1.1.2 Relative masses and mass spectrometry Quiz: Pearson Edexcel Chemistry, Unit 1

The 20 questions

1. What is the main purpose of a mass spectrometer?

   • To determine the relative masses and abundances of isotopes or ions
   • To measure the boiling point of a liquid sample
   • To identify functional groups by their absorption of infrared light
   • To separate mixtures by their solubility in solvents

2. In a mass spectrum, what is plotted on the horizontal axis?

   • Atomic number of the element
   • Retention time of each component in minutes
   • Mass-to-charge ratio, m/z
   • Relative abundance of each ion

3. What is the relative atomic mass of an element?

   • The sum of the masses of all the protons and neutrons found in one atom of the element
   • The weighted mean mass of its atoms compared with 1/12 of the mass of a carbon-12 atom
   • The mass in grams of one mole of its atoms, which is the same as its molar mass in grams
   • The mass of its most abundant isotope measured in kilograms on the standard carbon scale

4. In the mass spectrum of an organic compound, which peak gives the relative molecular mass?

   • The fragment ion peak with the smallest m/z value
   • The base peak with the greatest relative abundance
   • The peak at m/z 1 from hydrogen
   • The molecular ion peak, M+

5. What type of substance is the term 'relative formula mass' used for?

   • Only simple covalent molecules that contain a fixed number of atoms in each molecule
   • Only individual monatomic gases such as the noble gases at room temperature and pressure
   • Only gases at room temperature that consist of small molecules with a low molar mass
   • Compounds with giant structures, such as ionic compounds

6. An element has isotopes 10 (abundance 20%) and 11 (abundance 80%). What is its relative atomic mass?

   • 10.8
   • 11.0
   • 10.2
   • 10.5

7. Element Y has isotopes of mass 63 (69%) and 65 (31%). What is its relative atomic mass to one decimal place?

   • 63.3
   • 64.0
   • 63.6
   • 63.1

8. Chlorine has isotopes 35Cl (75%) and 37Cl (25%). What is its relative atomic mass to two decimal places?

   • 35.75
   • 35.50
   • 36.00
   • 35.25

9. An element has relative atomic mass 24.3 and two isotopes, 24 and 25 only. What percentage of the sample is the 25 isotope?

   • 25%
   • 10%
   • 30%
   • 70%

10. What is the relative molecular mass of ethanol, CH3CH2OH? (Use C = 12, H = 1, O = 16.)

    • 45
    • 46
    • 42
    • 44

11. What is the relative formula mass of calcium nitrate, Ca(NO3)2? (Use Ca = 40, N = 14, O = 16.)

    • 148
    • 172
    • 150
    • 164

12. Chlorine molecules, Cl2, contain isotopes 35 and 37. At which m/z values do molecular ion peaks appear?

    • 70, 74 and 76
    • 35, 37 and 74
    • 70, 72 and 74
    • 68, 70 and 72

13. In the mass spectrum of Cl2, what is the expected ratio of peak heights at m/z 70 : 72 : 74?

    • 1 : 2 : 1
    • 9 : 6 : 1
    • 3 : 2 : 1
    • 9 : 3 : 1

14. Why does the mass spectrum of Cl2 show three molecular ion peaks rather than one?

    • Chlorine has two isotopes, so molecules can contain 35Cl and 37Cl in different combinations
    • Chlorine exists as a mixture of separate Cl atoms and Cl2 molecules, which both give peaks
    • Each molecule fragments into three different charged pieces when it is ionised in the spectrometer
    • Electrons in chlorine occupy three different shells, and each shell gives its own separate peak

15. A mass spectrum of benzene shows its M+ peak at m/z 78. What is the relative molecular mass of benzene?

    • 79
    • 78
    • 77
    • 6

16. Which statement about ions in a mass spectrometer is correct?

    • All ions have the same m/z value
    • A singly charged ion has z = 1, so its m/z value equals its mass
    • Neutral molecules are deflected by the magnetic field
    • A doubly charged ion always appears at the same m/z as its molecular ion

17. The relative atomic mass of boron is 10.8. Boron has isotopes 10B and 11B. Which isotope is more abundant?

    • 10B, since its mass number is lower
    • 11B, since the mean is closer to 11
    • 10B, since the mean is closer to 10
    • Both are equally abundant

18. Explain why the relative atomic mass of most elements is not a whole number.

    • Atoms lose a small amount of mass when they form covalent bonds with neighbouring atoms
    • The 12C scale is defined using decimal values, so all relative masses are non-integer values
    • Most elements exist as mixtures of isotopes, so the value is a weighted mean of isotopic masses
    • Electrons add a small fractional mass to the nucleus of each atom, which shifts the average value

19. What is the mass of 2.0 mol of carbon dioxide, CO2? (Use C = 12, O = 16.)

    • 44 g
    • 88 g
    • 66 g
    • 22 g

20. A compound has peaks at m/z 180 and 182 of almost equal height. Which conclusion is best?

    • The compound contains two carbon atoms with different isotopes, which give two separate peaks
    • The compound contains one chlorine atom, whose isotopes 35Cl and 37Cl are present in equal abundance
    • The sample is a mixture of two different compounds, one of mass 180 and one of mass 182
    • The compound contains one bromine atom, whose isotopes 79Br and 81Br are almost equally abundant

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