This experiment is designed to give you an opportunity to collect an

1. This experiment is designed to give you an opportunity to
collect and analyze both gravimetric (mass) and volumetric
(volume) data. The data will be analyzed to discuss the
precision and accuracy of laboratory glassware. The first part of
this exercise involves the use of the top-loading (bench-top)
analytical balance and a
25-mL graduated cylinder
to reproducibly measure the mass of an assigned aliquot
(sample or portion) of water. Balances are frequently used
laboratory tools for measuring mass and it is important to be
thoroughly familiar with them. Be sure to read the procedures
carefully so you know what to do when you come to the
laboratory. The second part of the experiment is to use a 10-mL
volumetric pipet
to measure the aliquots of water while still using the top-
loading balance to measure the mass. The third part of this
exercise involves the use of a
graduated pipet
to measure varying amounts of water and correlating the
volume to mass (Density??).
Example Procedures
Use a 25-mL Graduated Cylinder to measure four 10.00 mL
aliquots of water into a 50-mL beaker.
Weigh the beaker empty and after each addition.
Repeat steps 1 and 2 using a 10-mL Volumetric Pipet instead of
the Graduated Cylinder.
Use a 10-mL Graduated Pipet to measure four aliquots of water
at 3, 5, 7, and 9 mL into a 50-mL beaker.

2. Weigh the beaker empty and after each addition.
Record the temperature of water, density of water, reference for
the density, and balance numbers.
Calculations and Questions (COPY/RE-WRITE and COMPLETE
in sequential order, the items in BLUE in your Notebook)
Data Given in "Excel for Expt 1 Measurements F21.xlsx" --
see above for file
PRECISION
of a measuring device relates to how consistently identical
measurements can be made. Consider your measurements of the
mass of 10.00 mL of water in Tables 1 and 2.
Standard Deviation
: Standard deviation is a statistical quantity used to give a range
within which the correct value for a measured quantity may be
found. The smaller the standard deviation, the more precise the
measurements and hopefully the more accurate. Standard
deviation values are expressed with the same number of decimal
places as the measured values and is calculated using the
following formula:
Where
xavg

3. is the mean (average) value,
xi
are the individual values and
n
is the number of measurements taken.
Calculate, using the formula above, the Standard Deviation of
the 4
masses
of water from the 25-mL graduated cylinder.
Show a sample set up for the calculation with your numbers
. Your answer should have the
same number of decimal places, and units, as your original data.
Also calculate the Standard Deviation for the 4 masses of water
from the 10-mL Volumetric pipet, but you do not need to show
the sample calculation.
Standard Deviation of the
masses of water
from the 25-mL grad. cyl: ________________
Standard Deviation of the
masses of water
from the 10-mL Vol. Pipet: _______________
Excel can also be used to do calculations. In the Excel
spreadsheet in the Experiment 1 module “
Excel for Expt 1 Measurements F21.xlsx
” notice that the calculations are now complete. If you click on
a cell, you can see the calculation formula in the Formula Bar.
Notice the Mass of Water was calculated using a subtraction
“=D9-C9”, whereas the average was calculated using
“=AVERAGE(E9:E12)”. You can display different number of
decimal places by formatting the cell. Also notice the Standard
Deviation was calculated using “=STDEV.S(E9:E12)” which is
the Sample Standard Deviation of the four aliquots of water and

4. should match your answer to 1 above.
Which device (cylinder or pipet) is more
precise
for you? _____________________.
Generally, the Standard Deviation will start to show uncertainty
(imprecision) in the same decimal place as the
least precise measurement
linked to the data. Even the best chemists would have Standard
Deviations of 0.10 to 0.50 g using the graduated cylinder and
0.01 g to 0.05 g using the Volumetric pipet.
Since the balance is very precise, what is the major difference
between the two volumetric devices that makes the pipet
approximately ten times more precise? Briefly explain why.
ACCURACY
relates to how closely a measurement compares to an accepted
standard.
Using only the
average mass for your aliquots of water
, and
the density of water (see spreadsheet)
at your temperature,
calculate the average
volume
of water
. (show one calculation with units)

5. Average
volume
of water using 25-mL Grad. Cyl.:_______________
Average
volume
of water using 10-mL Vol. Pipet:_______________
(Note: These are truly the volumes you measured!!! These are
“Accepted” values)
Percent Error (always positive) is a measure of accuracy and
can be calculated using the equation below. The 10.00 mL
readings from the devices
would have been your
experimental
volumes recorded
, but the true volume of water was determined from the mass of
water (above).
Use
your answer above in 2 as the
Accepted Volume
, and use
10.00 mL (average volume

6. reading)
as your
Experimental Volume
to calculate the Percent Error. (Show one sample calc)
????????????????????????????????????????????????=|?????????
???????−????????????????????????????????|??????????????????
??????????????????100%PercentError=|Expt−Accepted|Accepte
dx100%
% Error for 25-mL Grad.Cyl.
=___________________________
High or Low?
(High means the Experimental value is Higher than the
Accepted)
% Error for 10-mL Vol.Pipet =___________________________
High or Low?
Which Device is more
Accurate
for you
dispensing 10.00 mL of water? _______________
What does “TC” on a graduated cylinder mean?
___________________________
What does “TD” on a Volumetric pipet mean?

7. _____________________________
Knowing the Graduated Cylinder is a TC device, would you
expect a Percent Error for the graduated cylinder to be High or
Low? Briefly explain. (High/Low does not mean Big/Small)
The Excel file also generated a new Table #4 which shows the
mass and volume data for the 0, 3, 5, 7, and 9 mL of Water
aliquots. Use Excel to make a graph of the data obtained from
the 10-mL
Graduated
Pipet
(Table 4). There is a handout/screen recording on Canvas that
briefly explains how to use Excel to make a graph. Put the
Volume of Water as the x-axis (the independent variable) and
the Mass of Water as the y-axis (the dependent variable). Note
that we have a (0,0) data point since you weighed the empty
beaker correlating to zero mL.
Use the “Insert Trendline” option to show the best straight line
through the data points
. Select the option to show the equation of the line and the R-
squared value on the chart.
Save the Excel file with the spreadsheet and labeled
full size, landscape
graph (with title and axis labels). Print a copy of the
spreadsheet and graph and staple into your notebook. Again,
this should be on the left-hand page opposite the data section. .
What are the units for the slope? __________
What Physical Property of Water does the value for the slope

8. actually represent? _________________________________