Match List-I with List-II and select the correct answer using the code given below the Lists : List-I (Trade Name) — List-II (Chemical Name) A. Bleaching powder — 1. Sodium bicarbonate B. Baking soda — 2. Sodium carbonate, 10 water C. Washing soda — 3. Calcium oxychloride D. Plaster of Paris — 4. Calcium sulphate, ½ water Code :
- (a)A-3, B-1, C-2, D-4
- (b)A-3, B-2, C-1, D-4
- (c)A-4, B-2, C-1, D-3
- (d)A-4, B-1, C-2, D-3
Correct — A, A-3, B-1, C-2, D-4. Two of the four pairs can be fixed by the metal alone, which is the fastest way through the item. Bleaching powder and Plaster of Paris are both calcium compounds, so they must take the two calcium entries, 3 and 4; baking soda and washing soda are both sodium compounds, so they must take 1 and 2. That already eliminates any code that sends bleaching powder to a sodium entry. Within each pair the choice is settled by one word. Bleaching powder is made by the action of chlorine on dry slaked lime, so it is the chlorine-bearing calcium compound, calcium oxychloride, which is entry 3; Plaster of Paris is obtained by heating gypsum until it loses most of its water, leaving calcium sulphate hemihydrate — calcium sulphate with half a water molecule — which is entry 4. Baking soda is sodium hydrogencarbonate, the bicarbonate of entry 1, while washing soda is sodium carbonate with ten molecules of water of crystallisation, entry 2. That gives A-3, B-1, C-2, D-4.
- (b)A-3, B-2, C-1, D-4 — The two calcium pairs are placed correctly, but the two sodium ones are swapped. This code makes baking soda the decahydrate carbonate and washing soda the bicarbonate, which is the wrong way round — the hydrated one, with ten water molecules, is washing soda.
- (c)A-4, B-2, C-1, D-3 — Every pair is wrong here. Bleaching powder is sent to the sulphate and Plaster of Paris to the chlorine compound, and the two sodium salts are swapped as well.
- (d)A-4, B-1, C-2, D-3 — The sodium pairs are right, but the calcium ones are interchanged. It makes bleaching powder a sulphate, which cannot be — the compound owes its whole action to the chlorine in it — and Plaster of Paris a chlorine compound, which it is not.
Four of the commonest household and industrial chemicals go by trade names much older than their formulae. Bleaching powder is made by passing chlorine over dry slaked lime, and it bleaches and disinfects because it releases chlorine. Baking soda is sodium hydrogencarbonate, which gives off carbon dioxide on heating or on meeting an acid. Washing soda is sodium carbonate carrying ten molecules of water of crystallisation. Plaster of Paris is what gypsum becomes when heated to about 373 kelvin and loses most of its water; adding water turns it back into gypsum as a hard solid mass.
A four-pair match is best solved by finding the cheapest discriminator first rather than by working through all four in order. Here the metal does it: two calcium entries and two sodium entries split the list in half before any chemistry is needed. A candidate who then remembers only that bleaching powder involves chlorine has the whole answer. One point of terminology is worth carrying, because textbooks differ. The current NCERT writes bleaching powder as Ca(ClO)2 and adds that the actual composition is quite complex; the older and still common Indian textbook name for it is calcium oxychloride, CaOCl2, which is the name this paper uses. Either name refers to the same product of chlorine acting on slaked lime, and no exam turns on the difference — but knowing that both are in circulation prevents a moment of doubt in the hall.
- Bleaching powder is produced by the action of chlorine on dry slaked lime, calcium hydroxide.
- NCERT gives baking soda as sodium hydrogencarbonate, NaHCO3, made using sodium chloride as a raw material.
- Washing soda is Na2CO3.10H2O, obtained by recrystallising sodium carbonate, and is used to remove permanent hardness of water.
- Plaster of Paris is calcium sulphate hemihydrate, formed by heating gypsum at 373 kelvin, and it turns back into gypsum on mixing with water.
- Half a water molecule appears in the formula of Plaster of Paris because two formula units of calcium sulphate share one water molecule.
The metal halves the problem before any chemistry is needed.
- Swapping baking soda and washing soda; the hydrated carbonate with ten waters is the washing one.
- Forgetting that bleaching powder is a calcium compound, not a sodium one, even though it is made from common salt by way of chlorine.
- Reading half a water molecule as an error; two formula units share one water molecule, which is why it is written that way.
Almost always as a trade-name-to-formula match; the same four names recur, sometimes with slaked lime or gypsum swapped in as a fifth.
Match List I with List II and select the correct answer using the codes given below the lists: List I — I. Blue vitriol, II. Epsom salt, III. Baking soda, IV. Caustic soda; List II — A) Sodium bicarbonate, B) Sodium hydroxide, C) Magnesium sulphate, D) Copper sulphate
- (a) I-C, II-D, III-B, IV-A
- (b) I-D, II-C, III-A, IV-B
- (c) I-C, II-D, III-A, IV-B
- (d) I-D, II-A, III-B, IV-A
Answer(b) I-D, II-C, III-A, IV-B
The same kind of trade-name match on a different set of four, and baking soda appears in both with the same partner, sodium bicarbonate. Splitting the list by metal works there too — copper, magnesium and two sodium salts.
Match List–I with List–II and select the correct answer using the code given below the Lists: List–I (Name) A. Bleaching powder B. Baking soda C. Washing soda D. Slaked lime List–II (Formula) 1. NaHCO₃ 2. Na₂CO₃·10H₂O 3. Ca(OH)₂ 4. CaOCl₂
- (a) A B C D 4 1 2 3
- (b) A B C D 4 2 1 3
- (c) A B C D 3 2 1 4
- (d) A B C D 3 1 2 4
Answer(a) A B C D 4 1 2 3
Almost the same item four years earlier, with slaked lime in place of Plaster of Paris and formulae instead of chemical names. The three shared pairs are identical, and that paper spells bleaching powder as CaOCl₂ — the formula behind the name calcium oxychloride used here.
- practice — not a real PYQ
Plaster of Paris is obtained by heating which one of the following?
- (a)Limestone
- (b)Gypsum
- (c)Slaked lime
- (d)Washing soda
Answer(b) Gypsum — heating gypsum at about 373 kelvin drives off most of its water and leaves calcium sulphate hemihydrate, which is Plaster of Paris.
- practice — not a real PYQ
Which one among the following is used to remove the permanent hardness of water?
- (a)Baking soda
- (b)Washing soda
- (c)Bleaching powder
- (d)Plaster of Paris
Answer(b) Washing soda — sodium carbonate precipitates the calcium and magnesium salts that cause permanent hardness.