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Chemistry > Some Basic Concepts of Chemistry > How to Calculate Number of Moles?
Some Basic Concepts of Chemistry

How to Calculate Number of Moles?

How to Find Moles?

How to find moles in the solution is to calculate how many molecules the solution contains. Also, to do this you need to know the volume of the solution and how many solutes has been dissolved in the solution. Furthermore, you also need to know the molar mass of the solute.

Definition of Number of Moles

It refers to a huge number that we use to measure atoms. Moreover, it is equal to the number of atoms in 12 grams of carbon-12 that is just about 6.022 × 1023 atoms. Just like the way, it is easier to measure intergalactic (Space) distance in light-years relatively to measure it in inches. Also, it is easier to calculate atoms in a mole than in lakhs and crores.

how to find moles

Besides, one mole of any chemical compound or element is always the identical number. In addition, a mole of hydrogen is equal to a mole of glucose or a mole of uranium. However, their masses are different. Furthermore, they are expressed as ‘mol’.

How to Find Moles?

First of all, every element has a different molar mass and is expressed as gram per mole. For example, the Chlorine (Cl) has a molar mass of 35.4530 g/mol in the same way Sodium (Na) has a molar mass of 22.9898 g/mol.

Moreover, most of the molecules are made up of more than 1 element. So, for finding out the molar mass of the molecule you have to break it into elements to know its molar mass. Also, the periodic table can help you to find the molar mass of each element.

Example, If you want to find the molar mass of common salt (Sodium Chloride- NaCl) You add the mass of each element of it. Most noteworthy, each molecule has 1 Na (Sodium) and 1 Cl (Chloride) atom. So, in this way the mass of one mole of NaCl is the mass of Na and mass of Cl:

NaCl = Na + Cl

NaCl = 22.9898 g/L + 35.4530 g/L

Therefore, NaCl = 58.4538 g/L

Note: From compound to compound to a number of atoms in a molecule vary. For example, one molecule of H2O has two atoms of Hydrogen (H) and one atom of Oxygen (O). In the same way, HCl has one atom of Hydrogen (H) and one atom of Chlorine (Cl).

Molarity Calculation

It refers to the number of moles per litre of solution. Moreover, we express it as M. Besides, for calculating molarity we use the following equation:

Molarity = moles of solute / litres of solution

First of all, before you can use this equation you need to know how many moles of solute are there in the solution. For finding out this, you have to multiply the mass of solute by its molar mass conversion factor.

As an illustration, suppose you have mixed 25 g of NaCl (common salt) into 2 litres of water then first you have to determine the numbers of moles in 25 g of NaCl (Salt).

Besides, one mole of Sodium Chloride (NaCl) has a mass of approximately 58.5 grams. And it gives the conversion factor of 1 / 58.5.

Now multiply 25 g with 1 /58.5, which is same as dividing 25 / 58.5. This tells us that there are 0.427 moles of NaCl in the solution. Now you can use these numbers in the equations:

Molarity = moles of solute / litres of solution

Molarity = 0.427 / 2 = 0.214 M

Furthermore, the molarity factor is accurate to only three decimal places so we round off it to 3 decimal place.

Solved Question for You

Question. Mole is approximately equal to which of the following?

A. 12 gram of Carbon- 12

B. 14 gram of Carbon- 12

C. 10 gram of Carbon- 12

D. 15 gram of Carbon- 12

Answer. The correct answer is option A.

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