Question

A black coloured compound X turns to brown metal Y when reacts with hydrogen gas. Y
cannot liberate H2 gas with dil. HCl.
i) Identify X and Y and write the chemical equation for that reaction.
ii) Mention the type of reaction which has taken place.
iii) When Y is added to two test tubes containing ZnSO4 solution in one test tube and
AgNO3 solution in another test tube, in which test tube reaction takes place. Write
the chemical equation for that reaction.

Answer 1

Explanation:

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Answer 2

When compound X(black) reacts with H₂ gas to form metal Y(brownish) which cannot liberate H₂ gas when treated with dil. HCl

Explanation:

• A black colored compound means copper oxide (CuO) when reacted with hydrogen gas the metal Copper (Cu) is formed which is brown in color. So, compound X is CuO and compound Y is Cu.
• Chemical reactions involved is-

        CuO(X)  +  H₂(g)   →   Cu(Y)  +  H₂O

        (black)                       (brownish)

• It is a Redox reaction in which CuO get reduced to Cu and H₂ get oxidised to H₂O.
• When metal Cu is treated with dilute HCl then no reaction takes place reactivity of Cu is less than hydrogen means Cu comes under H₂ in reactivity series. Therefore, H₂ gas does not liberate.

           Cu  + dil. HCl →  no reaction

• When Cu is added in a test tube containing ZnSO₄ then no reaction will take place as Zn is more reactive than Cu. So, Cu will not going to displace Zn.
• But when Cu is added into AgNO₃ containing test tube copper nitrate and metal Ag is formed which is a displacement reaction. This happens because reactivity of Cu is more than Ag so it can easily displace Ag from AgNO₃ and form Cu(NO₃)₂.
• Reaction involved is -

           Cu +  ZnSO₄ → no reaction

           Cu +  AgNO₃ →  Cu(NO₃)₂ + Ag