How to Find Mass Percent
Understand atoms., Understand molecules., Understand moles., Understand chemical compounds., Understand atomic mass., Understand molecular mass., List the elements in the compound., Write down the atomic mass of each individual element., Find the...
Step-by-Step Guide
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Step 1: Understand atoms.
Atoms are basic units of matter, composed of protons, neutrons, and electrons.
These are the fundamental building blocks of everything around you. -
Step 2: Understand molecules.
Molecules are electrically neutral chemical groups of two or more atoms, which are held together by chemical bonds.
Water, for example, is made of the molecule H2O.
Each water molecule is composed of two hydrogen atoms, which are chemically bonded to one oxygen atom. , A mole is a unit of measurement used to express the amount of a chemical substance in a sample.
It is defined as the amount of any substance that contains
6.02 x10^ 23 elementary entities.
Use moles as a way to concisely express amounts of chemical substances.
6.02 x 10^23, which is approximately the number of carbon atoms in 12 grams (0.42 oz) of pure carbon, is also called “Avogadro’s Number.” , Chemical compounds are pure chemical substances that consist of two or more chemical elements.
Water, made up of the molecule H2O, is a chemical compound. , Atomic mass is the mass of an atomic particle, sub-atomic particle, or molecule.
It is expressed in grams per mole (g/mol).
Note that atomic mass is different from atomic weight and specifically refers to the total mass of the particle, subatomic particle, or molecule at rest. , Molecular mass is the mass of a single molecule.
In other words, it is the total mass of all of the individual atoms that make up a given molecule.
As with atomic mass, molecular mass differs from molecular weight. , For example, say you need to calculate the mass percent of citric acid, C6H8O7, as shown in the picture.
The elements of this compound are carbon (C), hydrogen (H), and oxygen (O). , Use the periodic table to locate these numbers.
It is usually located just below the atomic symbol, in the units of g/mol.
In the example above, you would note that the atomic mass of carbon is
12.01 g/mol, the atomic mass of hydrogen is
1.00 g/mol, and the atomic mass of oxygen is
15.99 g/mol. , The mass contribution of an element in a compound is the atomic mass of the element multiplied by the number of atoms in the element in a single molecule of the compound.
The numeric subscript after each atomic symbol signifies the number of atoms of that element in the compound.
In the example above, recall that each molecule of your compound is made up of 6 atoms of carbon, 8 atoms of hydrogen, and 7 atoms of oxygen.
Therefore, you would calculate the mass contribution of the elements as shown in the picture.
Mass contribution of carbon: 6 x
12.01 g/mol =
72.06 g/mol Mass contribution of hydrogen: 8 x
1.00 g/mol =
8.00 g/mol Mass contribution of oxygen: 7 x
15.99 g/mol =
111.93 g/mol , Total molecular mass of a compound is expressed as a sum of the mass contributions of the individual elements in the compound.
It represents the mass of a single molecule.
In the example above, calculate your total molecular mass as follows:
Molecular mass of C6H8O7 =
72.06 g/mol +
8.00 g/mol +
111.93 g/mol =
191.99 g/mol , The mass percent composition of an element is expressed as a ratio of mass contribution of the element and total molecular mass of the compound multiplied by 100%.
In the example above, calculate your mass percent of each element as shown in the photo.
You can therefore conclude that C6H8O7 consists of
37.53% carbon,
4.16% hydrogen, and
58.29% oxygen. -
Step 3: Understand moles.
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Step 4: Understand chemical compounds.
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Step 5: Understand atomic mass.
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Step 6: Understand molecular mass.
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Step 7: List the elements in the compound.
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Step 8: Write down the atomic mass of each individual element.
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Step 9: Find the mass contribution of each element in your compound.
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Step 10: Calculate the total molecular mass of your compound.
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Step 11: Find the mass percent composition.
Detailed Guide
Atoms are basic units of matter, composed of protons, neutrons, and electrons.
These are the fundamental building blocks of everything around you.
Molecules are electrically neutral chemical groups of two or more atoms, which are held together by chemical bonds.
Water, for example, is made of the molecule H2O.
Each water molecule is composed of two hydrogen atoms, which are chemically bonded to one oxygen atom. , A mole is a unit of measurement used to express the amount of a chemical substance in a sample.
It is defined as the amount of any substance that contains
6.02 x10^ 23 elementary entities.
Use moles as a way to concisely express amounts of chemical substances.
6.02 x 10^23, which is approximately the number of carbon atoms in 12 grams (0.42 oz) of pure carbon, is also called “Avogadro’s Number.” , Chemical compounds are pure chemical substances that consist of two or more chemical elements.
Water, made up of the molecule H2O, is a chemical compound. , Atomic mass is the mass of an atomic particle, sub-atomic particle, or molecule.
It is expressed in grams per mole (g/mol).
Note that atomic mass is different from atomic weight and specifically refers to the total mass of the particle, subatomic particle, or molecule at rest. , Molecular mass is the mass of a single molecule.
In other words, it is the total mass of all of the individual atoms that make up a given molecule.
As with atomic mass, molecular mass differs from molecular weight. , For example, say you need to calculate the mass percent of citric acid, C6H8O7, as shown in the picture.
The elements of this compound are carbon (C), hydrogen (H), and oxygen (O). , Use the periodic table to locate these numbers.
It is usually located just below the atomic symbol, in the units of g/mol.
In the example above, you would note that the atomic mass of carbon is
12.01 g/mol, the atomic mass of hydrogen is
1.00 g/mol, and the atomic mass of oxygen is
15.99 g/mol. , The mass contribution of an element in a compound is the atomic mass of the element multiplied by the number of atoms in the element in a single molecule of the compound.
The numeric subscript after each atomic symbol signifies the number of atoms of that element in the compound.
In the example above, recall that each molecule of your compound is made up of 6 atoms of carbon, 8 atoms of hydrogen, and 7 atoms of oxygen.
Therefore, you would calculate the mass contribution of the elements as shown in the picture.
Mass contribution of carbon: 6 x
12.01 g/mol =
72.06 g/mol Mass contribution of hydrogen: 8 x
1.00 g/mol =
8.00 g/mol Mass contribution of oxygen: 7 x
15.99 g/mol =
111.93 g/mol , Total molecular mass of a compound is expressed as a sum of the mass contributions of the individual elements in the compound.
It represents the mass of a single molecule.
In the example above, calculate your total molecular mass as follows:
Molecular mass of C6H8O7 =
72.06 g/mol +
8.00 g/mol +
111.93 g/mol =
191.99 g/mol , The mass percent composition of an element is expressed as a ratio of mass contribution of the element and total molecular mass of the compound multiplied by 100%.
In the example above, calculate your mass percent of each element as shown in the photo.
You can therefore conclude that C6H8O7 consists of
37.53% carbon,
4.16% hydrogen, and
58.29% oxygen.
About the Author
Marilyn Palmer
Enthusiastic about teaching practical skills techniques through clear, step-by-step guides.
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