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General Chemistry: Stoichiometry Flashcards

7 cards from real DAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. How many moles of oxygen gas are required to completely combust 2 moles of propane (C3H8)?

    Answer: 10 mol

    Balanced equation C3H8 + 5O2 → 3CO2 + 4H2O needs 5 mol O2 per mol propane, so 2 mol requires 10 mol.

  2. What is the percent composition by mass of carbon in CO2 (C=12, O=16)?

    Answer: 27.3%

    Carbon's 12 g out of CO2's molar mass of 44 g gives 12/44 = 27.3%.

  3. If 3 mol of N2 react with 6 mol of H2, which is the limiting reagent in N2 + 3H2 → 2NH3?

    Answer: H2

    3 mol N2 needs 9 mol H2 but only 6 mol is present, so H2 limits the reaction.

  4. How many grams are in 0.50 mol of NaCl (Na=23, Cl=35.5)?

    Answer: 29.25 g

    NaCl molar mass is 58.5 g/mol, so 0.50 mol equals 29.25 g.

  5. What is the empirical formula of a compound that is 40% C, 6.7% H, and 53.3% O by mass?

    Answer: CH2O

    Dividing by atomic masses gives a 1:2:1 mole ratio of C:H:O, the formula CH2O.

  6. How many molecules are in 2.0 mol of water?

    Answer: 1.2 × 10^24

    Multiplying 2.0 mol by Avogadro's number gives 1.2 × 10^24 molecules.

  7. In the reaction 2H2 + O2 → 2H2O, how many grams of water form from 4 g of H2 (excess O2, H=1, O=16)?

    Answer: 36 g

    4 g H2 is 2 mol, producing 2 mol water at 18 g/mol = 36 g.