Stations Lab: Scientific Measurement

Transcription

1 Stations Lab: Scientific Measurement Introduction Every measurement has an uncertainty, or built-in error. This error is due to limitations in the measurement scale, the manufacturing process, and the ability of the human eye to detect small differences. For example, when measuring volume with a graduated cylinder, the width of the scale lines, variations in glass thickness, and slight changes in your angle of sight when reading the scale are just some of the factors that can cause uncertainty. Because of this uncertainty, no measurement made in science should be thought of as an exact value, but rather as a value within a range that varies with the uncertainty. Purpose To become familiar with the measurement scale of electronic balances, graduated cylinders, and rulers; to make several different kinds of measurements and compare the uncertainty between them. Equipment balances (0.1, 0.01, and 0.001) ball beaker (100 ml and 250 ml) Erlenmeyer flask (125 ml) graduated cylinder (10 ml and 100 ml) meter stick ruler SmartBoard w/projector Materials Chemistry textbook pre-1982 pennies silicon metal Safety Considerations Sometimes chemicals from previous labs still remain in glassware and on other lab equipment. Wash all lab equipment before performing this lab. Procedure Station A Length 1. Using a ruler, measure and record the length, width and height of a lab station in centimeters. Repeat this measurement with a meter stick and record. 2. Using a ruler, measure and record the length, width and height of a Chemistry textbook in centimeters. Repeat this measurement with a meter stick and record. 3. Using a ruler, measure and record the thickness of the pages of a Chemistry textbook (not the covers). Count and record the number of pages you measured. 4. Using a meter stick, measure and record the width, length and height of the Chemistry classroom in meters. Station B Mass 1. Obtain a piece of silicon metal that is small enough to fit inside a graduated cylinder. Weigh the piece once on each of the three balances and record the measurement for each balance. Save this piece for use at Station C. 2. Obtain a pre-1982 penny. Weigh it once on each of the three balances and record the measurement for each balance.

2 3. Obtain nineteen more pre-1982 pennies, for a total of twenty. Using a beaker, weigh them once on the 0.01 balance and record. Station C Volume 1. Obtain a pre-1982 penny. Using a ruler, measure and record the width and thickness of the penny. 2. Fill a 100-mL graduated cylinder with exactly 50-mL of tap water (be sure the bottom of the meniscus, or curve of the water, is exactly on the 50 ml line). Place the penny in the water and record the new volume. Dump out the water in the sink. 3. Repeat step 2 with 20 pennies and record. 4. Repeat step 2 with the small piece of silicon metal from Station B and record. 5. Fill a 100-mL beaker to the 50-mL line with tap water. Pour this water into your graduated cylinder and record. Dump out the water in the sink. 6. Repeat step 5 with a 250-mL beaker and a 125-mL Erlenmeyer flask. Station D Accuracy & Precision 1. At the SmartBoard, obtain a ball. Step back about ten feet and throw your ball at the center of the target on the board (you may want to have your partner retrieve the ball for you to speed up the process). DO NOT THROW THE BALL TOO HARD IT COULD DAMAGE THE SMARTBOARD. Repeat for a total of ten times, aiming at center of the target. Draw your target results in the data table below as X s. 2. Using the eraser, remove all the marks on the SmartBoard target. Repeat step 1, except instead of aiming for the center of the target, aim for the upper-right corner. After throwing the ball ten times, draw your target results in the data table below as O s. 3. Repeat step 2, except instead of aiming at a particular point in the target, throw the ball ten times with your eyes closed. Draw your target results in the data table below as s and erase the target before leaving. Additional Clean-up and Disposal 1. Dry the silicon metal and return it to its container 2. Dry the pennies and return them to their container. 3. Return the meter stick to the side table. Data Table A Length Measurement Length (cm) Width (cm) Height (cm) Lab station Lab station Textbook Textbook Room 207 Measurement Thickness (cm) # pages Book pages

3 Data Table B Mass Measurement 0.1 balance 0.01 balance balance Silicon One penny 20 pennies Data Table C Volume Measurement Width (cm) Thickness (cm) Volume (cm 3 or ml) One penny 20 pennies Silicon 100-mL beaker 250-mL beaker 125-mL flask Data Table D Accuracy & Precision

4 Calculations 1. Calculate the volume of your lab station using your ruler data. Repeat this calculation with your meter stick data. 2. Calculate the volume of your textbook using your ruler data. Repeat this calculation with your meter stick data. 3. Calculate the volume of the classroom using your meter stick data. 4. Using your textbook pages data, calculate the thickness of one page of your book. 5. Using the combined mass of twenty pennies, determine the average mass of one penny. Calculate the percent error of this average based on the accepted mass of pre-1982 pennies of 3.11 g. 6. Using the width and thickness of a penny, calculate its volume using the equation V = πr 2 t, where r is radius and t is thickness. Using the combined volume of twenty pennies, calculate the average volume of one penny. Calculate the percent error for these two values using the accepted volume of a pre-1982 penny of cm Using your mass and volume measurements of zinc, calculate its density. Calculate the percent error using the accepted density of silicon of g/cm 3.

5 8. Using your volume measurements for the beakers and flask, calculate the percent error for each compared with the accepted value of 50.0 ml. Questions for discussion 1. How different were the measurements made on the three balances? Which balance do you think would be the best to use in lab activities? Why? 2. The method of determining the volume of an object by submerging it in water is called volume displacement. Identify one advantage and one disadvantage for this method. 3. What did you find to be true about the accuracy of the markings on the sides of beakers and flasks? Errors Think of two possible errors you may have committed in this lab that may have somehow affected your results and record them below. Explain the specific steps you will take to avoid each of these errors in the future Conclusion Describe what you learned while doing this lab: