Lab 3
Reading a Meniscus

Meniscus and Parallax
Reading and Recording Volumes
We use significant figures to indicate the
accuracy and precision of glassware.
 Significant figures for graduated glassware
are determined differently from those of
non-graduated glassware.
 You will need to correctly apply the
following rules every time you read a
volume from glassware, or use a volume in
a calculation, in order to appropriately
incorporate the precision of the volume into
the calculation.

Significant Figures:
Volumetric Glassware
Use the tolerance table on p. 94 to determine
glassware tolerance, unless it is printed on the
glassware.
 For example:

 The 50 mL volumetric flask has a tolerance of ± 0.05
mL. Whenever you use your 50 mL volumetric flask,
you will always report two zeros after the decimal, i.e.
50.00 mL.
Volumetric Flask
When this volumetric flask
is filled to the calibration
mark, what volume should
be reported?
Volumetric Pipet
When this pipet is used to dispense solution, what volume should be
reported?
Volumetric Pipet
When this pipet is used to dispense solution, what volume should be
reported? And to which line should the pipet be filled?
Significant Figures:
Graduated Glassware
Look at the glassware in question.
 Find the smallest graduation.
 Report your volume to the closest 10% of the
smallest graduation.

Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Reading Graduated Glassware
Smallest Graduation
A. Calculate major graduation – major
graduation
 B. Determine the number of spaces
between two major graduations
 Smallest Graduation = A / B

Reading Graduated Cylinders
What volume should be reported?
Reading Graduated Cylinders
Smallest graduation: 0.2 mL
 10% value: 0.02 mL
 Volume to the closest 10% of the SG:
6.62 mL

Reading Graduated Cylinders
What volume should be reported?
Reading Graduated Cylinders
Smallest graduation: 5 mL
 10% value: 0.5 mL
 Volume to the closest 10% of the SG:
293.5 mL

Reading Graduated Cylinders
What volume should be reported?
Reading Graduated Cylinders
Smallest graduation: 0.5 mL
 10% value: 0.05 mL
 Volume to the closest 10% of the SG:
11.50 mL

Reading Burets
What volume should be reported?
Reading Burets
Smallest graduation: 0.1 mL
 10% value: 0.01 mL
 Volume to the closest 10% of the SG:
41.15 mL

Reading Burets
What volume should be reported?
Reading Burets
Smallest graduation: 0.1 mL
 10% value: 0.01 mL
 Volume to the closest 10% of the SG:
15.48 mL

Balances

All sample/solution preparation should be
performed at your station. Balances (and
related counter space) should be used for
weighing only!
Density

Mass of a substance per unit volume.
d
m
V
Units for today is g/mL.
 Density changes with changing temperature.
 As a result, volume changes (but mass
stays constant unless you spill).

Mathematical Treatment of Data
m
d
V
% Error =
m
V
d
(| exp erimental value  accepted value |)
accepted value
x 100%
Example of Volume Calculation
Dry mass of a 50 mL beaker:
49.2345g
 Exactly 10.00 mL of water is transferred from a 10 mL
graduated cylinder into a 50 mL beaker.
 Mass of the 50 mL beaker with 10.00 mL of water:
59.2201g
 Mass of 10 mL water:
9.9856g
 Volume read:
10.00 mL (why 2 digits of precision?)

Example of Volume Calculation



Water temperature:
21.2 ºC
Density at this temperature (p. 96):
0.9979513 g/mL
Volume Calculation:
V
m
9.9856 g

 10.006 mL
d
0.9979513 g / mL
% Error Calculation
Volume Read  Volume Calculated
%Error 
x 100%
Volume Calculated
10.00 mL  10.006 mL
%Error 
x 100%
10.006 mL
0.006 mL
%Error 
x 100%  0.06%
10.006 mL
Safety Concerns

Reagent:
 Food coloring

Health Considerations:
 Avoid contact with skin and eyes.
 Do not inhale vapor or spray.
 Do not ingest.
Lab 4 Reminder
Complete and submit your pre-lab questions
by the deadline.
 Study for the next quiz.
 Submit your Lab 3 Report at the start of next
week’s lab.

Use these rules for “Volume Read”
Graduated Glassware
Look at the glassware
Find the smallest
division (graduation)
Report volume to 10%
of the smallest division
Volumetric Glassware
Find the glassware
tolerance on the
glassware or in Table
3.1
Report as many zeros
after the decimal point
for your volume, as
digits after the decimal
in the tolerance