# Worksheet: Percentage Composition

In this worksheet, we will practice calculating the percentage composition of a substance using chemical formulas or the masses of constituent elements.

Q1:

A 5.0 g sample of spinal fluid contains 3.75 mg (0.00375 g) of glucose. What is the percent by mass of glucose in spinal fluid?

Q2:

A bottle of a tile cleanser contains 135 g of and 775 g of water. What is the percent by mass of in this cleanser?

Q3:

A compound contains only the elements X and Y. A sample of the compound with a mass of 12.5 g is found to contain 6.50 g of X. What is the percentage composition of the compound?

• AX: , Y :
• BX: , Y:
• CX: , Y:
• DX: , Y:
• EX: , Y:

Q4:

A 10 g sample of silicon carbide is found to contain 3.0 g of carbon. What is the percentage composition of silicon carbide?

• A,
• B,
• C,
• D,
• E,

Q5:

What is the percentage composition of calcium carbonate ? State percentages to 1 decimal place.

• A: , : , :
• B: , : , :
• C: , : , :
• D: , : , :
• E: , : , :

Q6:

To 1 decimal place, calculate the oxygen content of a water molecule as a percentage of the total mass.

Q7:

A compound contains a known mass of element . What is the formula for expressing the mass of in compound as a percentage of the total mass?

• A
• B
• C
• D
• E

Q8:

A compound contains one atom of element per formula unit. The relative formula mass of is known. What is the formula for expressing the mass of in compound as a percentage of the total mass?

• A
• B
• C
• D
• E

Q9:

A sample of a compound composed of only elements and has a mass of 50 g. After elemental analysis, it is shown that the sample contains 45 g of . To the nearest percentage unit, what is the mass of in the sample as a percentage of the total mass?

Q10:

A sample of a compound has a mass of 80 g and is composed entirely of elements and . Elemental analysis shows that the sample contains 20 g of . To the nearest percentage point, what is the mass of in the sample as a percentage of the total mass?

Q11:

A 1.497 g sample of a tin alloy is dissolved in nitric acid and solid metastannic acid is precipitated. Heating of the precipitate generates 0.4909 g of tin(IV) oxide, . Calculate, to 1 decimal place, the mass of tin in the original alloy as a percentage of the total sample mass.

Q12:

A 2.5624 g sample of a pure solid alkali metal chloride is dissolved in water and treated with excess aqueous silver nitrate. The resulting precipitate, filtered and dried, weighs 2.1813 g.

To 4 significant figures, what is the mass of the chloride ion in the alkali metal salt as a percentage of the total sample mass?

What is the molecular formula of the alkali metal salt?

• A
• B
• C
• D
• E

Q13:

Ethanol has the formula .

As a percentage by mass, what is the oxygen content of the ethanol molecule, to 2 significant figures?

As a percentage by mass, what is the carbon content of the ethanol molecule, to 2 significant figures?

As a percentage by mass, what is the hydrogen content of the ethanol molecule, to 2 significant figures?

Q14:

Ethylene glycol has the formula . Which element constitutes the largest percentage by mass of the ethylene glycol molecule?

• A
• B
• C

Q15:

The molecular formulas and densities of five B vitamins are shown in the table.

Niacin1.473
Pantothenic acid1.266
Pyridoxal phosphate1.638
Biotin1.267
4-Aminobenzoic acid1.374

Which of these vitamins contains the most molecules per unit volume?

• ABiotin
• B4-Aminobenzoic acid
• CPyridoxal phosphate
• DPantothenic acid
• ENiacin

Which of these vitamins contains the fewest atoms per unit volume?

• APyridoxal phosphate
• BNiacin
• C4-Aminobenzoic acid
• DPantothenic acid
• EBiotin

Which of these vitamins contains the most hydrogen atoms per unit volume?

• ABiotin
• BPantothenic acid
• CPyridoxal phosphate
• D4-Aminobenzoic acid
• ENiacin

Which of these vitamins contains the most nonhydrogen atoms per unit volume?

• ABiotin
• BNiacin
• CPyridoxal phosphate
• D4-Aminobenzoic acid
• EPantothenic acid

Q16:

The molecular formulas and densities of five compounds found in analgesic drugs are shown in the table.

Ibuprofen1.03
Acetaminophen1.26
Aspirin1.40
Naproxen1.20
Caffeine1.23

Which of these compounds contains the fewest molecules per unit volume?

• AIbuprofen
• BAspirin
• CAcetaminophen
• DNaproxen
• ECaffeine

Which of these compounds contains the most atoms per unit volume?

• AAspirin
• BNaproxen
• CCaffeine
• DIbuprofen
• EAcetaminophen

Which of these compounds contains the fewest hydrogen atoms per unit volume?

• AAcetaminophen
• BAspirin
• CIbuprofen
• DNaproxen
• ECaffeine

Q17:

A vanadium compound has the molecular formula where is a whole number. If the percentage by mass of in is , what is the value of ?

Q18:

A compound with a relative formula mass of 84.2 is composed only of hydrogen and carbon. The compound is found to contain carbon and hydrogen by mass. What is the formula of this compound?

• A
• B
• C
• D
• E