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Class-8 Dalal Simplified Hydrogen ICSE Chemistry Solutions

Class-8 Dalal Simplified Hydrogen ICSE Chemistry Solutions Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-7. We Provide Step by Step Solutions of Exercise/Lesson -7 Hydrogen with Objective Type Questions, Fill in the blanks and Give reason , Match the following of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-8.

Hydrogen Class-8 Dalal ICSE New Simplified Chemistry Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-7


EXERCISE-7

Question 1.
State how hydrogen occurs in the free state. Name three compounds containing hydrogen in the combined state.
Answer 1:

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  • In free state : Hydrogen occurs in the earth’s crust, atmosphere and in volcanic gases, also in the interior of the sun in the free state.
  • In combined state : In combined state it occurs in organic compounds, plants and animals, in acids and in water.

Question 2.
Starting from zinc how would you obtain hydrogen using

(a) Steam
(b) A dilute acid
(c) An alkali

[ Give balanced equations for each & name the product formed in each case other than hydrogen]. Name a metal which will not react with the reactants above to give hydrogen.
Answer 2:
To obtain hydrogen using :

(a) Steam : Metals which are more reactive than hydrogen like Zn, Fe, Pb react with steam and form oxide

new-simplified-chemistry-class-8-icse-solutions-hydrogen - 3
Metals below [H] do not react even with steam. Metal are Cu, Hg, Ag, Pt and Au.
(b) With dil. acids : Metals which are more reactive than hydrogen like Zn, Fe and Pb react and form corresponding salt.

new-simplified-chemistry-class-8-icse-solutions-hydrogen - 3.1
Cu and metals below Cu do not react with dil. acids.
(c) An alkali :  Zn, Pb reacts with concentrated alkali to form metallic salts and release hydrogen on boiling..
new-simplified-chemistry-class-8-icse-solutions-hydrogen - 3.2

Question 3.
‘Hydrogen is obtained by electrolysis of acidified water’. Answer the following pertaining to the preparation of hydrogen by electrolysis,

(a) The meaning of the term ‘electrolysis’ and ‘electrolyte’,

(b) Name the electrode –

  1. through which the current enters the electrolyte.
  2. at which hydrogen is liberated.

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Answer 3:

(a) 

Electrolysis : “Electrolysis is the dissociation of water into hydrogen and oxygen gas when electric current is passed through it..”
new-simplified-chemistry-class-8-icse-solutions-hydrogen - 4

Electrolyte : “Electrolyte is a chemical compound in solution state which conducts electric current and decomposes later..”

(b)

1. Anode

2 Cathode

Question 4.
In the laboratory preparation of hydrogen from zinc & dilute hydrocholoric acid – state a reason for

(a) Addition of traces of copper [II] sulphate to the reaction medium
(b) Collecting the hydrogen by downward displacement of water and not air & collecting it after all the air in the apparatus is allowed to escape
(c) Having the end of the thistle funnel dip below the level of the acid in the flask.

Answer 4:

(a) It acts as a catalyst and increases the rate at which reaction is performed.

(b) Hydrogen is soluble in water and lighter than air.

(c) To stop the gas from escaping.

Question 5.
In the industrial method of preparation of hydrogen by the Bosch process – give

(a) Balanced equations for the first two main steps in the production of hydrogen
(b) The reason for use of addition of a promoter to the catalyst in the final step
(c) The name of the solution which absorbs the unreacted carbon monoxide.

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Answer 5:
(a) Bosch process for industrial production of hydrogen :

  • Step [I] : Preparation of water gas [CO + H2] by passing steam over white hot coke.
    new-simplified-chemistry-class-8-icse-solutions-hydrogen - 4.1
  • Step [II] : Reduction of steam to hydrogen by carbon monoxide.
    new-simplified-chemistry-class-8-icse-solutions-hydrogen - 4.2

(b) Promotor Cr2O3 is used to increase the efficiency of catalyst [Fe2O3].
(c) Ammoniacal cuprous Chloride [CuCl] solution absorbs unreacted CO.

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Question 6.
State the following pertaining to the physical properties of hydrogen :

(a) Colour & odour
(b) Solubility in water
(c) Effect on moist blue litmus paper.

Answer 6:

(a) Colourless & odourless

(b) Slightly soluble

(c) No – effect

Question 7.
Draw neat labelled diagrams for two different experiments to prove that – hydrogen is lighter than air.
Answer 7:

Prove-1 

Two balloons ‘A’ and ‘B’ were taken. Balloon A was filled with hydrogen gas and balloon B was filled with air and both of them were tied to the either side of a weighing scale. It was observed that the weighing scale tilted to the side where balloon B was tied.

(prove-2)

To show that H2 is lighter than air :
new-simplified-chemistry-class-8-icse-solutions-hydrogen - 5

Air from jar B being heavier runs down in jar A and H2 runs to jar B as it is lighter than air and burns with ‘pop’ sound in jar B if a burning splinter is brought there.

Question 8.
Starting from hydrogen gas how would you obtain

(a) A neutral liquid
(b) A basic gas
(c) A metal by reduction of its heated oxide.

[The metal formed is above iron in the activity series]
Answer 8:

(a)  Hydrogen reacts quietly with oxygen to form water which is a neutral liquid
2H2 + O2 → 2H20
(b) Ammonia is a basic gas produced when 3 volumes of H2 react with 1 volume of N2 gas in presence of Fe which acts as a catalyst
new-simplified-chemistry-class-8-icse-solutions-hydrogen - 6
(c)  Reduction of Fe2O3on heating to iron.
new-simplified-chemistry-class-8-icse-solutions-hydrogen - 6.1

Question 9.
Using a burning candle and a jar of hydrogen – how would you prove experimentally that (a) Hydrogen is a combustible gas (b) Hydrogen does not support combustion.
Answer 9:

(a)

Hydrogen gas is combustible and bums at the opening of the gas jar.

new-simplified-chemistry-class-8-icse-solutions-hydrogen - 6.2
(b)

Hydrogen extinguishes the candle when pushed inside the jar.

new-simplified-chemistry-class-8-icse-solutions-hydrogen - 6.3

Question 10.
State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.
Answer 10:

new-simplified-chemistry-class-8-icse-solutions-hydrogen - 7
Hydrogen removes oxygen from copper oxide and reduces it to metal which is reddish brown in colour.

Question 11.
With reference to the uses of hydrogen, give reasons for the following :

(a) Hydrogen is not used in air balloons
(b) A mixture of hydrogen & oxygen on burning, find application in welding & cutting metals
(c) Reaction of hydrogen with nitrogen under specific conditions finds industrial utility.

Answer 11:

(a) It is highly inflammable, for safety reasons it is not used in air balloons.

(b) Oxygen and hydrogen burn and produce high temperatures upto 2800°C and are used for welding and cutting metals.

(c) Ammonia is a basic gas produced when 3 volumes of H2 react with 1 volume of N2 gas in presence of Fe which acts as a catalyst

applications in fertilizers and nitric acid and explosives.

Question 12.
Give a test to differentiate between two gas jars – one containing pure hydrogen and the other hydrogen-air mixture.
Answer 12:

In the jar with pure hydrogen, Hydrogen bums with pale blue flame quietly, when a burning splinter is brought near the jar.

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