NASA-Threads
Electricity & Magnetism
Lesson 11: Atoms and Molecules
Homework
1. Platinum is an excellent conductor often used in electrical contacts. It is very dense for a
metal, with a density of 21.45 g / cm3. If you have a rectangular block of platinum
measuring 10 cm by 1 cm by 5 cm, what is the mass of the block in grams? In kilograms?
2. Gold has a density of 19.3 g / cm3. If you need to send a block of gold to the
International Space Station with a mass of 1 kg, what volume (in cubic centimeters)
must be reserved on the shuttle for shipping the block?
3. If you have 2.5 kg of lead, how many moles of lead can you brag to your friends that
you have? (The atomic weight of lead is 207.2 g/mol).
4. Space elevators have been proposed as a lower-cost alternative to shipping goods to
and from earth to a ship in geosynchronous orbit since as early as 1895. In theory,
an elevator could be tethered to a single cable stretched from the earth to a
counterweight approximately 35,000km from earth. Current materials are not
strong enough to sustain even the weight of the cable; however, let us assume that
diamonds, with a density of 3.5 g/cm3, can do the job. What would the mass of a
cable made of diamonds be if it was a cylinder with a radius of 2 cm? How many
atoms would be contained in such a structure? (Note that diamonds have a molar
mass of 12.01 g/mol.)
5. Silver is the most conductive metal. It is 9% more conductive than copper. If 1.0 cubic
centimeter of silver is available, how many valence electrons are available? (Hint:
atomic weight of Ag = 107.9 g/mol; density of Ag = 10.5 g/cm3)
6. Lightning protection systems consist of lightning rods that are installed on
structures, trees, monuments, bridges and even water vessels to protect from
lightning damage. Aluminum is often the conducting material used in these
protective devices. If a lightning rod contains 14 cubic centimeters of aluminum,
how many valence electrons are available? (Hint: atomic weight of Al = 26.98
g/mol and density = 2.702 g/cm3.)