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While working in the lab, you have to deal with so many chemicals and solutions. To make a specific product or solution, you first have to get the most right amount of constituting compounds.

Similarly, if you are doing an experiment or research within a lab-controlled environment, you need to keep the concentration of each chemical in the record. To do this, we use multiple parameters like molar mass, formula mass, and percentage composition.

What are these parameters, and what is the most correct and easiest way to calculate them? Let's find out!

Molar Mass

Suppose you are working on a lab project where you have been asked to add 1M (6.02×1023 particles) HCl to the reaction mixture.

Since we cannot weigh the number of particles physically, we will calculate the mass of these 6.02×1023 particles in grams.

But how would you know how many grams of HCl will be equal to one mole? It is the point where we get help from the Molar mass calculator.

However, before moving towards the definition of molar mass, we first have to recall what a mole is.

A mole refers to the 6.02×1023 particles. These particles could be either atoms, ions, electrons, or molecules. Since the same number of atoms are also found in 12.0g of C-12, we also define the mole such as

If the total number of atoms of a substance is equal to the total number of atoms in 12.0g of C-12, we say there is 1 mol of that substance present.

In a mole, we directly deal with several entities like atoms, ions, electrons. On the other hand, we specifically deal with the number of grams in molar mass. In simple words, the molar mass is the weight of 1 mole of a substance in grams.

We can also say that the molar mass is the mass of 6.02×1023 particles of a substance in grams. The chemical unit we used to represent molar mass is grams/mole. To find the molar mass of a compound, you have to add up the atomic masses of all the atoms present in a compound. Let us make it more clear through examples.

Related: How to find the molarity and molality of a solution

How to Find Molar Mass of HCL?

Suppose you have been asked to find the molar mass of HCl. To find it out, you have to follow these steps

1HCl = 1 atom of H, 1 atom of Cl

1.007g/mol + 34.453 g/mol = 36.46 g/mol

  1. Find out the number of total atoms present in the compound

    Since you are dealing with HCl, we first notice how many elements are present in one molecule of HCl.

  2. Find atomic masses of each element

    The atomic masses for each element are mentioned right below its symbol in the periodic table. You have to locate the symbol of that element and note its atomic mass from there.

    The atomic mass of hydrogen written in the periodic table is 1.007g/mol. The atomic mass for Cl is 34.453 g/mol.

  3. Add the atomic masses of each element to find the molar mass

    Since the atomic masses of hydrogen and chlorine are 1.007g/mol and 34.453 g/mol, respectively, we add them to find the molar mass of one molecule of HCl, such as

Now you know that one mole of HCl or 6.02×1023 particles of HCl are equal to 36.46 g/mol, and you can add this quantity to the reactant mixture in place of 6.02×1023 particles.

Formula Mass

Formula mass is usually confused with the molar mass, and it is identical to some extent. However, there are some major differences between these two parameters, which you should know.

  1. The formula mass of a compound is the sum of atomic masses of all the atoms present in its empirical formula. On the other hand, the molar mass is the mass of one mole of a compound in grams.
  2. Formula mass is specifically used to calculate the mass of compounds. On the other hand, molar mass can calculate the mass of any chemical entity, including atoms, ions, electrons, and molecules.
  3. The unit of formula mass is the atomic mass unit, while that of molar mass is g/mol.

The method for calculating the formula mass and molar mass is the same. In both cases, you have to add the atomic masses of all the elements present in a chemical compound. Let's clear this concept by considering an example of formula mass.

How to Calculate the Formula Mass of KNO3?

First of all, find the total number of atoms of each element present in the compound. As it is clear by the formula, there is one atom of K, one atom of N, and three oxygen atoms.

Now look for the atomic masses of each element from the periodic table and add them such as

K (1× 39.09) + N (1× 14.007) + O (3× 15.999) = 101. 02 amu.

In simple words, whenever you are asked to find the formula mass for a compound, you have to adopt the same procedure and change the unit from g/mol to amu.

Percentage Composition

A chemical compound is made up of many elements. Thus, percentage composition refers to the percentage of an element in that compound. The formula to find out the percentage composition is such as

Percentage composition = molar mass of element/total molecular mass of compound × 100

Let's make it more clear by considering the example of KNO3.

As we know that the molecular mass of KNO3 is 101g/mol, to find the percentage composition of K, we put the values in the given formula, such as

Percentage composition of K = molar mass of K/total molecular mass of KNO3 × 100 Percentage composition of N = 39/101×100 = 38.61%

Bottom Line

Mole, molar mass, formula mass, and percentage composition form the basics of chemistry and chemical calculations. All these parameters are interlinked with each other, and if you know about the value of anyone, you can find the others through it.