Exploring Metal-Acid Reactions: The Case of Zinc and Sulphuric Acid
Have you ever seen a metal fizz when it comes into contact with an acid? This fascinating chemical interaction is a fundamental concept in chemistry. The reactivity of different metals can vary significantly, leading to diverse reactions with various acids. In this activity, we'll explore the reaction between zinc metal and sulphuric acid and identify the gas produced.
Aim of the Activity
To observe the reaction between zinc granules and dilute sulphuric acid, and to identify the nature of the gas evolved during this reaction.
Materials & Apparatus
- Test tube
- Delivery tube
- Trough or beaker
- Soap solution
- Burning candle or matchstick
- Dilute Sulphuric Acid (H₂SO₄)
- Zinc granules (Zn)
- Dilute Hydrochloric Acid (HCl), Dilute Nitric Acid (HNO₃), Dilute Acetic Acid (CH₃COOH) - for extended observation
(Imagine setting up the apparatus for gas collection, typically involving a test tube with a delivery tube leading into a soap solution in a trough.)
Procedure
- Set up the apparatus: Assemble the experimental setup as instructed by your teacher for collecting gas (e.g., a test tube fitted with a cork and delivery tube leading into a soap solution).
- Add reactants: Pour approximately 2 ml of dilute sulphuric acid into the test tube. Carefully add a few pieces of zinc granules to the acid.
- Observe the reaction: Pay close attention to the surface of the zinc granules. What changes do you observe? (e.g., formation of bubbles).
- Collect the gas: Allow the gas being evolved from the reaction to pass through the delivery tube and bubble into the soap solution.
- Note bubble formation: Observe why bubbles are formed in the soap solution. (Hint: The gas is being trapped).
- Test the gas: Carefully bring a burning candle or a lit matchstick near a gas-filled bubble that rises from the soap solution.
- Record the sound: What do you observe when the flame comes into contact with the gas-filled bubble?
- Extended observation (Optional): Repeat steps 2-7 with other dilute acids such as Hydrochloric Acid (HCl), Nitric Acid (HNO₃), and Acetic Acid (CH₃COOH).
- Compare observations: Are the observations (especially the gas test) the same or different across all the acids tested?
Observation
When a burning candle is brought near a gas-filled bubble, the gas ignites with a characteristic "popping" sound. This distinctive sound is a key indicator for the presence of a specific gas.
Conclusion
The popping sound confirms that the gas evolved during the reaction is hydrogen gas (H₂). This occurs because zinc metal is more reactive than hydrogen, and thus displaces hydrogen from the sulphuric acid.
Chemical Equation:
Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)↑
This activity clearly demonstrates a typical single displacement reaction where a more reactive metal displaces hydrogen from an acid.
Important Caution
This experiment involves handling acids and generating flammable gas. It must only be performed under the strict supervision and direct assistance of a qualified teacher or adult.