A 1.00 mL ampule of a 0.150 M solution of naphthalene in hexane is excited with...

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A 1.00 mL ampule of a 0.150 M solution of naphthalene in hexaneis excited with a flash of light. The naphthalene emits 12.5 J ofenergy at an average wavelength of 349 nm. What percentage of thenaphthalene molecules emitted a photon?

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4.1 Ratings (881 Votes)

First use the formula, E = hc/Î»

(6.626 x 10^-34 Js x 3 x 10⁸ ms^-1)/ (349 x 10^-9 m) = 5.695 x 10^-19J

Number of the photons emitted = (12.5 J) / (5.695 x 10^-19J) photons

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 2.195 x 10^-19 photons

Moles of naphthalene = volume in (L) x molarity

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = (0.001 x 0.150) mole

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = (1.50 x 10^-4) mole

Number of its molecules = Moles / Avogrado number

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = (1.50 x 10^-4) x (6.023 x 10²³)

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 9.035 x 10^-19 molecules

Percentage of the naphthalene molecules emitted a photon = (2.195 x 10^-19) / (9.035 x 10^-19) x 100

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 24.3%

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