The percentage mass of a molecule is the percentage of each individual element in the mass of a molecule. The percentage mass of an element in a compound is expressed as the proportion of the element's molar mass to the total molecular mass, multiplied by 100. It sounds complicated, but finding the mass percentage is actually a simple process!
Steps
Method 1 of 2: Understanding the Basics
Step 1. Understanding atoms
Atoms are the basic unit of measurement of matter and are composed of protons, neutrons and electrons. They are the basic building blocks of everything around you.
Step 2. Understanding the molecules
Molecules are electrically neutral groups of two or more atoms held together by chemical bonds.
Water, for example, is made up of the H molecule2O. Each water molecule is made up of two hydrogen atoms chemically bonded by one oxygen atom.
Step 3. Understanding the moles
The mole is a unit of measurement used to express the amount of a chemical in a sample. It is defined as the amount of any substance that contains 6.02 x 1023 elementary entities.
6.02 x 1023 is, approximately, the number of carbon atoms in 12 grams of pure carbon and is also called Avogadro's number.
Step 4. Understanding Chemical Compounds
Compounds are pure chemicals made up of two or more chemical elements.
Water, being composed of the H molecule2Or, it's a chemical compound.
Step 5. Understanding the atomic mass
This is the mass of an atomic, sub atomic or molecule particle and is expressed in grams per mole (g / mol).
Attention: the atomic mass is different from the atomic weight and refers specifically to the total mass of the particle, subatomic particle or molecule at rest
Step 6. Understanding the molecular mass
It is the mass of a single molecule. In other words, it is made up of the total mass of all the individual atoms that make up a given molecule.
As in the case of the atomic mass, the molecular mass differs from the molecular weight
Method 2 of 2: Calculate the Percentage Mass
Step 1. Isolate the elements of the compound
For example, let's say you are asked to calculate the percentage mass of citric acid C.6H.8OR7, as shown in the figure. The elements of this compound are carbon (C), hydrogen (H) and oxygen (O).
Step 2. Write down the atomic mass of each individual element
Use the periodic table of elements to find these numbers. The value of the atomic mass of the elements is located just below the atomic symbol, expressed in g / mol.
In the example above you will notice that the atomic mass of carbon is 12.01 g / mol, the atomic mass of hydrogen is 1.00 g / mol and that of oxygen is 15.99 g / mol
Step 3. Determine the molar mass of each element in the compound
The molar mass of an element is composed of the atomic mass of the element multiplied by the number of atoms of the element in a single molecule of the compound. The numeric subscript placed after each atomic symbol indicates the number of atoms of that element in the compound.
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In the example above, remember that each molecule of the compound is made up of 6 carbon atoms, 8 hydrogen and 7 oxygen atoms. So, if you want to calculate the molar mass of the elements, you have to do as shown in the figure.
Molar mass of carbon: 6 x 12.01 g / mol = 72.06 g / mol
Molar mass of hydrogen: 8 x 1.00 g / mol = 8.00 g / mol
Molar mass of oxygen: 7 x 15.99 g / mol = 111.93 g / mol.
Step 4. Calculate the total molecular mass of the compound
This value is expressed as the sum of the molar mass of the individual elements of the compound and represents the mass of a single molecule. # * In the above example you would calculate the total molecular weight as follows: Molecular mass of C6H.8OR7 = 72.06 g / mol + 8.00 g / mol + 111.93 g / mol = 191.99 g / mol.
Step 5. Find the percent mass
The percentage mass of an element is expressed by the ratio of the molar mass of an element to the total molecular mass of the compound, multiplied by 100. # * In the above example, we will calculate the mass percentage of each element as shown in the figure. It can therefore be concluded that C.6H.8OR7 it is composed of 37.53% carbon, 4.16% hydrogen and 58.29% oxygen.
