Worksheet: Formula Masses

In this worksheet, we will practice calculating formula masses by summing the relative atomic masses of the constituent elements.

Q1:

A sample of neon contains 91.84%20Ne (mass 19.9924 u), 0.47%21Ne (mass 20.9940 u), and 7.69%22Ne (mass 21.9914 u). Calculate to 4 significant figures the average atomic mass of neon in this sample.

Q2:

A sample of magnesium contains 78.70%24Mg (mass 23.98 u), 10.13%25Mg (mass 24.99 u), and 11.17%26Mg (mass 25.98 u). Calculate the average atomic mass of magnesium in this sample.

Q3:

What is the molar mass of methane (CH4)?

Q4:

What is the molar mass of diborane (BH26)?

  • A35.6 g/mol
  • B19.7 g/mol
  • C66.9 g/mol
  • D36.0 g/mol
  • E27.7 g/mol

Q5:

What is the molar mass of hydrazine (NH26)? Approximate your answer to 3 significant figures.

Q6:

What is the molar mass of CaCO3 to 2 decimal places?

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