IB Chemistry SL 1.2.2 Isotopes Questions

Use isotope notation to distinguish nuclei, calculate relative atomic mass from isotope composition, and explain how nuclear differences affect physical and chemical behaviour.

Exam points

Define isotopes and read nuclear notation (Z and A) to identify the same element, isotope identity and proton/neutron relationships.
Calculate relative atomic mass or isotope abundance from isotope masses and percentage composition, including enriched samples and molecular isotopic composition.
Compare isotope physical and chemical behaviour by relating mass or nuclear composition to density, radius, ionization energy, chemical properties and isotope peak combinations.

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Study 1.2.2—Isotopes conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 4]

Chlorine occurs in Group 7, the halogens.

(a)

Two stable isotopes of chlorine are ${ }^{35} \mathrm{Cl}$ and ${ }^{37} \mathrm{Cl}$ with mass numbers 35 and 37 respectively.

[ 4 ]

(i)

Define the term isotopes of an element.

[ 2 ]

(ii)

Using the mass numbers of the two isotopes and the relative atomic mass of chlorine from Table 5 of the Data Booklet, determine the percentage abundance of each isotope.

Percentage abundance ${ }^{35} \mathrm{Cl}$ :

Percentage abundance ${ }^{37} \mathrm{Cl}$ :

[ 2 ]

$\left(\right.$ for $\left.{ }^{35} \mathrm{Cl}: x \%\right) 35 x+3700-37 x=3545$ ;

Marking guidance:

Allow other alternative mathematical arrangements.
${ }^{35} \mathrm{Cl}=77.5 \%$ and ${ }^{37} \mathrm{Cl}=22.5 \%$ ;

Award [1 max] for correct percentages if no correct working is shown.

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IB Chemistry SL 1.2.2 Isotopes Questions question 1

Question (a)

Question (i)

Question (ii)