Page 154 - Chemistry ICSE Class X

140 ICSE Chemistry – 10
42. The empirical formula of a gaseous compound is AB . Its empirical formula mass is equal to its vapour density.
2
What is the molecular formula of the compound? [Ans. A 2 B 4 ]
43. A hydrocarbon contains 82.8% of carbon. Its vapour density is 29. Find its molecular formula. [Ans. C H ]
4
10
44. Calculate the percentage of carbon dioxide (CO ) in calcium carbonate (CaCO ). [Ans. 44%]
2
3
45. Calculate the percentage of oxygen in sugar (C H O ). Relative atomic masses are: C = 12, H = 1, and O = 16.
12
11
22
[Ans. 51.5%]
46. Calculate the formula mass of each of the following substances:
(a) BaCl 2 (b) Fe (SO )
2
4 3
(c) Na HPO .12H O (d) K SO .Al (SO ) .24H O
2
4
2
4 3
2
2
2
4
Relative atomic masses are:
Ba = 137, Cl = 35.5, Fe = 56, S = 32, O = 16, Na = 23, H = 1, P = 31, K = 39, Al = 27. [Ans. (a) 208 u (b) 400 u (c) 358 u (d) 948 u]
47. *QY OWEJ NKOG KU HQTOGF YJGP I QH ECNEKWO PKVTCVG KU JGCVGF #NUQ ſPF VJG XQNWOG QH PKVTQIGP FKQZKFG
evolved. [Ans. 28 g; 22.4 L]
48. The reaction between marble and nitric acid is
CaCO (s) + 2HNO (aq) o Ca(NO ) (aq) + H O + CO (g)
2
3 2
3
2
3
Calculate:
(a) mass of anhydrous calcium nitrate formed from 15 g of marble chips.
(b) volume of carbon dioxide evolved under STP. [Ans. (a) 24.6 g (b) 3.36 L]
49. For the reaction
Al C 3 + 12H O o 3CH 4 + 4Al(OH) 3
2
4
Calculate the volume of methane at STP released from 14.4 g of Al C . [Ans. 6.72 L]
4
3
50. For the reaction,
MnO 2 + 4HCl o MnCl 2 + 2H O + Cl 2
2
when 1.74 g of pure MnO is heated strongly with conc. HCl, calculate
2
(a) moles of MnO used (b) moles of MnCl formed
2
2
(c) mass of MnCl formed (d) mass of chlorine evolved
2
(e) volume of chlorine evolved (at STP) (f) mass of the acid required.
[Ans. (a) 0.02 mol (b) 0.02 mol (c) 2.52 g (d) 1.42 g (e) 0.448 L (f) 2.92 g]
51. Tick (9) the correct answer.
(i) Volume-volume relationship for a reaction between gases is given by
(a) Charles’ law ‰
(b) Boyle’s law ‰
(c) Avogadro’s law ‰
(d) Gay-Lussac law ‰
(ii) The mass percentage of hydrogen in water is
(a) 1.11 ‰
(b) 88.9 ‰
(c) 8.89 ‰
(d) 11.11 ‰
(iii) The accepted unit of atomic and molecular masses is
(a) kilogram ‰
(b) gram ‰
(c) pound ‰
(d) atomic mass unit ‰
(iv) Chemists commonly express the amount of any substance in the unit of
(a) mass ‰
(b) density ‰
(c) mole ‰
(d) volume ‰