Advanced Higher Chemistry
Investigation Report
Analysis of
Irn Bru
Russell Mackay
050010694
Wick High School
Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Contents
Abstract ...................................................................................................................................... 3
Underlying Chemistry ................................................................................................................ 4
Iron ......................................................................................................................................... 4
Determination of Iron Content by Redox Titration ............................................................... 4
Determination of Iron by Colorimetry ................................................................................... 5
Determination of Glucose Using Titration ............................................................................. 8
Determination of pH .............................................................................................................. 9
Experimental Procedures ......................................................................................................... 10
Determination of Iron Content by Redox Titration ............................................................. 10
Colorimetric Analysis of Fe2+ in Irn Bru ................................................................................ 10
Determination of Sugars Using Titration ............................................................................. 11
Determination of Glucose Content by Calibration Curve .................................................... 11
Determination of pH of Irn Bru ............................................................................................ 11
Results ...................................................................................................................................... 13
Determination of Iron Content by Redox Titration ............................................................. 13
Determination of Glucose by Calibration Curve .................................................................. 16
Determination of pH of Irn Bru ............................................................................................ 17
Conclusions .............................................................................................................................. 18
Evaluation ................................................................................................................................ 19
Evaluation of Procedures ..................................................................................................... 19
Evaluation of Results............................................................................................................ 20
References ............................................................................................................................... 22
Figure References .................................................................................................................... 23
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Abstract
The aims of this investigation were to:

Investigate quantitatively how much iron (Fe2+) is actually in Irn Bru.

Investigate quantitatively how much sugar is in Irn Bru.

Investigate the pH of Irn Bru.

Compare the findings of the above to results obtained for Diet Irn Bru.
The main findings of the investigation are that the percentage concentrations of Fe2+ in both
Irn Bru and Diet Irn Bru are the same (0.72%), the reducing sugar content of Irn Bru is higher
than that of Diet Irn Bru (10.8%), however, the non-reducing sugar content of Diet Irn Bru is
much higher than that of Irn Bru (9%) and Irn Bru and Diet Irn Bru are both slightly acidic
solutions (~3.5).
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Underlying Chemistry
Iron
Iron is one of the essential minerals required by the body. It is an important constituent of
the oxygen-carrying protein, haemoglobin, which is the main molecule in red blood cells. A
lack of iron in the diet leads to a condition called anaemia, the main symptom of this is
chronic fatigue. (Rutter, 2004)
Figure 1: Structural Formula of Haemoglobin
(sugars4life.com, 2011)
Determination of Iron Content by Redox Titration
The Fe2+ content of Irn Bru can be determined by a Redox titration. A redox reaction is
where both oxidation and reduction takes place. A redox titration is a titration which relies
on a
Figure 2: Tertiary Structure of Haemoglobin
(molecularstation.com, 2011)
redox reaction that takes place
between the analyte and the
titrant.
Permanganate (MnO4-) is an oxidising agent. It therefore ‘accepts’ electrons and it becomes
reduced to Manganese ions. This can be summarised in the following equation:
MnO4-(aq) + 8H+ + 5e- ⇋ Mn2+(aq) + 4H20(l)
Permanganate ions are purple and Manganese ions are colourless, so a redox equation
which uses MnO4- does not require a separate indicator.
In the experiment the MnO4- is the electron acceptor from the reduction of Fe2+ (aq):
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Fe2+ (aq) ⇋ Fe3+(aq) + e-
To summarise this, we can write a redox equation:
MnO4-(aq) + 8H+(aq) + 5Fe2+(aq)  Mn2+(aq) +4H20(ℓ) + Fe3+(aq)
(NB: that in the actual experiment, the H+ ions were provided by the dilute sulphuric acid).
As soon as a consistent pale pink colour appears (because the reducing agent has been used
up) the end point of the reaction has been reached.
From the results of the titration, the mass and percentage of Fe2+ in the sample is
calculated, because the equation states that 1 mole of MnO4- reacts with 5 moles of Fe2+, so
when the end point is reached, it can be worked out, from the volume of KMnO4 used, the
number of moles required and use simple proportion to find out the same for Fe 2+ and thus
% Fe2+. (homepage.smc.edu)
Determination of Iron by Colorimetry
The Fe2+ content of a solution can be determined by colorimetry. Solutions appear coloured
because they absorb some wavelengths of the electromagnetic spectrum and transmit the
others. Our eyes detect these transmitted waves, within a small range, known as the visible
range and perceive them as colours. (lsc.unm.edu)
The electromagnetic spectrum is made up of 6 visible colours:
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Figure 3: The Electromagnetic Spectrum (lsc.unm.edu, 2011)
So, Irn Bru appears as an orange solution because the solution absorbs yellow, green blue
and violet wavelengths of light, but reflects the red/orange wavelengths, thus appearing
orange.
The colorimeter is used to determine how much coloured light Irn Bru will absorb compared
to other standard solutions of Fe2+ (which have been reacted with a ligand to give it a red
colour). This is useful because an equation exists which can be used to convert absorption
to concentration.
This law is called the Beer-Lambert Law which states that:
A = ecb
Where
A = absorbance,
B = Molar absorvity in lmol-1
b = the path length of the sample in cm
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
c = Concentration of the solution in moll-1
This equation can be manipulated to show what the concentration of Iron is in solution.
However, in this experiment, a more reliable and simple method was used. The method
used a standard calibration curve. This is when samples of known concentration of Iron are
tested with a colorimeter, and a graph drawn of the results. A reading can then be done
with the Irn Bru, and the unknown concentration can be taken from the calibration curve.
A complex ion has a metal ion at its centre with a number of other ions surrounding it.
These are attached to the central ion by dative covalent bonds. A covalent bond is formed
by two atoms sharing a pair of electrons. The atoms are held together because the electron
pair is attracted by both of the nuclei. In the formation of a simple covalent bond, each
atom supplies one electron to the bond - but that doesn't have to be the case. A dative
covalent bond is a bond in which both electrons come from the same atom.
The molecules or ions surrounding the central metal
ion are called ligands. All ligands have active lone
pairs of electrons in the outer energy levels. All
ligands are electron donors.
Figure 4: Structure of Potassium Thiocyanate
(wikipedia.org, 2011)
Note that in the experimental procedure, Fe3+ solution is used to calibrate the colorimeter,
because they react with potassium thiocyanate according to the equation below:
Fe3+ (aq)
+
SCN- (aq)

Fe(SCN)2+ (aq)
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Determination of Glucose Using Titration
Benedict’s solution is used as a test for the presence of reducing sugars. A reducing sugar is
a sugar with an aldehyde or ketone group. This group allows it to become a reducing agent.
Benedict’s solution contains blue CuSO4 which is reduced to red CuO during a reaction with
a reducing sugar. So, when Benedict’s reacts with a reducing sugar, it turns from blue to
brick-red.
A titration was run with the Irn Bru as the titrant and Benedict’s as the analyte. The
experiment would then be repeated, with a sample of Irn Bru with Hydrochloric Acid added
to it, this is to hydrolyse any non-reducing sugars. (techknow.org)
The exact molar quantities involved with this method are not
known, however it is known that 1 mole of glucose always
reacts with close to 6.5 moles of copper(II). This is useful
because the concentration of glucose in the unknown can then
be calculated. (sserc.org)
Figure 5: Aldehydes and Ketones
(elmhurs.edu, 2011)
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Determination of pH
pH is a unit of measurement of the Hydrogen ion concentration of a solution. It can be
defined as the negative logarithm of the hydrogen ion concentration: pH = -log[H+]
Irn Bru is a weak acid because it is in equilibrium with CO2, added to make it fizzy. The pH of
a solution can be determined with a pH meter. (Kaulmann, 2003)
A pH meter works because it forms a simple cell with the solution it is immersed in. The
e.m.f. of a cell, with a glass electrode (the pH meter probe) is proportional to the logarithm
of the concentration of the hydrogen ions – in other words – the pH. (Atkins, 1988)
Figure 6: Glass Electrode (periodni.com, 2011)
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Experimental Procedures
Determination of Iron Content by Redox Titration
A burette was set up ready for titration. Three 50cm3 samples of Irn Bru were measured
into conical flasks. 100cm3 of 0.001M KMnO4 solution was measured into a beaker. The
burette was then cleaned by rinsing it with distilled water and then three times with KMnO 4
solution. The burette was then filled with KMnO4 solution. The volume was recorded to the
nearest 0.01 cm3. 50cm3 of Concentrated H2SO4 was pipette into a beaker with 150cm3 of
H2O. The beaker was washed into a 250cm3 volumetric flask and made up to the mark with
distilled water. 15cm3 of this 1M H2SO4 was then added to one of the three samples of Irn
Bru. This was then immediately titrated with the KMnO4 solution. When a light yellow
colour developed in the Irn Bru, 1cm3 of 85% H3PO4 was added. The titration was continued
until a persistent pink colour appears. The volume in the burette was recorded to 0.05 cm 3.
The titration was repeated with the other two samples, or until concordant results had been
recorded. This procedure was then repeated with Diet Irn Bru.
Colorimetric Analysis of Fe2+ in Irn Bru
A colorimeter was calibrated by placing a sample of distilled water into a cuvette, and then
into the colorimeter. The calibration button was then pressed to make the reading zero.
Standard solutions of Fe3+ were prepared at concentrations of 0.0050%, 0.0025%, 0.0013%,
0.0010% and 0.0005%. These were prepared with volumetric flasks, for example, for
0.0050%, 0.01g of Fe3+ was made up to 200cm3.
5cm3 of each of the Fe3+ samples were mixed with 5cm3 of 1.0M potassium thiocyanate
solution. These samples were then placed in cuvettes, and analysed with the colorimeter.
The results were then used to produce a calibration curve.
5cm3 Irn Bru and Diet Irn Bru samples were then mixed with 5cm3 of 1.0M potassium
thiocyanate solution. These samples were then placed in cuvettes and analysed with the
colorimeter. The result was then plotted on the calibration curve, and from this the
concentration of Fe2+ ions could be determined.
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Determination of Sugars Using Titration
25cm3 of Benedict’s solution was poured into a conical flask and 3g of anhydrous sodium
carbonate was added, to keep the solution alkaline. Some anti-bumping granules were
added, and the mixture was then brought to a simmer. Irn Bru was added to a burette, and
a titration carried out until the blue colour of the Benedict’s disappeared. This process was
repeated until concordant results were recorded.
NB: The Benedict’s solution had to be kept hot during the titiration otherwise the reaction
would have been too slow.
The entire procedure above was repeated for the following solutions:

Irn Bru + 5cm3 Hydrochloric Acid

Diet Irn Bru

Diet Irn Bru + 5cm3 Hydrochloric Acid

1% Glucose Solution (1g Glucose Powder in 100cm3 Distilled Water)
The glucose concentration was calculated by comparing the volume of 1% Glucose solution
required to discolour the Benedict’s solution.
Determination of Glucose Content by Calibration Curve
The following standard solutions of glucose were made using volumetric flasks, 20%, 15%,
10%, 5%, 2.5% and 1%. 20cm3 of each solution were put in test tubes and a couple of drops
of Benedict’s reagent was added to each. The test tubes were placed in boiling water, and
timed to see how long it took the solution to turn from blue to brick red. This process was
repeated. A standard curve was produced from the results.
20cm3 Irn Bru and Diet Irn Bru were added to test tubes, and the above process repeated.
The results were then plotted on the graph. The % concentration of glucose could then be
determined.
Determination of pH of Irn Bru
A pH meter was calibrated using the following method:
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
100cm3 of pH 7.01 buffer and 100cm3 of pH 4.01 buffer were made up. The pH and
temperature probes were attached to the meter and the storage cap was removed from the
probe. The meter was then switched on, and the oC key pressed. The probe was rinsed in
water, and then immersed in the 7.01 buffer solution. The temperature was noted, and the
pH button was pressed. When the pH reading stabilised, a small screwdriver was used to
adjust the “STD” trimmer on the meter, according to the table below (for the 7.01 buffer).
Temperature (oC)
pH Buffer 4.01
pH Buffer 7.01
0
4.01
7.13
5
4.00
7.10
10
4.00
7.07
15
4.00
7.04
20
4.00
7.03
25
4.01
7.01
30
4.02
7.00
35
4.03
6.99
40
4.04
6.98
45
4.05
6.98
50
4.06
6.98
55
4.07
6.98
60
4.09
6.98
65
4.11
6.99
70
4.12
6.99
The probes were rinsed and placed in 4.01 buffer solution. Again the temperature was
taken, and the pH reading adjusted accordingly. The probes were again rinsed.
The probe was submerged in Irn Bru, when the pH stabilised, this was the reading taken.
This was repeated twice, the probe rinsed between each immersion. This was then
repeated for Diet Irn Bru.
A control of distilled water was used in this experiment.
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Results
Determination of Iron Content by Redox Titration
Irn Bru
Volume of Irn Bru
(cm3)
Initial Burette
Reading (cm3)
Final Burette
Reading (cm3)
Volume KMnO4
Used (cm3)
Sample 1
Sample 2
Sample 3
Sample 4
50
50
50
50
15
14
8.6
16.1
26.5
22.2
16.1
23.6
11.5
8.2
7.6
7.5
Discard, since results <10cm3
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Irn Bru
Sample 1
Sample 2
Sample 3
50
50
50
4.4
1.0
5.4
21.3
18.0
22.3
16.8
17.0
16.9
Moles Fe2+ in Irn Bru
6.5x10-4
6.5x10-4
6.5x10-4
Mass Fe2+ in Irn Bru (g)
0.036
0.036
0.036
% Fe2+ in Irn Bru
0.072
0.072
0.072
Volume of Irn Bru
(cm3)
Initial Burette Reading
(cm3)
Final Burette Reading
(cm3)
Volume KMnO4 Used
(cm3)
Average % Fe2+ in Irn Bru
0.072
Sample Calculation:
Sample 1: Volume Used – 16.8cm3 of 0.001M solution
16.8g of 0.001M = 1.0168g of 1M
1 mole Fe = 55.8g
( 1 mole KMnO4 = 127.4g)
So, 55.8 x 6.5x10-4
=1.3x10-4 Moles KMnO4
= 0.036g Fe2+
So, 5x1.3x10-4 Moles Fe2+
% Fe2+ = 0.036 x 100 = 0.072%
5x1.3x10-4 = 6.5x10-4 moles Fe2+
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Diet Irn Bru
Volume of Irn Bru
(cm3)
Initial Burette Reading
(cm3)
Final Burette Reading
(cm3)
Volume KMnO4 Used
(cm3)
Moles Fe2+ in Diet Irn
Bru
Mass Fe2+ in Diet Irn
Bru (g)
% Fe2+ in Diet Irn Bru
Sample 1
Sample 2
Sample 3
50
50
50
1.5
8.1
3.2
18.3
25.1
20.0
16.8
17.0
16.8
6.5x10-4
6.5x10-4
6.5x10-4
0.036
0.036
0.036
0.072
0.072
0.072
Average % Fe2+ in Diet Irn Bru
0.072
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Determination of Glucose by Calibration Curve
20
15
10
5
2.5
1
Standard Results
Time Taken (Seconds)
Sample 1
Sample 2
47.22
51.32
58.09
61.12
71.22
72.28
76.93
78.42
82.35
83.26
90.34
91.84
Irn Bru
Irn Bru + HCl
Diet Irn Bru
Diet Irn Bru + HCl
Irn Bru Samples
Time Taken (Seconds)
1
2
66.75
66.82
55.4
55.9
70.50
70.09
50.03
50.10
% Glucose Solution
Sample
Average
49.27
59.61
71.75
77.68
82.81
91.09
Average
66.79
55.65
70.30
50.07
100
90
Time Taken (Seconds)
80
70
60
50
40
30
20
10
0
1
2.5
5
10
15
20
% Glucose Solution
Irn Bru
Diet Irn Bru
16
% Glucose
10.8
8.2
% Non-Reducing Sugar
4.2
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Determination of pH of Irn Bru
Irn Bru
Diet Irn Bru
Control
1
3.43
3.63
7
2
3.46
3.63
7
pH
3
3.45
3.63
7
Average
3.45
3.63
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Conclusions

The Iron content of both Diet, and normal Irn Bru is 0.072%.

The average glucose content of Irn Bru is 10.8% and the average non-reducing
content is 4.2%. The average glucose content of Diet Irn Bru is 8.2% and the average
non-reducing content is 9%.

18
The average pH of Irn Bru is 3.45 and the average pH of Diet Irn Bru is 3.63.
Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Evaluation
Evaluation of Procedures
The determination of iron by redox titration was a successful method. The main source of
error in this experiment would be just by error in judgement of the end-point, however, the
titration was done on a white tile to make the end-point more apparent and a ‘reference’
sample was kept, so that the same end point was used each time. The main problem with
this experiment was getting the correct concentration of KMnO4. Through trial and error
the concentration of permanganate changed from 2M to 0.001M. The very low
concentration was expected. The reliability of the results was increased by repeating the
experiment and averaging the results.
However, the determination of iron by colorimetry was totally unsuccessful. After changing
the concentration of the potassium thiocyantate various times, no colour change was
apparent at all. This was probably due to the colouring of the Irn Bru being so strong, and
not changing at all – even when very strong solutions of thiocyanate were added. Also,
because of the fairly low concentration of Fe2+ meant that any change in colour would be
fairly slight anyway.
The titration method of finding glucose concentration was successful, however results did
seem to vary quite a lot. This would probably be due to the Benedict’s not always being at a
stable temperature when the titration was running. This could of been modified so that the
Benedict’s was in a stable water bath, keeping the temperature the same each time.
The calibration curve method of finding sugar concentration was very successful. The
results were all concordant and showed a general trend of as glucose concentration
increases, time taken to reach the end point decreased. The high sugar concentration was
expected, however, the fact that ‘sugar free’ Diet Irn Bru had such a high level of nonreducing sugars was unexpected. These non-reducing sugars could be artificial sweeteners
though, like aspartamine, however, further investigation would be required to determine
this.
The pH of Irn Bru experiment was done with a pH meter. It was calibrated manually, and
this was the main source of error – if the meter was calibrated incorrectly, then the results
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
would be wrong. To reduce the risk of this happening, the meter was totally re-calibrated
between each reading. The experiment was repeated to increase reliability. The results
again were concordant. The acidity of Irn Bru was expected, since it is in equilibrium with
carbon dioxide.
Evaluation of Results
????????? I can’t do these stupid error things!
Where about do I put these pictures??
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
References
Rutter P., 2004, Community Pharmacy: Symptoms, Diagnosis and Treatment, Churchill
Livingstone, University of Portsmouth, UK, p76
Kaulmann F. K., 2003, What is pH and how is it measured?, Hach Company, USA, p3-8
Atkins P. W., 1988, Chemistry: Principles and Applications, Longman Group UK, UK, p207
URL: http://homepage/smc/edu/kline_peggy/Chem_12/labs/iron_titration.pdf
Visited, August 2010
URL: http://www.sserc.org.uk/members/SafetyNet/bulls/201/chemistry.htm
Visited, September 2010
URL:
http://www.techknow.org.uk/wiki/index.php?title=Determination_of_glucose_using_titrati
on
Visited, September 2010
URL: http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/beers1.htm
Visited, August 2010
URL: http://www.creative-chemistry.org,uk/alevel/modules/documents/n-ch5-02.pdf
Visited, August 2010
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Advanced Higher Chemistry Investigation
Analysis of Irn Bru
Figure References
Figure 1: Structural Formula of Haemoglobin
URL: http://www.sugars4life.com/images/haemoglobin-healthy.png,
Accessed: February 2011
Figure 2: Tertiary Structure of Haemoglobin
URL: http://www.molecularstation.com/molecularbiologyimages/data/505/Haemoglobin.png,
Accessed: February 2011
Figure 3: The Electromagnetic Spectrum
URL: http://www.lcse.umn.edu/specs/labs/images/spectrum.gif
Accessed: February 2011
Figure 4: Structure of Potassium Thiocyanate
URL: http://upload.wikimedia.org/wikipedia/commons/4/4a/Potassium-thiocyanate-xtal3D-vdW-B.png,
Accessed: February 2011
Figure 5: Aldehydes and Ketones
URL: http://www.elmhurst.edu/~chm/vchembook/images3/700carbonyl.GIF,
Accessed: February 2011
Figure 6: Glass Electrode
URL: http://glossary.periodni.com/image/glass_electrode.gif,
Accessed: February 2011
23