AP Chemistry 1.2: Mass Spectra of Elements
Practice AP Chemistry 1.2 questions on identifying isotopes from mass spectra, interpreting relative abundance, and estimating average atomic mass.
- Syllabus
- Effective Fall 2025
- Course
- AP Chemistry
Exam points
- Identify isotopes from mass-spectrum peak positions and infer relative abundance from peak heights or lines.
- Calculate average atomic mass as a weighted mean of isotope masses and their measured abundances.
Covered syllabus points
1.2 Mass Spectra of Elements question 1
[Maximum number: 2]
Answer the following questions about magnesium.
Question (a)
(a)
An incomplete mass spectrum for magnesium is shown in the diagram.
The percent abundance of magnesium-24 is 79\%. The percent abundances of the other two
natural isotopes of magnesium, magnesium-25 and magnesium-26, are approximately equal.
[ 2 ]
Question (i)
(i)
Complete the mass spectrum in part A by drawing thick lines in the appropriate locations
to represent the percent abundance of magnesium-25 and magnesium-26.
[ 1 ]
A (i) For the correct plotted lines:
Point 01
The abundance for the two lines should be between 10 and 11.
Question (ii)
(ii)
Describe the difference in atomic structure that accounts for the difference in mass
between magnesium-25 and magnesium-26.
[ 1 ]
(ii) For the correct answer:
Point 02
Magnesium-26 has one more neutron than magnesium-25 does.
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