Study of First Element Hydrogen Exe-6D Descriptive Answer Chemistry Class-9 ICSE Selina Publishers

Study of First Element Hydrogen Exe-6D Descriptive Answer Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-6. Step By Step ICSE Selina Concise Solutions of Chapter-6 Study of First Element Hydrogen with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

Study of First Element Hydrogen Exe-6D Descriptive Answer Chemistry Class-9 ICSE Concise Selina Publishers

Board ICSE
Publications Selina Publication
Subject Chemistry
Class 9th
Chapter-6 Study of First Element Hydrogen
Book Name Concise
Topics Solution of Exercise – 6D Descriptive Answer Type
Academic Session 2023-2024

D. Exercise – 6D Descriptive Answer Type

Study of First Element Hydrogen Class-9 Chemistry Concise Solutions  

Page-119

Question 1.

Is it essential that oxidation and reduction must occur side by side in a chemical reaction? Explain

Answer:

In a chemical reaction, if one substance is oxidised, the other substance must necessarily be reduced. This is because the electrons lost during oxidation are simultaneously gained during reduction and vice versa.

For example: Zinc reacts with copper sulphate to form zinc sulphate and copper.

CuSO4 + Zn → ZnSO4 + Cu
Cu + 2SO42- + Zn →Zn + 2SO42- + Cu

Writing the half reaction,

Zn → Zn2+ + 2e (Oxidation)
Cu2+ + 2e→ Cu (Reduction)

They occur simultaneously as

Cu2+ + Zn→ Zn2++ Cu

Thus, oxidation and reduction always occur simultaneously.

Question 2.

Describe briefly the ionic concept of oxidation and reduction. Give an equation to illustrate.

Answer:

In the electronic concept, oxidation is a process in which an atom or ion loses electron(s).

Zn → Zn2+ + 2e

Oxidation is also defined as a chemical process which involves

Addition of oxygen

Addition of electronegative ion

Removal of hydrogen

Removal of electropositive ion (element)

In the electronic concept, reduction is a process in which an atom or ion gains electrons.

Cu2+ + 2e→ Cu

Reduction is also defined as a chemical process which involves

Removal of oxygen

Addition of electropositive ion

Addition of hydrogen

Removal of electronegative ion

Question 3.

State the similarity of hydrogen with group 1 elements and group 17 elements.

Answer:

Similarity of hydrogen with group 1 elements:

(a) Electronic configuration — Both hydrogen and alkali metals have only one electron in their outermost orbits.

(b) Ion formation — Both form a cation by loss of an electron.
H ⟶ H+ + e
Na ⟶ Na+ + e

(c) Valency — Both have the valency 1.

(d) Reducing power — Both act as reducing agents.
CuO + H2 ⟶ Cu + H2O
CuO + 2Na ⟶ Cu + Na2O

(e) Reaction with Oxygen — Both react with oxygen to form respective oxides.
Hydrogen forms H2O
Sodium forms Na2O

Similarity of hydrogen with group 17 elements:

(a) Electronic configuration — Hydrogen and halogens have one electron less than the nearest inert gas.

(b) Physical state — Like halogens (fluorine and chlorine), hydrogen too is a gas.

(c) Ion formation — Both form an anion by accepting an electron.
H + e ⟶ H
Cl + e ⟶ Cl

(d) Valency — Both have the valency 1.

(e) Atomicity — Hydrogen as well as halogens exist in the form of diatomic molecules (H2, F2, Cl2, Br2, I2).

Question 4.

Which is the most preferred metal for the laboratory preparation of hydrogen. Why is any other metal not used?

Answer:

Zinc is the most preferred metal in the laboratory preparation of hydrogen.

Other metals are not used because of the following reasons:

  • Sodium and potassium react violently with acid.
  • Calcium and magnesium are expensive.
  • Aluminium forms a protective coating of Al2O3 due to its great affinity for oxygen. Due to the coating of Al2O3, aluminium does not give hydrogen with acid.
  • Iron has to be heated, but then the hydrogen thus produced contains impurities like hydrogen sulphide and sulphur dioxide.
  • Lead reacts with dil. sulphuric acid or hydrochloric acid and forms an insoluble coating of lead sulphate or lead chloride. Therefore, further reaction is prevented.
  • Hydrogen cannot be prepared from metals that are below in the metal reactivity series such as copper and mercury, since only metals that are more reactive than hydrogen can displace it from acids.

Question 5.

Describe the laboratory preparation of hydrogen with a labelled diagram? How are the impurities removed.

Answer:

Reactants : Granulated zinc, dil. hydrochloric acid or dil. sulphuric acid.

Procedure : Place some pieces of granulated zinc in a flat bottom flask fitted with an air tight cork with two holes. Through one hole, pass a thistle funnel with a long stem provided with a stopper, and through the other, a long delivery tube.

Pour dilute hydrochloric acid (or dilute sulphuric acid) through the funnel.

Describe the laboratory preparation of hydrogen with a labelled diagram? How are the impurities removed.

Zn + 2HCl (dil.) ⟶ ZnCl2 + H2 ↑

Zn + H2SO4 (dil.) ⟶ ZnSO4 + H2 ↑

Observation : Reaction will gradually start in the form of effervescence and evolution of gas. When all the air from the apparatus has been expelled, collect the gas over water by downward displacement of water.

Impurities can be removed from hydrogen by passing it through :

  1. Silver nitrate solution [to remove arsine and phosphine].
    AsH3 + 6AgNO3 ⟶ Ag3As + 3AgNO3 + 3HNO3
    PH3 + 6AgNO3 ⟶ Ag3P + 3AgNO3 + 3HNO3
  2. A drying agent used to dry the gas. Common drying agents such as fused calcium chloride, caustic potash stick and phosphorus pentoxide remove water vapour.

Thus, the gas is purified and dried and then collected over mercury because mercury has no reaction with it.

Question 6.

How is hydrogen manufactured? Describe with the equation(s) involved.Answer:Hydrogen is manufactured by Bosch process. It consists of following steps:1. Production of water gasHow is hydrogen manufactured? Describe with the equation(s) involved.

Reactants : White hot coke and steam
Temperature : Around 1000°C
Process : Passage of steam over white hot coke [carbon]
Chamber : Specially designed convertor

2. Reduction of steam to hydrogen by carbon monoxide

How is hydrogen manufactured? Describe with the equation(s) involved.

Reactants : Water gas and excess steam
Temperature : Around 450°C
Catalysts : Iron [III] oxide [Fe2O3], promoter chromic oxide [Cr2O3]
Process : Excess steam is mixed with water gas, passed over a catalyst at elevated temperatures.
[CO is converted to CO2 with a further yield of hydrogen.]

3. Separation of carbon dioxide [CO2] and carbon monoxide from the above mixture

(a) CO2 is removed by dissolving mixture in water under pressure [30 atmospheres], or caustic potash solution to dissolve CO2.

2KOH + CO2 ⟶ K2CO3 + H2O

(b) CO is removed by dissolving mixture in ammoniacal cuprous chloride solution.

CuCl + CO + 2H2O ⟶ CuCl.CO.2H2O.

Thus, hydrogen gas is left behind.

—  : End of Study of First Element Hydrogen Exe-6D Descriptive Answer Class-9 ICSE Chemistry Solutions :–

Return to  Return to Concise Selina ICSE Chemistry Class-9 

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