Chapter-6 Study of First Element Hydrogen Concise Class-9 Selina ICSE Solutions

Study of First Element Hydrogen Chapter-6 Selina Publishers Revised Chemistry

Chapter-6 Study of First Element Hydrogen Concise Class-9 Selina ICSE Solutions. Step by Step Selina Concise Solutions for ICSE Class-9 Chemistry of Chapter-6 Exercise Questions . The Solutions of Exercise-6(A), Exercise-6(B) , Exercise-6(C)  and Exercise-6 (D) for Selina Concise Chemistry ICSE Class-9. Visit official website cisce for detail information about icse class -9 Chemistry.

Chapter-6 Study of First Element Hydrogen Concise Class-9 Selina ICSE Solutions


–: Select Topics :–

Exercise-6(A),

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Exercise-6(B)

Exercise-6(C) 

Exercise-6(D).


Study of the First Element-Hydrogen Exercise 6(A) Chapter-6 Selina Concise ICSE Chemistry Solutions Class 9

 Question 1

Justify the Position of Hydrogen in the periodic table.

Answer  1

Hydrogen is the first element in the periodic table. Its atomic number is 1, and it has only one electron in its valence shell. So, it belongs to the first group and the first period of the periodic table.

Question 2

Why does hydrogen show dual nature?

Answer  2

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Hydrogen shows dual nature because it resembles the alkali metals of Group IA and the halogens of Group VIIA.

Question 3

Compare hydrogen with alkali metals on basis of:

(i) Ion formation

(ii) Reducing power

(iii) Reaction with oxygen

(iv) Oxide formation

Answer  3

(i) Each of them can form a cation by loss of an electron.

H → H+ + e

Li →Li+ + e

(ii) Both alkali metals and hydrogen act as reducing agents.

CuO + H2 → Cu + H2O

CuO + Na → Cu + Na2O

(iii) Hydrogen burns in oxygen to form its oxide. It burns with a pop sound.

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2H2 + O2 → 2H2O

Alkali metals also burn vigorously when heated in oxygen to form their respective oxides.

Lithium forms monoxide.

4Li + O2 → 2Li2O

(iv) Hydrogen burns in oxygen to form its oxide. It burns with a pop sound.

2H2 + O2 → 2H2O

Alkali metals also burn vigorously when heated in oxygen to form their respective oxides.

Lithium forms monoxide.

4Li + O2 → 2Li2O

Question 4

In what respect does hydrogen differ from:

(i) alkali metals

(ii) halogens?

Answer  4

(i) Oxides of alkali metals are basic in nature, whereas the oxide of hydrogen H2O is a neutral oxide.

(ii)Hydrogen atom has only one shell, but halogens have two or more shells.

Question 5

Give the general group study of hydrogen with reference to

(i) valence electrons

(ii) burning

(iii) reducing power

Answer  5

(i) Hydrogen has one valence electron in its outermost orbit.

(ii) Hydrogen burns in oxygen to form its oxide. It burns with a pop sound.

2H2 + O2 → 2H2O

(iii) Hydrogen acts as a reducing agent.

CuO + H2 → Cu + H2O

Question 6

Why hydrogen was called ‘inflammable air’?

Answer  6

Hydrogen was called inflammable air because of its combustible nature.

Question 7

State some sources of hydrogen.

Answer  7

In the free state, hydrogen is found in traces in the earth’s crust and atmosphere.

And In the combined state, plant and animal tissues are made of compounds of hydrogen with carbon, oxygen and nitrogen.

Question 8

Compare hydrogen and halogens on the basis of:

(i) physical state

(ii) ion formation

(iii) valency

(iv) reaction with oxygen

Answer  8

(i) Like halogens (fluorine and chlorine), hydrogen too is a gas.

(ii) Both show a tendency to form anions because they are one electron short of the nearest inert gas configuration.

H + e → H

Cl + e →Cl

(iii) Both have valency 1.

(iv) Hydrogen reacts with oxygen to form neutral oxide, H2O. Halogens react with oxygen to form acidic oxides like Cl2O and Cl2O7.

Question 9

Which metal is preferred for preparation of hydrogen.

(i) from water?

(ii) from acid?

Answer  9

(i) Reactive metals such as potassium, sodium and calcium.

(ii) Magnesium, aluminium, zinc and iron.

Question 10

(i) Write the reaction of steam with red hot iron.

(ii) Why this reaction is considered as reversible reaction?

(iii) How the reaction can proceed continuously?

Answer  10

(i) 3Fe + 4H2O ⇋ Fe3O4 + 4H2

(ii) The reaction is reversible because if hydrogen formed is not removed, then the iron oxide formed is reduced back to iron.

(iii) Because the reaction is a reversible reaction, equilibrium is attained at 700°C. At this stage, the amount of reactants and products does not change.

Question 11

 why zinc and aluminium are considered to have unique nature.   Give balanced equations to support your explanation.

Answer 11

They react with acids and can even react with hot concentrated alkalis to form hydrogen and a soluble salt.

Zn + 2NaOH → Na2ZnO2 + H2

2Al + 6NaOH→ 2Na2Al O3 + 3H2

Oxides and hydroxides of zinc and aluminium are amphoteric. They react with both bases and acids to give salt and water.

ZnO + 2HCl → ZnCl2 + H2O

ZnO + 2NaOH →Na2ZnO2 + H2O

Question 12

Write balanced equations for the following:

(i) Iron reacts with dil. HCl

(ii) Zinc reacts with caustic soda solution

(iii) Lead reacts with potassium hydroxide

(iv) Aluminium reacts with fused sodium hydroxide

Answer 12

(i) Fe +2 HC l → FeCl2 + H2

(ii) Zn + 2NaOH → Na2ZnO2 + H2

(iii) Pb + 2KOH → K2PbO2 + H2

(iv) 2Al + 6NaOH→ 2Na2Al O3 + 3H2

Question 13

Write the balanced equations and give your observations when the following metals react:

(i) Sodium with cold water

(ii) Calcium with cold water

(iii) Magnesium with boiling water

(iv) Magnesium with steam

Answer 13

(i) The reaction is highly exothermic and vigorous with the evolution of hydrogen.

2Na + 2H2O →2NaOH + H2

(ii) Calcium sinks in water and the reaction is less vigorous.

Ca + 2H2O → Ca(OH)2 + H2

(iii) Magnesium reacts slowly with boiling water and forms a base, magnesium hydroxide, liberating hydrogen gas.

Mg + 2H2O →Mg(OH)2 + H2O

(iv) Magnesium burns in steam with an intense white light liberating hydrogen gas and white ash, i.e. magnesium oxide.

Mg + H2O → MgO + H2

Question 14

(i) Under what conditions iron reacts with water.

(ii) Give the balanced equation of the reaction.

(iii) What is noticed if the products are not allowed to escape?

Answer 14

(i) Iron is less reactive than zinc, but red hot iron reacts with steam, forming triferric tetra-oxide and hydrogen gas.

(ii) 3Fe + 4H2O ⇋ Fe3O4 + 4H2

(iii) If the product formed, i.e. hydrogen is not removed, then the iron oxide formed is reduced back to iron.

Question 15

From the knowledge of activity series, name a metal which shows the following properties

(i) It reacts readily with cold water.

(ii) It displaces hydrogen from hot water.

(iii) It displaces hydrogen from dilute HCl.

(iv) It forms a base which is insoluble in water.

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