Reaction Between Zinc and Sodium Hydroxide: A Chemical Exploration
In the world of chemistry, not all metals react with acids, and interestingly, some metals can react with bases too! This activity, often covered in the chapter on Acids, Bases, and Salts, demonstrates a unique reaction between a metal and a strong base. Let's explore how zinc interacts with sodium hydroxide and what gas is produced.
Aim of the Activity
To observe the chemical reaction between a metal (zinc) and a base (sodium hydroxide solution), and to identify the gas evolved during this reaction.
Materials & Apparatus
- Zinc granules
- Sodium hydroxide solution (dilute)
- Test tube
- Test tube holder
- Bunsen burner or spirit lamp (for heating, if required)
- Beaker or trough (for soap solution)
- Soap solution
- Delivery tube (to pass gas into soap solution)
- Dropper
- Matchstick or candle
Procedure
- Set up: Take a few pieces of zinc granules in a clean test tube. Secure the test tube in a test tube holder.
- Add base: Carefully add about 2 mL of dilute sodium hydroxide solution to the test tube containing the zinc granules.
- Observe initial reaction: Observe the surface of the zinc granules. Do you see any immediate changes?
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Gas collection setup: Fit the test tube with a delivery tube. Invert the other end of the delivery tube into a beaker or trough containing soap solution.
(Note: A diagram of the apparatus, similar to that used for metal-acid reactions, would typically show the test tube connected via a delivery tube to a beaker of soap solution.)
- Test the evolved gas: As gas bubbles rise from the soap solution, bring a burning candle or a lit matchstick near a gas-filled bubble.
- Note the sound: Listen carefully for any sound produced when the flame touches the bubble.
Observation
Upon adding sodium hydroxide solution to zinc granules, we observe the formation of bubbles on the surface of the zinc granules. This indicates that a gas is being evolved from the reaction.
Test for the Evolving Gas
When the gas evolved from the reaction is passed into the soap solution, it forms gas bubbles. Bringing a burning candle or a lit matchstick near these bubbles causes them to burst with a distinct "pop" sound.
Explanation of the Reaction
Zinc reacts with the aqueous sodium hydroxide solution to form sodium zincate (a salt) and hydrogen gas.
2NaOH(aq) + Zn(s) → Na₂ZnO₂(aq) + H₂(g)↑
Sodium hydroxide (aqueous) + Zinc (solid) → Sodium zincate (aqueous) + Hydrogen gas (gaseous)
The hydrogen gas produced gets trapped within the soap film, forming the bubbles we observe. The "pop" sound when a burning candle is brought near these bubbles is the characteristic test for hydrogen gas, confirming its presence. This is because hydrogen gas is highly flammable.
Conclusion
This activity successfully demonstrates that certain metals, like zinc, can react with strong bases such as sodium hydroxide solution, producing a salt (sodium zincate) and releasing hydrogen gas. This highlights the diverse chemical properties of metals and bases.
Frequently Asked Questions (FAQs)
1. What does the ‘pop’ sound indicate?
The ‘pop’ sound is the characteristic test for hydrogen gas, indicating its presence.
2. Can this activity be done with other metals?
While some other metals might react, zinc is particularly notable because it is amphoteric in nature, meaning it can react with both acids and strong bases.
3. Which salt is formed in this activity?
The salt formed is Sodium Zincate (Na₂ZnO₂).
4. Name the gas that evolved when metal reacts with a base.
The gas evolved is Hydrogen gas (H₂).
5. Give the chemical equation for the reaction.
Zn + 2NaOH → Na₂ZnO₂ + H₂
6. Name the type of reaction.
This reaction is a type of single displacement reaction, where zinc displaces hydrogen from the base.
Important Precaution
This experiment involves handling a strong base (sodium hydroxide) and generating flammable hydrogen gas. It must be performed only under the strict supervision and direct assistance of a qualified teacher or adult. Always wear appropriate safety goggles.