PreLab Questions
2. a) Andrea’s balance is more precise than Andrew’s. b) Brian’s balance is more accurate than Brenda’s.
What important characteristics of the four balances are implied by these statements? Give examples.
Andrea will be able to read her balance to a greater number of significant figures than Andrew since her balance is more precise. Her successive measurements will also be less variable than Andrew’s measurements.
Ex. If three measurements are taken by Andrea (1.7 mL, 1.7 mL and 1.8 mL) we know that her spread in measured values will be small and, thus, the average measurement will be more precise than Andrew.
Brian will be able to be closer to the true value that he is measuring than Brenda since his balance is more accurate than hers.
Ex.: If the true measurement is 2.1 mL, Brian will be able to state that his measurement is 2.1 mL where Brenda may only be able to state that her measurement is 2 mL.
3. For Part C, does it matter if you use a different balance for some of the five weighings? Give your reasoning. How would you use the tare option in these weighings?
Yes, it matters. I should use the same balance for all of the five weighings so I know that my baseline data is the same for each weighing (the balances could be slightly off and skew my numbers). I could use the tare option in these weighings (i.e. subtract the weight of the empty graduated cylinder from the gross weight to determine the weight of the water). Using the tare weight would account for any discrepancies in the weight of different graduated cylinders.
4. a) In Part B, you are instructed to deliver “about 2 mL” of water from a buret “with a precision of 0.01 mL.” Which of the following quoted volumes is/are consistent with these instructions?
1.87 mL it follows instructions for precision, but not necessarily for accuracy
1.999 mL this does not use the number of significant digits we are supposed to use (3 sd would be 1.99 mL)
2.03 mL it
What important characteristics of the four balances are implied by these statements? Give examples.
Andrea will be able to read her balance to a greater number of significant figures than Andrew since her balance is more precise. Her successive measurements will also be less variable than Andrew’s measurements.
Ex. If three measurements are taken by Andrea (1.7 mL, 1.7 mL and 1.8 mL) we know that her spread in measured values will be small and, thus, the average measurement will be more precise than Andrew.
Brian will be able to be closer to the true value that he is measuring than Brenda since his balance is more accurate than hers.
Ex.: If the true measurement is 2.1 mL, Brian will be able to state that his measurement is 2.1 mL where Brenda may only be able to state that her measurement is 2 mL.
3. For Part C, does it matter if you use a different balance for some of the five weighings? Give your reasoning. How would you use the tare option in these weighings?
Yes, it matters. I should use the same balance for all of the five weighings so I know that my baseline data is the same for each weighing (the balances could be slightly off and skew my numbers). I could use the tare option in these weighings (i.e. subtract the weight of the empty graduated cylinder from the gross weight to determine the weight of the water). Using the tare weight would account for any discrepancies in the weight of different graduated cylinders.
4. a) In Part B, you are instructed to deliver “about 2 mL” of water from a buret “with a precision of 0.01 mL.” Which of the following quoted volumes is/are consistent with these instructions?
1.87 mL it follows instructions for precision, but not necessarily for accuracy
1.999 mL this does not use the number of significant digits we are supposed to use (3 sd would be 1.99 mL)
2.03 mL it