Laws of Chemical Combination — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Laws of Chemical Combination MCQs with step-by-step solutions (9 questions). Part of Atoms, Molecules & Structure. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Laws of Chemical Combination · medium · theory
The law of conservation of mass states that in a chemical reaction, mass is:
A. neither created nor destroyed ✓ Correct
B. converted into energy
C. always decreased
D. always increased
Solution: The total mass of the reactants equals the total mass of the products.
Q2 — Laws of Chemical Combination · hard · theory
The law of constant (definite) proportions states that a pure chemical compound always contains the same elements combined in a:
A. ratio of 1:1 always
B. variable ratio by mass
C. fixed ratio by mass ✓ Correct
D. ratio that depends on temperature
Solution: A given compound always has its constituent elements in the same fixed mass ratio.
Q3 — Laws of Chemical Combination · hard · numerical
In water, hydrogen and oxygen are always combined in the mass ratio 1 : 8. The mass of oxygen that combines with 3 g of hydrogen is:
A. 3 g
B. 24 g ✓ Correct
C. 11 g
D. 8 g
Solution: Ratio 1 : 8 means $3 \times 8 = 24$ g of oxygen combines with 3 g of hydrogen.
Q4 — Laws of Chemical Combination · hard · numerical
When 12 g of carbon burns completely in 32 g of oxygen, the mass of carbon dioxide formed (by conservation of mass) is:
A. 20 g
B. 32 g
C. 384 g
D. 44 g ✓ Correct
Solution: Mass of products = mass of reactants $= 12 + 32 = 44$ g.
Q5 — Laws of Chemical Combination · medium · theory
The law of constant proportions was proposed by the scientist:
A. Newton
B. Rutherford
C. Bohr
D. Proust ✓ Correct
Solution: Joseph Proust put forward the law of definite (constant) proportions.
Q6 — Laws of Chemical Combination · easy · theory
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Who first established this law through careful experiments?
A. Antoine Lavoisier ✓ Correct
B. J.J. Thomson
C. John Dalton
D. Joseph Proust
Solution: Antoine Lavoisier established the law of conservation of mass by weighing reactants and products in closed systems.
Q7 — Laws of Chemical Combination · medium · numerical
Pure water always contains hydrogen and oxygen in a fixed mass ratio of 1:8. If 9 g of water is completely decomposed, what mass of oxygen is obtained?
A. 1 g
B. 4.5 g
C. 8 g ✓ Correct
D. 9 g
Solution: By the law of definite proportions the H:O mass ratio is 1:8, so in 9 g of water oxygen = 8/9 x 9 = 8 g (and hydrogen = 1 g).
Q8 — Laws of Chemical Combination · medium · numerical
Carbon forms two oxides. In one, 12 g of carbon combines with 16 g of oxygen; in the other, 12 g of carbon combines with 32 g of oxygen. The masses of oxygen that combine with the same mass of carbon are in the ratio:
A. 3:4
B. 1:2 ✓ Correct
C. 1:1
D. 2:3
Solution: For a fixed 12 g of carbon the oxygen masses are 16 g and 32 g, a simple whole-number ratio of 1:2, illustrating the law of multiple proportions.
Q9 — Laws of Chemical Combination · hard · theory
Assertion: Pure water collected from a river and pure water prepared in a laboratory both contain hydrogen and oxygen in exactly the same ratio by mass. Reason: This is explained by the law of multiple proportions. Which is correct?
A. Both assertion and reason are true, and the reason correctly explains the assertion
B. Both the assertion and the reason are false
C. The assertion is true but the reason is false ✓ Correct
D. The assertion is false but the reason is true
Solution: A pure compound always has the same composition by the law of definite (constant) proportions, not multiple proportions. So the assertion is true but the stated reason is false.