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AP®ChemistryCollege BoardExam QuestionsUnit 1: Atomic Structure & PropertiesMass Spectra of Elements

Mass Spectra of Elements (College Board AP® Chemistry)

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Mass Spectra of Elements

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Mass Spectra of Elements

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1a1 mark

Carbon-14 is a radioactive isotope used in carbon dating.The mass spectrum of a carbon sample is shown below, with two peaks at m/z = 12 and m/z = 14.

Graph showing mass spectrum with a peak at mass-to-charge ratio 12, relative abundance 98.93%, and a peak at mass-to-charge ratio 14, relative abundance 1.07%.

Explain the significance of the relative heights of the peaks in the mass spectrum.

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1b2 marks

Calculate the relative atomic mass of carbon in the sample.

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1c1 mark

Carbon-14 is present in very small amounts in nature compared to Carbon-12.

Explain why the low abundance of Carbon-14 does not prevent it from being used for dating ancient artifacts.

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2a1 mark

The mass spectrum of copper shows two peaks at m/z = 63 and m/z = 65, with relative abundances of 69.15% and 30.85%, respectively.

Define what is meant by the term relative atomic mass.

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2b2 marks

Use the given data to calculate the relative atomic mass of copper.

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2c1 mark

Sketch the expected mass spectrum for copper, indicating the m/z values and relative abundances of the peaks.

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3a1 mark

The mass spectrum of neon shows three peaks, with the following data:

m/z

Relative abundance (%)

20

90.48

21

0.27

22

9.25

What does the presence of three peaks in the mass spectrum indicate about neon?

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3b2 marks

Calculate the relative atomic mass of neon using the given data.

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3c1 mark

A scientist claims that a sample of neon is enriched in 22Ne.

Explain how the mass spectrum of such a sample would differ from that of natural neon.

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1a2 marks

The mass spectrum of a sample of Cerium (Ce) shows four isotopes. The data for three isotopes is given below:

  • 136Ce: Mass = 136 amu, Relative Abundance = 0.19%

  • 138Ce: Mass = 138 amu, Relative Abundance = 0.25%

  • 140Ce: Mass = 140 amu, Relative Abundance = 88.45%

The sample’s average atomic mass is 140.12 amu. The mass number (m) and abundance of the fourth isotope, mCe, are unknown.

Explain how the mass spectrum can provide information about the isotopes and their relative abundances.

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1b2 marks

Using the data provided, calculate the mass number (m) and the relative abundance of mCe.

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2a2 marks

Boron has two naturally occurring isotopes: 10B (mass = 10.0 amu) and 11B (mass = 11.0 amu). A naturally occurring sample of boron has a relative atomic mass of 10.8 amu.

Explain why the relative atomic mass of boron (10.8 amu) is not a whole number and why it is closer to 11.0 than to 10.0.

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2b2 marks

Calculate the relative abundances of 10B and 11B in the sample. Include appropriate calculations.

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3a2 marks

The mass spectrum of chlorine gas is shown.

chlorine-mass-spectrum

Explain the origin of the peaks at m/z = 35 and m/z = 37.

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3b2 marks

Explain the presence and relative abundance of the peak at m/z = 74.

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