Chapter 03 Atoms and Molecules Questions-01
Questions
1. In a reaction, $5.3 g$ of sodium carbonate reacted with $6 g$ of acetic acid. The products were $2.2 g$ of carbon dioxide, $0.9 g$ water and $8.2 g$ of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + acetic acid $\rightarrow$ sodium acetate + carbon dioxide + water
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Answer
Law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction.
It means the mass remains the same. So, we add the mass of the reactants on LHS and add the mass of all products on RHS
LHS $=5.3 g+6 g=11.3 g$
RHS $=8.2 g+2.2 g+0.9 g=11.3 g$
LHS $=$ RHS
So, the observations are in agreement with the law of conservation of mass.
2. 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?
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Answer
‘Law of constant proportions’ states that composition of a compound is always fixed.
Applying this
$\because 1 g$ of hydrogen gas combines with oxygen $=8 g$
$\therefore 3 g$ of hydrogen gas will combine with oxygen $=8 \times 3=24 g$
3. Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
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Answer
Following postulate of Dalton’s atomic theory is the result of the law of conservation of mass. ‘Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.’
4. Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
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Answer
Following postulate of Dalton’s atomic theory can explain the ’law of definite proportions'.
‘The relative number and kinds of atoms are constant in a given compound.’
