Worksheet library · A Level

Chemistry A Level Sciences Worksheets, Questions and Revision

21 original Chemistry worksheet packs - 243 printable pages with full mark schemes. Atomic structure, bonding, chemical reactions, rates and the rest of the specification. View any pack in the browser or open the print-ready PDF.

AQAOCREdexcelWJECEduqas
See the method: Atomic Structure

Gallium exists as two isotopes, 69Ga (60.0% abundance) and 71Ga (40.0% abundance). Calculate the relative atomic mass of gallium, giving your answer to 1 decimal place.

  1. Convert each percentage abundance to a decimal: 60.0% = 0.600 and 40.0% = 0.400.
  2. Multiply each isotope's mass number by its decimal abundance: 69 x 0.600 = 41.4, and 71 x 0.400 = 28.4.
  3. Add the two products together: 41.4 + 28.4 = 69.8.
  4. Check the abundances sum to 100% (60.0 + 40.0 = 100), confirming no isotopes are missing.
  5. Final answer: relative atomic mass of gallium = 69.8
2.1 Atomic Structure6p + answers · 90 marks · PDF
2.2 Bonding and Structure6p + answers · 140 marks · PDF
2.3 Energetics and Thermodynamics6p + answers · 103 marks · PDF
2.4 Kinetics and Equilibria7p + answers · 126 marks · PDF
2.5 Redox and Electrochemistry5p + answers · 93 marks · PDF
2.7 Organic Chemistry6p + answers · 146 marks · PDF
2.8 Analytical Techniques6p + answers · 118 marks · PDF

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