S1.2 The atom
Practice exam-style IB Chemistry questions for The atom, aligned with the syllabus and grouped by topic.
Question 1
What are the relative charge and location of a proton?
A.
−1, outside the nucleus
B.
+1, in the nucleus
C.
+1, outside the nucleus
D.
0, in the nucleus
Question 2
What are isotopes?
A.
Atoms of different elements with the same number of neutrons
B.
Ions of the same element with different numbers of electrons
C.
Atoms with the same mass number and different atomic numbers
D.
Atoms of the same element with different numbers of neutrons
Question 3
An ion has the nuclear symbol ²⁷₁₃Al³⁺. What are the numbers of protons, neutrons and electrons?
A.
13 protons, 14 neutrons, 16 electrons
B.
14 protons, 13 neutrons, 10 electrons
C.
13 protons, 14 neutrons, 10 electrons
D.
27 protons, 13 neutrons, 24 electrons
Question 4
Why do neutral isotopes of the same element usually have very similar chemical properties?
A.
They have identical physical properties
B.
They have the same number of neutrons
C.
They have the same electron arrangement
D.
They have the same mass number
Question 5
In Rutherford’s gold foil experiment, a very small number of alpha particles were deflected through large angles. What conclusion follows from this observation?
A.
Most of the atom’s positive charge is concentrated in a small dense nucleus
B.
Positive charge is spread uniformly throughout the atom
C.
Electrons make up most of the mass of an atom
D.
Neutrons occupy the space outside the nucleus
Question 6
What determines the identity of an element?
A.
The number of protons in the nucleus
B.
The number of occupied electron shells
C.
The total mass of the atom in grams
D.
The number of neutrons in the nucleus
Question 7
In an elemental mass spectrum, what is plotted on the horizontal axis?
A.
Mass-to-charge ratio, m/z
B.
Ionization energy, kJ mol⁻¹
C.
Percentage abundance, %
D.
Atomic number, Z
Question 8
What is a fragment ion in mass spectrometry?
A.
A proton emitted from the nucleus during radioactive decay
B.
An electron outside the nucleus with negligible mass
C.
A charged piece of a molecule formed when the molecule breaks apart
D.
A neutral atom with a different number of neutrons
Question 9
Define the term isotope.
[1]
State why isotopes of the same element have different mass numbers.
[1]
Question 10
An ion has the nuclear symbol ⁸⁰₃₅Br⁻.
State the number of protons.
[1]
Calculate the number of neutrons.
[1]
State the number of electrons.
[1]
Question 11
An element has two isotopes, ⁶³X and ⁶⁵X. The abundance of ⁶³X is 70.0%. What is the relative atomic mass of the element?
A.
65.0
B.
64.0
C.
64.4
D.
63.6
Question 12
An atomic radius is 120 pm and a nuclear radius is 6.0 fm. Approximately how many times larger is the atomic radius than the nuclear radius?
A.
2.0 × 10⁻²
B.
2.0 × 10¹
C.
7.2 × 10⁵
D.
2.0 × 10⁴
Question 13
An elemental mass spectrum shows a peak at m/z = 29 for singly charged ions. What is the mass number of the isotope represented by this peak?
A.
14.5
B.
30
C.
29
D.
58
Question 14
An elemental mass spectrum contains three peaks of equal height at m/z 24, 25 and 26. What is the best interpretation?
A.
The element has three isotopes present in approximately equal abundance
B.
The element has one isotope with three different charges
C.
The element has three different atomic numbers
D.
The element has isotopes with identical mass numbers
Question 15
A calculated relative atomic mass from an estimated mass spectrum is slightly different from the data booklet value. What is the most likely reason?
A.
Peak heights were estimated and mass numbers were used instead of precise isotopic masses
B.
The electron mass was counted as one atomic mass unit
C.
The relative atomic mass must always be a whole number
D.
The number of protons changed during the analysis
Question 16
A sample of element Y contains 79.0% ²⁴Y and 21.0% ²⁶Y.
Write the expression used to calculate the relative atomic mass.
[1]
Calculate the relative atomic mass of Y.
[1]
Explain why the answer is not a whole number.
[1]
Question 17
Rutherford directed alpha particles at thin gold foil.
State the observation showing that most of the atom is empty space.
[1]
State the observation showing that the nucleus is positively charged and dense.
[1]
Explain why the electron’s mass is usually neglected in mass-number calculations.
[1]
Question 18
A nucleus has a diameter of 8.0 fm and its atom has a diameter of 1.6 × 10⁻¹⁰ m.
Convert 8.0 fm into metres.
[1]
Calculate how many times larger the atomic diameter is than the nuclear diameter.
[1]
Question 19
A mass spectrum of element M shows peaks at m/z 54, 56 and 57 with relative intensities 6.0, 92.0 and 2.0.
State what each peak represents.
[1]
Identify the most abundant isotope.
[1]
Calculate the approximate relative atomic mass.
[1]
Question 20
In a mass spectrum, the horizontal axis is labelled m/z.
State what z represents.
[1]
State the relationship between m/z and isotope mass number for singly charged ions.
[1]
Question 21
Define the term mass spectrum.
[1]
Define the term fragment ion.
[1]
Question 22
The graph shows the distribution of alpha-particle scattering angles in a Rutherford-type experiment.
Describe the main trend shown by the graph.
[1]
State what the most common scattering result suggests about the structure of the atom.
[1]
Explain what the rare large-angle scattering events suggest about the nucleus.
[1]
Question 23
The table gives the isotopic composition of a naturally occurring sample of element R.
| Isotope | Mass number | Abundance / % |
|---|---|---|
| R-48 | 48 | 73.7 |
| R-49 | 49 | 5.5 |
| R-50 | 50 | 20.8 |
Identify the most abundant isotope.
[1]
Calculate the relative atomic mass of R.
[1]
Suggest why the calculated value may differ slightly from a data booklet value.
[1]
Question 24
The table shows information for four particles represented by nuclear symbols.
| Particle | Nuclear symbol | Protons | Neutrons | Electrons |
|---|---|---|---|---|
| A | ²³₁₁Na | 11 | 11 | |
| B | ²⁴₁₂Mg²⁺ | 12 | 12 | |
| C | ³⁵₁₇Cl | 17 | 18 | 17 |
| D | ³⁷₁₇Cl | 17 | 20 | 17 |
Complete the missing number of neutrons for one particle.
[1]
Complete the missing number of electrons for one ion.
[1]
Identify two particles in the table that are isotopes of the same element.
[1]
Explain your choice in part (c).
[1]
Question 25
A mass spectrum of element Q has peaks at m/z 10 and 11 with relative intensities 1.0 and 4.0. What is the relative atomic mass of Q?
A.
21.0
B.
10.8
C.
10.5
D.
11.0
Question 26
Two elemental spectra have similar average masses. Spectrum I has one peak, while spectrum II has two peaks of similar height separated by two m/z units. What feature most clearly distinguishes the elements?
A.
Their nuclear charges measured as peak heights
B.
Their electron arrangements shown directly on the spectrum
C.
Their isotope patterns
D.
Their melting points shown by the m/z values
Question 27
A spectrum has peaks at m/z 64, 66 and 68 with relative intensities 3, 2 and 1. What relative atomic mass is calculated from these data?
A.
65.3
B.
65.0
C.
198
D.
66.0
Question 28
Two neutral isotopes of the same element are compared.
State one subatomic particle number that is the same in the two isotopes.
[1]
State one subatomic particle number that is different.
[1]
Suggest why their rates of diffusion may differ slightly.
[1]
Question 29
An ion of element E contains 20 protons, 22 neutrons and 18 electrons.
Deduce the mass number.
[1]
Deduce the charge on the ion.
[1]
Write the nuclear symbol using E as the element symbol.
[1]
Question 30
A researcher replaces some oxygen atoms in a reactant with the isotope ¹⁸O.
State the purpose of using an isotope tracer.
[1]
Explain why ¹⁸O can be followed through the reaction.
[1]
State why the labelled reactant usually has similar chemical behaviour to the unlabelled reactant.
[1]
Question 31
The mass spectrum of element N contains peaks at m/z 35 and 37. Their relative intensities are in the ratio 3:1.
Convert the ratio into percentage abundances.
[1]
Calculate the relative atomic mass.
[1]
Explain why the value is closer to 35 than to 37.
[1]
Question 32
A student calculates Aᵣ = 78.8 from a printed mass spectrum. The data booklet gives Aᵣ = 78.96.
State one experimental or data-handling reason for the difference.
[1]
State one reason related to the isotope masses used.
[1]
Suggest why a natural sample from a different source may give a slightly different spectrum.
[1]
Question 33
Two elements, P and Q, both have relative atomic masses close to 80. Element P shows one dominant peak. Element Q shows two peaks of similar height separated by two m/z units.
State what the single dominant peak for P suggests about its isotopic composition.
[1]
State what the two similar peaks for Q suggest.
[1]
Explain why mass spectra can distinguish P and Q even if their Aᵣ values are similar.
[1]
Question 34
The graph compares the rate of diffusion of molecules containing two different isotopes of the same element at the same temperature.
Identify which isotopic molecule diffuses faster.
[1]
State the relationship between isotopic mass and diffusion rate shown by the graph.
[1]
Explain why the two molecules are expected to have similar chemical properties.
[1]
Suggest why their physical properties are not identical.
[1]
Question 35
A reaction mechanism was investigated using an ¹⁸O-labelled reactant. The table shows whether ¹⁸O was detected in the reactant, intermediate and products.
| Stage | Species | ¹⁸O detected |
|---|---|---|
| Start | Reactant R | Yes |
| During reaction | Intermediate I | Yes |
| End | Product P | No |
| End | Product Q | Yes |
Identify the species in which the labelled oxygen is found at the end of the reaction.
[1]
State what this shows about the path of that oxygen atom.
[1]
Explain why using ¹⁸O is suitable for tracing oxygen atoms.
[1]
Suggest one limitation of this evidence when proposing a mechanism.
[1]
Question 36
The mass spectrum of element T is shown.
Identify the isotope with the greatest abundance.
[1]
Calculate the relative atomic mass from the spectrum.
[1]
Explain why the calculated value lies between the lowest and highest m/z values.
[1]
Question 37
Mass spectra for two unknown elements, U and V, are shown. Their relative atomic masses are similar.
Compare the number of isotope peaks in the two spectra.
[1]
Identify which element has a more even distribution of isotope abundances.
[1]
Explain why the two elements can be distinguished by their spectra.
[1]
Suggest one use of comparing isotope patterns.
[1]
Question 38
A mass spectrum has isotope peaks at m/z 90, 91 and 92 with relative intensities 50, 30 and 20.
Explain why the intensities do not need to be converted to percentages before calculating Aᵣ.
[1]
Calculate the relative atomic mass.
[1]
State the m/z value of the least abundant isotope.
[1]
Question 39
A compound gives fragment-ion peaks at m/z 15 and m/z 29 in its mass spectrum.
State what information fragment ions can provide.
[1]
Suggest why a peak at m/z 15 may be useful in structural analysis.
[1]
Explain why an elemental isotope pattern and a molecular fragmentation pattern are interpreted differently.
[1]
Question 40
The table gives peak data from a mass spectrum. The intensities are relative intensities, not percentage abundances.
| Isotope | m/z / 1 | Relative intensity / a.u. |
|---|---|---|
| X-84 | 84 | 6 |
| X-86 | 86 | 105 |
| X-87 | 87 | 75 |
| X-88 | 88 | 885 |
Calculate the total relative intensity.
[1]
Calculate the percentage abundance of one specified isotope.
[1]
Calculate the relative atomic mass.
[1]
State why the tallest peak is not necessarily at the relative atomic mass.
[1]
Question 41
Mass spectra of samples W₁ and W₂ of the same element from two sources are shown.
State one similarity between the spectra that shows the samples contain the same element.
[1]
Describe one difference between the spectra.
[1]
Suggest how the difference would affect the calculated relative atomic mass.
[1]
Explain why isotope abundances may vary slightly between natural samples.
[1]
Question 42
A molecular mass spectrum contains several fragment-ion peaks. The table gives selected m/z values and proposed fragment ions.
| m/z | Relative intensity / % | Proposed fragment ion |
|---|---|---|
| 15 | 24 | CH3+ |
| 27 | 12 | C2H3+ |
| 29 | 35 | C2H5+ |
| 43 | 100 | CH3CO+ |
| 57 | 41 | C3H5O+ |
| 71 | 9 | C4H7O+ |
Identify the fragment ion with the greatest relative intensity.
[1]
State what the m/z value of a singly charged fragment ion represents.
[1]
Use the table to suggest one group present in the original molecule.
[1]
Explain how fragment-ion data differ from isotope peak data for an element.
[1]
Question 43
Outline the relative charge, relative mass and location of protons, neutrons and electrons.
[1]
Explain how Rutherford’s alpha-particle scattering experiment supports the nuclear model of the atom.
[1]
Question 44
| Isotope | Mass number, A | Abundance / % |
|---|---|---|
| X-24 | 24 | 78.99 |
| X-25 | 25 | 10.00 |
| X-26 | 26 | 11.01 |
Define relative atomic mass and isotope.
[1]
sample contains three isotopes of element X. Discuss how isotope abundance leads to a non-integer relative atomic mass and how this relates to chemical and physical properties of isotopes.
[1]
Question 45
For the ion ⁵⁸₂₈Ni²⁺, deduce the numbers of protons, neutrons and electrons.
[1]
Evaluate the statement: “The nucleus determines all chemical properties of an atom.”
[1]
Question 46
Outline how an isotope tracer can be used to follow atoms through a reaction.
[1]
Evaluate the usefulness and limitations of isotope-tracer evidence when proposing a reaction mechanism.
[1]
Question 47
Outline how peak position and peak height are interpreted in an elemental mass spectrum.
[1]
spectrum contains several isotope peaks with relative intensities. Evaluate how the spectrum can be used to determine Aᵣ and why the result may differ from a data booklet value.
[1]
Question 48
Describe two features of a mass spectrum that can be used as an isotope pattern.
[1]
Compare how two elements with similar relative atomic masses could be distinguished using their mass spectra.
[1]
Question 49
Distinguish between an elemental isotope peak and a molecular fragment-ion peak in a mass spectrum.
[1]
Discuss how mass-spectral data can provide information about both isotopic composition and molecular structure.
[1]
Question 50
Calculate the relative atomic mass of an element from a spectrum with isotope peaks at m/z 50, 52 and 54 and relative intensities 5, 3 and 2.
[1]
Evaluate the reliability of using a printed mass spectrum to identify an element from its relative atomic mass alone.
[1]
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