In this topic of IBDP Chemistry, we will be learning about the concept of moles in chemistry, Avodagro's Constant and calculations involving Avogadro's Constant.

**Moles and Avogadro's Constant**

In IBDP Chemistry, the world '**mole'** is a term to describe a number. Like length is measured in metres, the amount of chemicals is measured in moles. If someone say that they have the same amount of two chemicals, they mean that they have the same number of moles.

The use of the word 'mole' is parallel to the word 'dozen'. The word 'dozen' represents the number 12. Similarly, the word 'mole' represents the number **6.02 x 10**^{23}. This number is also known as **Avogadro's Constant**, and is an extremely important number in chemistry.

In IBDP Chemistry, you are expected to be able to use Avogadro's constant to perform calculations. These types of calculations include:

- Determining the number of moles of an element when given the number of atoms.
- e.g. If I have 18.06 x 10
^{23}atoms of an element, how many moles do I have? - Determining the number of atoms of an element when given the number of moles.
- e.g. If I have 2 moles of an element, how many atoms of the element do I have?

In order to perform these calculations, you will need to know how to convert between the number of particles and the quantities in moles.

- Avogadro's constant gives us the number of particles in a mole - i.e. there are 6.02 x 10
^{23}particles in a mole. - Thus,

You can substitute the given values into the above equation, and solve for the unknown value in order to determine the number of particles or the number of moles.

**Examples of Calculations involving Avogadro's Constant**

In IBDP Chemistry, you will be expected to be able to calculate the number of moles or the number of particles using avogadro's constant. Below are some examples of calculations which you will be expected to know how to do.

- You have 3.01 x 10
^{22 }atoms of carbon. How many moles is this? - In this question, you are given the number of particles (3.01 x 10
^{22}), and you know Avogadro's Constant (6.02 x 10^{23}). Simply substitute and solve for the number of moles.

- You have 6.02 x 10
^{24}molecules of water (H_{2}O). How many moles of hydrogen are present? - This question is a little more complex than the one above, since it tells you the number of molecules of water present, instead of the number of hydrogen particles.
- You will first need to figure out the number of hydrogen particles from the number of water molecules.
- In each molecule of water, there are two hydrogen particles and one oxygen particle. Thus, given that you have 6.02 x 10
^{24}molecules of water, this means you have twice the amount of hydrogen particles (i.e. you have 2 x 6.02 x 10^{24}= 12.04 x 10^{24 }hydrogen particles). - Thus,

- How many atoms of fluorine are there in 2.5 moles of tetrafluoromethane (CF
_{4})? - For this question, instead of figuring out the number of moles, you have to calculate the number of fluorine particles.
- In order to do so, you will need to know the number of moles of fluorine - this can be calculated from the information given.
- For every molecule of CF
_{4}, there are 4 fluorine atoms. So, if you are given 2.5 moles of CF_{4}, you will have 4 times the amount of fluorine atoms (i.e. you will have 4 x 2.5 = 10 moles of fluorine). - Thus,

With these questions, it is important to practice a lot. The more you practice, the easier they become. If you are looking for more practice or guidance with these questions, feel free to reach out and get in touch with our tutors!

This is the end of this topic.