Worksheet: Percentage Composition from Molecular Formulas

In this worksheet, we will practice converting between elemental percentage compositions, empirical formulas, and molecular formulas.

Q1:

Adding aqueous silver(I) nitrate to aqueous gallium(III) bromide results in the precipitation of silver(I) bromide. A sample of gallium(III) bromide weighing 0.165 g was dissolved in water and treated with silver(I) nitrate, resulting in the precipitation of 0.299 g of silver(I) bromide. Calculate the quantity of the reacted gallium present in the sample of gallium(III) bromide, as a percentage of the total mass.

Q2:

What is the empirical formula of a compound containing 40.00%C, 6.71%H, and 53.28%O?

  • ACHO4
  • BCHO24
  • CCHO2
  • DCHO32
  • ECHO222

Q3:

What is the empirical formula for a substance that is 46.6% oxygen and 53.4% manganese by mass?

  • AMnO2
  • BMnO3
  • CMnO
  • DMnO34
  • EMnO23

Q4:

What is the empirical formula for a substance that is 32.0% oxygen and 68.0% vanadium by mass?

  • AVO
  • BVO23
  • CVO25
  • DVO2

Q5:

Which of the following compounds has the highest percentage mass of carbon?

  • ACHCHBr2
  • BCHCHF2
  • CCHCH33
  • DCHCl3
  • ECH4

Q6:

A major textile dye manufacturer developed a new yellow dye. The dye has a percent composition of 75.95% C, 17.72% N, and 6.33% H by mass with a molar mass of about 240 g/mol.

What is the empirical formula of the dye?

  • ACHN452
  • BCHN33
  • CCHN542
  • DCHN55
  • ECHN46

What is the molecular formula of the dye?

  • ACHN15153
  • BCHN993
  • CCHN15126
  • DCHN12156
  • ECHN12183

Q7:

A hydrocarbon is composed of 85.7% carbon and 14.3% hydrogen by mass.

What is the empirical formula?

  • ACH2
  • BCH3
  • CCH2
  • DCH4
  • ECH

If 1.56 g of the hydrocarbon occupies a volume of 1.00 L at 0.984 atm and 50C, what is the molecular formula?

  • ACH510
  • BCH610
  • CCH22
  • DCH36
  • ECH38

Q8:

What is the empirical formula for a substance that is 43.7% oxygen and 56.3% phosphorus by mass?

  • APO23
  • BPO4
  • CPO5
  • DPO25
  • EPO3

Q9:

A compound of carbon and hydrogen contains 85.6%C and has a molar mass of 28.1 g/mol. What is its molecular formula?

  • ACH24
  • BCH4
  • CCH22
  • DCH26
  • ECH36

Q10:

A major textile dye manufacturer developed a new yellow dye. The dye has a percent composition of 75.95%C, 17.72%N, and 6.33%H by mass with a molar mass of about 240 g/mol.

What is the empirical formula of the dye?

  • ACHN46
  • BCHN55
  • CCHN452
  • DCHN542
  • ECHN33

What is the molecular formula of the dye?

  • ACHN12183
  • BCHN12156
  • CCHN15126
  • DCHN993
  • ECHN15153

Q11:

Which of these molecules has the highest percentage mass of hydrogen?

  • ACH4
  • BCHCl3
  • CCHCHCHCHCH32223
  • DCH24
  • ECHO12106

Q12:

Which of these minerals has the highest mass percentage of oxygen?

  • ATurquoise, CuAl(PO)(OH)(HO)644824
  • BMalachite, Cu(OH)CO223
  • CLimestone, CaCO3
  • DBeryl, BeAlSiO32618
  • EHalite, NaCl

Q13:

What is the mass percentage of ammonia in Co(NH)Cl363?

Q14:

In the metal complex Co(NH)Cl363, which element makes up the largest proportion by mass?

  • AChlorine
  • BNitrogen
  • CHydrogen
  • DCobalt

Q15:

Analysis of a 12.04 g sample of a liquid compound composed of carbon, hydrogen, and nitrogen showed it to contain 7.34gC, 1.85gH, and 2.85gN. What is the percent composition of this compound?

  • A61.0%C, 15.4%H, 23.7%N
  • B40.9%C, 13.2%H, 45.9%N
  • C15.3%C, 23.7%H, 61.0%N
  • D55.6%C, 16.0%H, 28.4%N
  • E60.1%C, 14.3%H, 25.6%N

Q16:

Nicotine, an alkaloid in the nightshade family of plants that is mainly responsible for the addictive nature of cigarettes, contains 74.02% C, 8.710% H, and 17.27% N. If 40.57 g of nicotine contains 0.2500 mol nicotine, what is the molecular formula?

  • ACHN614
  • BCHN57
  • CCHN4208
  • DCHN10142
  • ECHN1682

Q17:

The bacterial fermentation of grain to produce ethanol forms a gas with a percent composition of 27.29% C and 72.71% O. What is the empirical formula for this gas?

Distillery - 72 ppi
  • ACO2
  • BCO
  • CCO24
  • DCO23
  • ECO2

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