CALCULATIONS BASED ON FORMULAE

7.2 - Mole Concept

The scientific definition of a mole is as follows:

• 1 mole of ¹²C is exactly 12 grams.
  (in section 3.2 we learned that carbon-12 is a naturally occurring isotope of carbon)
  
• 1 mole of any substance contains 6.022 x 10²³ particles (rounded to 4 significant figures).

In the above definition, do you realize that when we talk about the mole,

• it has an equivalent mass (1 mole = 12 grams ¹²C)
• it is a counting unit, a quantitiy of things (1 mole of any substance contains 6.022 x 10²³ particles)

Why do we use the mole as a counting unit?

4 good reasons!

1. In chemistry, the particles that make up matter are very small (section 3.1). So, counting by the mole is convenient.
2. We need to scale up to see what we are working with.
3. We need to scale up to do laboratory work.
4. In chemistry, we count by weighing.
   
   

Section 8.1
Calculation of Mole of Units. Avogadro's Number (N) ..p189

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