Mole concept and easy method to calculate number of moles. Firstly, let me teach you the concept of relative masses and molar masses. For example, consider a single carbon atom. We know that its relative atomic mass is 12 amu. Secondly, consider a single oxygen atom.
We know that its relative atomic mass is 16 amu. Thirdly, consider a single nitrogen atom. We know that its relative We know that its relative atomic mass is 14 amu.
Remember that we cannot see, touch or do chemistry with relative masses because they are very very small. For example, I cannot touch and see one atom of carbon or 12 amu of a carbon atom. Now, to solve this issue, scientists put forward the concept of molar masses. Now, instead of 12 amu, I take 12 gm of carbon atom. We can see that in 12 amu of carbon, there is only one atom of carbon.
While in 12 gm of carbon, there are 6.023 x 10 to the power 23 atoms of carbon are present. Similarly, instead of 16 amu of oxygen, we take 16 gm of oxygen. And there are 6.023 x 10 to the power 23 atoms of oxygen are present in 16 gm.
Also, instead of 14 amu of nitrogen, we take 14 gm of nitrogen. And there are 6.023 x 10 to the power 23 atoms of nitrogen are present in 14 gm of nitrogen. Remember that now we can see, touch and do chemistry with 12 grams of carbon.
Thus 12 amu, 16 amu and 14 amu are relative atomic masses while 12 grams, 16 grams and 14 grams are molar masses or gram atomic masses. Therefore, note it down that to study mole concept, we do not consider relative masses. We always play with molar masses.
Here let me clear the biggest confusion of students. How 12 gram of carbon or 16 gram of oxygen or 14 gram of nitrogen is equal to 6.023 and to 10 to the power 23 atoms? Well, if I ask you to give me one dozen pencils, how many pencil will you give me?
If I again ask you to give me one dozen eggs, how many eggs will you give me? Well, you will definitely say 12 pencils. and 12 eggs.
Because you know that one dozen pencil is equal to 12 pencils and one dozen eggs is equal to 12 eggs. So we can write that one dozen of anything is equal to 12 items. Similarly, molar mass of any atom is equal to 6.023 x 10 to the power 23 atoms.
Just like 12. 6.023 1023 is a simple number, which is commonly known as Avogadro's number. Now listen carefully, one mole of any atom is equal to its molar mass. Let me repeat this important statement. One mole of any atom is equal to its molar mass. For example, one mole of carbon atom is equal to 12 gram, one mole of oxygen atom is equal to 16 gram and one mole of nitrogen is equal to 14 gram.
So if I ask you, give me one mole of carbon. How many grams of carbon will you give me? I hope you know the answer.
You will definitely give me 12 grams of carbon because the molar mass of carbon is 12 gram. If I again ask you that, how many atoms of carbon are there in 1 mole of carbon? Your answer is simple.
There are 6.023 x 10 to the power 23 atoms of carbon are there and this 1 mole are 12 grams of carbon. Thus, in one mole of carbon, there are 12 gm of carbon atoms or there are 6.023 x 10 to the power 23 number of atoms are present. It means we have to modify this definition of a mole. One mole is equal to molar mass or one mole of any substance contains 6.023 x 10 to the power 23 particles.
Here particles mean atoms, molecules are ions. If you are still confused, let me further explain it. Consider 1 kg potatoes. If I ask you how many potatoes are there in 1 kg? Well, you can count it and your answer is 6 potatoes.
1 kg is the mass of potatoes and in 1 kg there are 6 potatoes are present. And we can see that 6 is the simple number of potatoes. Similarly, 1 mol is the molar mass of any atom like 12 gm of carbon and in 1 mol there are 6.023 and 10 to the power 23 atoms are present. So 6.023 and 10 to the power 23 is a number just like a 6. To summarize the mol concept, we can say that 1 mol of carbon atom is equal to 12 gm. Secondly, In one mole of carbon, there are 6.023 x 10 to the power 23 atoms of carbon are present.
So, we say that this is mass m relationship and this is number n relationship. Secondly, 1 mole of oxygen atom is equal to 16 gms. This is m relationship.
1 mole of oxygen atom contains 6.023 x 10 to the power 23 atoms of oxygen. This is n relationship. Thirdly, 1 mole of nitrogen atom is equal to 14 gms. This is m relationship.
In one mole of nitrogen atom, there are 6.023 x 10 to the power 23 atoms of nitrogen. This is n-relationship. Now I will use m-relationship and n-relationship to calculate any mole-based question without using any formula.
So note it down this relationship. For example, calculate the number of moles in 32 gram of oxygen atom, 16 gram of carbon atom. and 4 gram of hydrogen atom. And the question, we are given masses of the different atoms so in this type of numericals always write m relationship of moles.
We know that 1 mole of oxygen is equal to 16 grams. Just like this relationship, we can say that let x moles are there and 32 grams. Cross multiply them.
I get 16 into x is equal to 32 into 1. Dividing both sides by 16, I get x is equal to 2 moles. So there are 2 moles of oxygen atom are present and 32 gram. Secondly, in case of carbon, 1 mole of carbon atom is equal to 12 grams.
Let x moles are there and 6 gram of carbon. Now cross multiply them. I get 12 x is equal to 6 x 1. Dividing both sides by 12, I get x is equal to 0.5 moles.
So there are 0.5 moles are present in 6 gm of carbon. Thirdly, in case of hydrogen, 1 mole of hydrogen is equal to 1 gm. Let x moles are there in 4 gm of hydrogen.
Now cross multiply them. I get x is equal to 4. So, there are 4 moles of hydrogen are present in 4 gram. Therefore, in such type of numericals, we use M-relationship to calculate the number of moles.
Also, let me teach you the second type of calculation. Calculate the number of moles in 12 x 10 to the power 23 atoms of oxygen and in 18 x 10 to the power 23 atoms of carbon. Find the question, we are given number of atoms. So, we have to create n relationship of moles in such type of numericals. Now in case of oxygen, we say that one mole of oxygen atom contains 6 x 10 to the power 23 atoms.
Note it down that I use 6 x 10 to the power 23 not 6.023 x 10 to the power 23 just for easy calculation. Create an x mole. There are 12 x 10 to the power 23 atoms of carbon are present. Now cross multiply them.
I get 6 x 10 to the power 23 x is equal to 12 x 10 to the power 23 x 1. Dividing both sides by 6 x 10 to the power 23, I get 2 moles. So there are 2 moles of oxygen are present and 12 x 10 to the power 23 atoms. Secondly, in case of carbon, one mole of carbon contains 6 into 10 to the power 23 atoms.
Let in x moles, there are 18 into 10 to the power 23 atoms of carbon are present. Now cross multiply them. I get 6 into 10 to the power 23 into x is equal to 18 into 10 to the power 23 into 1. Dividing both sides by 6 into 10 to the power 23. I get 3 moles.
So there are 3 moles of carbon are present and 18 x 10 to the power 23 atoms of carbon. Therefore, in such type of numericals always use the number and mole relationship to calculate the number of moles. Now, let me take you to the medium level. Calculate the number of moles in 28 gm of nitrogen atom, in 28 gm of nitrogen gas and in 49 gm of H2SO4. Now, in case of nitrogen atom, we know that 1 mole of nitrogen atom is equal to 14 gm.
So there are x moles present in 28 gm of nitrogen. After calculation, I get n is equal to 2 moles. So there are 2 moles present in 28 gram of nitrogen.
While in the case of nitrogen gas, we know that there are n2 molecules are present in the nitrogen gas. First of all, I need to find the molar mass of n2 molecules. I write n plus n are 14 plus 14 and I get 28 gram.
So, the molar mass of N2 molecules is 28 gms. Hence we say that 1 mole of nitrogen gas is equal to 28 gms. Let there are x moles present in 28 gms of nitrogen gas.
After calculation, I get 1 mole. Thus remember that in 28 gm of nitrogen atom, there are 2 moles present of nitrogen. While in 28 gm of nitrogen gas. There is only one mole of nitrogen gas is present. Thirdly, in the case of 49 gm of H2SO4, first of all, I need to find the molar mass of H2SO4.
I write 2H plus S plus 4O because there are two atoms of hydrogen, one atom of sulfur and four atoms of oxygen are present and H2SO4. The atomic mass of hydrogen is 1. That of sulfur is 32 and that of oxygen is 16. I get 2 into 1 plus 32 plus 4 into 16 or I get 98 g. So the molar mass of H2SO4 is 98 g.
Hence we say that 1 mole of H2SO4 is equal to 98 g. Let there are x moles of H2SO4 are present and 49 g. After calculation, I get 0.5 moles. So there are 0.5 moles are present in 49 gram of H2SO4.
I hope that you have understood the mole concept.