IB Chemistry HL 1.2.3 Hl Mass Spectrometry Questions

Use real HL exam questions to interpret isotope mass spectra, calculate weighted relative masses and justify isotope-proportion conclusions.

Exam points

Interpret m/z peaks and relative intensities to identify isotopes and explain isotope-pattern abundance, including diatomic isotope combinations.
Calculate relative atomic or molecular mass from isotope m/z values and measured relative abundances, showing the weighted calculation and appropriate rounding.
Select or apply mass spectrometry to determine isotope proportions and use an isotope spectrum to report the relevant mass or abundance conclusion.

[Maximum number: 2]

Magnesium is a group 2 metal which exists as a number of isotopes and forms many compounds.

Mass spectroscopic analysis of a sample of magnesium gave the following results:

Calculate the relative atomic mass, $A_{\mathrm{r}}$ , of this sample of magnesium to two decimal places.

$A_r=\frac{24(78.60)+25(10.11)+26(11.29)}{100} =24.3269 =24.33$

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