Worksheet: Formula Mass

In this worksheet, we will practice defining formula mass and calculating its value for given molecular formulas using atomic masses.

Q1:

Which of these substances has the highest molar mass?

  • AThe herbicide paraquat, CHNCl121422
  • BUrea, CO(NH)22
  • CThe anesthetic halothane, CHBrClF23
  • DCaffeine, CHNO81042
  • EA typical soap, CHCONa17352

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 A(A)r and A(B)r, the relative atomic masses of A and B?

  • AA(A)A(B)rrโˆ’
  • BA(A)+A(B)rr
  • CA(A)ร—A(B)rr
  • DA(A)รทA(B)rr

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?

  • AA(A)+A(B)rr2
  • B2(A(A)+A(B))rr
  • CA(A)+2A(B)rr
  • DA(A)+(A(B))rr2
  • E2A(A)+A(B)rr

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)?

Q16:

The displayed formula for 1,3,5-tribromocyclohexane is shown below. What is its relative formula mass? Give your answer to the nearest whole number.

CCHCHHBrCHCBrCHHHHBrH

Q17:

What is the relative formula mass of Al(OH)3?

Q18:

Which of the following compounds has a relative formula mass of 44?

  • ANO2
  • BCH36
  • CLiCl
  • DNaF
  • ECO2

Q19:

Tricalcium phosphate (Ca(PO))342 is an anticaking agent that prevents granular food from forming lumps. The chemical equation for the production of Ca(PO)342 is shown below. CaCO+CaPOCa(PO)+CO32273422

Which compound has the largest relative formula mass?

  • ACa(PO)342
  • BCaPO227 and Ca(PO)342
  • CCaCO3
  • DCO2
  • ECaPO227

Q20:

The balanced equation for the oxidation of an organic molecule is shown below. The total relative formula mass of the products is 96. Identify what compound A is. 2CHOH+O2A+2HO322

  • ACHO242
  • BCHO2
  • CCO2
  • DCHO263
  • ECH26

Q21:

The atomic mass unit (u) is defined as 112th of the mass of an atom of carbon-12. What is the mass of a silicon-30 atom in atomic mass units?

Q22:

The atomic mass unit (u) is defined as 112th of the mass of an atom of carbon-12. What is the mass of a fluorine-19 atom in atomic mass units?

Q23:

The relative atomic mass of an element is the average mass of one atom on a scale .

  • Awhere hydrogen-1 has a mass of 1
  • Bwhere carbon-12 has a mass of 12
  • Cwhere the most common isotope of the element has a mass of 100
  • Dfrom 0โ€“100, where 0 is the mass of hydrogen and 100 is the mass of the heaviest element

Q24:

A scientist is given the chemical formula and the relative formula mass of two unknown compounds, as shown below. ChemicalformulaXYChemicalformulaXY23๐‘€=64๐‘€=80๏Ž๏Ž If the atomic mass of element X is twice that of element Y, which of the following are elements X and Y?

  • AX=Ne, Y=Ar
  • BX=Ni, Y=Si
  • CX=Li, Y=N
  • DX=S, Y=O
  • EX=C, Y=Mg

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