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