Investigating the pH change in typical Acid-Alkaline Titration
Objective

To follow the change in pH of different Acids-alkaline titrations using datalogger system
with a pH probe.
Chemicals and Apparatus (per group)
Deionised water
100 cm3
0.5 M sodium hydroxide solution
100 cm3
0.5 M hydrochloric acid solution
200 cm3
0.5 M sodium carbonate solution
100 cm3
10-mL pipette and pipette filler
x1
Burette
x1
Magnetic stirrer / Hot plate magnetic stirrer
x1
250-mL beaker / 100-mL beaker
x1
PASCO Airlink / Airlink 2 datalogger interface
(or equivalent)
x1
PASPORT pH probe (or equivalent)
x1
IPad and SPARKvue app (or equivalent)
x1
Washing bottle
x1
Curriculum link

Topic IV
Acids and Bases (Chemistry and Combined Science (Chemistry Part))
Safety precautions

Wear safety glasses and disposable protective gloves.

Be careful when handling acids or alkalis. In case of spills, report to your teacher and
rinse the affect area with plenty of water for at least 3 minutes.

Dispose the used chemicals in the waste container.
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Background
During a typical Acid-alkaline titration, indicators are usually used to determine the end point
of the titration. Since indicators only change colour sharply at a particular pH range, choosing
a suitable indicator for the titration is important.
In this titration experiment, you will learn how to choose a suitable indicator for the titration
based on the titration curve.
Question
Which of the followings is the most probable graph you might expect for the change of pH
when an alkaline is titrated with acid over time?
pH
pH
A
B
Time
pH
Time
pH
C
D
Time
Time
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System Setup (for reference if a different model of datalogger is used)
1. Switch on the Airlink Interface and connect it to the pH probe.
2. Switch on the Bluetooth device in IPad.
3. Press “Airlink2” in the Bluetooth setting page of the IPad. The Airlink device and the
IPad would be connected automatically (Figure 1).
Figure 1: IPad Bluetooth setting
4. Open the app SPARKvue. Press + to start a new
experiment.
5. Add title (e.g. “Titration”) and description (e.g.
“Titrating sodium hydroxide with hydrochloric acid”).
6. Select pH from measurement and 2 Hz from sampling
rate and then press Done (Figure 2).
7. Press the “experiment title” on the list to start the
experiment.
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Figure 2: SPARKvue setting for pH
measurement
Experimental procedures
1. Wash a 10-mL pipette first with deionised water and then with the dilute sodium
hydroxide solution.
2. Transfer 10.0 cm3 of the dilute sodium hydroxide solution in a beaker using the pipette
and pipette filler.
3. Wash a burette with deionised water and then with the acid.
4. Close the stopcock. Fill the burette with the acid. Clamp the burette vertically in a stand.
5. Open the stopcock for a few seconds so as to fill the tip of the burette with acid.
6. Put the beaker containing 10.0 cm3 of the dilute sodium
hydroxide solution on a Heating Plate and put a magnetic
stirrer and the pH probe into the beaker. Ensure that the
glass bulb is completely immersed while the magnetic
stirrer can be spinning smoothly (Figure 3).
7. Switch on the stirrer (Remember not to switch on the
heater!).
8. Run the acid from the burette to the beaker and start
at the same time to record the pH change by pressing
Figure 3: Datalogger with pH
probe and titration setup
the green button using SPARKvue. DO NOT adjust
the flow rate during recording.
9. Press the red button to stop recording the change.
10. Press the “Home button” and “Power switch” of the iPad at the same time to capture the
screen.
11. Repeat Step 1 to 10 using sodium carbonate solution instead of sodium hydroxide
solution.
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Data and Analysis
(i)
Titration of sodium hydroxide with hydrochloric acid (Graph A)
(Attach the titration plot in the space provided.)
(ii) Titration of sodium carbonate with hydrochloric acid (Graph B)
(Attach the titration plot in the space provided.)
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(iii) The table below shows some acid-base indicators and the approximate pH range where
there is a change in colour:
Acid-base indicator
pH range correspond to the change in colour
Litmus
4.5 – 8.3
Methyl orange
3.1 – 4.4
Phenolphthalein
8.2 – 10.0
Refer to the experimental results (Graph A and Graph B), suggest suitable acid-base
indicators from the table for the following experiments:
(I)
Titration of sodium hydroxide with hydrochloric acid
(II) Titration of sodium carbonate with hydrochloric acid
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Discussion questions
1.
Describe briefly the change of pH in Graph A.
2.
In the space below, sketch a possible graph for:
(i)
Titration of oxalic acid (COOH)2 with sodium hydroxide
pH
Time
(ii) Titration of phosphoric acid (H3PO4) with sodium hydroxide
pH
Time
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