Metric Measurement Scientist Mass Lab Class Date 2015 Objective: To use a triple-beam balance to these 3 together = 1 pt KEY a) to measure mass directly usually a SOLID b) to find mass by difference usually a LIQUID c) to measure out a substance usually a POWDER When asked, label this diagram: these 4 together = 1 pt 1 = PAN 2 = RIDERS 3 = BEAMS 4 = POINTER 5. In what amount does the middle beam measure? 100 s these 4 together = 1 pt 6. In what amount does the back beam measure? 10 s 7. In what amount does the front beam measure? 1 s 8. Your measurements should always be recorded to what unit? GRAMS PART A: Measuring Mass Directly. Read and follow the directions for Part A on your laminated Mass Lab directions sheet first column = 2 pts; second column = 2 pts Data Table 1 remember, if you label the table, you don t need to write units after every value! Object Mass (_g_) Part D Mass (_g ) Large Paper clip Your answers should be ~ 3.4 close. There were a Rubber Stopper couple of different kinds ~ 4.9 Magnifier of stoppers though ~ 107.7 First Copy of Book, book # ~ 572.4 (±10g) Second Copy of Book, book # Close to Book A If you don t have units for all the Data Tables, -1 pt.; missing 2 = -1/2 pt. Also, if your part A and Part D answers are close, that s good for credit too!
9. Which rider on the balance should always be moved first when finding the mass of an object? 100 s 10. What would be the mass of the largest object your balance is able to measure? 610.0g 11. What would be the mass of the smallest object your balance is able to measure? 0.1g 12. After using your balance, how should it always be left? _all riders on zero / zeroed PART B: Finding Mass by Difference. Read and follow the directions for Part B on your laminated Mass Lab directions sheet Data Table 2 = 1 pt these 4 together = 1 pt Mass of Empty Beaker (_g ) If you don t have units for all the Data Tables, -1 pt.; missing 2 = -1/2 Mass of Beaker with 50 ml of Water (_g _) should be ~50g more than mass of empty beaker pt. 13. Sketch the steps you used with the triple beam balance and graduated cylinder to find the mass of 50 ml of water. Include any other equipment you used as well. Sketches = 3 pts Analysis 14. Use Data Table 2 and calculate the mass of 50 ml of water in the space below Subtract (mass of beaker and water) from (mass of beaker) = mass of 50 ml of water Answer: should be 50 g; are you close?
Critical Thinking and Application 15. Use your answer from #14 to calculate the mass of 1 ml of water in the space below. Divide mass of 50 ml of water by 50 = mass of 1 ml of water. Answer: should be 1.0g; are you close? 16. The metric system was designed so that the mass of 1 ml of water is 1g. Did you get that answer? yes or no If you answered yes, good for you! However, many students will probably NOT get the exact answer. Why do you think that is? What are some possible sources of error here? Possible sources of error : 2 pts The accuracy of the triple beam balance and the skill of the students using it. The accuracy of measuring 50 ml of water with the graduated cylinder Any other reasonable answers Part C: Measuring Out a Substance. Read and follow Part C on your laminated Mass Lab directions sheet. Data Table 3 pt. Mass of Mass Boat (_g ) around 2g Mass of Mass Boat and Salt (_g _) should be 5g more than mass of boat alone 17. Describe how you could find the mass of a certain quantity of milk that you poured into a drinking glass. NOTE: The milk is already in the glass, so you cannot exactly replicate the process you used above! If you include a cookie, it might help you figure this out Since the milk is already in the glass, find the mass of the glass and the milk together. Drink the milk (maybe eat a couple of cookies, too?) Find the mass of the empty glass. Subtract to find the mass of the milk you just drank! #17 = 2 pts If you don t have units for all the Data Tables, -1 pt.; missing 2 = -1/2
18. If you were baking a cake and the recipe called for 250 g of sugar, how would you use the triple-beam balance to obtain this amount? #18 = 2 pts Find the mass of a mass boat. Add 250 to that amount and move the riders to that value. Add sugar to the mass boat until the balance is zeroed. Viola! 250g of sugar! Part D: Experiment and Evaluate: Do one of the following: (circle which you and your partner choose) 1) Use the same balance and measure the objects in a different tote tray 2) Use a different balance and measure the objects in your tote tray. Record your data in the last column of Data Table 1 19. Did you get the same values as you did in Part A? (probably not) Check with several other groups. Did it matter if they chose 1 or 2? Why do you think you all measured the same objects but got different results? #19 = 2 pts Answers need to have at least 2 different reasons. Some possible reasons are listed. Other reasonable explanations are acceptable as well. Different people using the balance Different balances Moving the balances or not zeroing balance correctly Even though it is the same object, such as a paper clip, not every single paper clip will have the same mass there are slight differences between even similar objects b. What do you think: How close is close enough to be correct? #19b = 2 pts Reasonable answers are acceptable. Answers need to show thought and understanding. A short sentence is not enough. Here are some things that answers can include: The balances are accurate to 0.1g so we could be very accurate. The variation in the masses of any one object (like 2 stoppers) could make it hard to have answers that are precise. However,
it would not be expected for 2 paper clips to have masses that are 10g apart! The percent error would be huge! Close enough also depends on the size of the object being massed. The masses of smaller objects need to be closer to one another than the masses of larger objects. You have a little more room for error with larger objects. For example, being off by 0.5g on something with a mass of 290.0g is not the same as being 0.5g off on something with a mass of 2.9g. If answers show knowledge and understanding of % error, accuracy and precision, give +0.5 pts. extra credit! 20. CREATE: You work for a publisher who has to ship several thousand copies of the same book. You have found out in this lab that almost every individual item, even of the same kind of thing, has a different mass. But you have to use the mass of the books to calculate shipping costs. You don t want to pay too much for shipping; nor can you underpay the shipping company, so it is important to know the mass of the books you need to ship. You also don t want to find the mass of every single book! What process should you use to figure out the shipping cost? #20 = 2 pts Find the mass of 10 or 20 books and calculate their average mass to get a value for the mass of an average book. Use that value to calculate shipping costs it will be close enough!