The number of moles (n) of a substance can be calculated using the following formula:

n = m / M

where:

• n = number of moles (mol)
• m = mass of the substance (grams, g)
• M = molar mass of the substance (grams per mole, g/mol)

Molar mass: The molar mass is essentially the weight of one mole of a substance. It’s like a unique identifier for each substance based on the atomic or molecular weights of its components. You can find molar masses on the periodic table or reference books.

Example

Let’s calculate the number of moles in 10 grams of sodium chloride (NaCl).

1. Find the molar mass of NaCl:
   • Look up the atomic masses of sodium (Na) and chlorine (Cl) on the periodic table:
     • Na = 22.99 g/mol
     • Cl = 35.45 g/mol
   • Add the atomic masses to find the molar mass of NaCl:
     • M (NaCl) = 22.99 g/mol (Na) + 35.45 g/mol (Cl) = 58.44 g/mol
2. Apply the formula:
   • n (NaCl) = 10 grams / 58.44 g/mol = 0.171 moles

Therefore, there are approximately 0.171 moles of sodium chloride in 10 grams of NaCl.