Mr. Citta – Honors Chemistry
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Dimensional Analysis - #5 – Take Home Exam Review
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Do the following exercises using Dimensional Analysis, using your calculators.
***You must show all work*****answer with correct number of sig figs.
Useful conversion factors you can use:
Avagodro’s Number - (1 mole = 6.02 x 1023 atoms/electrons/photons)
Angstrom – (1 angstrom = 1 x 10-9 meters)
Metric – ( 1 km = 1000 meters) or (103 meters)
1. Convert a wavelength of light at 655 nm (nanometers) to meters. (ans = 6.55 x 10-7 m)
2. Convert a wavelength of light at 2.45 x 10-7 meters to Å (angström). (ans = 2450 Å)
3. What is the diameter of an atom in meters if it has a diameter of 7.56 Å (angström)
(ans = 7.56 x 10-10 m)
4. Convert an energy of 355 kJ/n (kilojoules/mole) to a unit of joules/atom.
(ans = 5.90 x 10-19 joules/atom)
5. Convert an energy of 5.61 x 10-19 joules/electron to units of kJ/mole. (495 kJ/mole)
Turn over your paper and complete the back…
Problems (Do using Dimensional Analysis, show all work!!!)
6. How long (in years) does it take a photon that is 6.25 x 1015 kilometers from earth to reach earth if the speed of a photon is
3.00 x 108 meters/sec?
(ans = 661 years)
7. If light passes by you with a frequency of 3.65 x 1014 waves/second, how many waves past by you in 5.00 days?
(ans = 1.58 x 1020 waves)
8. If a light travels for 4.25 x 1010 km at 3.00 x 1017 nanometers/sec , how many days was it travelling for?
(ans = 1.64 days)
9. How many pounds are in 355 grams of gold?
(Use the following conversion factors, 1 pound = 16 ounces, 1 ounce = 28.3 g)
(ans = 0.784 pounds)
10. How many pure copper pennies can be made from 3.74 x 1024 atoms of copper?
(Use the following conversion factors,
1 penny = 2.5 grams, 63.5 grams = 1 mole, 1 mole = 6.02 x 1023 atoms)
(ans = 158 pennies Cu)