Download UNIT 2.3 • Data Analysis ACCURACY & PRECISION Idea 1 and more Schemes and Mind Maps Chemistry in PDF only on Docsity! CHEMISTRY NOTES – DATA AND MEASUREMENTS UNIT 2.3 • Data Analysis A C C U R A C Y & P R E C I S I O N Idea 1: Measurements (3.25 cm) ___________________________________________ numbers (3.14159265). Measurements represent an action by someone with ______________________________ Measurements have built-in uncertainty; no measurement ______________________ Measurements have ____________________ Idea 2: The uncertainty in a measurement needs to be communicated. Definitions: accuracy – how close a measurement is to _______________________________ precision – how close a measurement is to _______________________________ Precision versus Accuracy: Look at each target below and decide whether the situation is accurate, precise, both, or neither: (Note: it is “accepted” that the bull’s eye is the place everyone aims for.) Accurate?: Yes / No Precise?: Yes / No Accurate?: Yes / No Precise?: Yes / No Accurate?: Yes / No Precise?: Yes / No _________________________________ measures Precision ___________________________________ measures Accuracy Error range = Average ± range of values Precision Problems: Several lab groups measure the density of aluminum. Here is their data: Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Team 7 2.65 g/cm3 2.75 g/cm3 2.80 g/cm3 2.77 g/cm3 2.60 g/cm3 2.65 g/cm3 2.68 g/cm3 What is the average density? ________g/cm3 Subtract the highest value from the lowest value: _________ Divide this number by 2: _______ The precision of the measurement can be shown as ________±_____ g/cm3. This is called __________ CHEMISTRY NOTES – DATA AND MEASUREMENTS Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Team 7 2.65 g/cm 3 2.73 g/cm 3 2.71 g/cm 3 2.74 g/cm 3 2.65 g/cm 3 2.64 g/cm 3 2.78 g/cm 3 Find the error range for the new samples above. Is this more precise, less precise, or the same precision as the previous set of data? Accuracy Problems: % error = actual value experimental value actual value − x 100 1. Working in the laboratory, a student find the density of a piece of pure aluminum to be 2.85 g/cm3. The accepted value for the density of aluminum is 2.699 g/cm3. What is the student's percent error? 2. A student experimentally determines the specific heat of water to be 4.29 J/g x Co. He then looks up the specific heat of water on a reference table and finds that it is 4.18 J/g x Co. What is the percent error? 3. A student takes an object with an accepted mass of 200.00 grams and masses it on her own balance. She records the mass of the object as 196.5 g. What is her percent error? 4. Often, with accuracy we are concentrating on one measurement. However, we can also look at a collection of measurements and simply take the average. Does this target represent someone who is accurate? _____ Precise? ____
