Chalk and marble are different forms of
- (a)Calcium hydrogen carbonate
- (b)Calcium carbonate
- (c)Calcium acetate
- (d)Sodium carbonate
Correct — B, calcium carbonate. Chalk, marble and limestone are all naturally occurring forms of the same compound, calcium carbonate (CaCO3). Chalk is a soft sedimentary form and marble is the metamorphosed, crystalline form; they share the formula CaCO3 but differ in texture and hardness.
- (a)Calcium hydrogen carbonate — Ca(HCO3)2 exists only dissolved in hard water; it is not the solid that makes up chalk or marble.
- (c)Calcium acetate — Calcium acetate is a salt of acetic acid and is unrelated to the mineral forms of chalk and marble.
- (d)Sodium carbonate — Sodium carbonate (washing soda, Na2CO3) contains sodium rather than calcium and is a manufactured chemical, not chalk or marble.
Calcium carbonate, CaCO3, occurs widely in nature as limestone, chalk and marble, and also in shells and corals. Heating it (calcination) drives off carbon dioxide to give quicklime (CaO), which is the basis of the lime and cement industries.
The options separate three calcium salts from one sodium salt. Since both chalk and marble are calcium minerals, drop sodium carbonate at once; among the calcium options only the neutral carbonate CaCO3 forms solid rock.
- Chalk, marble and limestone are all forms of calcium carbonate, CaCO3.
- Marble is metamorphosed limestone; chalk is a soft sedimentary carbonate.
- Heating CaCO3 gives quicklime (CaO) and carbon dioxide.
- Calcium hydrogen carbonate, Ca(HCO3)2, exists only in solution (temporary hardness of water).
- Confusing calcium carbonate (solid rock) with calcium hydrogen carbonate (dissolved in hard water).
- Picking sodium carbonate (washing soda) because both are carbonates.
Asked by naming everyday materials (chalk, marble, limestone) and asking for the common chemical compound.
Match List I (Naturally occurring substances) with List II (Elements) and select the correct answer using the codes given below the Lists: List I — I. Diamond, II. Marble, III. Sand, IV. Ruby; List II — A) Calcium, B) Silicon, C) Aluminium, D) Carbon.
- (a) I-C, II-A, III-B, IV-D
- (b) I-D, II-B, III-A, IV-C
- (c) I-B, II-A, III-C, IV-D
- (d) I-D, II-A, III-B, IV-C
Answer(d) I-D, II-A, III-B, IV-C
Uses the same fact that marble is a calcium (carbonate) mineral; here chalk and marble are identified together as calcium carbonate.
Which one of the following does not represent the salt, Calcium Carbonate?
- (a) Lime water
- (b) Limestone
- (c) Chalk
- (d) Marble
Answer(a) Lime water
Directly the same compound — chalk and marble are calcium carbonate; there the odd one out is lime water (a calcium hydroxide solution), reinforcing which everyday materials are CaCO3.
- practice — not a real PYQ
On strong heating, calcium carbonate decomposes to give calcium oxide and
- (a)hydrogen
- (b)carbon dioxide
- (c)oxygen
- (d)water vapour
Answer(b) carbon dioxide — leaving quicklime, CaO.
- practice — not a real PYQ
Which one of the following is chemically the same compound as marble?
- (a)Gypsum
- (b)Limestone
- (c)Quartz
- (d)Feldspar
Answer(b) Limestone — both are calcium carbonate, CaCO3.