GCC CHM152LL: SAMPLE LAB WRITE-UP 1 of 4
Note: This is not an experiment for CHM152 students – this is an
example to illustrate the proper format for a lab report.
• Pages 1-2 provide the experiment that was performed
• Pages 3-4 show the sample lab report that a student would
write and submit to be graded.
*Formal Lab reports must be neatly handwritten or typed, or a
combination of the two. Reports cannot be pages torn from your
lab notebook.
ANALYSIS OF VINEGAR VIA TITRATION
INTRODUCTION
In an acid-base neutralization reaction, an acid reacts with a base to produce water and a salt:
HX (aq) + MOH (aq) ⇒ H2O (l) + MX (aq) (1)
acid base salt
The protons (H+) from the acid react with the hydroxide ions (OH–) from the base to form the
water. The salt forms from the cation from the base and the anion from the acid. Because
water is always formed, acids will always react with bases; whether the salt is soluble or
insoluble does not determine whether the reaction occurs.
In this experiment, you will use a dilute solution of sodium hydroxide, NaOH (aq) to determine
the molar concentration of acetic acid present in a sample of vinegar. You will measure out a
small volume of vinegar and use a buret to determine the volume of sodium hydroxide required
to completely neutralize the vinegar. The process of slowly adding one solution to another until
the reaction between the two is complete is called a titration. The reaction between acetic
acid, HC2H3O2 (aq), and sodium hydroxide, NaOH (aq), is shown below:
HC2H3O2 (aq) + NaOH (aq) ⇒ H2O (l) + NaC2H3O2 (aq) (2)
When carrying out an acid-base neutralization reaction in the laboratory, you observe that
most acid solutions and base solutions are colorless, and the resulting water and soluble salt
solutions are also colorless. Thus, it is impossible to determine when a reaction has occurred,
let alone when it is complete. To monitor the progress of a neutralization reaction, you use an
acid-base indicator, a solution that changes color depending on the pH (or acid-content) of
the solution. One commonly used indicator is phenolphthalein, which is colorless in acidic and
neutral solutions and pink in basic (or alkaline) solution. During a titration, the indicator is
added to the solution being titrated (the analyte). The titrant (or standard) is slowly added to
the analyte until the endpoint, when the indicator changes color, signaling that the reaction
between the two is complete. Note that phenolphthalein turns pink only when excess sodium
hydroxide, NaOH (aq), has been added.
The equivalence point in a titration is when there are equal numbers of moles of acid and
base present in the solution. Thus, for the reaction between KHP and sodium hydroxide, at the
equivalence point
