Multiple choice

1.204 × 1021 molecules are removed from 392 mg of sulphuric acid. How many moles of sulphuric acid are left?

  1. 1.5 × 10-3

  2. 2.0 × 10-3

  3. 2.5 × 10-3

  4. 3.0 × 10-3

  5. 3.5 × 10-3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Used sulphuric acid = 392 mg = 0.392 g Number of moles of sulphuric acid = 0.392/98 = 0.004 Since N = nNA                  (NA = Avogadro’s number) Hence, n = N/NA = 1.204 × 1021/ 6.023 × 1023 = 0.002 moles The number of moles left = 0.004 – 0.002 = 0.002 = 2.0 × 10-3

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