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Date November 2012 Marks available 4 Reference code 12N.3.SL.TZ0.5
Level Standard level Paper Paper 3 Time zone Time zone 0
Command term Describe, Determine, and Explain Question number 5 Adapted from N/A

Question

This question is about atomic energy levels.

Outline a laboratory procedure for producing and observing the atomic absorption spectrum of a gas.

[3]
a.

(i) Describe the appearance of an atomic absorption spectrum.

(ii) Explain why the spectrum in (a) provides evidence for quantization of energy in atoms.

[4]
b.

The principal energy levels of the hydrogen atom in electronvolt (eV) are given by

En=13.6n2

where n is a positive integer.

Determine the wavelength of the absorption line that corresponds to an electron transition from the energy level given by n=1 to the level given by n=3.

[3]
c.

Markscheme

shine white light through;
a tube of the gas;
then observe with spectroscope/grating/prism;

a.

(i) continuous spectrum crossed by dark lines;

(ii) dark lines formed by the absorption of photons;
the absorbed photons have specific/discreet wavelengths;
indicating discreet differences in energy;
which can only be explained by existence of energy levels;

b.

E=13.6[112132]=12.1eV;
12.1eV=12.1×1.6×10–19J =hcλ;
λ=102nm or 103nm;
Award [3] for a bald correct answer.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 7: Atomic, nuclear and particle physics » 7.1 – Discrete energy and radioactivity
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