Chapter 3: Atoms and Molecules

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Atoms and Molecules


Q.2: When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?


Carbon reacts with oxygen to form carbon dioxide.

According to the question, 3g of carbon will burn with 8g of oxygen gas to form 11g of carbon dioxide gas.

The total mass of the reactant is equal to the total mass of the product. This proves the law of conservation of mass.

The carbon will react with oxygen in constant proportions. This means that the carbon dioxide formed will contain carbon and oxygen in a fixed ratio of 3:8 by mass. Thus, this also proves the law of constant proportions.

According to the law of constant proportions, when 3g of carbon reacts with 50g of oxygen gas, 11g of carbon dioxide will form. The rest of the oxygen gas will remain unreactive.

Unreactive oxygen gas = 50g – 8g =42g.

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