Common Stoichiometry / Formula Stoichiometry

Stoichiometric calculations relate the quantities and quantities of chemical elements.

The concept of mol is widely used in these calculations. It is very important to know how to turn the gram unit into mol. You can use the following formula:

n = mol number (amount of matter)
m = mass in grams
MM = molar mass (g / mol)


How many grams are in 2 mol of CO2?


This calculation can also be done by rule of three:

For calculations with a rule of three, we must always place the equal units one below the other, as in the example above.

See other examples of stoichiometric calculations involving only the chemical formula:

  • How many moles are there in 90g H2O?

90 = 18. x

5 mol = x

  • How many water molecules are there in 3 moles of H2O?

x = 3. 6.02.1023
x = 18.06. 1023 or 1,806.1024 molecules

  • What is the volume occupied by 4 moles of gas Cl2 on CNTP?

x = 4 x 22.4
x = 89.6L

  • 4) How many moles are there in 89.6L of CO gas2 on CNTP?

x = 4 mol