Percent Error

        Things to remember.

  1. Percent error is a comparison and is calculated with a simple formula.     

     %E = Observed - Accepted   X 100

    Accepted

  1. The accepted value is usual given or from literature.  The observed value is the value or measurement obtained in the lab.

Examples

1.  Accepted value  = 57.9 g/mole  

    Observed value = 59.6 g/mole

    %E = ((59.6 - 57.9)/57.9) X 100

            Answer: %E = 2.9%

 

  1. Accepted value = 217.9 ° C
Observed = 231.0° C
%E=((231.0 – 217.9)/217.9) X 100
Answer: %E = 6.0%

Density

    Things to Remember

  1. Density can be calculated with a formula.

    2. Mass

    Density = Volume

  2. This formula can also be changed in order to find the volume or mass of an object.

Examples

  1. Mass = 9.38 g

    2. Volume = .750 cm3

    Density = 9.38 g/.750 cm3

    Answer: Density = 12.50 g/cm3

  2. Mass = 9.38 g

    3. Density = 2.65 g/cm3

    2.65 g/cm3 = 9.38 g/volume Cross multiple and then divide.

    Volume = 9.38 g/2.65 g/cm3

    Answer: Volume = 3.54 cm3

  3. Volume = 965 cm3
Density = 10.5 g/cm3
10.5 g/cm3 = mass/965 cm3 Cross multiple.
Mass = (10.5 g/cm3)(965 cm3)
Answer: Mass = 10132.5 g or 10.1 Kg

Accuracy and Precision

    Things to remember.

  1. Accuracy is how close a measurement comes to the accepted value.
  2. Precision is if a set of measurements are close together.

Examples

  1. . These five students are precise but not accurate. They are precise because all of their measurements are (close together) with .01 cm of each other. But they are not accurate because the accepted value is 15.55 cm and the student’s measurements were .21 - .22 cm short.

Significant Figures

    Things to remember

1.