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Rahul took some zinc granules in a test tube and added dilute HCl to it. He observed that the colour of zinc granules changed to
  • a)
    yellow
  • b)
    brown
  • c)
    black
  • d)
    white
Correct answer is option 'C'. Can you explain this answer?
Most Upvoted Answer
Rahul took some zinc granules in a test tube and added dilute HCl to i...
Explanation:


When zinc granules are added to dilute hydrochloric acid (HCl), a chemical reaction takes place. The zinc reacts with the hydrogen ions in the acid to produce zinc chloride and hydrogen gas. This reaction is known as a single displacement reaction, where one element (zinc) displaces another element (hydrogen) from its compound (HCl). The reaction can be represented as follows:

Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)

Now, let's look at the colour change of the zinc granules:

  • Yellow: Zinc metal is typically shiny and silvery in colour. When exposed to air, it can form a thin layer of zinc oxide on its surface, which appears as a dull yellow colour. However, this is not the colour change observed in this reaction.

  • Brown: A brown colour could indicate the presence of impurities or contaminants in the zinc granules. However, this is not a typical colour change observed in this reaction.

  • Black: When the reaction takes place, the zinc granules react with the HCl to form zinc chloride, which is a white solid. However, if the zinc granules are not fully covered by the acid, they may react with the oxygen in the air to form zinc oxide, which appears as a black colour. Therefore, the black colour observed in this reaction may be due to the formation of zinc oxide on the surface of the zinc granules.

  • White: Zinc chloride is a white solid, and it is the product formed in this reaction. Therefore, the most likely colour change observed in this reaction is a change from silver or yellowish to white due to the formation of zinc chloride.



Therefore, the correct answer is option C (black). However, it is important to note that the colour change observed may vary depending on the purity of the zinc granules and the conditions under which the reaction takes place.
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Community Answer
Rahul took some zinc granules in a test tube and added dilute HCl to i...
Option D is correct as,
reaction involved:
Zn+ 2Hcl--->Zncl2+H2
This reaction is known as single replacement reaction, where zinc metal displaces the hydrogen to form hydrogen gas and zinc chloride, a salt.  
where the initial colour of zn is bluish silver
and after reaction the formation of zinc chloride is of white
(the colour of zinc changes from grey to white because it forms a compound)
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Rahul took some zinc granules in a test tube and added dilute HCl to it. He observed that the colour of zinc granules changed toa)yellowb)brownc)blackd)whiteCorrect answer is option 'C'. Can you explain this answer?
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