MCQ
MCQ
Which of the following pairs of substances illustrate the law of multiple proportions?
(a) MgO and Mg(OH)2
(b) H2O and D2O
(c) NaCl and NaBr
(d) CO and CO2
Solution:
In CO, 12 parts of carbon combines with 16 parts of oxygen.
In CO2, 12 parts of carbon combines with 32 parts of oxygen.
So, the ration of oxygen in both the compounds is 1:2. This illustrates law of multiple proportions.
Correct option is (d).
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Law of definite proportions does not apply to nitrogen oxide because
(a) Atomic weight of N is not constant
(b) Molecular weight of nitrogen is variable
(c) Atomic weight of oxygen is variable
(d) Nitrogen has different valencies in different oxides
Solution:
In different oxides of nitrogen, the valencies of nitrogen varies from +1 to +5. So, law of definite proportions does not apply to oxides of nitrogen.
Option (d) is correct.
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Irrespective of the source, pure sample of water always yields 88.89 % mass of oxygen and 11.11% mass of hydrogen. This is explained by the law of
(a) Conservation of mass
(b) Multiple proportions
(c) Definite proportions
(d) Constant volume
Solution:
This illustrates law of definite proportions.
Correct option is (c).
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Carbon forms two oxides containing 42.9 % and 27.3 % carbons respectively. Which law of chemical combination does this illustrate?
Solution:
In 100 g of first oxide, carbon is 42.9 g and oxygen is (100-42.9) = 57.1 g
So, 42.9 parts of carbon contains 57.1 g of oxygen. The ratio of oxygen:carbon = 57.1:42.9 or 1.33:1
Similarly, in 100 g of 2nd oxide, carbon is 27.3 g and oxygen is (100-27.3) = 72.7 g
So, 27.3 parts of carbon contains 72.7 g of oxygen. The ratio of oxygen:carbon = 72.7:27.3 or 2.66:1
Ratio of masses of oxygen in both oxides is 1.33:2.66 or 1:2.
This illustrates law of multiple proportions.
Correct option is (b).
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3 g of a hydrocarbon on combustion with 11.2 g of oxygen produces 8.8 g of CO2 and 5.4 g of H2O.The data illustrates the law of
(a) Conservation of mass
(b) Multiple proportions
(c) Definite proportions
(d) Avogadros law
Solution:
Masses of hydrocarbon and oxygen = 3 g + 11.2 g = 14.2 g
Masses of CO2 and H2O = 8.8 g + 5.4 g = 14.2 g
Masses of reactants = masses of products
So, law of conservation of mass is illustrated. Correct option is (a).
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Hydrogen combines with chlorine to form HCl. It also combines with sodium to form NaH. If sodium and chlorine also combine with each other, they will do so in the ratio of their masses as
(a) 23:35.5
(b) 35.5:23
(c) 1:1
(d) 23:1
Solution:
Atomic masses of H, Na and Cl is 1, 23 and 35.5 g/mol respectively.
In HCl, 1 part of H combines with 35.5 parts of Cl.
In NaH, 23 parts of Na combines with 1 part of H.
The ratio of H in both compounds is 1:1.
According to law of multiple proportions, Na and Cl will combine in the ratio of their masses as 23:35.5.
So, correct option is (a).
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3 g of a hydrocarbon on combustion with 11.2 g of oxygen produces 8.8 g of CO2 and 5.4 g of H2O.The data illustrates the law of
(a) Conservation of mass
(b) Multiple proportions
(c) Definite proportions
(d) Avogadros law
Solution:
Masses of hydrocarbon and oxygen = 3 g + 11.2 g = 14.2 g
Masses of CO2 and H2O = 8.8 g + 5.4 g = 14.2 g
Masses of reactants = masses of products
So, law of conservation of mass is illustrated. Correct option is (a).
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Hydrogen combines with chlorine to form HCl. It also combines with sodium to form NaH. If sodium and chlorine also combine with each other, they will do so in the ratio of their masses as
(a) 23:35.5
(b) 35.5:23
(c) 1:1
(d) 23:1
Solution:
Atomic masses of H, Na and Cl is 1, 23 and 35.5 g/mol respectively.
In HCl, 1 part of H combines with 35.5 parts of Cl.
In NaH, 23 parts of Na combines with 1 part of H.
The ratio of H in both compounds is 1:1.
According to law of multiple proportions, Na and Cl will combine in the ratio of their masses as 23:35.5.
So, correct option is (a).
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Zinc sulphate contains 22.65% Zn and 43.9% H2O. If the law of constant proportions is true, then the mass of Zinc required to give 40 g crystal will be
(a) 90.6 g
(b) 9.06 g
(c) 0.906 g
(d) 906 g
Solution:
As each crystal of zinc sulphate will contains 22.65% Zn, so 40 g crystal will also contain 22.65% Zn.
Zn in the crystal = 22.65% of 40 g
=(22.65/100) x 40 = 9.06 g
Correct option is (b).
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Phosphorus forms two oxides P2O3 and P2O5. Which law can be proved by the weights of P and O?
(a) Constant composition
(b) Multiple proportions
(c) Gay Lussac law
(d) Conservation of mass
Solution:
The law of multiple proportions can be proved by the weights of P and O in these two compounds.
Atomic mass of P is 31 g/mol
Atomic mass of O is 16 g/mol.
In P2O3, 62 parts of P combines with 48 parts of O.
In P2O5, 62 parts of P combines with 80 parts of O.
The ratio of O in both compounds is 48:80 or 3:5 which is a simple whole number ratio.
This proves the law of multiple proportions.
So, correct option is (b).
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