Hydrogen ICSE 9 QA

HYDROGEN

Question 1

State properties of Hydrogen.

Solution

1. Non-metallic character and Atomicity:- Hydrogen is a non-metal like halogens and like halogens, it is diatomic (H₂) whereas metals are monoatomic.
2. Valency:- Just like halogens, hydrogen may also show -1 valency by accepting an electron, e.g. NaH (Sodium hydride).
H + 1e^- H^-
3. Nature of compounds:- Hydrogen combines with non-metals like carbon, silicon, etc. to form covalent compound like halogens e.g. CH₄ and CCl₄.

Question 2

(a) A atom of an element is represented as _.
(i). What does value 39 indicate ?
(ii). What does value 19 indicate ?
(iii). What is the number of protons in X ?
(iv). What is the number of electons in X ?
(v). What is the number of neutrons in X?

(b) Give reasons.
(i). Atom is electrically neutral.
(ii). Mass of an atom is concentrated inside the nucleus of an atom.
(iii). Atom as a whole is an empty space.
(iv). Hydrogen was previously used in meteorological balloons.
(v). Hydrogen is no longer used in meteorological balloons.

Solution

(a)
(i). Mass number of X
(ii). Atomic number of X
(iii). 19
(iv). 19
(v). 20
(b)
(i). An atom is electically neutral because the number of positively charged particles i.e., protons is equal to the number of negatively charged particles i.e., electrons.
(ii). Mass of an atom is contributed by the mass of the protons and neutron present inside the nucleus of an atom and the electron present outside the nucleus are of negligible mass therefore mass of an atom is concentrated inside the nucleus of an atom.
(iii). The size of the nucleus is very small as compared to the size of an atom, therefore, atom as a whole is an empty space.
(iv). Hydrogen was previously used in meteorological balloons because of its lowest density and high lifting power.
(v). Hydrogen is now no longer used in meteorological balloons as it is highly inflammable in nature. i.e., it catches fire very easily.

Question 3

(i) Name the process in which water gas is used for the manufacture of hydrogen.
(ii) Give balanced chemical equation for the large scale preparation of hydrogen from water gas.
(iii) How are carbon dioxide and carbon monoxide removed from hydrogen produced?

Solution

(i) Bosch Process

(ii)

(iii) The hydrogen obtained by this process contains the impurities of carbon monoxide in traces and carbon dioxide. Carbon monoxide can be removed by passing it through ammoniacal cuprous chloride solution. Carbon dioxide can be removed by passing through cold water under pressure.

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Question 4

Write balanced chemical equations for the reaction of hydrogen with-
(i) Oxygen
(ii) Sulphur

Solution

(i)    2H₂     +     O₂    →      2H₂O

   Hydrogen     Oxygen         Water

(ii)    H₂     +      S    →           H₂S

   Hydrogen    Sulphur  Hydrogen sulphide

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Question 5

What will be the reaction between metals like magnesium and aluminium with hot water or steam?

Solution

Metals like, magnesium and aluminium react with hot water or steam to form hydrogen gas.

1. Magnesium: Magnesium reacts with hot water or steam to produce magnesium oxide and librates hydrogen gas.

Mg  +  H₂O  →  MgO  +  H₂ ↑

2. Aluminium: Aluminium is difficult to get in its pure form. This is because, aluminium has a great affinity towards oxygen. Thus, it is coated with aluminium oxide (Al₂O₃). This oxide layer on the surface of aluminium can be removed by rubbing it with sand paper. Thus, aluminium obtained in its pure form reacts with hot water or steam to produce hydrogen gas.

2Al + 3H₂O →  Al₂O₃ + 3H₂ ↑

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Question 6

Explain the laboratory preparation of hydrogen gas.

Solution

The Zinc granules are placed in a flat-bottom flask fitted with an air tight cork having two holes. Thistle funnel with a long stem is passed through one hole and a delivery tube is passed through the other hole. Dilute hydrochloric acid is added to the flask through the funnel. Zinc granules react with Dilute hydrochloric acid to give zinc chloride and hydrogen gas is released. The same reaction is carried out by using dilute sulphuric acid. The reactions are-

Zn +  2HCl  →  ZnCl₂  +  H₂  ↑

        (dilute)

Zn  +  H₂SO₄ → ZnSO₄  +  H₂ ↑

        (dilute)

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Question 7

Give the conditions and equations involved in the industrial manufacture of hydrogen by Bosch process.

Solution

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Question 8

What are the common impurities found during the preparation of hydrogen?

Solution

(i) Hydrogen sulphide
(ii) Sulphur dioxide
(iii) Oxides of nitrogen
(iv) Phosphine
(v) Arsine
(vi) Carbon dioxide
(vii) Water vapour

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Question 9

How hydrogen acts as a reducing agent?

Solution

Hydrogen reduces the oxides of the less active metals, viz. removes oxygen from strongly heated metal oxides when passed over them, and in the process gets oxidized itself to water.

Both alkali metals and Hydrogen acts as a reducing agent which is proved by the following reactions:-
CuO + H₂ Cu + H₂O
CuO + 2Na Cu + Na₂O

In both cases CuO is oxidised.

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Question 10

What is the role of hydrogen in the extraction of metals?

Solution

 
Question 11

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Give three uses of hydrogen.

Solution

Uses of hydrogen:

(i) As a fuel : As hydrogen has got high heat of combustion,so it is used as fuel in the form of:
(a) Coal gas, (b) Water gas, (c) Liquid hydrogen.
(ii) Oxy-hydrogen torch: A mixture of hydrogen and oxygen is burnt in a specially designed apparatus called an oxy-hydrogen torch.The flame is used for cutting and welding of metals.
(iii) Atomic hydrogen torch: creates a high temperature which is used for welding alloys containing metals like manganese, chromium etc.
(iv) Haber process: It is used for the manufacture of ammonia.
N₂ + 3H₂ 2NH₃

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Question 12

Describe the position of Hydrogen in the periodic table.

Solution

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

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Question 13

Hydrogen is not prepared by the reaction of aluminium with dilute acids. Give reason.

Solution

Aluminium forms a protective coating of Al₂O₃ due to its great affinity for oxygen. Hence, it prevents the further reaction of acid with metal.

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Question 14

Explain reaction of hydrogen with non-metals.

Solution

1. Oxygen and hydrogen: Hydrogen burns with a pop sound in oxygen.It burns with a pale blue flame forming water.

2H₂ + O₂ → 2H₂O

2. Chlorine and hydrogen: Hydrogen and chlorine (in their equal volumes) react slowly in diffused sunlight but reacts explosively in direct sunlight. A spontaneous reaction takes place with the release of a large amount of energy.

H₂ + Cl₂ → 2HCl

3. Nitrogen and hydrogen: (Haber process): Three volumes of hydrogen and one volume of nitrogen react at temperature 450^oC-500^oC at the pressure of 200-900 atm, in presence of a finely divided iron which acts as a catalyst, and promoter molybdenum.

4. Sulphur and hydrogen: Hydrogen gas when passed through molten sulphur, it reacts to give another gas, hydrogen sulphide.

H₂ + S  →  H₂S

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Question 15

Write the names of method of preparation of hydrogen gas.

Solution

The following are the methods by which hydrogen gas can be prepared:-
(i) Laboratory preparation of hydrogen gas by using zinc granules and dilute hydrochloric acid or dilute sulphuric acid.

(ii) Hydrogen is commercially obtained by the elecrolysis of acidulated water.

(iii) By Bosch process.

(iv) From natural gas.

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Question 16

What is the action of air on Hydrogen?

Solution

Hydrogen burns in air explosively with pop sound. Alkali metals are so reactive that they get tarnished rapidly when exposed to air due to the formation of oxides, hydroxides and finally carbonates at their surfaces.

For example,

4Na  +  O₂ → 2Na₂O

Na₂O  +  H₂O → 2NaOH

2NaOH + CO₂ →  Na₂CO₃ + H₂O

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Question 17

Why is the position of Hydrogen in the periodic table anomalous?

Solution

Hydrogen is the first element in the periodic table. Its atomic number is 1. It has only one electron in its outermost (valence) shell. Hence, it belongs to the first group and the first period of the periodic table. Though the properties of Hydrogen should be similar to those of the other members of the 1st group, but this is not the case. This is because some of the properties of hydrogen resemble the properties of Group IA elements (Alkali metals), and some of it resembles the properties of Halogens (VIIA), so Hydrogen was put at the top of the periodic table so that the symmetry of the modern periodic table is not disturbed.

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Question 18

What would happen to the following mixtures, when they are kept in a closed vessel at over 400^oC?
(a) iron filings and steam.
(b) hydrogen and magnetic oxide of iron.

Solution

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Question 19

According to the activity series, which of the following can successfully displace hydrogen?
K/Na/Pb/Ag/Pt/Fe/Al

Solution

K and Na - can displace hydrogen from acids by reacting violently.
Pb - displaces hydrogen from only hot concentrated acids.
Ag, Pt - do not displace hydrogen from acids at all.
Fe - displaces hydrogen gently from acids.
Al - displaces hydrogen from acids vigorously.

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Question 20

What is the principle behind collection of hydrogen by the downward displacement of water?

Solution

Hydrogen is collected by the downward displacement of water, because:
(i) It is virtually insoluble in water.
(ii) It forms an explosive mixture with air and therefore, cannot be collected by downward displacement of air, even though it is lighter than air.