Question

4 g of calcium is burnt with 2.4 g O2 in a closed vessel. Which reactant is left and how much?

Choose answer:

O2, 0.8 g


Ca, 0.4 g


O2, 1.2 g


Ca, 2.8 g

Answer 1

Answer:

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Explanation:

Answer 2

The correct answer is option A , i.e., the reactant which is left is O2 and its amount is 0.8 g.

- The chemical equation of burning of calcium with oxygen can be written as:

2Ca + O2 --->2CaO

- Here 2 moles of calcium react with 1 mole of oxygen.

- It means 32 gm oxygen react with 80 gm of calcium to form 112 g calcium oxide

- 4 g of calcium = 0.1 Moles of Ca

- 2.4 g of O2 = 0.075 moles of oxygen

- No of moles of oxygen actually required for 0.1 mole of Ca is 0.05. Hence, Calcium is the limiting reagent in this case

- so number of moles of O2 left = 0.075 – 0.05 = 0.025 moles

- Grams of O2 left = 32 * 0.025 = 0.8 grams