Overview of the UK Experiment Chemistry is pHun focusing on preparing buffers.

1. General Chemistry Laboratory
University of Kentucky
Chemistry is pHun

2. Buffers
 A solution capable of maintaining its
pH at a constant value with the
addition of a small amount of acid or
base.
 Composed of an acid and its
conjugate base.
 pKa should be ± 1 of desired pH
 Conjugate base from acid differs by
only one H+

3. Preparing a Buffer Solution
 Dilute your acid to 0.1 M using a
volumetric flask
 Determine the mass of the salt that
should be added to 100 mL of the
acid to prepare your assigned pH

4. Dilution Calculations
 Dilution formula
 Only use for dilutions and not for
titrations
M1V1 = M2V2

5. Using a
Volumetric
Flask

6. Henderson-Hasselbalch
Equation
 To determine the mass of the salt,
use this equation:
pH = pKa + log [Conjugate Base]
[acid]

7. Ways to determine the pH
 Litmus Paper: indicates if acidic, basic,
or neutral by color.
 pH paper: Gives an approximate pH of
solution by color of the paper.
 Indicators: a chemical added to the
solution which tells pH by color change.
 pH Meter: monitors pH using a probe
and software and gives a readout of the
measured pH

8. Buffer Capacity
 Can be determined experimentally
by adding acid or base to solution
and monitoring the pH change.
Buffer Capacity = (# mol OH- or H+ added)
(pH change)(vol buffer in L)
 You will use your graph of pH vs. vol
OH- or H+ to determine this.

9. Calculations
 See the additional information
posted in the Experiment 16 Module
on Canvas to get help with the
calculations
 You MUST have them completed
and checked by the TA before you
start the experiment

10. Calculations
 Find your assigned pH in the last
prelab question on Sapling
 You need the calculated information
in order to complete the lab
experiment