Worksheet: Relative Formula Mass

In this worksheet, we will practice defining relative formula mass and calculating its value for given molecular and structural formulas.

Q1:

Which of these substances has the highest molar mass?

  • ACaffeine, CHNO81042
  • BA typical soap, CHCONa17352
  • CThe anesthetic halothane, CHBrClF23
  • DUrea, CO(NH)22
  • EThe herbicide paraquat, CHNCl121422

Q2:

To the nearest g/mol, what is the relative formula mass ()Mr of NaO2 (sodium oxide)?

Q3:

What is the Mr of phosphorus trifluoride (PF)3?

Q4:

What is the Mr of silane (SiH)4?

Q5:

What is the Mr of xenon difluoride (XeF)2?

Q6:

The relative atomic mass (Ar) of sodium is 23 g/mol, that of oxygen is 16 g/mol, and that of hydrogen is 1 g/mol. What is the relative formula mass (Mr) of NaOH (sodium hydroxide)?

Q7:

Using the Periodic Table to find the relative atomic masses of its elements, calculate the relative formula mass (Mr) of CO2 (carbon dioxide) to the nearest g/mol.

Q8:

Using the Periodic Table to find the relative atomic masses of its elements, calculate the relative formula mass ()Mr of CHO2 (formaldehyde).

Q9:

What is the relative formula mass ()Mr of CHOH3 (methanol)? Use the periodic table to find the relative atomic masses of the elements.

Q10:

What is the relative formula mass ()Mr of MgF2 (magnesium fluoride)?

Q11:

What is the relative formula mass ()Mr of NH3 (ammonia)?

Q12:

A substance has the formula unit AB. What is the relative formula mass of this substance in terms of Ar(A) and Ar(B), the relative atomic masses of A and B?

  • A A ( A ) × A ( B ) r r
  • B A ( A ) ÷ A ( B ) r r
  • C A ( A ) A ( B ) r r
  • D A ( A ) + A ( B ) r r

Q13:

A substance has the formula unit AB2. What is the relative formula mass of this substance in terms of A(A)r and A(B)r, the relative atomic masses of A and B?

  • A A ( A ) + ( A ( B ) ) r r 2
  • B A ( A ) + A ( B ) r r 2
  • C A ( A ) + 2 A ( B ) r r
  • D 2 ( A ( A ) + A ( B ) ) r r
  • E 2 A ( A ) + A ( B ) r r

Q14:

The relative atomic mass ()Ar of carbon is 12 g/mol, and the Ar of oxygen is 16 g/mol. What is the relative formula mass ()Mr of CO (carbon monoxide)?

Q15:

The relative atomic mass (Ar) of carbon is 12 g/mol, and the Ar of hydrogen is 1 g/mol. What is the relative formula mass (Mr) of CH4 (methane)?

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