LAWS OF CHEMICAL COMBINATION AND CONSTANT PROPORTIONS

1. Name the scientist who gave the law of conservation of mass.
2. What is the unit of measurement of atomic radius?
3. Name the scientist who gave atomic theory, which was a turning point in the study of matter.
4. Name the scientist who gave the law of constant proportion and what does this law state.
5. (a) Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
(b) Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
6. Hydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas
would be required to react completely with 3 g of hydrogen gas?
7. Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide. When 10 g of
calcium carbonate is decomposed completely then 5.6 g of calcium oxide is formed. Calculate the mass of
carbon dioxide formed. Which law of chemical combination will be used in solving this problem? Explain
that law.
8. A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron
and 0.144 g of oxygen. Calculate the percentage composition of the compound by mass.
9. State the postulates of the Dalton’s Atomic Theory. What are its drawbacks?
10. Give an experiment to verify the law of conservation of mass.
11. Sodium carbonate reacts with ethanoic acid to form sodium ethanoate, carbon dioxide and water. In an
experiment, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid to form 8.2 g of sodium
ethanoate, 2.0 g of carbon dioxide and 0.9 g of water. Show that this data verifies the law of conservation
of mass.
12. In an experiment, 1.288 g of copper oxide was obtained from 1.03 g of copper. In another experiment,
3.672 g of copper oxide gave on reduction 2.938 g of copper. Show that these figures verify the law of
constant proportions.
13. When 3 g of carbon is burnt in 8 g of oxygen, 11 g of carbon dioxide is produced. What mass of carbon
dioxide will be formed when 3 g of carbon is burnt in 50 g of oxygen? Which law of chemical
combination will govern your answer?
14. “If 100 grams of pure water taken from different sources is decomposed by passing electricity, 11 grams of
hydrogen and 89 grams of oxygen are always obtained”. Which chemical law is illustrated by this
statement?
15. “If 100 grams of calcium carbonate (whether in the form of marble or chalk) are decomposed completely,
then 56 grams of calcium oxide and 44 grams of carbon dioxide are obtained.” Which law of chemical
combination is illustrated by this statement?
16. Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. What mass of
oxygen gas would be required to react completely with 24 g of magnesium?
17. Write the symbols for the following elements as given by Dalton – Iron, oxygen, lead, mercury, gold
platinum, silver, phosphorus and sulphur.
TYPE – B
ATOMS AND ATOMIC MASS
18. What is an atom? Why can’t we see atom with a naked eye?
19. Which institute approves the name of elements?
20. From which words are the symbols of iron, sodium and potassium derived.
21. Which element is taken as the standard reference for measuring atomic masses?
22. What is atomic mass of an element? Which symbol is used to represent atomic mass.
1
23. Why did scientists initially took
of the mass of an atom of naturally occurring oxygen as 1 atomic
16
mass unit?
24. Write the chemical symbols of the following elements:–
hydrogen, carbon, nitrogen, oxygen, sodium, magnesium, sulphur, chlorine and calcium.
25. In which form does atom exists?
26. What is meant by saying that “the atomic mass of oxygen is 16”?
27. Which is the smallest atom and what is its size?
28. Define atomic mass unit.
29. What is the significance of the symbol of an element?
30. Name the elements represented by the following symbols :–
Hg, Pb, Au, Ag, Sn.
31. Is it possible to see atoms these days? Explain with examples.
32. (i) Give two symbols which have been derived from the “English names” of the elements.
(ii) Give two symbols which have been derived from the “Latin names” of the elements.
33. Write the chemical sybmols for the following elements:–
Sodium, Potassium, Iron, Copper, Mercury, Silver.
34. Write the relation between nanometer and meter.
35. What information is conveyed by the formula H
O?
36. State the valencies and formula of the following ions.
(i) Ammonium (ii) Calcium (iii) Ferrous
(iv) Ferric (v) Nitride (vi) Phosphide
(vii) Nitrate (viii) Zinc (ix) Cupric
(x) Bromide (ix) Phosphate (xii) Hydroxide
(xiii) Silver (xiv) Hydride (xv) Sulphite
TYPE – C
MOLECULES AND IONS
37. What is a molecule?
38. Atoms of the same element or of different elements can join together to form molecules. Justify this
statement with example.
39. Write down the atomicity of the following elements:
Iron, Oxygen, Phosphorus, Chlorine, Ozone, Helium, Aluminium, Sulphur, Hydrogen and Argon.
40. Given reasons:
Atomicity of noble gases is one
Atomicity of metals is one.
41. What is the ratio of mass of combining
elements in carbon dioxide?
42. What is an ion?
43. What is a poly atomic ion? Give four examples.
44. Give example of twp elements which have more than one valency.
TYPE – D
CHEMICAL FORMULA
45. Write down the constituting elements and the ratio of mass of the constituting elements in the following
compounds:
(a) Calcium oxide (b) Magnesium sulphide (c) Sodium chloride
46. Write down the names of compounds represented by the following formulae:
(i) Al
(SO
)
(ii) CaCl
(iii) K
SO
2
4
3
2
2
4
(iv) KNO
(v) CaCO
(vi) KMnO
3
3
4
47. How many atoms are present in a
(a) H
S molecule? (b) PO
ion?
3–
2
4
48. What is the symbol of phosphate ion and ferric ion?
49. What are the rules which one has to follow while writing a chemical formula of a compound?
Write down the chemical formula of following compounds:
(i) Hydrogen sulphide (ii) Carbon tetrachloride (iii) Magnesium chloride
(iv) Aluminium oxide (v) Sodium nitrate (vi) Calcium hydroxide
(vii) Calcuium bicarbonate (viii) Nitric acid (ix) Potassium hydroxide
50. Work out the formula for aluminium sulphate.
51. The valencies of two elements A and B are given below:
Element Valency
A 1 +
B 2 +
(i) What is the formula of sulphate of A?
(ii) What is the formula of nitrate of B?
52. The formula of the chloride of a metal is MCl
. What will be the formula of its sulphate?
2
TYPE – E
MOLECULAR MASS
53. If the atomic mass of sodium is 23 u, what will be the atomic mass of sodium ion?
54. What is the formula unit and formula mass of an ionic compound?
55. Calculate the formula mass of Potassium carbonate.
Given:
Atomic mass: (K = 39 u, C = 12 u, O = 16 u)
56. Define gram atomic mass. What is the gram atomic mass of oxygen?
57. Define gram molecular mass. What is the gram molecular mass of oxygen?
58. What is an Avogadro Number? How is it represented?
59. Calculate the number of moles for the following:
(i) 52 g of He (finding mole from mass)
(ii) 12.044 × 10
number of He atoms (finding mole from number of particles).
23
60. Calculate the mass of the following:
(i) 0.5 mole of N
gas (mass from mole of molecule)
2
(ii) 0.5 mole of N atoms (mass from mole of atom)
(iii) 3.011 × 10
number of N atoms (mass from number)
23
(iv) 6.022 × 10
number of N
molecules (mass from number)
23
2
61. Calculate the number of particles in each of the following:
(i) 46 g of Na atoms (number from mass)
(ii) 8 g of O
molecules (number of molecules from mass)
2
(iii) 0.1 mole of carbon atoms (number from given moles)

62. Calculate the molar masses of the following substances:
(a) Ethyne, C
H
(b) Sulphur molecule, S
2
2
8
(c) Phosphorus molecule, P
(d) HydroChloric acid, HCl
4
(e) Nitirc acid, HNO
3
63. How many moles are present in 5 grams of calcium? (Atomic mass of calicum = 40 u).
64. What is the mass of 4 moles of aluminium atoms?
65. Calculate the number of atoms in 0.2 moles of sodium (Na).
66. How many moles are present in 9.033 × 10
atoms of helium (He)?
24
67. Caclulate the number of iron atoms in a piece weighing 2.8 g (Atomic mass of iron = 56 u).
68. If one mole of carbon atoms weighs 12 grams, what is the mass in grams of an atom of carbon?
69. Which has more number of atoms, 100 grams of sodium or 100 grams of iron?
(Atomic masses : Na = 23 u; Fe = 56u)
70. If 1 g of carbon contains ‘X’ number of atoms, what will be the number of atoms in 1 g of magnesium?
(C = 12 u, Mg = 24 u)
71. How many grams of Neon will have the same number of atoms as 4 grams of Calcium?
(Atomic masses : Ne = 20 u, Ca = 40 u)
72. The mass of a single atom of an elment X is 2. 65 × 10
g. What is its atomic mass?
–23

ANSWER KEY
TYPE – A
TYPE – D
1. Lavoiser in 1774
46. (i) Aluminium sulphate
2. Nanometer
(ii) Calcium chloride
3. Dalton
(iii) Potassium sulphate
6. 24 g
(iv) Potassium nitrate
7. 4.4 g of carbon dioxide
(v) Calcium carbonate
8. 40% boron and 60% oxygen
(vi) Potassium permanganate
16. 16 g oxygen
47. (a) 3 (b) 5
48. Phosphate ion (PO
) and ferric ion (Fe
)
3–
3+
4
TYPE – B
49. (i) H
S, (ii) CCl
,
2
4
19. IUPAC
(iii) MgCl
, (iv) Al
O
,
2
2
3
20. Iron – ferrum, sodium – natrium,
(v) NaNO
, (vi) Ca(OH)
,
3
2
potassium – kalium
(vii) CaHCO
, (viii) HNO
,
3
3
21. Carbon – 12
(ix) KOH
24. H, C, N, O, Na, Mg, S, Cl, Ca
51. (i) A
SO
(ii) B(NO
)
2
4
3
2
30. Mercury, Lead, Gold, Silver, Tin
32. (i) H, He (ii) Na, K
TYPE – E
33. Na, K, Fe, Cu, Hg, Ag
53. 22 for Na
+
34. 1 metre = 10
nanometres
55. Potassium carbonate = 138
9
36. (i) NH
(ii) Ca
59. (i) 13 moles (ii) 2 moles
+
2+
4
(iii) Fe
(iv) Fe
60. (i) 14 g (ii) 7 g
2+
3+
(v) N
(vi) P
(iii) 7 g (iv) 28 g
3–
3–
(vii) NO
(viii) Zn
61. (i) 12.044 × 10
atoms

2+
23
3
(ix) Cu
(x) Br
(ii) 1.5 × 10
atoms
3+

23
(xi) PO
(xii) OH
(iii) 0.6022 × 10

23
43–
(xiii) Ag
(xiv) H
+

62. (a) 26 u (b) 256 u
(xv) SO
(c) 124 u (d) 36.5 u
32–
(e) 363 u
TYPE – C
1 moles
63. 8
44. Copper and iron
64. 108 u
65. 1.2044 × 10
atoms
23
67. 2.011 × 10
22