Using Measurements Worksheet
Transcription
Using Measurements Worksheet
Name_____________________________________ Period _____ Date _________ ACCURACY & PRECISION Idea 1: Measurements (3.25 cm) are different than other numbers (3.14159265). Measurements represent an action by someone with some measuring instrument. Measurements have built-in uncertainty; no measurement is exact. Measurements have units. Idea 2: The uncertainty in a measurement needs to be communicated. Definitions: 1. accuracy – how close a measurement is to _______________________________ 2. precision of measurement – ___________________________________________ 3. precision of instrument - _____________________________________________ Precision Problems: Several lab groups measure the density of aluminum. Here is their data: Team 1 Team 2 3 2.65 g/cm Team 3 3 2.75 g/cm Team 4 3 2.80 g/cm Team 5 3 2.77 g/cm Team 6 3 2.60 g/cm Team 7 3 2.65 g/cm 2.68 g/cm3 4. What is the average density? ________g/cm3 5. Subtract the highest value from the lowest value: _________ This is the range of values. 6. Divide the range number by 2: _______ 7. The precision of the measurement can be shown as _____________ g/cm3. 8. Here is more data. Is this more precise, less precise, or the same precision as the above data? ____________ Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Team 7 2.60 g/cm3 2.70 g/cm3 2.80 g/cm3 2.75 g/cm3 2.65 g/cm3 2.62 g/cm3 2.78 g/cm3 9. Each of five students used the same ruler to measure the length of the same pencil. These data resulted: 15.33 cm, 15.34 cm, 15.33 cm, 15.33 cm, 15.34 cm. The actual length of the pencil was 15.85 cm. Describe whether accuracy and precision are each good or poor for these measurements. Make measurements use the pictures on the right. Show the correct number of significant figures. 10. ________________ Temperature in oC (close up of thermometer) 11. ________________ Volume in mL (graduated cylinder) 12. ________________ Length of line in cm (ruler) Use the following information to answer questions 13 to 17. A chemistry student wants to measure the mass of a test tube he is planning to use in lab. There are two balances in the room - Balance A and Balance B. Balance A is marked to the nearest 0.1 g and Balance B is marked to the nearest 0.01 g. 13. Which balance is the more precise instrument? The student recorded the following data: Balance A Balance B Trial 1 3.12 g 3.431 g Trial 2 3.17 g 3.552 g Trial 3 3.13 g 3.348 g 14. Average 15. Range 16. Which balance had the most precise measurements? 17. If the true mass of the test tube is 3.14 g, which balance was the most accurate? 18. ________________ Volume in mL delivered from a buret. Final volume - initial volume = volume delivered.