Question

why are first bubble of hydrogen are not collected when the gas is prepared in the laboratory by the reaction of granulated zinc and dilute sulphuric acid​

Answer 1

Answer:

Since there is air mixed with the hydrogen gas in the first few bubbles, they shouldn't be collected. Air and hydrogen combined together can explode.

Explanation:

• It is lighter than air, but because it mixes explosively with air, it cannot be recovered by air displacement downward.
• The first few gas bubbles should be allowed to escape due to this reaction to make sure there is no air in the apparatus.
• Since pure zinc is non-porous by nature, it is not employed in the laboratory to prepare hydrogen. Reaction would therefore happen very slowly.
• Therefore, contaminants like copper are added to the zinc, speeding up the process.
• In order to prepare hydrogen gas in a lab, zinc granules are often subjected to the action of diluted sulfuric acid or hydrochloric acid.
• Granulated zinc is perfect for creating hydrogen gas in chemical laboratories because it typically contains a small quantity of copper, which can act as a catalyst for the linked chemical reaction and so speed up the reaction without actually participating in it.

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Answer 2

Answer:

The answer is as follows

Explanation:

• Hydrogen is the most abundant element which is present in the universe.
• It occurs in both free state as well as in combined state.

Preparation of Hydrogen in lab :

• Hydrogen can be prepared in lab by forming the reaction of the zinc with the alkali metals.
• The metals which lie above hydrogen in the electrochemical series displace hydrogen from dilute mineral acids such as HCl and H2SO4 and they liberate hydrogen gas.

1. Zn + H2SO4  →  ZnSO4 + H2

Here,

ZnSO4 is zinc sulphate.

2. Zn + 2HCl  →  ZnCl + H2

Here,

ZnCl is zinc chloride.

• In above reactions, we use only dilute acids.
• If we use concentrated H2SO4, then SO2 gas will evolve instead of H2 gas.
• If we use concentrated HCl, hydrogen gas will contain impurities of volatile HCl gas.
• Also, we do not use pure zins while performing the H2 has reaction.
• Because, the rate of reaction of pure zinc with Dilute H2SO4 is slow.
• So, in order to increase the rate of the reaction, we use granulated zinc.
• In granulated zinc, Cu is present.
• The Cu in granulated zinc acts as the catalyst for the reaction and increases the rate of the reaction.
• Few amphoteric metals like Zn, Al and Sn react with both acids and alkalis and liberate the Hydrogen gas.

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