how do you determine the percent by mass of an element?

Here is a good explaination of it. Look at the examples.

He works with one mole, and that is the grams in the denominator.

thank you!

To determine the percent by mass of an element in a compound, you need to know the molar mass of the element and the molar mass of the entire compound. Here's a step-by-step process to determine the percent by mass of an element:

1. Determine the molar mass of the element: The molar mass is the mass of one mole of atoms of the element. It is given by the atomic weight on the periodic table, and it is measured in grams per mole.

2. Determine the molar mass of the compound: The molar mass of the compound is the sum of the molar masses of all the elements present in it. Multiply the subscript of each element by its molar mass and add them all up.

3. Calculate the percent by mass: Divide the molar mass of the element by the molar mass of the compound and multiply the result by 100 to get the percent by mass.

Here's the formula to calculate the percent by mass of an element:

Percent by mass = (molar mass of element / molar mass of compound) x 100

Let's take an example to demonstrate this process:
What is the percent by mass of carbon (C) in carbon dioxide (CO2)?

1. Molar mass of carbon (C): Approximately 12.01 g/mol.

2. Molar mass of carbon dioxide (CO2):
Carbon: 1 (subscript) x 12.01 g/mol = 12.01 g/mol
Oxygen: 2 (subscript) x 16.00 g/mol = 32.00 g/mol
Total molar mass of CO2 = 44.01 g/mol

3. Calculate the percent by mass of carbon:
(12.01 g/mol / 44.01 g/mol) x 100 ≈ 27.28%

Therefore, carbon represents approximately 27.28% by mass in carbon dioxide.