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 9 1 . 8 4 % 2 0 N e (mass 19.9924 u), 0 . 4 7 % 2 1 N e (mass 20.9940 u) and 7 . 6 9 % 2 2 N e (mass 21.9914 u). Calculate to 4 significant figures the average atomic mass of neon in this sample.

Q2:

A sample of magnesium contains 7 8 . 7 0 % 2 4 M g (mass 23.98 u), 1 0 . 1 3 % 2 5 M g (mass 24.99 u) and 1 1 . 1 7 % 2 6 M g (mass 25.98 u). Calculate the average atomic mass of magnesium in this sample.

Q3:

What is the molar mass of methane ( C H 4 )?

Q4:

What is the molar mass of diborane ( B H 2 6 )?

  • A 36.0 g/mol
  • B 66.9 g/mol
  • C 35.6 g/mol
  • D 27.7 g/mol
  • E 19.7 g/mol

Q5:

What is the molar mass of hydrazine ( N H 2 6 )?

Q6:

What is the molar mass of C a C O 3 to 2 decimal places?

  • A 27.02 g/mol
  • B 68.09 g/mol
  • C 61.04 g/mol
  • D 100.09 g/mol
  • E 84.31 g/mol

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