Mass Spectra of Elements (College Board AP® Chemistry): Exam Questions

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

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

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

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.

A sample of a metallic element M is analyzed by mass spectrometry. The resulting mass spectrum shows two peaks, as shown in the table below.

Identify which isotope of element M has more neutrons. Justify your answer.

Calculate the average atomic mass of element M based on the spectrum data. Show your working.

Use your result from (b) to determine the identity of element M. Justify your answer.

Compare the number of protons, neutrons, and electrons in isotopes M-63 and M-65.

Explain why the average atomic mass of an element may vary slightly between samples from different sources.

A student suggests that this mass spectrum might be from a mixture of two different elements. Explain whether the spectrum supports this claim.

The sample is enriched in M-65 to 90% abundance. Predict how the new mass spectrum would differ from the original, and calculate the new average atomic mass.

A coin is made from element M and claimed to be ancient. The mass spectrum of the coin is shown below.

Determine whether the coin is likely to be genuine. Justify your reasoning.

A chemist is comparing two samples of an unknown transition metal J. One sample is made entirely of isotope J-50, and the other is made entirely of isotope J-52. Both are used to synthesize J₂O₃, a common oxide of metal J.

i) Calculate the molar mass of J₂O₃ in each case and determine the difference.

ii) Explain why this difference could be significant in analytical chemistry.

A student analyzes a metallic sample believed to contain only one element, Q. The resulting mass spectrum is shown below.

After reviewing periodic table values, the student suspects the metal is zinc or germanium.

Based on the spectrum, how many isotopes of the element are present?

Explain how the student knows the sample only contains one element.

i) Use the mass spectral data to calculate the average atomic mass of element Q. Show your work.

ii) The 62.0 amu isotope has the highest relative abundance in the sample.
Explain how this affects the calculated average atomic mass.

A sample of Q analyzed has a mass of 1.91 g.

i) Calculate the number of moles in the sample.

ii) Calculate the total number of atoms in the sample,

Q forms a Q²⁺ ion and reacts with chlorine gas.

i) Write a balanced equation for the reaction between the metal and chlorine.

ii) Determine the empirical formula of the compound formed.

iii) Predict the type of bonding in this compound and justify your answer.

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.

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

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.

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

The mass spectrum of chlorine gas is shown.

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

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