Unit 2 Unit 2 Percent Error We know that measurements can be described in terms of precision (how close a group of measurements are to each other) and accuracy (how close a measurement to the accepted value). A way to represent the accuracy of a measurement is to calculate the percent error. The percent that a measured value differs from the accepted value is called the percent error.

Percent Error Accepted Value (also known as theoretical value) - a quantity used by general agreement of the scientific community - “what you are supposed to get” Experimental Value (also known as the actual value) - a quantitative value measured during an experiment - “what you got”

Percent Error Error = the difference between the accepted value and the experimental value Percent Error = the percent that a measured value differs from an accepted value % Error = Experimental Value – Accepted Value x 100 Accepted Value OR % Error = (What you got) – (What you were supposed to get) x 100 (What you were supposed to get)

Percent Error Practice 1.The boiling point of water is 100°C. During an experiment, water came to a boil at 97°C according to the thermometer that was being used. What is the percent error of the thermometer? 2.An experiment was performed to determine the density of water. The results of the experiment showed that water had a density of 1.15 g/mL. What was the percent error in this experiment?

Percent Error Practice 3. An experiment was conducted to find the mass of one mole of carbon atoms. The results of the experiment showed that a mole of carbon atoms had a mass of g. The accepted value of a mole of carbon atoms is grams. What is the percent error in this experiment? 4. An experiment performed to determine the density of lead yields a value of g/cm 3. The accepted value for the density of lead is g/cm 3. Find the percent error.