Experiment 1 Determination of the Acetic Acid Content of
During this experiment you will gain
experience in working with volumetric glassware, and gain
knowledge on how to determine the uncertainties in the volumes
delivered by these. In addition, you will use a suitable
titration to determine the concentration of acetic (ethanoic)
acid in vinegar samples.
On completion of the laboratory you should be able to:
- Demonstrate proper techniques for using `pipette, burette and
- Assess the random error in the volume delivered from the
pipette and a burette.
- Accurately dilute a sample.
- Use a suitable titration to determine the concentration of
ethanoic acid in vinegar.
All measurements (volumes, lengths, weights etc.) have associated
errors. Some, called gross errors, arise from mistakes (writing
down the wrong number, recording the wrong units, etc.) but these
can be easily avoided by working carefully. Others, called
systematic errors, arise from equipment or instruments not
operating according to their specifications (for example if a
pipette always delivered 4.96 cm3 rather than the stated 5.00 cm3) or
something was wrong with the measurement procedure (for example
there was something unexpected in the sample being studied (called
an interferant) that resulted in the measurement being different
from what it would be if the interferant was absent).
Systematic errors lead to inaccurate results but may be avoided
if the cause of the error can be identified. The final type of
error is called random error and results from unavoidable
fluctuations in the measurement process (for example the possible
variations in a burette reading that results from attempts to
assess the second decimal place). Random errors cannot be
avoided, only minimized by adherence to good laboratory
practices. Throughout this semester you will investigate some
methods used to assess random and systematic errors.
In this experiment you will start to consider random errors by
assessing their magnitudes in the volumes delivered by the
pipette, volumetric flask and burette that you use in a titration
of an acid (acetic acid) of unknown concentration in vinegar with
a base (sodium hydroxide) of known concentration. In subsequent
weeks you will calculate the random errors in the determined
From the volumes of the acid (pipette) and the base (burette)
used and knowledge of the stoichiometry of the reaction that
takes place and the concentration of the base, the moles of acid
involved in the reaction can be calculated and from that the
concentration of acetic acid in the vinegar.
During this experiment you will be working with a weak acid
and strong base. You must wear eye protection at all times. In
the event that any reagent used in this investigation comes in
contact with your skin or eyes, wash the affected area
immediately with lots of water. Notify your instructor.
Directly record all observations onto your worksheet.
Carefully pipette, using a cleaned pipette and a pipette filler
and the procedures demonstrated to you, 5.00 cm3
of vinegar into a 100 cm3 volumetric flask. Be sure to
drain your pipette properly (slowly rotate the pipette while it
is draining and discharge the final drop by touching the pipette
tip to the side of your titration flask; do not blow out
the last drop). Add distilled water up to the bottom of the stem
of the flask, mix well and then make up to the 100.00 cm3 mark.
To ensure the solution is homogeneous, mix thoroughly by slowly
inverting the flask at least ten times. Pipette 10.00 cm3 of this
diluted vinegar into a 100 cm3 conical flask.
Clean and fill you burette with the provided standard sodium
hydroxide solution and titrate the vinegar solution, using
phenolphthalein as indicator. Repeat the titration until
two titres agree to within 0.20 cm3, i.e. you obtain concordant
results. Be sure to read your burette to two decimal places
(±0.02 cm3). If there are any doubts, ask your
As indicated on your worksheet
a) Calculate the concentration of acetic acid in your
sample of vinegar.
b) Estimate the error in your pipette and volumetric flask
c) Estimate the error in each burette reading.
d) Calculate the error in each titration volume and the
error in the average titration volume.
Apparatus per student
25 cm3 (or 50 cm3) burette, a funnel to fit the burette,
10 cm3 pipette, 100 cm3 volumetric flask, 100 cm3
beaker or conical flask, wash bottle, white tile, burette stand and burette clamp.
Chemicals per student
15 cm3 of vinegar, 50 cm3 of standard
sodium hydroxide solution (~ 0.05 mol dm-3) and phenolphthalein indicator.
(a) the molar concentration of acetic acid in the original sample
(b) the mass of acetic acid per 100g of solution (the density of
acetic acid solution is 1.01 g/cm3 ).
Compare this value [from (b)] for the three different brand names
of vinegar provided. For each brand name use the average of at
least three (list them) values obtained from your classmates.
Complete your Lab. worksheet and submit it tomorrow.
Answer the following questions on your worksheet.
1. What is the accuracy of the quantities measured using
(i) the pipette?
(ii) the burette?
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Copyright © 2002-2014 by Department of
Chemistry, UWI, Mona all rights reserved.
Created and maintained by Prof. Robert J.
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.
Created Oct 2002. Links checked and/or last
modified 31st August 2014.