Problem Index & Selected Answers

Problem Pages

Isotopes

Reacting Quantities & Equations 

Relative Molecular Masses

Concentration

Calculating Molecular Masses

Percent Composition

 

Answers to Selected Problems

Isotopes

  1. 24.32 (no units, it’s relative)
  2. 20% B-10, 80% B-11
    3.

    Element name

    Atomic number

    Number of protons

    Number of electrons

    Positive charge in nucleus

    Mass number

    Number of neutrons

    Carbon

    6

    6

    6

    6

    12

    6

    Neon

    10

    10

    10

    10

    20

    10

    Hydrogen

    1

    1

    1

    1

    1

    0

    Lithium

    3

    3

    3

    3

    7

    4

    Helium

    2

    2

    2

    2

    4

    2

    Calcium

    20

    20

    20

    20

    40

    20

    Sodium

    11

    11

    11

    11

    23

    12
  3. 50, 50, tin, +50
  4. a:e, c:d
  5. 10.18
  6. Cu-62.93 = 69%
  7. -

 

The Mole

2 Cr + 3 O (end of text)

 

Relative Molecular Mass

  1. 2 mol He
  2. 2 mol CO2
  3. 3.01 × 1023 molecules
  4. 10.0g H2
  5. 8.8g CF4
  6. 3.01 × 1023 molecules, 6.02 × 1022 molecules
  7. 14.0g, 2.80g
  8. 3.01 × 1012 years (3,010,000,000 or a bit over 3 million millenia)
  9. 1.91 × 1013 years
  10. 80.6g, 29.25g, 6.35g, 3.398g
  11. 0.5 mol, 5 mol, 0.01 mol
  12. 60g, 320g, 1778g, 407g, 20.4g
  13. 35mol = 2.107 × 1025 molecules
  14. a. 12g
  15. a. 5 mol (it’s diatomic)

 

Calculating Molecular Masses

  1. 44g
  2. 64.1g
  3. 166g
  4. 37g
  5. 28g
  6. 19g
  7. 154g mol-1
  8. 3.65g
  9. 58g mol-1, 1, 6.02 × 1023, 14, 14, 14, 8.4 × 1024
  10. 3.27 × 10-22g atom-1, 1.50 × 10-3mol
  11. S8
  12. 2.0, 0.5, 0.1, 0.02, 5 × 10-3, 0.1
  13. 64.1g, 70g, 2.0g, 16g, 13.5g, 6.56g
  14. A + 4B → AB4, (d)

 

Reacting Quantities & Equations

  1. 225g H2O
  2. 49.75g MgO
  3. 40.9g FeS
  4. 4.4g CO2
  5. 72kg O2
  6. 2Na(s) + 2H2O(l) → H2(g) + 2Na+(aq) + 2OH-(aq), 0.05mol H2, 0.1g H2
  7. CuO(s) + H2(g) → Cu(s) + H2O(g), 3.19g
  8. -
  9. C6H12O6 + 6O2 → 6CO2 + 6H2O, 5.6 people
  10. -
  11. a. 0.01M, 0.02M, 0.0146M, 0.0292M, b. I got 0.975g Cu(OH)2, but I could easily have made a mistake along the way.

 

Concentration

  1. 3.28g
  2. -
  3. -
  4. -
  5. -

 

Percent Composition

  1. 53.3%
  2. -

Empirical Formula

CH2O

Molecular Formula

C2H4O2, for example CH3COOH

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