2 HYDROGEN

Objectives

To enumerate the properties of

hydrogen

To relate the properties of

hydrogen to its industrial uses

OCCURENCE OF

HYDROGEN

most abundant element in the

universe

90% of the atoms of sun and stars

11% by mass H in water

9th most abundant element on the

earth’s crust

3 isotopes of hydrogen:

1. Protium, H-1

99.9844%

2. Deuterium, H-2

0.0156%

3. Tritium, H-3

very small

PROPERTIES OF

HYDROGEN

It is a diatomic gas under most

conditions, H2

It is colorless, odorless, tasteless gas at

normal temperatures

It does not support combustion but it

burns

it is insoluble in water

B.P. - 252.7oC

F.P. - 259.2oC

It is a reactive element.

a) It reacts with active metals

forming compounds called

hydrides.

Examples : NaH, CaH2

b) It is displaced from non-oxidizing

acids by metals above it in the

activity series of metals

Example:

Zn(s) + HCl(aq) ZnCl2 +

H2(g)

see p. 136 Central Science

c) It is displaced vigorously from water

by metals located at the top of the

activity series of metals.

2 Na(S) + 2 H2O 2 NaOH +

H2(g)

d) It reacts with other non-metals.

Example:

H2(g) + Cl2(g) 2 HCl(g)

5. It has a very low density

compared to air at any given

conditions.

COMMERCIAL PREPARATION OF

HYDROGEN

1. Water Gas Method

Reactions: Ni

C(S) + H2O(steam) CO(g) +

H2(g)

water gas

CO(g) + H2(g) + H2O(steam) CO2(g) + 2

H2(g)

2 methods of separating CO2 & H2

mixture:

*Passing the CO2 and H2 mixture through water under pressure

*Passing the CO2(g) and H2(g) mixture over lime (CaO).

CO2(g) + H2(g) + CaO(s) CaCO3(s) + H2(g)

2. Steam-Hydrocarbon Method

Ni

CH4(g) + 2 H2O(steam) CO2(g) + 4 H2(g)

heat

*The hydrogen is separated from carbon

dioxide as in the water gas method.

3. Electrolysis of Water

Reaction:

electricity

2 H2O 2 H2(g) + O2(g)

USES OF HYDROGEN

1.It is used as fuel for rockets in

space

2 a. It is used in making other

compounds such as ammonia,

hydrochloric acid and methanol

b. It is used in the catalytic

hydrogenation of oils and semi-

solid fats for the making of

margarine, household shortening

and soap

c. It is used as a reducing agent for the

production of certain metals from their

metal oxides

To illustrate:

CuO(s) + H2(g) Cu(s) + H2O

WO(s) + H2(g) W(s) + H2O

3. It is used to fill balloons and

dirigibles.