Experiment 01: Volume Measurements using Liquids and Solutions
Objectives:
►Demonstrate proficiency in use of a buret, volumetric flask and pipet.
►Compare Precision of several pieces of laboratory equipment and
laboratory methods. (know difference between precision and accuracy)
►Perform data analysis and show how repeated measurements can be
used to determine precision of results. (know average and standard
deviation – see appendix of lab manual)
Procedure I: Volume of a Cone by Two Methods
Part I.A: Measurement and Calculation
This is just an example – you will
need to cut your cone down so
that its height is between 5-7 cm,
as shown below.
For this whole cone, the height is
calculated:
h = 15.0 – 5.5 = 9.5 cm
The diameter of this cone was
measured to be
d = 6.8 cm
The radius would be
r = ½ d = 3.4 cm
Use the equation provided in the
prelaboratory assignment:
V = (1/3)π r2 h
When cutting the cup down to size, cut with a slight curve so that when the shape is
expanded to a three-dimensional cone the base will be level. Remember that height is
vertical height – not lateral length of the side of the cone. Also, remember to calculate
the Volume with radius, not diameter. Remember: 1 cm3 = 1 mL
Part I.B: Determination of Volume with Buret
~4.30 mL
~6.12 mL
Volume by difference
V = 6.12 - 4.30 mL = 1.82 mL
Overfilled water
Cone
Do not overfill the
cone resulting in
higher volume
measurements…
Procedure II: Density of Known Saltwater Solution
Part II.A:
Use 25.00 mL as calibration of pipet.
Part II.B: Density of Saltwater – Solution with Known Concentration
KimWipes
Weighing Vials labeled NaCl
Weighing by Difference: This is an analytical balance – digits read to 0.0001g
Mass of Salt (g) = 22.1818 g – 19.7586 g = 2.4232 g
(see lab manual appendix for directions on significant figures in addition and subtraction)
Dissolve NaCl (sodium chloride) with D.I. H2O (deionized water) and transfer to a
100.00mL Volumetric Flasks
100.00 mL Volumetric Flask
Pipet Bulb
250 mL Beaker
50 mL Erlenmeyer Flask
Rubber Stopper
25.00 mL Pipet
The bottom of the meniscus just
touches the horizontal line on
the neck:
V = 100.00 mL
Transfer solution to an Erlenmeyer flask or Beaker (should be at least 100 mL, right?)
Use the pipet to deliver a 25.00 mL aliquot to a 50 mL Erlenmeyer flasks – determine
mass of solution and flask together. Perform 3 trials. Repeat the entire Part II.B procedure
twice more.
Suction fill the pipet using the
bulb or pump and adjust until
the bottom of the meniscus just
touches the horizontal line on
the upper part of the pipet as
shown. When the pipet is
drained to deliver the sample
into the flask, leave the small
amount of fluid at the tip of the
pipet – do not shake or blow it
out – the pipet is calibrated to
account for this remaining
volume. Volume delivered is:
V = 25.00 mL
Data Analysis:
Volume of Cone:
Read the introduction, prelaboratory assignment; and, read
the appendix on Significant Figures and Statistical Treatment
of Data.
Calibration of Pipet: Omit this step. V = 25.00 mL was given information.
Use a CRC to determine density of water to 5 significant figures – you need the
temperature of the lab at the time of the experiment. CRC (Chemical Rubber
Company) books are checked out from the chemistry stockroom.
The following page is from the CRC book above. There are similar charts posted in the
lab room near the barometer.
Calculation of the Density of Saltwater:
Remember that in Procedure II.B parts 9-10 you are repeating the experiment
several times to be able to average results – you will generate 3 average
densities.
1. Calculate the density of saltwater solutions in each of the three trials:
D1 = M1 / V1
D2 = M2 / V2
D3 = M3 / V3
Calculate and Average Density: Dave1 .
In Procedure IIB. Part 10 your repeat the experiment two more times, yielding two
more average densities: Dave2 . Dave3 .
Calculate a Standard Deviation between these three average densities. – use
the appendix Significant Figures and Statistical Treatment of Data in your lab
manual.
2. Percent composition by mass: I used my original density from Part IIB.1-4.
Summary Table of Results:
Conclusion:
Precision is reflected in the number of significant figures. Please complete these
questions with clear, complete sentences.
Think about the precision of measurements and the equipment used in labs – if
student data indicates a volume of 10.00 mL – the instrument used would be
10.00 mL volumetric flasks –graduated cylinders are not that precise.
If a data report indicates a mass of 2.1234 g – the instrument used was an
analytical balance – the only balance that measures with that precision. Could
you have identified the following:
DATA
1.2 g
1.23 g
1.234 g
1.2345 g
What instrument used?
decigram balance
centigram balance
milligram digital balance
analytical balance
250 mL
250.0 mL
25.00 mL
250.00 mL
beaker or Erlenmeyer flask?
graduated cylinder
pipet or 25.00 mL volumetric flask
volumetric flask (pipets not that large)