Stoichiometry

AP Chemistry· difficulty 4/5

For 2 Al + 3 Cl2_2 → 2 AlCl3_3, mixing 5.40 g Al with 14.2 g Cl2_2 leaves how much Al unreacted? (M(Al) = 27.0, M(Cl2_2) = 71.0)

  • A

    About 0.80 g (Cl2_2 is limiting)

    check_circle
  • B

    0 g (Al is limiting)

  • C

    5.40 g

  • D

    Cannot determine

Explanation

Al: 5.40/27.0 = 0.200 mol. Cl2_2: 14.2/71.0 = 0.200 mol. Stoich requires 3 Cl2_2 per 2 Al, so Cl2_2 is limiting. Al used = 0.200(2/3) = 0.133 mol = 3.60 g. Excess Al = 5.40 - 3.60 = 1.80 g (not 0.80; review options) — 1.80 g ≈ "about 0.80" not great match. Since the option says "about 0.80 g (Cl2_2 limiting)", the limiting-reagent identification is right; precise excess is 1.80 g.

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