Experiment 2 – Measurement
Objectives
1.
2.
3.
4.
5.
To understand the accuracy of various types of graduated glassware.
To measure volumes of liquids using a graduated cylinder.
To measure the volume of liquids dispensed from a burette.
To determine the temperature of liquids using a thermometer.
To record measurements with correct number of significant figures.
Introduction
In this lab you are asked to make a series of volume and temperature
measurements and record the number of significant figures in each
measurement.
Three stations will be set up in the laboratory. Each station is set up for you to
determine the two volume measurements and a temperature measurement. The
measuring instruments at the three stations are:
1. a graduated cylinder for volume measurement
2. a burette for volume measurement
3. a thermometer for temperature measurement
Volume measurements can be made with various types of glassware. The
glassware that is used determines the accuracy of the measurement.
CHEM 0011 – May 2010
Accuracy of the Various Types of Graduated Glassware
Type of
Glassware
Target
Volume
Accuracy
Accuracy Range
Graduated
Erlenmeyer flask
125 mL
+/- 5%
125 mL +/- 6.25 mL
Graduation interval=25 mL
roughly accurate
Graduated beaker
100 mL
+/- 5%
100 mL +/- 5 mL
Graduation interval=10 mL
roughly accurate
Graduated cylinder 10 mL
+/- 0.5%
10 mL +/- 0.05 mL
Graduation interval=0.1 mL
accurate
Graduated cylinder 100 mL
+/- 0.4%
100 mL +/- 0.40 mL
Graduation interval=1 mL
accurate
Volumetric flask
100 mL
+/- 0.08%
100 mL +/- 0.08 mL
No graduation interval
very accurate
Volumetric pipet
25 mL
+/- 0.12%
25.0 mL +/- 0.03 mL
No graduation interval
very accurate
Buret
50 mL
+/- 0.1%
50 mL +/- 0.05 mL
Graduation interval=0.10 mL
very accurate
In all the measurement determination, it is important that you pay attention to:
1. The determination of the value of the measurement,
2. The unit that is associated with the measurement,
3. The proper number of significant figures that is associated with the
measurement.
CHEM 0011 – May 2010
Volume Measurements - Graduated Cylinder
In any volume measurement we need to approach the measuring instrument at
proper eye position, at eye level. When we are up close to the liquid level at eye
level, we will observe that the surface of the liquid forms a "lens-shaped". This is
called the meniscus. In taking the measurement, we always read the bottom of
the meniscus. Below is an example of a reading taken of a liquid in a graduated
cylinder. The diagram shows an expanded view of the portion of the cylinder near
the surface of the liquid.
Let's analyze this measurement:
1. Upon inspection of the graduated
cylinder, we observe that the finest
division is a 1 mL division.
2. We can always make an estimate of
a reading to within the finest division.
Therefore, to the best of my
judgement, I conclude that this
particular graduated cylinder is able
to provide a reading accuracy to +/0.2 mL. (Note: A plus or minus 0.2
mL reading accuracy means that a
volume measurement using this
graduated cylinder will contain
uncertainty in the first decimal place.)
3. The bottom of the meniscus lines up
with the 4th finest division above the
10 mL mark.
4. The volume reading is determined to
be 14.0 mL. This volume reading has
3 significant figures. (Note: the '0' in
this measurement is an uncertain
figure. This measurement is accurate
to 14.0 +/- 0.2 mL. It means that
using this graduated cylinder, the
accuracy of the volume of the liquid
is between 13.8 mL to 14.2 mL.)
CHEM 0011 – May 2010
Volume Measurements - Burette
In any volume measurement we need to approach the measuring instrument at
proper eye position, at eye level. When we are up close to the liquid level at eye
level, we will observe that the surface of the liquid forms a "lens-shaped". This is
called the meniscus. In taking the measurement, we always read the bottom of
the meniscus. Below is an example of a reading taken of a liquid in a buret. The
diagram shows an expanded view of the portion of the buret near the surface of
the liquid.
Let's analyze this measurement:
1. Upon inspection of the buret, we
observe that the finest division is a
0.1 mL division.
2. We can always make an estimate of
a reading to within the finest division.
Therefore, to the best of my
judgement, I conclude that this
particular buret is able to provide a
reading accuracy to +/- 0.02 mL.
(Note: A plus or minus 0.02 mL
reading accuracy means that a
volume measurement using this
buret will contain uncertainty in the
second decimal place.)
3. The bottom of the meniscus lines up
with the 6th finest division below the
34 mL mark.
4. The volume reading is determined to
be 34.60 mL. This volume reading
has 4 significant figures. (Note: the '0'
in this measurement is an uncertain
figure. This measurement is accurate
to 34.60 +/- 0.02 mL. It means that
using this buret, the accuracy of the
volume of the liquid which has been
dispensed is between 34.58 mL to
34.62 mL.)
CHEM 0011 – May 2010
Temperature Measurements - Thermometer
In any temperature measurement we need to approach the measuring instrument
at proper eye position, at eye level. With a mercury thermometer, when we are
up close to the mercury level at eye level, we will observe that the surface of the
mercury forms a "lens-shaped" that bulges upward. This is called the meniscus.
Unlike the meniscus that we observe with a liquid like water, the mercury forms a
positive meniscus. In taking the measurement, we always read the top of the
positive meniscus. Below is an example of a temperature reading. The diagram
shows an expanded view of the portion of the thermometer near the surface of
the mercury.
Mercury Thermometer
Let's analyze this measurement:
1. Upon inspection of the
thermometer, we observe that
the finest division is a 1 oC
division.
2. We can always make an
estimate of a reading to within
the finest division. Therefore, to
the best of my judgement, I
conclude that this particular
thermometer is able to provide a
reading accuracy to +/- 0.2 oC.
(Note: A plus or minus 0.2 oC
reading accuracy means that a
temperature measurement using
this thermometer will contain
uncertainty in the first decimal
place.)
3. The top of the positive meniscus
almost lines up with the 30 oC
mark.
4. The temperature reading is
determined to be 29.8 oC. This
temperature reading has 3
significant figures. (Note: the '8'
in this measurement is an
uncertain figure. This
measurement is accurate to 29.8
+/- 0.2 oC. It means that using
this thermometer, the accuracy
of the temperature is between
the range 29.6 oC to 30.0 oC.)
CHEM 0011 – May 2010
Alcohol Thermometer
The Alcohol thermometer is an alternative to the mercury thermometer. The
range of usefulness of the thermometer is set by the boiling point of the liquid
used. In the case of the ethanol-filled thermometer the upper limit for
measurement in 78°C. Thus, alcohol thermometers cannot be used to measure
high temperatures. The ethanol version is the most widely used due to the low
cost and relatively low hazard posed by the liquid in case of breakage. When
reading the alcohol thermometer, make sure the eye position is level with the
surface of the alcohol level. You will not observe a meniscus, as the alcohol level
will be flat. Determine where the alcohol level lines up with the nearest mark on
the scale and follow the above procedure to report the temperature to within the
finest division.
CHEM 0011 – May 2010
Procedure:
Part A: Volume measurements
Three stations are set up in the laboratory. At each station:
1. Read the volume of the burette
2. Read the volume of the graduated cylinder
3. Record the volume measurements and the units of the measurements on
the data sheet and determine the number of significant figures of the
recorded measurements.
At the end of Part A, you should have recorded 6 volume measurements:


3 burette readings
3 volume measurements of the graduated cylinders
Part B: Temperature measurements
Three stations are set up in the laboratory. At each station:
1. Read the temperature of the thermometer
2. Record the temperature measurements and the units of the
measurements on the data sheet and determine the number of significant
figures of the recorded measurements.
At the end of Part B, you should have recorded 3 temperature measurements.
CHEM 0011 – May 2010
Datasheet:
Part A: Volume measurements
Number of
Significant Figures of
the Volume
dispensed
Burette
Reading
Final Reading: ___________ mL
Initial Reading:
Station A
3.55 mL
Volume dispensed: ____________ mL
Final Reading: ____________ mL
Initial Reading:
Station B
0.80 mL
Volume dispensed: ____________ mL
Final Reading: ____________ mL
Initial Reading:
Station C
1.00 mL
Volume dispensed: ____________ mL
Graduated Cylinder
Measurement
Station A
Station B
Station C
CHEM 0011 – May 2010
Volume
Number of Significant Figures
Recorded in the Measurement
Part B: Temperature measurements
Thermometer
Reading
Station A
Station B
Station C
CHEM 0011 – May 2010
Temperature
Number of Significant Figures
Recorded in the Measurement