Relative masses and mass spectrometryEdexcel A-Level Chemistry: Mind map

Exam questions on Relative masses and mass spectrometry

1. A sample of magnesium was analysed by mass spectrometry. It contains three isotopes: ²⁴Mg (78.6%), ²⁵Mg (10.1%) and ²⁶Mg (11.3%).
   Explain why the relative atomic mass of magnesium is not a whole number, even though the mass number of each isotope is a whole number.2 marks
2. Chlorine consists of two isotopes, ³⁵Cl and ³⁷Cl, in an abundance ratio of 3 : 1. A sample of chlorine gas, Cl₂, is analysed in a mass spectrometer in which each molecule is ionised to form a Cl₂⁺ ion.
   Predict the relative heights of the peaks in the Cl₂⁺ region of the mass spectrum of chlorine. Show your working.2 marks
3. A sample of copper from a coin was analysed by mass spectrometry. The spectrum of Cu⁺ ions has two peaks: m/z 63 with relative abundance 69.1 and m/z 65 with relative abundance 30.9. A second sample of copper, from a meteorite, has a relative atomic mass of 63.75.
   Calculate the relative atomic mass of the copper from the coin. Give your answer to 3 significant figures.3 marks