In-text Questions — Salts and Chemicals from Common Salt — Acids, Bases and Salts

1. 11 markNCERT Cl-10 Science, In-text Qs after §2.4.4, Q1

   What is the common name of the compound Ca(ClO)₂?

   Hint. This is the same compound made in the chlor-alkali section when chlorine acts on slaked lime.

   Step 1 — Recall where this compound was introduced. The chapter names Ca(ClO)₂ directly as the product formed when chlorine gas acts on dry slaked lime.

   Step 2 — Give its common name. Calcium hypochlorite, Ca(ClO)₂, is commonly known as bleaching powder, since this is the same compound the textbook names in that reaction.

   ✦ Answer: Bleaching powder.

   Where students slip. Confusing this with washing soda or baking soda — those are sodium compounds; Ca(ClO)₂ is a calcium compound, specifically bleaching powder.

2. 21 markNCERT Cl-10 Science, In-text Qs after §2.4.4, Q2

   Name the substance which on treatment with chlorine yields bleaching powder.

   Hint. It has to be dry, not just any form of the same base.

   Step 1 — Recall the reaction. 2Ca(OH)₂ + 2Cl₂ → Ca(ClO)₂ + CaCl₂ + 2H₂O.

   Step 2 — Name the reacting substance. The substance treated with chlorine is dry slaked lime, calcium hydroxide, Ca(OH)₂, since that's what reacts on the left-hand side of the equation above.

   ✦ Answer: Dry slaked lime (calcium hydroxide, Ca(OH)₂).

   Where students slip. Naming quicklime (CaO) instead — it's specifically slaked lime, Ca(OH)₂ (and dry, not in solution), that reacts with chlorine to give bleaching powder.

3. 31 markNCERT Cl-10 Science, In-text Qs after §2.4.4, Q3

   Name the sodium compound which is used for softening hard water.

   Hint. This compound is also used in the glass, soap and paper industries, mentioned in the same section.

   Step 1 — Recall the section's list of uses. Among the sodium compounds discussed (baking soda, washing soda), one is specifically credited with removing permanent hardness of water.

   Step 2 — Name it. Washing soda, sodium carbonate, Na₂CO₃·10H₂O, since the chapter credits it specifically with removing permanent hardness.

   ✦ Answer: Washing soda (sodium carbonate, Na₂CO₃·10H₂O).

   Where students slip. Naming baking soda (NaHCO₃) instead — baking soda's uses are cooking and as a mild antacid; softening hard water is washing soda's job.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §2.4.4, Q4

   What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

   Hint. This is a decomposition — think about what a hydrogencarbonate typically breaks down into on heating.

   Step 1 — Identify the reaction type. Heating sodium hydrogencarbonate (baking soda) decomposes it, since carbonates and hydrogencarbonates are broken down by heat.

   Step 2 — Write the equation. 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(l) + CO₂(g) [heat].

   ✦ Answer: It decomposes into sodium carbonate, water and carbon dioxide: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ (on heating).

   Where students slip. Writing NaOH as a product — heating sodium hydrogencarbonate gives sodium carbonate (Na₂CO₃), not sodium hydroxide.

5. 52 marksNCERT Cl-10 Science, In-text Qs after §2.4.4, Q5

   Write an equation to show the reaction between Plaster of Paris and water.

   Hint. This is the reverse of the reaction that makes Plaster of Paris in the first place.

   Step 1 — Recall what Plaster of Paris is made from. Heating gypsum (CaSO₄·2H₂O) at 373 K removes water to give Plaster of Paris (CaSO₄·½H₂O).

   Step 2 — Write the reverse reaction with water. CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O, reforming gypsum as a hard solid mass — which is exactly why Plaster of Paris must be stored away from moisture.

   ✦ Answer: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O (Plaster of Paris + water → Gypsum).

   Where students slip. Writing whole-number water molecules on both sides — the half-water-molecule notation is deliberate, since two formula units of CaSO₄ share one water molecule between them.

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.