AP Chemistry 1.2.A: Mass Spectra of Elements
Explore AP Chemistry 1.2.A questions on using mass spectra to identify isotopes, interpret relative abundance, and estimate weighted average atomic mass.
- Syllabus
- Effective Fall 2025
- Course
- AP Chemistry
Exam points
- Use moles, molar mass and particle relationships to calculate quantities and interpret chemical composition.
- Apply dimensional analysis and conservation of matter to solve quantitative chemistry problems from data.
1.2.A—Explain the quantitative relationship between the mass spectrum of an element and the masses of the element’s… 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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