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Related Topics: More Chemistry Lessons

In these lessons, we will learn

- how to calculate the relative formula mass or relative molecular mass
- how to use the relative molecular mass to calculate the percent mass of an element in a compound
- how to use the relative molecular mass to calculate the percent mass of water in a compound

The

*Example: *

What is the relative mass formula of hydrogen gas? (Relative atomic mass: H = 1)

*Solution: *

The relative mass formula of hydrogen gas is

*Example: *

What is the relative mass formula of water? (Relative atomic masses: H = 1, O = 16)

*Solution: *

The relative mass formula of water is

*Example: *

What is the relative mass formula of sodium chloride? (Relative atomic masses: Na = 23, Cl = 35.5)

*Solution: *

The relative mass formula of sodium chloride is

How to use

*Example: *

What percentage of the mass of ammonium nitrate is nitrogen? (The formula for ammonium nitrate is NH_{4}NO_{3}, Relative atomic masses: H = 1, O = 16, N = 14)

*Solution: *

Mass of hydrogen in the formula = 28

Mass of hydrogen as a fraction of the total =

Mass of hydrogen as percentage of total mass

*Example: *

What percentage of the mass of O in NaNO_{3}? (Relative atomic masses: Na = 23, O = 16, N = 14)

*Solution: *

Mass of O as a fraction of the total =

Mass of O as percentage of total mass

The following video gives an example of calculating percent mass of elements in a compound.

Finding the percent by mass means finding the mass of the elements in the compound and adding the masses for the total mass.

Mass Percent Composition of an Element in a Compound

How do calculate the mass percent composition (or simply, the mass percent) of an element in a compound.

How to use

*Example: *

What percentage of the mass of magnesium sulfate is water? (Given that the formula for magnesium sulfate is , Relative atomic masses: H = 1, O = 16, S = 32, Mg = 24)

*Solution:*

Mass of water in the formula =

Mass of water as a fraction of the total =

Mass of hydrogen as percentage of total mass

This video outlines how to determine the percent, by mass, of water trapped in a hydrate's crystal lattice.

Compounds in this video CuSO

You can use the Mathway widget below to practice Algebra or other math topics. Try the given examples, or type in your own problem. Then click "Answer" to check your answer.