Transcript Volumetric Glassware - University of Alaska Anchorage

Volume Determination
and Density
Lab 3
Outline
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Reading a meniscus
Volume determination and significant digits
Balances
Mathematical treatment of data
Safety Concerns
Next Assignment
Summary of Significant Figure Rules for Glassware
Reading a Meniscus
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Meniscus and Parallax
Very Important
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Every time you read a volume from a piece
of glassware in lab, or report a volume for a
calculation, you need to use the
appropriate level of precision of the
glassware used.
Study the following rules and use them
correctly and consistently.
Significant Figures:
Volumetric Glassware
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Use the Tolerance table on p. 98 to determine
glassware tolerance, unless it is printed on the
glassware.
For example:
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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
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2.
3.
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
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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
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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
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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
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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
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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
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Smallest graduation: 0.1 mL
10% value: 0.01 mL
Volume to the closest 10% of the SG:
15.48 mL
Balances
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Cleaning
Two methods of weighing
Recording of significant figures
All sample/solution preparation should be
performed at your station. Balances (and related
counter space) should be used for weighing only!
Density
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Mass of a substance per unit volume.
d
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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
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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
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Water temperature:
21.2 ºC
Density at this temperature (p. 100):
0.9979513 g/mL
Volume Calculation:
V
m
9.9856 g
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 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
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Reagent:
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Food coloring
Health Considerations:
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Avoid contact with skin and eyes.
Do not inhale vapor or spray.
Do not ingest.
Next Assignment – Lab 4:
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Read the required reading sections in your textbook and
lab manual.
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Complete and submit your pre-lab questions by the
deadline.
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Remember to study for your quiz.
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Remember to complete and submit the Lab 3 report at
the start of the next lab.
Lab 4 Pre-lab Questions
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If you haven’t started this pre-lab yet, do so as soon as
possible.
Read the lab write-up in your manual (pp 115 - 140).
Complete the pre-lab questions (pp. 115 - 140) in
MicroLab™ in the SCICom lab (NSB 204), Chemistry
Resource Center (CPSB 302K) or on your personal
computer if you download the program. The program may
be downloaded from http://www.microlabinfo.com under
the Downloads link.
Take this exercise seriously. You will be required to
complete a similar exercise in lab next week without help
from your lab manual.
Skill Evaluations – Next Week
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Will occur after the Lab 4 in-class
assignment if time allows.
Review the skill evaluation pages for
graduated glassware, safety, and
calibration curves.
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