Mass Percent: Videos & Practice Problems

Mass percent, or weight percent, quantifies the percentage of a specific element in a compound. It is calculated by dividing the mass of the element by the total mass of the compound and multiplying by 100. This concept is essential for determining the percent composition of elements within compounds, aiding in various chemical analyses. Understanding mass percent is crucial for applications in stoichiometry, where it relates to molar mass and the composition of substances, enhancing comprehension of chemical reactions and properties.

Mass Percent Concept

Here we're going to say that mass percent, also known as weight percent, is a percentage of a given element in a compound. Now we're going to say here it deals with the molar mass in grams of the selected element and 1 mole of the compound. So this translates to say that mass percent equals the mass or grams of an element divided by the grams of the compound and then multiplying that by 100. Using this helps us to determine the percent composition of any particular element within a given compound.

Mass Percent Example

Here it says to calculate the mass percent of carbon within sodium carbonate. So sodium carbonate is Na₂CO₃. We're looking for the mass percent of carbon, so that means we're gonna need the grams of carbon over the grams of the compound itself times 100. Alright. So sodium carbonate has within it 2 sodiums, 1 carbon, and 3 oxygens. We're gonna multiply them each by their atomic masses from the periodic table. So sodium is 22.99 grams, carbon is 12.01 grams and oxygen is 16 grams. So, multiplying them out, we get 45.98 grams, 12.01 grams, and 48 grams. Add them all together, that comes out to 105.99 grams. Take those numbers. So for carbon, its mass is 12.01, and for the compound itself, it's 105.99. So we do 12.01105.99. When we do that we get 11.3% as the mass percent of carbon within sodium carbonate.

Determine the percent composition of nitrogen and oxygen with nitrogen dioxide, NO₂.

Here it says, determine the percent composition of nitrogen and oxygen within nitrogen dioxide. Alright. So what we need to do here is we need to find the mass percent of nitrogen, and then the mass percent of oxygen. Remember, this will be the grams of nitrogen within the grams of the compound times 100. And for oxygen, it'll be grams of oxygen divided by the grams of the compound also times 100. If we look at nitrogen dioxide, it's composed of 1 nitrogen, and it's composed of 2 oxygens. Multiply them by their atomic masses, which you find from the periodic table. Nitrogen weighs 14.01 grams, oxygen weighs 16 grams. Multiply them, and then add up your totals, so the mass of the compound is 46.01 grams. So that's the number that goes here and here. And then all we need to do is plug in what we have for nitrogen, and then when we do that we're going to get here for nitrogen its mass percent as 30.4%. And then for oxygen, you could plug it into this formula. You could also say that we know that 100% of the compound is made up of just nitrogen and oxygen. So you could say 100% minus 30.4% gives us also the percentage of oxygen. So this will come out to 69.6%. So here we have both the mass percent of nitrogen and oxygen. Giving the percentages of all the compounds with all the elements within the compound are classified as the percent composition of the compound. So, the compound is made up of 30.4% nitrogen and 69.6% oxygen.

Here’s what students ask on this topic:

What is mass percent and how is it calculated?

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.

Why is mass percent important in chemistry?

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.

How do you find the mass percent of an element in a compound?

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.

What is the difference between mass percent and mole percent?

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.

Can you provide an example of calculating mass percent?

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%.