TO PREPARE HYDROGEN GAS IN LABORATORY AND STUDY ITS PROPERTIES

APPARATUS REQUIRED

i) Woolf is bottle

ii) Thistle funnel

iii) Delivery tube

iv) Trough

v) Gas  jar

vii) Bee-hive shelf

CHEMICAL REQUIRED

i) Piece of Zn metal

ii) Dil.H₂SO₄

iii) KMnO₄ solution

iv) K₂Cr₂O₇ solution

v) Fe Cl₃ solution

THEORY

Hydrogen gas is prepared in the laboratory by treating zinc metal with dil. H2SO₄ solution and collected in the gas jar by the downward displacement of water because hydrogen gas is insoluble in water.

Reaction involved

Zn+dil. H₂SO₄ ————> ZnSO₄ + H₂ ↑

Nascent hydrogen and Molecular hydrogen:

The term nascent hydrogen is used to call hydrogen that is liberated during a chemical reaction. It is considered that hydrogen liberated during the progression of a chemical reaction is initially in the atomic state; it is then combined to form molecular hydrogen and released as hydrogen gas ( or else, this atomic hydrogen will react with some other available ion). For example:

Zn +dil. H₂SO₄————-> ZnSO₄ + 2[H] Nascent hydrogen

Zn + dil. H₂SO₄ ————-> ZnSO₄ +H ₂ ↑ Molecular hydrogen

PROCEDURE

Small piece of Zn metal was taken in Woolfe’s bottle and dilute H₂SO₄ was poured into the bottle with the help – of thistle funnel. The apparatus was fitted as shown in figure. The hydrogen gas was collected in the downward displacement of water.

OBSERVATION TABLE:

S.N.	Experiment	Observation	Inference
1.	The color and odor was noted.	No color and odor was observed.	H2 gas was colorless and odorless .
2.	The burning match stick into gas jar containing H2 was introduced.	Burning match stick was extinguished but burning at the mouth of the jar.	H2 gas was burned itself but not a supporter of the burning.
3.	A test tube full of H2 gas was taken and inverted over it and ignited.	H2 gas was burned with “pup” sound.	H2 was lighter than air.
4.	The moist red or blue litmus paper was inserted into the jar full of H2 gas.	No change in color of litmus paper.	H2 gas was neutral .

Test for Nascent and Molecular hydrogen:

Both nascent and molecular hydrogen are reducing agents but nascent hydrogen is a more powerful reducing agent than molecular hydrogen. This was proved by the following experiments.

S.N.	Experiment	Observation	Inference
1.	1 ml of acidified solution of KMnO4 was taken and hydrogen gas was passed through it .	Pink color of KMNO4 was not discharged .	Molecular H2 cannot reduce KMNO4 solution.
2.	A piece of Zn metal was put on the acidified solution of KMNO4 .	Pink color of KMnO4 was discharged .	Nascent H2 can reduce KMnO4 solution .
3.	1 ml of acidified solution of K2Cr2O7 was taken and hydrogen gas was passed through it.	Orange color of  K2Cr2O7 was not discharged .	Molecular H2 cannot reduce  K2Cr2O7 solution.
4.	A piece of Zn metal was put on the acidified solution of K2Cr2O7.	Orange color of  K2Cr2O7 was changed to green.	Nascent H2 can reduce  K2Cr2O7 solution.
5.	1 ml of acidified solution of FeCl3 was taken and hydrogen gas was passed through it .	No change in color .	Molecular H2 cannot reduce FeCl3 solution.
6.	A piece of Zn metal was put on the acidified solution of FeCl3 .	Reddish yellow of FeCl3 was changed into light green .	Nascent H2 can reduce the FeCl3 solution.

TEST REACTION

a. With acidified solution of KMnO₄

2KMnO₄ + 3H₂SO₄ + 10[H]——————-> K₂SO₄ + 2MnSO₄ + 8H₂O

colorless

b. With acidified solution of K₂ Cr₂ O₇

K₂Cr₂O₇ + 4H₂SO₄ + 6 [H] ————-> K₂SO₄ + Cr₂ (SO₄)₂ + 7H₂O

green

c. With acidified solution of FeCl₃

FeCl₃ + [H] ————->  FeCl₂ + HCl

 Yellow                           light green

RESULT

Hydrogen gas was prepared in the laboratory by treating zinc with dil. H₂SO₄ and performed the test of nascent and molecular hydrogen.

CONCLUSION

In this way, hydrogen gas can be prepared by treating metal with acid by the downward displacement of water.

PRECAUTION

1. The apparatus should be air tight.

2. The tip of thistle funnel should be dipped into the solution.

3. The glass apparatus should be handled carefully