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The mass of P4O10 that will be obtained from the reaction of 1.33 gram of P4 and 5.07 of oxygen is___________?

Correct answer: B. 3.05 gram

  • A. 2.05 gram
  • B. 3.05 gram
  • C. 4.05 gram
  • D. 5.05 gram

Explanation

The balanced reaction is P4 + 5O2 -> P4O10. Moles of P4 = 1.33 g ÷ 123.9 g/mol = 0.0107 mol, while the 5.07 g O2 provides 5.07 g ÷ 32.0 g/mol = 0.158 mol, enough for the reaction, so P4 is limiting. Mass of P4O10 = 0.0107 mol x 283.9 g/mol = 3.04 g, approximately 3.05 g, making option b correct; students may choose d by treating oxygen as the limiting reactant without checking the stoichiometric ratio.

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About Limiting and Excess Reactants

Limiting and excess reactants are identified from the balanced chemical equation and the available amounts of each substance. The limiting reactant determines the maximum product formed, while the excess reactant remains after completion, so questions require mole ratios, theoretical yield and sometimes percentage yield calculations.

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