How to Determine Percentage Mass: 11 Steps

2024 Author: Samantha Chapman | [email protected]. Last modified: 2024-01-15 13:47

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.

• 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.