In-text Questions — Reactions with Metals, Bases and Oxides — Acids, Bases and Salts

1. 12 marksNCERT Cl-10 Science, In-text Qs after §2.1.6, Q1

   Why should curd and sour substances not be kept in brass and copper vessels?

   Hint. Curd and sour foods are mild acids — think about what an acid does to a metal.

   Step 1 — Recognise curd and sour substances as mild acids. Curd contains lactic acid, and most sour foods contain some acid, so keeping them in a metal vessel is really an acid-and-metal reaction sitting in your kitchen.

   Step 2 — What that reaction does. Brass (a copper-zinc alloy) and copper both react with acids, since a metal reacting with an acid gives a salt (of that metal) plus hydrogen gas. Over time, the acid corrodes the vessel and produces metal salts that dissolve into the food.

   Step 3 — Why that matters. These metal salts (of copper or zinc) are harmful if consumed in more than trace amounts, so the food becomes contaminated and unsafe to eat.

   ✦ Answer: Curd and sour substances contain acids, which react with the copper and zinc in brass/copper vessels to form metal salts. These salts dissolve into the food and are harmful to health, so such vessels should not be used for storing sour or acidic foods.

   Where students slip. Saying the vessel just 'gets damaged' without explaining the food-safety consequence — the actual reason to avoid this is that the reaction contaminates the food with metal salts, not just that the vessel corrodes.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §2.1.6, Q2

   Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

   Hint. This is exactly Activity 2.3 from earlier in the chapter — recall what happened when the gas met a burning candle.

   Step 1 — Name the gas. Hydrogen gas (H₂) is liberated when an acid reacts with a (reactive) metal.

   Step 2 — Give an example. Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g), as seen in Activity 2.3 with zinc granules and dilute sulphuric acid.

   Step 3 — Test for the gas. Pass the gas through a soap solution to form gas-filled bubbles, then bring a burning candle or matchstick close to a bubble — since hydrogen is flammable, the gas burns with a pop sound, confirming it is hydrogen.

   ✦ Answer: Hydrogen gas, e.g. Zn + H₂SO₄ → ZnSO₄ + H₂. Test: pass it through soap solution to form bubbles, then bring a burning candle near a bubble — it burns with a characteristic 'pop.'

   Where students slip. Confusing this test with the limewater test for CO₂ — a 'pop' sound with a flame is hydrogen's test; CO₂ is identified by turning limewater milky, not by burning.

3. 33 marksNCERT Cl-10 Science, In-text Qs after §2.1.6, Q3

   Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

   Hint. A gas that puts out a flame, rather than burning, is a strong clue to which gas this is.

   Step 1 — Identify the gas. A gas that extinguishes a burning candle (rather than burning itself) is carbon dioxide, CO₂ — it doesn't support combustion.

   Step 2 — Identify compound A. Effervescence plus CO₂ on reacting with an acid is the signature of a metal carbonate (Metal carbonate + Acid → Salt + CO₂ + Water). Since one product is calcium chloride, the metal here is calcium, so A is calcium carbonate, CaCO₃.

   Step 3 — Write and balance. CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g).

   ✦ Answer: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). Compound A is calcium carbonate.

   Where students slip. Naming the gas as hydrogen because 'acid + metal compound' sounds familiar from the previous question — the extinguishing effect specifically points to CO₂, which comes from a carbonate, not a free metal.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc102.pdf) — five in-text question sets (19 questions total) plus one end-of-chapter Exercise (15 questions, not 20 as some older manifests claim). Bleaching powder is written as Ca(ClO)₂ in the current text, matching the chapter's own in-text question.. Questions are referenced from the NCERT textbook for identification.