WATER, WATER EVERYWHERE… AND NOT A DROP TO DRINK
This lab is about precision and accuracy. Precision is defined as how closely
your data from a sample fit your averages. Accuracy, however, is how closely
your data fit the standard value (or the correct data).
Here is a good analogy. Let’s look at these dart boards below and assume
the thrower aiming for a bull’s-eye.
_____________ ______________ ______________ ______________
See, doesn’t that help?
In this lab, you must be very precise and very accurate. So, there are a
couple of things that you need to keep in mind. First, READ THE DIRECTIONS
CAREFULLY!! Second, transfer water carefully!! Third, NEVER TRUST EXACT
MEASUREMENTS TO LARGE CONTAINERS!!
Procedure:
0A. Start by collecting two graduated cylinders (label, somehow, one of them #1
and one of them #2 – don’t get them confused!!), one large beaker (450 mL), one
small beaker (250 mL), and one Erlenmeyer Flask, hereafter referred to as an E.
Flask. Also, grab an extra large beaker that is at least 450 mL large. This will be
used as your “junk” or “waste” beaker. Take all containers back to your work
area.
0B. From the tap, fill your junk beaker to about its maximum calibrated volume.
Take this back to your seats where you and your partner will be working.
1. Fill the graduated cylinder #1 with 5 ml of water. Fill graduated cylinder #2
with 55 ml of water. Fill the large beaker with 200 ml of water. Fill the small
beaker with 30 ml of water. Fill the E. Flask with 90 ml of water. Do this by
transferring the said amount from your junk beaker. Set your junk beaker aside.
2. Transfer 10 ml from graduated cylinder #2 to graduated cylinder #1.
3. Transfer 75 ml from the large beaker to the small beaker.
4. Remove 5 ml from graduated cylinder #1 and pour it into the E. Flask.
5. Transfer 60 ml to the large beaker. Do this by moving the water from the small
beaker.
6. You are going to remove 45 ml of water from the small beaker. Take 20 ml of
that 45 and put it in the E. Flask. Place the remaining 25 ml in the graduated
cylinder #1.
7. Remove 30 ml of water from the large beaker and dump it into the junk
beaker.
8. Add 75 ml of water to the large beaker by subtracting it from the E. Flask.
9. Fill graduated cylinder #1 to its maximum calibrated volume by transferring
water to it from the large beaker.
10. Add 10 ml of water to each container except for the graduated cylinder #1.
Take the 10 ml for each other container from graduated cylinder #1.
11. Add 20 ml of water to each container. Use the water in your junk beaker. If
your junk beaker does not contain enough water, add more water from the tap so
you do have enough.
12. Transfer 50 ml of water from graduated cylinder #2 to your large beaker.
13. Move 20 ml from the small beaker to graduated cylinder #1.
14. Take 10 ml from the large beaker. Move this 10 ml to the E. Flask.
15. You need to add 30 ml to the large beaker. Do this by taking this amount
from the graduated cylinder #1.
16. Transfer 100 ml from the large beaker to the small beaker.
17. Transfer 70 ml from the graduated cylinder #1 to the E. Flask.
18. Pour the entire contents of the large beaker into the graduated cylinder #1.
19. From the small beaker, transfer 75 ml to the graduated cylinder #2 and 105
ml to the large beaker.
20. Now, add 50 ml of water to the small beaker by transferring it from the E.
Flask.
21. Remove 30 ml of water from both of the large beaker and the E. Flask. This
water goes into the junk beaker.
22. You will be moving a total of 60 ml of water from the large beaker. 10 ml of it
will go into the graduated cylinder #1 and 50 ml of it will go into graduated
cylinder #2.
23. Transfer 30 ml from graduated cylinder #1 to the E. Flask.
24. Move 15 ml of water from the graduated cylinder #2 to the large beaker.
25. Add 155 ml of water to the large beaker. Take 50 of this 155 from the small
beaker and the remaining 105 from the E. Flask.
26. 13 ml of water needs to be moved from the graduated cylinder #1 to the E.
Flask and 16 ml of water needs to be transferred from the graduated cylinder #2
to the small beaker.
27. Transfer 60 ml from graduated cylinder #2 to the E. Flask.
28. Add 100 ml of water to the large beaker. Get this from either your junk
beaker or the tap.
29. Transfer only 5 ml of water from the graduated cylinder #2 to the large
beaker.
30. Minus 60 ml from the large beaker and add 60 ml to the small beaker.
31. DO YOU REMEMBER ME SUGGESTING THAT YOU SHOULD NEVER TRUST
EXACT MEASUREMENTS TO LARGE SCALE CONTAINERS???!? …
Exactly, how many milliliters of water do you have in each of your
containers?
_______
GC#1
_______
GC#2
_______
LB
Show your teacher your answers if you are confident…
Score #1:
Max = 30/30
Score #2:
Max = 25/30
Score #3:
Max = 22/30
Score #4:
Max = 19/30
________/________ +/- 2 ml
________/________ +/- 4 ml
________/________ +/- 6 ml
________/________ +/- 10 ml
_______
SB
_______
E.Flask