LSM 1101 Biochemistry of Biomolecules
2013/2014 Semester II

Practical 1

Name
:
Ang Chin Khye Gareth (A0122077M)
Ang Ju Hui (A0131255R)
Bench
:
1
TA
:
Goh Kah Yee

1. Introduction
The titration of a strong base (NaOH) against a weak acid (Histidine monohydrochoride ) enables us to know of properties of the weak acid (histidine). Such properties include the pKa of the acid and the pH range of the buffering capacity. One way to relate pH to pka would be through the Henderson – Hasselbalch equation as stated below. pH = pKa + log ([Conjugate Base]/[Acid])
Using this equation and the mid-point of the buffering capacity of the acid, we will be …show more content…

When 5ml of NaOH is added, there is a difference by 0.02 in pH but it is not significant. Thus, I would conclude that the experimental values that we gather are pretty accurate.
(g)(i) There are 2 ionisable groups in histidine at the initial pH of the experiment.
(g)(ii) The first pKa of 6.3 is cause by imidazole ring (-NH+) while the 2nd pKa of 9.3 is cause by the amine (NH) group on histidine.
(h)

3. Experiment 2: Effect Of Buffer pKa on buffering capacity
3.1 Introduction
In this experiment, instead of using a pH meter to measure the pH, we will be using the universal pH indicator to indicate the endpoint of the reaction. The universal indicator will change colour when the certain pH is reached. In this case, the indicator will change from green to red when the mixture reached an acidic pH, and from green to purple when the pH reach a basic pH.
A buffer contains both the acid and conjugate base of the species, which prevents drastic change in pH when a minute amount of acid and base is added. In order to know how good a buffer is, we should know how well a certain type of buffer is able to withstand acid and base.
3.2 Aim
To determine how a buffer`s pKa determines how well it can buffer against acid or base.
3.3 Result
Table 2: No. of drops of HCl and KOH needed for potassium phosphate and Tris-HCl to reach endpoint.
Buffer
No. of