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Postby OwenSumter_2F » Fri Oct 16, 2020 9:04 am

I'm having some trouble with this problem.

1B.7 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 understand part (a) and was able to get the right answer (3.37x10-17 but I am confused as to how to proceed.

Luveia Pangilinan 1A
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Re: 1B.7

Postby Luveia Pangilinan 1A » Fri Oct 16, 2020 9:13 am

Since you're only asking for b and c help I'll just answer that :D

B.) you're going to convert mg to g first, so
5.00 mg* (1g/1000mg)= 5.00 x 10^-3g Na

then you'll use the molar mass of Na to determine the energy emitted by an excited Na

5.00x10^-3 g Na * (1 mol Na/ 23g Na) * (6.022 x10^23 atoms Na/ 1 g Na) = 1.31 x10^20 atoms of Na

(1.31 x10^20 atoms Na) * (3.37x 10^-19 J) = 44.1 J

C.) for this part of the question, you pretty much do the exact same thing in B

1 mol Na * (6.022 x 10^23 atoms Na/ 1mol Na) = 6.022 x 10^23 atoms Na

(6.022 x 10^23 atoms Na) * (3.37 x 10^-19J) = 202941.4J or 2.03 x10^5 J

and there you go :D

Hope this helps!

John Pham 3L
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Re: 1B.7  [ENDORSED]

Postby John Pham 3L » Fri Oct 16, 2020 9:14 am

You'll need to convert 5.00 mg Na into atoms with 5.00 mg -> g -> moles -> atoms.
It should be 500 mg * (1 g/ 10^3 mg) * (1 mol/ 22.99 g) * (6.022*10^23 atoms/ 1 mol)
Once you solve for this, you can multiply the energy per atoms by the total number of Na atoms

Part C is solved the same way as part B.
This time all you need to do is convert moles to atoms with Avogadro's constant

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