
5. Ammonia from an aqueous solution of ammonia E: Distillation

Answer 2:

List I List II
1. Naphthalene from Naphthalene and Sodium Chloride B: Sublimation
2. Cream from milk D: Centrifugation
3. Kerosene oil from kerosene oil & water A: Separating funnel
4. Lead nitrate from an aqueous solution of lead nitrate E: Distillation
5. Ammonia from an aqueous solution of ammonia C: Boiling

 

Question-.3. 

The diagram represents fractional distillation for separation of mixtures. Answer the following :

new-simplified-chemistry-class-8-icse-solutions-elements-compounds-mixtures - 17.2

  1. Can two immiscible liquids be separated by this process?
  2. Separation of liquids by this process is based on which physical property?
  3. If methyl alcohol & water are to be separated, which liquid will remain in flask ‘X’ after condensation.
  4. Give a reason for the above answer.
  5. State the function of the fractionating column in the apparatus.

Answer-3

  1. No, they can be separated by separating funnels only.
  2. The difference in their boiling points
  3. Water, because it has a boiling point of 100-degree celsius.
  4. Alcohol has a boiling point lower than that of water, hence it evaporates fast and water remains back in the flask as it takes longer to evaporate.
  5. The fractionating column cools the hot vapour of the evaporating liquid and condenses it get back into the distillation flask ‘X’

Question-.4. 

Select the correct answer from the choice in bracket to complete each sentence :

  1. Dust in the air is an example of _____ (homogeneous/heterogeneous) mixture.
  2. A soluble solid is separated from an insoluble solid by ______(fractional crystallisation/ solvent extraction)
  3. The reactive element from the two monoatomic elements is ___ (neon/ silicon)
  4. Compounds are _____(homogeneous or hetrogeneous/ always homogeneous) in nature.
  5. An example of a monoatomic molecule is____ (hydrogen/ helium)

Answer-4

  1. Homogeneous
  2. Extraction
  3. Silicon
  4. Always homogeneous
  5. Helium

Question-.5. 

Give reasons for the following statements :

  1. Components in a mixture can be separated by physical methods only.
  2. Centrifugation can be used for separating a heavier insoluble solid, present in an – insoluble solid-liquid mixture.
  3. The filter paper made into a cone & placed in a funnel for filtering out the solid particles in a solid-liquid mixture should be moistened before placing.
  4. Brass & Bronze are examples of mixtures while copper sulphate and lead nitrate are examples of compounds.
  5. Zinc is considered an element, while zinc sulphide is a compound.

Answer-5

  1. Particles which are separate, i.e. they have not undergone a chemical reaction can be separated physically only.
  2. The heavier insoluble solid settles at the bottom when the bottle of the mixture is rotated upside-down.
  3. Moisture on filter paper helps it to stick to the walls of the funnel.
  4. In brass & bronze, the elements and compounds are mixed in a particular proportion or mass, while in compounds of copper sulphate and lead nitrate have a fixed ratio for the mass of elements.
  5. Zinc cannot be broken down any further to substances which can exist independently, while zinc sulphide is made of two elements zinc & sulphur which can exist independently.

.– : End of Simplified Dalal Class-8 Elements Compounds & Mixtures Solutions :–


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