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 silver(I) bromide. As a percentage of the total mass, calculate the quantity of gallium present in the sample of gallium(III) bromide.

Q2:

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

  • A C H O 4
  • B C H O 2 4
  • C C H O 2
  • D C H O 3 2
  • E C H O 2 2 2

Q3:

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

  • A M n O 2
  • B M n O 3
  • C M n O
  • D M n O 3 4
  • E M n O 2 3

Q4:

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

  • A V O
  • B V O 2 3
  • C V O 2 5
  • D V O 2

Q5:

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

  • A C H C H B r 2
  • B C H C H F 2
  • C C H C H 3 3
  • D C H C l 3
  • E C H 4

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?

  • A C H N 4 5 2
  • B C H N 3 3
  • C C H N 5 4 2
  • D C H N 5 5
  • E C H N 4 6

What is the molecular formula of the dye?

  • A C H N 1 5 1 5 3
  • B C H N 9 9 3
  • C C H N 1 5 1 2 6
  • D C H N 1 2 1 5 6
  • E C H N 1 2 1 8 3

Q7:

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

What is the empirical formula?

  • A C H 2
  • B C H 3
  • C C H 2
  • D C H 4
  • E C H

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?

  • A C H 5 1 0
  • B C H 6 1 0
  • C C H 2 2
  • D C H 3 6
  • E C H 3 8

Q8:

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

  • A P O 2 3
  • B P O 4
  • C P O 5
  • D P O 2 5
  • E P O 3

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?

  • A C H 2 4
  • B C H 4
  • C C H 2 2
  • D C H 2 6
  • E C H 3 6

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?

  • A C H N 4 6
  • B C H N 5 5
  • C C H N 4 5 2
  • D C H N 5 4 2
  • E C H N 3 3

What is the molecular formula of the dye?

  • A C H N 1 2 1 8 3
  • B C H N 1 2 1 5 6
  • C C H N 1 5 1 2 6
  • D C H N 9 9 3
  • E C H N 1 5 1 5 3

Q11:

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

  • A C H 4
  • B C H C l 3
  • C C H C H C H C H C H 3 2 2 2 3
  • D C H 2 4
  • E C H O 1 2 1 0 6

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?

  • A 6 1 . 0 % C , 1 5 . 4 % H , 2 3 . 7 % N
  • B 4 0 . 9 % C , 1 3 . 2 % H , 4 5 . 9 % N
  • C 1 5 . 3 % C , 2 3 . 7 % H , 6 1 . 0 % N
  • D 5 5 . 6 % C , 1 6 . 0 % H , 2 8 . 4 % N
  • E 6 0 . 1 % C , 1 4 . 3 % H , 2 5 . 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?

  • A C H N 6 1 4
  • B C H N 5 7
  • C C H N 4 2 0 8
  • D C H N 1 0 1 4 2
  • E C H N 1 6 8 2

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