# Lesson Worksheet: Percentage Composition Chemistry • 10th Grade

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?

• A,
• B,
• C,
• D,
• E,

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 Y contains one atom of element X per formula unit. The relative formula mass of Y is known. What is the formula for expressing the mass of X in compound Y 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?