Spectroscopy and Electromagnetic Spectrum

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AP Chemistry › Spectroscopy and Electromagnetic Spectrum

Questions 1 - 5

What photon wavelength can promote a transition from the n = 1 (ground state) to the n = 3 (excited state)?

204 nm

306 nm

102 nm

408 nm

1 m

Explanation

$\Delta E = (-2.18 , x , 10^{-18} , J)(\frac{1}{3^2} -\frac{1}{1^2}) = 1.94 , x, 10^{-18} , J$

$E =\frac{hc}{\lambda }$ ; $\lambda =\frac{hc}{E} = \frac{(6.626 , x , 10^{-34}, J \cdot s)(3.00, x, 10^8 m/s)}{1.94 , x , 10^{-18} , J} = 1.02 , x, 10^{-7} m = 102 nm$

What is the energy of a photon that has a wavelength of 540 nm?

$3.68 x 10^{-19} J$

$3.68 x 10^{-17} J$

$3.68 x 10^{-28} J$

$7.36 x 10^{-17} J$

None of the above

Explanation

$E= \frac{hc}{\lambda}$ ; $E = \frac{(6.626 , x , 10^{-34} J\cdot s)(3.00, x, 10^{-8} m/s)}{5.40 , x , 10^{-7} m/s}$ ; $E = 3.68 , x , 10^{-19}, J$

A student has a Blue #1 dye with a molar absorptivity of 1.30 x 105 M-1 cm-1 at 631 nm. If the student runs this sample through a spectrophotometer and finds it has an absorption of 0.500 what is the dye’s molarity? Assume a path length of 1.0 cm.

$1.9 , x , 10^{-6} M$

$11.5 , x , 10^{-5} M$

$1.9 , x , 10^{-5} M$

$3.9 , x , 10^{-5} M$

$3.9 , x, 10^{-6} M$

Explanation

$A = \varepsilon bc$ ; $c =\frac{ A}{\varepsilon b}= \frac{0.500}{(1.30, x , 10^5 M^{-1} cm^{-1})(1.00 cm)} = 3.9 , x , 10^{-6} M$

A 3.0 eV light is shined on Gold ( Փ = 5.1 eV), silver (Փ =4.26 eV), Cesium (Փ = 2.1 eV), and Platinum (Փ = 6.35). If Փ is the work function of the metal, what metal would have electrons ejected?

Au, Ag, and Pt

Explanation

The work function is the energy required to remove an electron from a metal. Only Cs metal has a work function less than the energy of the light.

What transition would emit the longest wavelength of light?

n = 4 to n = 1

n = 3 to n = 1

n = 2 to n = 1

n = 4 to n = 3

Not enough information given

Explanation

Wavelength is inversely proportional to energy. Since the transition from n=4 to n=3 is the lowest energy transition, it would have the longest wavelength.

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