Experiment 13: LABORATORY PREPARATION OF AMMONIA GAS
OBJECTIVE
LABORATORY PREPARATION OF AMMONIA GAS AND INVESTIGATING ITS PROPERTIES
APPARATUS REQUIRED
- Round bottom flask
- Thistle funnel
- Delivery tube
- Cork
- Gas jars
- Test tube
CHEMICALS REQUIRED
- Dilute HCl
- Ca(OH)2
- NaOH
- NH4Cl
- FeCl3
- CuSO4
- Litmus paper
THEORY
Ammonium salts treated with alkali give off ammonia gas. Ammonia gas is prepared in the laboratory by heating a paste of ammonium chloride and slaked lime. The gas is produced according to the following chemical reaction.
PROCEDURE
A paste of ammonium chloride and dry-slaked lime was prepared by dissolving it in water. The paste was introduced in the round bottom flask. The apparatus was fitted as shown in the figure. The flask was clamped in a slightly inclined position. The flask was heated gently so that the reaction started and the gas was produced. Since the gas is highly soluble in water and lighter than air, it is collected in the gas jar by downward displacement of air.
OBSERVATION TABLE
| Experiment | Observation | Inference |
| 1. The physical properties were noted: i. Colour ii. Odour iii. Solubility: The gas jar filled with NH3 gas was inverted over a water trough. | 1. i. No colour ii. Pungent odour iii. Water rises up in the jar. | 1. The gas is i. colourless ii. has a pungent odour iii. highly soluble in water. |
| 2. A burning candle was introduced into the gas jar full of NH3 gas | 2. The burning candle extinguished. | 2. NH3 gas is neither combustible nor the supporter of combustion. |
| 3. Moist blue litmus paper was brought in contact with NH3 gas. | 3. Red litmus paper turned blue. | 3. NH3 gas is basic. |
| 4. The gas filled in a round bottom flask was inverted over a water trough with a few drops of phenolphthalein. | 4. Water enters in the flask in the form of fountain and the solution turned pink. | 4. The gas is highly soluble and the solution is alkaline. |
| 5. The glass rod is moistened with HCl gas was brought near to ammonia gas. | 5. Dense white fumes were produced. | 5. Formation of fumes of NH4Cl. |
| 6. Ammonia gas was passed through copper sulphate solution. | 6. A blueish-white precipitate first formed which gets dissolved in excess NH3 and gives a deep blue solution. | 6. Initially cupric hydroxide was formed and then tetra amine copper sulphate was formed. |
| 7. Ammonia gas was passed through a ferric chloride solution. | 7. A brown precipitate was formed. | 7. Formation of ferric hydroxide |
Reactions involved
1. Action with water
NH_{3} +H_{2}O\rightleftharpoons NH_{4}OH \rightleftharpoons NH_{4}^{+}+OH^{-}5. Action with conc. HCl
NH_{3} +HCl \rightarrow \underset{dense\ white\ fume}{NH_{4}Cl}6. Action with CuSO4 solution
7. Action with FeCl3 solution
RESULT
Hence, ammonia gas was prepared and its properties were studied.
CONCLUSION
Hence, in this way, the gas is prepared in the laboratory and its properties are studied
PRECAUTIONS
- The round bottom flask should be inclined.
- The cork should be fitted tightly.
- Heat should be gentle.
