When performing a laboratory experiment, it is important to determine how much product was produced. This can be done using calculations such as the mass determination and the percent yield. Based on the grams of product produced, it is possible to determine the number of moles produced. Calculating the moles of product is useful for determining experimental errors and writing laboratory conclusions. It is a process that can be done with simple mathematical operations and concepts.
Write out the chemical reaction for the experiment. Many times, this equation is provided within the lab manual; if it is not, write it out and balance it. For example, in the synthesis reaction of sodium and chlorine, the chemical equation is Na + Cl2, which gives you NaCl2.
Determine the mass of the product. When the experiment is completed, the mass is typically calculated by weighing the product with a gram balance. For example, the final mass of the product may be 202.0 grams of sodium chloride (NaCl2).
Determine the molar mass of the product. By looking up the molar masses of the elements of the product and adding them together, you can determine the molar mass of the product. For example, the molar mass for Na is 22.99 g. The molar mass for Cl is 35.45. In NaCl2, there are 2 moles of Cl, so multiply 35.45 by 2. This gives you 70.90 g. Adding 22.99 g and 70.90 g gives you a molar mass of 93.89 g/mol of NaCl2.
Use dimensional analysis to write the ratios for the mole calculation. In the first ratio, write 202.0 g NaCl2 over 1. In the second ration, write 1 mole of NaCl2 over 93.89 g of NaCl2.
Multiply both ratios together to determine the number of moles of product produced. The final answer should be 2.152 moles of NaCl2.
- Jack Hollingsworth/Photodisc/Getty Images