Mass Percent: Videos & Practice Problems

Mass percent, also known as weight percent, quantifies the percentage of a specific element in a compound. It is calculated using the formula:

$\frac{\mathrm{mass} \left(g\right) of \mathrm{element}}{\mathrm{mass} \left(g\right) of \mathrm{compound}} \times 100$

This formula helps determine the percent composition of any particular element within a given compound, which is essential for various chemical analyses and understanding the composition of substances.

Mass percent is crucial in chemistry because it helps determine the percent composition of elements within compounds. This information is essential for stoichiometry, which involves calculating the quantities of reactants and products in chemical reactions. Understanding mass percent allows chemists to predict how much of each element is present in a compound, aiding in the analysis of chemical properties and reactions. It also helps in quality control, formulation of mixtures, and various industrial applications where precise composition is necessary.

To find the mass percent of an element in a compound, follow these steps:

1. Determine the molar mass of the compound by summing the atomic masses of all the elements in the compound.
2. Find the mass of the specific element in one mole of the compound.
3. Use the formula:

$\frac{\mathrm{mass} \left(g\right) of \mathrm{element}}{\mathrm{mass} \left(g\right) of \mathrm{compound}} \times 100$

This will give you the mass percent of the element in the compound.

Mass percent and mole percent are both ways to express the composition of a mixture or compound, but they differ in what they measure:

• Mass percent: This measures the mass of a specific element or component as a percentage of the total mass of the compound or mixture. It is calculated using the formula:

$\frac{\mathrm{mass} \left(g\right) of \mathrm{element}}{\mathrm{mass} \left(g\right) of \mathrm{compound}} \times 100$

• Mole percent: This measures the number of moles of a specific component as a percentage of the total number of moles in the mixture. It is calculated using the formula:

$\frac{\mathrm{moles} \left(n\right) of \mathrm{component}}{\mathrm{total} \mathrm{moles} \left(n\right) in \mathrm{mixture}} \times 100$

While mass percent focuses on mass, mole percent focuses on the number of moles.

Sure! Let's calculate the mass percent of hydrogen in water (H₂O).

1. First, determine the molar mass of water: H₂O = 2(1.01 g/mol) + 16.00 g/mol = 18.02 g/mol.
2. Next, find the mass of hydrogen in one mole of water: 2(1.01 g) = 2.02 g.
3. Use the formula:

$\frac{2.02 \left(g\right) of H}{18.02 \left(g\right) of H}$₂O × 100

This gives:

$11.21\%$

So, the mass percent of hydrogen in water is 11.21%.