Names:
Activity 4: Atoms and Molecules
1. a. Given that the mass of the neutron is 1.674954
×
10 -27 kg, the mass of a proton is 1.6726430
×
10 -27 kg and the mass of an electron is
9.1093897
×
10 -31 kg, what is the mass (in kg) of a single carbon-12 atom? Pay attention to sig figs! b. Based on the definition of an atomic mass unit, what is the mass (in u) of a single carbon-12 atom? c. 1 atomic mass unit has a mass of 1.66054
×
10 -27 kg. Use this factor to convert your answer to part b into kg. d. Your answers to part a and part c should be the same but they aren’t.
Calculate the difference in mass between the two answers.

e. This difference in mass is the amount of matter that is converted to energy which holds the nucleus together (nuclear binding energy).
Nuclear binding energy is the source of energy in nuclear reactions.
Convert the mass from part d to energy (joules) using Einstein’s famous equation, E = mc 2 . One Joule = 1 kg m 2 /s 2 and c = 3.00
×
10 8 m/s.
2. Copper has two naturally-occurring isotopes, Cu-63 and Cu-65. Their natural abundances are 69.2% and 30.8%, respectively. Cu-63 has an isotopic mass of 62.9298 amu. What is the isotopic mass of Cu-65?

3. Write the chemical symbol for an isotope which has 8 protons, 10 neutrons and 10 electrons. Hint: is this isotope also an ion?
4. Describe the subatomic structure of phosphorus-32, a commonly used “tracer” isotope, indicating the number and placement (relative to the nucleus) of subatomic particles.
5. a. Epsom salts, MgSO
•7H
2
O.
4
•7H
2
O, is an example of a hydrate. It crystallizes with water as part of the crystal structure. Determine the mass of a mole of MgSO
4 b. Determine the mass of S in 15.692 g of Epsom salts.