NCERT Exemplar Solutions
Class 10 - Science - CHAPTER 2: Acids, Bases and Salts - Long Answer Questions
Question 43

Question. 43

43. In the following schematic diagram for the preparation of hydrogen gas as shown in Figure 2.3, what would happen if following changes are made?

(a) In place of zinc granules, same amount of zinc dust is taken in the test tube

(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken

(c) In place of zinc, copper turnings are taken

(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated

Answer:

(a) Hydrogen gas will evolve with greater speed (because powder has larger surface area).
(b) Almost same amount of gas is evolved (HCl is also a strong acid; Zn + 2HCl → ZnCl₂ + H₂).
(c) Hydrogen gas is not evolved (copper is less reactive than hydrogen and does not react with dilute acid under normal conditions).
(d) If NaOH (a strong base) is used with zinc and heated, hydrogen gas is evolved and sodium zincate is formed: \(\mathrm{Zn + 2NaOH \xrightarrow{\Delta} Na_2ZnO_2 + H_2}\).

Detailed Answer with Explanation:

Steps: (a) More surface area → faster reaction. (b) Both H₂SO₄ and HCl react with Zn to give H₂. (c) Copper is below hydrogen in reactivity series so it won't displace H₂ from acids. (d) Zinc reacts with hot concentrated alkali to give hydrogen and zincate ion.

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NCERT Exemplar Solutions Class 10 – Science – CHAPTER 2: Acids, Bases and Salts – Long Answer Questions | Detailed Answers