CHEM 21131 Physical Chemistry Laboratory
2014
Pre Lab–Experiment C4
Determination of the Basicity, pKa Values and Strength of an Unknown Weak
Polybasic Acid
1. Define the term ‘basicity’ in case of an acid.
2. Write the Henderson-Hasselbalch equation for an acid denoted as HA. Define the terms
of the equation.
3. A solution of an aqueous ethanoic acid (0.10 mol dm-3, 101.0 mL) was mixed with a
solution of aqueous sodium hydroxide (0.1 mol dm-3, 1.0 mL). At a particular
temperature the H+ ion concentration of this mixture was 0.004 mol dm-3. Calculate the
pKa value of the acid at this temperature.
4. Sketch the titration curve that can be obtained, when NaOH (0.10 M) is titrated with a
weak acid HA (0.10 M, 25.00 mL). Label the vertical portion, equivalence point and
the buffer regions of the curve.
5. What is the difference between end point and equivalence point of a titration?
Bonus Question (Not compulsory)
Sketch a diagram of an Ion Selective Electrode (ISE) labeling all the parts of it.
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