Homework Problem 1B.7

[Talia Dini - 3I]

Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at this wavelength?

I'm having trouble solving part b and c of this problem. Can someone please walk me through it?

[Helena Xu 3L]

For part b, you would convert the 5.00 mg of sodium atoms to 0.005 g and then to moles, and multiply that by Avogadro's number to find the number of sodium atoms. You would then multiply that by the energy found in part a to get the answer. For part c, you would also use the answer from part a and multiply it by Avogadro's number, since it involves 1 mol of sodium atoms. Hope this helps!

[Asia Yamada 2B]

For part b, you find the atoms of sodium in 5.00 mg of sodium by converting from milligrams to grams, then from grams to moles (molar mass of sodium), then from moles to atoms (Avogadro's number). Since you know the energy emitted by one excited sodium atom (part a), you multiply that energy by the amount of sodium atoms you just found to find how much energy is emitted from 5.00 mg of sodium atoms.
For part c, you convert the moles into atoms of sodium using Avogadro's number, just like you did in part b. Again, since you know the energy emitted by one excited sodium atom, you just multiply that energy by the amount of sodium atoms you just found to find how much energy is emitted from 1.00 mol of sodium atoms.