pH Adaptor & Electrode
14
9.
Type 0 into the ‘enter value’ box and close.
Note: Enter the TOTAL volume of acid added so far.
10.
Turn the tap on the burette to add a measured amount e.g. 2 cm
3
. Let the solutions mix and
take a sample. Enter the volume of acid added e.g. 2.
11.
Vary the amount of acid added as required.
12.
Tap or click on the Stop icon to finish recording.
In this titration 2 cm
3
was added for the first 6 readings then the amount of acid added was reduced
to 1 cm, then after 19 cm
3
(closer to the expected end-point) it was reduced to 0.5 cm
3
How to create a mV to pH calibration graph
Buffers. You will need a minimum of two buffers, preferably three or more e.g. 4, 7 and 10.
If you are only using two then its best if one is a ‘neutral’ buffer with a pH of 7, and the second is near
to the expected pH of the samples you will be testing. For example buffers with a higher pH (10) are
best for measuring bases, whereas buffers with a low pH (4) are best for measuring acidic samples.
Once you have chosen your buffers allow them all to reach the same temperature. Pour your buffers
into individual beakers for calibration. Check the temperature of the room and label the value of each
buffer with its pH value at that temperature.
For example: Values of pH buffers a various temperatures:
Temperature ˚C
pH 4.0 buffer
pH 7.0 buffer
pH 10.0 buffer
10˚
4.00
7.05
10.10
20˚
4.00
7.00
10.00
25˚
4.01
6.99
9.945
30˚
4.01
6.98
9.90
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