November 18, 2010: Mole Conversions

Converting Between Moles and Mass:
- To convert between moles and mass we use molar mass as the conversion factor
- Be sure to cancel the appropriate units.
Example 1: How many grams are there in 1.5 mol of H2?

Step 1: 1.5 mol. x [(2(1.0 g.)) / (1 mol.)] = ?
Step 2: 1.5 mol. x [(2 g.) / (1 mol.)] = ?
Step 3: 1.5 mol. x [(2 g.) / (1 mol.)] = 3 g.

There are 3 grams of H2 in 1.5 moles.

Example 2: A sample of HCl contains 0.72 mol. How many grams of HCl are there?

Step 1: 0.72 mol. x [(1(1.0 g.)) / (1 mol.)] = ?
Step 2: 0.72 mol. x [(35.5 g.) / (1 mol..)] = ?
Step 3: 0.72 mol. x [(35.5 g.) / (1 mol.)] = 26 g.

There are 26 grams of HCL in 0.72 mol.

Example 3: How many moles are there in 110 grams of Fe2O3?

Step 1: 110 g. x [(1 mol.) / (2(55.8 g.) + 3(16.0 g.)] = ?
Step 2: 110 g. x [(1 mol.) / (159.6 g.)] = ?
Step 3: 110 g. x [(1 mol.) / (159.6 g.)] = 0.689 mol.

In 110 grams of Fe2O3 there is 0.689 mol.