Procedure:
- Action of conc. Nitric acid on copper metal.
Note:
- NO
2 is also prepared by the action of heat on nitrates of heavy metals like lead nitrate.
- NO
2 is given off together with oxygen when nitrates of heavy metals are heated.
- It is best prepared by heating lead (II) nitrate in a hard glass test tube.
Lead (II) nitrate is the most suitable because it crystallizes without water of crystallization (like other nitrates) which would interfere with preparation of nitrogen (IV) oxide that is soluble in water.
- The gas evolved passes into a U-tube immersed in an ice-salt mixture.
Observations:
- The heated white lead (II) nitrate crystals decompose and decrepitates (cracking sound) to yield red lead (II) oxide; which turns yellow on cooling.
- A colourless gas, oxygen is liberated, followed immediately by brown fumes of nitrogen (IV) oxide.
- Nitrogen (IV) oxide is condensed as a yellow liquid; dinitrogen tetroxide (N
2O
4); and is collected in the U-tube.
Note:
- At room temperature, nitrogen (IV) oxide consists of nitrogen (IV) oxide and dinitrogen tetroxide in equilibrium with each other.
The oxygen being liberated does not condense because it has a low boiling point of -183
oC.
Kavungya answered the question on
April 27, 2019 at 10:27