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CHE 105/110 Introduction to Chemistry - Exercises and Answers

Masses of Atoms and Molecules

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QUESTION ANSWER

1.

Define atomic mass unit. What is its abbreviation?

1.

The atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. Its abbreviation is u.

3.

Estimate the mass, in whole numbers, of each isotope.

  1. hydrogen-1
  2. hydrogen-3
  3. iron-56

3.

  1. 1
  2. 3
  3. 56

5.

Determine the atomic mass of each element, given the isotopic composition.

  1. lithium, which is 92.4% lithium-7 (mass 7.016 u) and 7.60% lithium-6 (mass 6.015 u)
  2. oxygen, which is 99.76% oxygen-16 (mass 15.995 u), 0.038% oxygen-17 (mass 16.999 u), and 0.205% oxygen-18 (mass 17.999 u)

5.

  1. 6.940 u
  2. 16.000 u

7.

How far off would your answer be from Exercise 5a if you used whole-number masses for individual isotopes of lithium?

7.

We would get 6.924 u.

9.

  1. What is the atomic mass of an oxygen atom?
  2. What is the molecular mass of oxygen in its elemental form?

9.

  1. 15.999 u
  2. 31.998 u

11.

Determine the mass of each substance.

  1. F2
  2. CO
  3. CO2

11.

  1. 37.996 u
  2. 28.010 u
  3. 44.009 u

13.

Determine the mass of each substance.

  1. Na
  2. B2O3
  3. S2Cl2

13.

  1. 22.990 u
  2. 69.619 u
  3. 135.036 u

15.

Determine the mass of each substance.

  1. GeO2
  2. IF3
  3. XeF6

 

15.

  1. 104.64 u
  2. 183.898 u
  3. 245.281 u

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