Describe what happens when a piece of copper foil is added into a test tube containing concentrated nitric acid in a fume cupboard.
When a piece of copper foil is added into a test tube containing concentrated nitric acid in a fume cupboard, a series of reactions occur.
Firstly, the nitric acid, being a strong oxidizing agent, reacts with the copper metal to form copper nitrate and nitrogen dioxide gas. The chemical equation for this reaction is:
Cu + 4HNO3 -> Cu(NO3)2 + 2NO2 + 2H2O
The copper nitrate (Cu(NO3)2) formed is soluble in water, so it dissolves in the remaining nitric acid in the test tube.
Simultaneously, the nitrogen dioxide gas that is produced is released into the fume cupboard. Nitrogen dioxide is a red-brown gas with an irritating odor and is also a toxic substance. Therefore, conducting this experiment in a fume cupboard ensures proper ventilation and safety.
Overall, the addition of copper foil to concentrated nitric acid generates copper nitrate while liberating nitrogen dioxide gas.
When a piece of copper foil is added into a test tube containing concentrated nitric acid in a fume cupboard, the following series of steps occur:
1. Safety precautions: The experiment is conducted inside a fume cupboard to control and vent any harmful fumes that may be produced during the reaction. The operator should wear appropriate personal protective equipment, such as gloves and goggles, to ensure safety.
2. Oxidation of Copper: Nitric acid (HNO3) is a strong oxidizing agent. As the copper foil is added to the test tube containing concentrated nitric acid, the nitric acid molecules act as an oxidizing agent and react with the copper. The reaction can be represented by the following equation:
Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
In this reaction, copper (Cu) reacts with nitric acid (HNO3) to form copper(II) nitrate (Cu(NO3)2), nitrogen dioxide gas (NO2), and water (H2O).
3. Observations: As the reaction takes place, several observable changes occur. The copper foil may start to dissolve or react with the nitric acid, producing a blue-green solution of copper(II) nitrate. Additionally, brownish-red nitrogen dioxide gas may be liberated, which can be seen as reddish-brown fumes in the test tube.
4. Release of nitrogen dioxide gas: Nitrogen dioxide (NO2) is a highly toxic gas. When the copper foil reacts with nitric acid, it produces nitrogen dioxide gas as a by-product. The evolved gas can be harmful if inhaled, which is why the experiment is conducted in a fume cupboard to prevent its dispersion into the laboratory.
5. Continuous reaction: The reaction between copper and nitric acid is highly exothermic. As a result, the reaction may continue spontaneously once initiated, even after removing the heat source. The reaction will proceed until one of the reactants is consumed.
It is essential to note that working with concentrated nitric acid can be extremely hazardous due to its corrosive nature and the possible formation of toxic gases. Hence, caution must always be exercised, and the experiment should only be performed by trained individuals in a controlled laboratory setting.