Atoms and Molecules
NIOS · Class 10 · Science & Tech
Flashcards for Atoms and Molecules — NIOS Class 10 Science & Tech. Quick Q&A cards covering key concepts, definitions, and formulas.
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Get startedWhat is the law of conservation of mass?
Answer
In every chemical reaction, the total mass of reactants is equal to the total mass of products. Lavoisier established this by heating mercury in a sealed flask and comparing the masses before and afte…
What is the law of definite or constant proportions?
Answer
A pure compound always contains the same elements combined in the same fixed proportion by mass, no matter where it comes from or how it is prepared. For example, pure water always has hydrogen and ox…
Why does pure water always have hydrogen and oxygen in the ratio 1:8 by mass?
Answer
Because water is a pure compound with a fixed composition. Its mass composition is always 11.11% hydrogen and 88.89% oxygen, so the mass ratio of hydrogen to oxygen remains 1:8.
A sample of water gives 9.0 g on decomposition. How much hydrogen and oxygen are present?
Answer
In pure water, hydrogen and oxygen are in the mass ratio 1:8. So 9.0 g of water contains 1.0 g hydrogen and 8.0 g oxygen.
What did Lavoisier conclude from his mercury heating experiment?
Answer
He concluded that total mass remains unchanged in a chemical reaction. When mercury was heated in air, mercury(II) oxide formed, and on strong heating it broke into mercury and oxygen. The mass of pro…
How did Proust support the law of constant proportions?
Answer
Proust showed that a given compound always has a fixed composition by mass. He demonstrated this in 1808 for compounds such as pure water and sodium chloride.
What is Dalton's atomic theory?
Answer
Dalton arranged earlier ideas into a theory in 1803. Its main postulates are: matter consists of indivisible atoms; atoms of the same element are identical in mass and properties; atoms of different e…
Why did Dalton's theory help explain chemical laws?
Answer
It explained the law of conservation of mass because atoms are rearranged, not created or destroyed in a reaction. It also explained the law of constant proportions because atoms combine in fixed whol…
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