1. Percent Difference Calculations How do experimentally determined values compare to actual values?

2. Covered in this lesson This lesson will demonstrate how to compare a calculated density from an experiment to the "actual" density reported in reference sources. Comparing the actual or theoretical density to a density determined by an experiment (experimental density) involves a percent formula.

3. Percent Error Percent error or percent difference calculations use the following formula. %error = theoretical value – experimental value X 100 theoretical value Where the theoretical value is looked up in a resource book. The answer is positive, an absolute value.

4. Example In a lab a piece of aluminum was found to have an experimental density of 2.86 g/mL. According to the Mineralogy Database the density of aluminum is 2.72 g/mL. Find the % error (http://webmineral.com)http://webmineral.com

5. Percent Error of Aluminum Experimental value 2.86 g/mL Theoretical value 2.72 g/mL %error = theoretical – experimental X 100 theoretical % error = 2.72 g/mL – 2.86 g/m = 5.15% 2.72 g/mL

6. Practice Problems 1.The experimental value of gold was found to be 11.9 g/mL and the theoretical value is 19.3 g/mL. What is the percent error? 1.In an experiment the density of iron was found to be 8.75 g/mL. If theoretical value is 8.71g/mL, what is the percent error? (http://webmineral.com)http://webmineral.com

7. Answers Practice Problems 1.% error = 38.3% (is this really gold) 2.% error = 0.459%