Lee Wonjae, Extended Essay

Wonjae Lee 003562–045 What is the effect of pH on the adsorption of caffeine by activated carbon?
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International Baccalaureate
What is the effect of pH on the adsorption of caffeine by activated
carbon?
Extended Essay – Chemistry
QUEENSLAND ACADEMY FOR HEALTH SCIENCES
Wonjae Lee
Date: 12/7/2013
Candidate number: 003562–045
Session number: November 2013
Word count: 3979

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Contents
Abstract........................................................................................Error! Bookmark not defined.
Introduction................................................................................................................................ 3
Method....................................................................................................................................... 5
Results and Analysis ................................................................................................................... 7
Results..................................................................................................................................7
Analysis................................................................................9Error! Bookmark not defined.
Conclusion................................................................................................................................ 11
Evaluation................................................................................................................................. 11
General evaluation............................................................................................................... 11
Evaluation of sources...........................................................13Error! Bookmark not defined.
Unresolved questions and direction for further investigation.................................................... 13
Bibliography............................................................................................................................. 15
Appendices ...................................................................................Error! Bookmark not defined.
Appendix I: Apparatus......................................................................................................... 17
Appendix II: Raw Quantitative Data..................................................................................... 18
Appendix III: Propagated uncertainty.................................................................................... 19
Appendix IV: Information about chemicals ........................................................................... 20

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Abstract
Caffeine is undoubtedly the most consumed and used drug in the world while the activated
carbon is renowned for its applications in removal of undesirable organic chemicals. This
experiment aims to investigate the effect of solvent (water) pH on the adsorption of 0.100g of
caffeine onto 0.100g of powdered activated carbon (PAC) after undergoing 25 hour of batch
treatment test. The research question that summarises this investigation is: “What is the
effect of pH on the adsorption of caffeine by activated carbon?”
Caffeine solutions of were prepared by dissolving No-Doz® tablets (100mg caffeine per tablet)
in 50ml of distilled water. The solutions underwent standard batch treatment with powdered
activated carbon (PAC) after the manipulation of pH using hydrochloric acid and sodium
hydroxide. The liquid-liquid separation technique with ethyl acetate was used separate the
caffeine from water. The amount of caffeine separated from the solution via ethyl acetate was
measured.
The results indicate that the decaffeination process through PAC is pH dependent process.
The percentage removal of Caffeine via PAC was 16% for pH 2; 24% for pH 3; 22% for pH
6.3; 52% for pH 9 and 58% for pH 11. Percentage removal versus pH graph suggested two
models: the exponential relationship, or the plateau model at a lower pH (< 6.31). Both
models indicate that the adsorption of caffeine onto PAC is significantly higher at a higher
pH. The PAC will adsorb the caffeine better from the basic solution then the acidic solution.
The result was attributed to the basicity of the caffeine where caffeine deprotonates with the
presence of strong base in the solution.
Word count: 266

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Introduction
The aim of this experiment was to investigate whether the different pH of solution would
improve the efficiency of the adsorption of caffeine onto powdered activated carbon (PAC).
Hence the research question is: “What is the effect of pH on the adsorption of caffeine
onto activated carbon?”
Caffeine
Caffeine (1, 3, 7-trimethylxanthine) is a xanthine alkaloid with three methyl groups attached
(see appendix IV). In the room temperature, it forms a bitter tasting clear crystal and is the
world’s most consumed and used drug (Shalmashi & Golmohammad 2010, pp. 283-285). It
occurs in common food and beverages such as chocolate, coffee, tea and various energy
drinks and is commonly used as a central nervous system (CNS) stimulant in the
pharmaceutical industry (Silverman, K & Griffiths, R 2001). With increasing abuse of
caffeine consumptions in urban society, its effect in human physiology and behaviour is
subjected for extensive research. Decaffeinated product, therefore, has attracted significant
attraction. For example, Swiss Water® decaffeination process1 is a method which is widely
practiced in coffee industry that utilises activated carbon to remove caffeine from coffee bean.
The solubility of caffeine at room temperature (25°C) is approximately 0.105M
(1020mg/50ml), therefore 100mg of caffeine will completely dissolve in 50ml (Open
Notebook Science Challenge, 2013). According to Spiller (ed.1998, p. 5), caffeine act as a
weak base with pKa value of is 14.2 at 19°C therefore reacts with acid. Its basic property is
characterised by single nitrogen with lone pair of electron. In the reaction, the caffeine salt is
formed which is readily hydrolysed. Spiller (ed.1998, p. 5), also found the evidence of
protonated caffeine formation at pH 0. The measured pH is closely related to the solubility of
caffeine in the water, typically due to the ionic bond form between water and caffeine to
create conjugate salt. With the presence of acid, caffeine will act as a cation (Cammack, J
2012, p. 3) which increases its water solubility. Conversely in the basic solute, caffeine will
remain neutral with little polarity.
Fig. 1 interaction of caffeine with water – When the caffeine is under acidic condition, because caffeine is
basic, it attracts proton (hydrogen) from the environment and attach it to one of the lone pairs of nitrogen2.
(Cammack, J 2012, p. 3)
1
Swiss Water Decaffeinated Coffee Company n.d., Science of Decaffeination,
http://www.swisswater.com/trade/the-swiss-water-experience/science-of-decaffeination
2
Cammack, J 2012, Lab 5: Extraction of caffeine from tea, Chemeketa Community College

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Adsorption
Bansal & Goyal (2005, p. 8) states that adsorption as the process which occurs “when a solid
surface is brought into contact with a liquid or gas.” Due to the surface energy, this contact
causes the surface between the solid surface and the gas/liquid to interact, which ultimately
causes ions, atoms and molecules (adsorbate) to be attracted to the solid surface (adsorbent),
such as activated carbon. This process accumulation of substances onto solid surface is
known as adsorption.
Activated carbon
Activated carbon is a versatile adsorbent (Bansal & Goyal 2005) and its adsorptive properties
characterised by its mesopores and macropores in the carbon structure. Activated carbon is
applied extensively in the field of purification, including the removal of taste, order, colour
and other organic and inorganic contaminant from food, waste water and air, while further
applications to its use is still building up. In the food processing industry, use of activated
carbon is also a safer alternative to the use of harmful chemicals such as chloroform and
dichloromethane.
Adsorption isotherms can be described as amount of impurity absorbed from aqueous media
by the absorbent such as activated carbon at an adsorptive equilibrium. This adsorptive
character is readily affected by the various properties of the target contaminant such as
molecular size, structure and mass, solubility and polarity. Experimental condition such as
the ionic strength and pH also influences the adsorptive character. Activated carbon involves
two types of adsorption: chemical and physical adsorption. Chemical adsorption refers to
situation in which the adsorbent and adsorbate shares and exchange electron which creates
much stronger bond then physical adsorption which involves van der Waals interaction.
László et al. (2007, p. 95) claims that pH of the solvent may modify the adsorptive surface of
the activated carbon. Interaction of water organic solute such as caffeine can alter with pH,
which may also influence the strength of attraction with activated carbon.
Solvent extraction
Solvent extraction is a common technique which is used to isolate the organic compound
present in the targe aqueous media. Ethyl acetate is an organic solvent commonly used as an
organic solvent due to its immiscibility with water, less toxic property then other organic
solvents and its ability to attract caffeine due to its polarity. Caffeine readily dissolves in
ethyl acetate. The solubility of caffeine on ethyl acetate at room temperature (25°C) is
approximately 0.041M. 100mg of caffeine will therefore dissolve in 15ml of ethyl acetate
(Open Notebook Science Challenge, 2013) which makes ethyl acetate a good organic solvent
when isolating caffeine from its aqueous media. Caffeine, however, is much more soluble in
water, therefore addition of base in the caffeine solution or the increase in the solvent pH will
http://faculty.chemeketa.edu/jcammack/CH241-3B%20Lab/CH241B%20Labs/CH241%205%20Caffeine%20Extraction.pdf
[Accessed 28 May 2013]

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improve the extraction due to change in solubility. Addition of salt such as sodium chloride
(NaOH) may also increase the efficiency of extraction as water is more attracted to salt then
caffeine (Cammack, J 2012, p. 3). Since ethyl acetate has lower density then water, the ethyl
acetate layer will be formed above the water.
Method
Preparation of caffeine solution
The caffeine solution was prepared carefully using the appropriate apparatus and a method
under a room temperature (25°C). On a single 100ml beaker, add approximately 40ml of
distilled water and then drop one No-Doz® Caffeine tablet (100mg of caffeine). The 100ml
beaker was left untouched until the tablet completely dissociated3. Undissolved solids were
then filtered out onto a 50ml volumetric flask using a filter paper and a funnel. The distilled
water was carefully added to the volumetric flask to 50ml margin. During this process
distilled water was added through the filter paper and the funnel which was used to filter in
order to flush down any caffeine solution remaining on the apparatus. Cap of the volumetric
flask was closed to minimise the interaction between air and caffeine solution made. Repeat
the above steps to prepare total of 18 identical caffeine solutions.
Manipulating pH
Initially, pH probe was calibrated using the pH 7 and pH 4 buffers. Two pH titration stations
were set up using the burette clamp and a retort stand: one for 1M hydrochloric acid solution
(HCl) and the other for 1% sodium hydroxide solution (NaOH). The retort clamp was also
used to hold the pH probe in a stationary position during the titration. The caffeine solution
was first transferred into a 100ml beaker and was placed below the burette. pH probe was
then placed inside the beaker so that the sensor of the probe is completely submerged inside
the caffeine solution4. After the pH probe reached equilibrium on its measurement, add drops
of either HCl or NaOH until desired pH has been reached (pH 2, 3, 9 and 11).
PAC batch treatment
PAC batch treatment (Norit Activated Carbon, 2001) refers to isotherm test where a certain
amount of PAC is dosed to a solution to investigate the change in the mass of the target
molecule. Approximately 100mg of powdered activated carbon (PAC) was obtained through
measurement using the electronic balance (±0.001g). The activated carbon was then added to
the caffeine solution which has already undergone pH moderation as written in the
“Manipulating pH” section. A stir bar was dropped gently into the beaker which was then
placed on the magnetic stirrer and was set the medium stirring speed5. Watch glass was
placed on top of each beaker to minimise its interaction of solution with air. The stirring
underwent for 24 hours. Upon completing of stirring, the PAC was then filtered out from the
3
May takeup to 1 hour
4
100ml beaker was swirled gently after every drop of HCl or NaOH
5
6 stirring station was set up at once

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caffeine solution using double layer of laboratory filter paper. This was done to minimise the
amount of PAC which penetrate through the filter paper.
Controlling pH
In order to control the pH of the solvent, following procedures were performed before
undergoing liquid solvent separation:
1. Additional HCl solution (1M) was added to caffeine solution that the total amount
of HCl solution present in the solution is exactly 0.75ml. This means that if the
solution already contained HCl solution due to “Manipulating pH” procedure, the
amount of HCl added was 0.75ml subtracted by the amount HCl solution already
present in the solution6.
2. The same rule was applied for NaOH solution as HCl so that the amount of NaOH
solution present in the caffeine solution was always 6ml. This was done to
maintain pH 11 for all trials to increase the effectiveness of liquid-liquid separation.
Liquid-liquid separation
The filtered caffeine solution was poured into a separatory funnel. 15ml of ethyl acetate was
then added into a same separatory funnel using the 10ml graduated pipette. The separatory
funnel was inverted 3 times and then the stop cock was opened to release the gas. This was
repeated 4 times. The solution was then settled for 15 minute, and then the organic solvent
(ethyl acetate) layer (upper layer) was collected onto 100ml beaker which its mass has been
measured prior to this event. The beaker was placed in a water bath (80°C) to speed up the
evaporation of ethyl acetate. When the ethyl acetate evaporated completely, clear and dry
caffeine crystal complexes were formed. The mass of the beaker was measured again and was
recorded. This procedure was repeated for all 17 other solutions.
(See appendix I for the full list of apparatus and materials used in the experiment)
6 With 0.75ml HCl present in the caffeine solution, the pH is approximately 4.00

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Results and Analysis
Results
The mass of caffeine collected after the liquid-liquid separation process was determined by
finding the difference between the mass of the beaker when it was empty and after the
caffeine crystal is formed (see appendix 2 for Raw Data).
Table 1: Table of yields of caffeine after PAC batch treatment procedure (0.100 ±0.001g of PAC)
for different pH
pH ±0.01
Mass ofCaffeine
collected (trial 1)
/g ±0.002
Mass ofCaffeine
collected (trial 2)
/g ±0.002
Mass ofCaffeine
collected (trial 3)
/g ±0.002
Average mass of
caffeine collected
/g ±0.002
2.11 0.013 0.014 0.015 0.014
3.10 0.013 0.014 0.011 0.013
6.31 0.012 0.012 0.015 0.013
9.14 0.008 0.009 0.007 0.008
11.03 0.008 0.005 0.008 0.007
Table 2: Control for comparison: Table of yields of caffeine without PAC batch treatment
procedure (0.100 ±0.001g ofPAC) without the manipulation of pH
pH ±0.01
Mass ofCaffeine
collected (trial 1)
/g ±0.002
Mass ofCaffeine
collected (trial 2)
/g ±0.002
Mass ofCaffeine
collected (trial 3)
/g ±0.002
Average mass of
caffeine collected
/g ±0.002
6.17 0.015 0.019 0.016 0.017
It is important to analyse the effectiveness of liquid-liquid separation of caffeine in an
aqueous state using ethyl acetate. Single caffeine tablet contained 100mg of caffeine,
therefore the efficiency of the ethyl acetate liquid separation of caffeine was found in
percentage.
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 100 ×
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑓𝑓𝑒𝑖𝑛𝑒 𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑒𝑑
0.100𝑔⁄
= 100 × 0.017
0.100⁄
= 17%
Therefore ethyl acetate can absorb 17% of caffeine present in 50ml of distilled water
containing 0.100g of caffeine at a standard condition7. Therefore in order to fully understand
the effectiveness PAC on caffeine removal, the percentage removal of caffeine was found and
compared to observe the effect of pH on adsorption of caffeine onto PAC.
Percentage removal of caffeine is defined as:
7
Temperatureof 25°C, atmospheric pressureand no manipulation of pH

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100 ×
𝑐𝑜𝑛𝑡𝑟𝑜𝑙 𝑓𝑜𝑟 𝑐𝑜𝑚𝑝𝑎𝑟𝑖𝑠𝑜𝑛 − 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑎𝑓𝑓𝑒𝑖𝑛𝑒 𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑒𝑑
𝑐𝑜𝑛𝑡𝑟𝑜𝑙 𝑓𝑜𝑟 𝑐𝑜𝑚𝑝𝑎𝑟𝑖𝑠𝑜𝑛
*Control for comparison is always 0.017g
For example, if this is applied to pH 2.11, the percentage removal of caffeine is determined as:
100 ×
0.017 − 0.013
0.017
≈ 16%*
*NOTE: the stated value of “control for comparison” or the “average mass of caffeine
collected” is only an estimate up to three decimal places. Exact value may differ due to
averaging.
Table 3: Percentage removal ofcaffeine after PAC batch treatment procedure for different pH
pH ±0.01
Average mass of
caffeine collected /g
±0.002
Average mass of
caffeine removed from
0.017g /g ±0.004
Percentage removal of
caffeine via PAC (%)
2.11 0.014 0.003 16
3.10 0.013 0.004 24
6.31 0.013 0.004 22
9.14 0.008 0.009 52
11.03 0.007 0.010 58

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The pH can be plotted against the percentage removal of caffeine via PAC on a scatter gram
to investigate the interrelationship between each other and independent and dependent
variable.
The above graph establishes exponential relationship between pH and the percentage of
caffeine removed via adsorption onto PAC. In the graph, it is evident that with increasing pH
of the solution increases the amount caffeine adsorbed onto 0.100g of PAC when exposed for
24 hours.
Analysis
Uncertainties
The propagated uncertainty of the average value of both solvent pH and the caffeine removed
(%) was found and was used for the error bars on graph 1 instead of instrumental error for.
The uncertainty of weighing scale was particularly high due to small quantity of caffeine
extracted and low precision of the scale. The table 3 shows the uncertainty of the average
mass of caffeine removed which was ±0.004g which is extremely high compared to the actual
measurement (e.g. 0.003g).
See appendix III for more information on the propagated uncertainty
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Caffeineremoved/%
pH/ ±0.01
Graph 1: Caffeine removed from the watervia adsorption
onto PAC with varying pH

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General discussion of trend
Instead of the mass of caffeine removed from water, the in percentage removal was plotted
against pH as it provides information on effectiveness of the use of activated carbon.
Percentage removal indicates the amount of caffeine removed relative to the initial amount of
caffeine present in the solution. The increasing percentage removal also suggests that more
caffeine is adsorbed into same amount of activated carbon, which proposes increase in the
efficiency of PAC.
From Graph 1, it can be seen that while increasing the pH may increase the adsorption of
caffeine onto PAC, however it is difficult to conclude whether decreasing the pH would
reduce the adsorption of caffeine. There are two suggested interpretations of results from the
graph. Firstly, if the exponential relationship is true, then the percentage removal of caffeine
via PAC and the rate of increase of the removal augment with increasing pH, therefore
decreasing pH reduce the percentage removal of caffeine but considerably at a much slower
pace.
Secondly, the graph may also be interpreted as a curve with one plateau reaching the
minimum at lower (acidic) pH (< pH 6.31). The data from pH 2.11, 3.10 and 6.31 shares
extremely similar results (0.014, 0.013 and 0.013 respectively) where all data falls into an
error bar. The percentage removal of caffeine is only slightly higher for pH 3.10 then pH 6.31,
which is a signal that the decrease in pH after a specific pH may have no influence on the
efficiency of adsorption of caffeine onto activated carbon. This indicates that the percentage
removal of caffeine plateaus and move towards its minimum as pH decreases. Considering
the pKa of caffeine which is 14.2 at 19°C (ed.1998, p. 5) most caffeine maybe already
protonated due to acidic condition therefore further decrease in pH have lesser effect on the
solution and solubility of caffeine. According to the graph, the equivalence point may exist
between pH 6.31 and 9.14 where the removal of caffeine is at its average efficiency. At a
higher pH (pH 9 and pH 11) shares rather similar results as well (52% and 58% respectively)
and therefore it can be suggested that the percentage removal of caffeine also plateaus and
move towards its maximum as pH increases. The explanation is similar to the one on acidic
pH this as most caffeine maybe deprotonated at a high pH, however there is lack of data point
at a basic pH (> pH 7) to reach this conclusion. The fact that no pH over 14.2 was tested does
not give us clear indication as to whether the percentage removal of caffeine is only
influenced by the change in solubility due to pH.
In both of the interpretation agree that when the pH of caffeine solution is higher, the
percentage removal of caffeine via adsorption onto PAC increases, therefore the
decaffeination process will be more effective under basic condition above pH 9.14.

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Conclusion
The results showed that the increase in pH to the basic region (> pH 7) significantly
improved the adsorption of caffeine by powdered activated carbon (PAC) after being exposed
to PAC for 24 hours; hence answering the research question: “What is the effect of pH on
the adsorption of caffeine by activated carbon?”
The percentage removal of Caffeine was 16% for pH 2.11; 24% for pH 3.10; 22% for pH
6.31; 52% for pH 9.14 and 58% for pH 11.03. Graph 1 suggested exponential relationship or
a curve with plateau at a lower pH (< 6.31). These relationships suggest that the increasing
basicity of solution increases the adsorption of caffeine via PAC, and as the solution becomes
more acidic, adsorption decreases only slightly or plateaus to the minimum. This suggests
that the adsorption of caffeine most efficient when the pH of the solvent (water) is higher
than pH 11.
Evaluation
General evaluation
There were generally a lot more problems during the experiment then predicted. These
problems involve both random and systematic errors as well as assumptions which may have
impacted the results significantly.
The possible random error was identified in the mass of caffeine isolated and measured. The
weighing scale could read up to a milligram while the mass of caffeine extracted was mostly
just over or below 10mg, therefore the results was found in either one or two significant
figures. After several subtractions of between the results to find the mass of caffeine removed
from the solution, the measurement error and the propagated uncertainty increase, while the
propagated uncertainty reached 130% for the percentage removal of caffeine at pH 3.10. This
random error impacted the precision of the data significantly, which questions whether the
results of this experiment are reliable. Nonetheless the solution for this problem is rather
simple. It is recommended that more caffeine tablets are used for each caffeine solution (e.g.
2 caffeine tablets per 50ml). This will increase the overall magnitude of the data where more
caffeine is adsorbed or extracted, therefore increasing the precision of the data. It is also
suggested that the amount PAC and used is increased as well. With 200mg of caffeine per
50ml, 0.200mg of activated carbon should be used to match the mass with the mass of
caffeine present in the solution. Another alternative solution is to use much more precise
weighing scale to increase precision, possibly the one that can measure down to 0.1mg.
It was extremely difficult to control same stirring speed for all PAC batch treatment test due
to inconsistency in the stirring apparatus. Some stirring bar worked much more efficiently
while some magnetic stirrer produced much stronger magnetic field. Out of 6 magnetic
stirrers which were used in the experiment, one of the magnetic stirrers was exceptionally fast

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even if when the stirring speed was set to low. It is implied that slight difference in the
stirring speed may have contributed to the overall lower precision of the results.
Amount of caffeine extracted from liquid-liquid separation using ethyl acetate was much less
than which was expected. The use of ethyl acetate which was used as a solvent during the
liquid-liquid separation was only 17% efficient from isolating caffeine from its aqueous state.
This Ethyl acetate can also be changed for more effective organic solvent. The investigation
by Shalmashi (2010, p.283-285) concludes that caffeine is most soluble in chloroform
(CHCl3). Caffeine is also extremely soluble in dichloromethane (CH2Cl2) and acetone
(CH3COCH3) which any of these three organic solvent can be a perfect and better alternative
to ethyl acetate. If the solvent is more soluble, it is possible that more caffeine is extracted
from the liquid-liquid separation technique, which will increase the overall precision of the
data.
Atomssa and Gholap (2011, p.1-8) have proposed that the concentration of for caffeine
present in various solvent including water can be investigated using the UV-vis spectroscopy
at ultra violet region. When caffeine is dissolved in water, λmax occurs at 272.8 nm, and using
the calibration curve, the concentration of caffeine can be found. This procedure can replace
liquid-liquid separation process and provide much more precise measurement of the amount
of caffeine present after the filtration.
The way in which the caffeine solutions were prepared has implication which may have
influenced the data significantly. Despite the fact that the 50ml volumetric flask in which the
caffeine solution was stored was sealed with the glass cap, most of the solution contained
small culture of fungi which all had similar visible structure. Its green colour and a shape
resembled those of Penicillium expansum, which further research into this area, showed that
the particular penicilium called Penicillium commune, is capable of degrading the caffeine
(Long, 2013). This systematic error maybe the explanation for the small mass of caffeine (<
0.020g) extracted from liquid-liquid separation procedure for all trials, therefore it was
appropriate to use percentage removal of caffeine rather than the mass of caffeine removed.
However it is extremely difficult to conclude which direction of problem is caused by the
presence of fungi. The culture may be indicating the possible impurities in the caffeine
solution such as glucose, which is the common filler in the tablet and main food for fungi.
The growth of fungi can be controlled and prevented by simply storing all the caffeine
solutions in a laboratory refrigerator, then let the solution reach the room temperature just
before the experimentation.
One of the biggest assumptions in the experiment regarding with the caffeine solution was its
purity. It was assumed that simple filtration with the standard laboratory filter paper maybe
enough to remove all the unnecessary fillers from the caffeine tablet out of the caffeine
solution. It is possible that the impurities in the caffeine solution may have interacted with the
activated carbon and therefore reducing the overall percentage removal of caffeine due to
competitive adsorption. This systematic error may decrease overall accuracy of the results.

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However it is difficult to conclude whether the results were accurate or inaccurate due to
absence of literature value which can be compared with.
Evaluation of sources
The sources generally can divide into two categories: primary and secondary sources.
Primary sources are considered more reliable, however the secondary sources were only used
after examining references mention and see whether the statement is reliable, therefore the
uncertainty of using the secondary sources decreased. Books generally conceived more
reliable than the webpages, the reliability of the information from the webpage is rather
debatable. The use of journal articles was most successful as they are primary sources.
Wide variation of literature value of pKa was found from various sources. The pKa value was
taken from a book written by Spiller (ed.1998, p. 5); however it is important to question its
validity. It is suggested that prior to the experiment, the pKa value of caffeine should be
found through experimentation by creating a pH titration curve, which will provide valid pKa
of caffeine to be considered in the introduction and discussion. Investigation into pKa of
caffeine and its isoelectric point may also be an interesting approach for a further
investigation.
Unresolved questions and direction for further investigation
The lack of data point for the graph 1 left one fundamental question as to what exactly is the
relationship between pH and the adsorption of caffeine onto activated carbon. Whether the
relationship is one of the two theories suggested (exponential relationship, or the plateau at
low pH) or the other relationship. If more results from wide variety of pH are plotted, the
relationship between the percentage removal of caffeine and the pH will be more distinct.
Many research in the field of adsorption investigate adsorption isotherms (Bansal & Goyal
2005). Finding the adsorptive isotherms of caffeine on powdered activated carbon may give
more useful information. Adsorptive isotherm will provide with adsorption equilibrium of
caffeine solution at a specific pressure and temperature, general adsorptive characteristics of
caffeine as well as the properties of PAC such as its pores volume, the surface area and the
size distribution. Since the properties of PAC that was used in the experiment provided itself
with no written physical properties, it will be interesting to investigate the properties of the
PAC and perhaps compare with the activated carbon with the different property.
There exists alternative ways of investigating the effectiveness of adsorption of caffeine
dissolved in water onto activated carbon. Granular activated carbon (GAC), characterised by
bigger carbon particle size compared to PAC, is also commonly used in a waste water
treatment due to its high surface area and volume ratio (Sotelo et al. 2012). Sotelo et al. (2012,
p.967-974) investigated the removal of caffeine in fixed bed column design utilising GAC
which is also an interesting and reliable method of investigating the adsorption of caffeine
onto activated carbon.

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The question as to whether the caffeine crystals extracted using the liquid-liquid separation is
pure remains unresolved. It had been assumed in the experiment that the caffeine extracted
using the liquid-liquid separation was pure caffeine crystals and it would be interesting to
investigate the purity of the content. The purity can be examined using a melting point
determination test which is designed specifically to investigate the purity of crystals such as
caffeine8, although the difficulties lies in caffeine’s ability to sublime at an atmospheric
pressure. Alternatively, temperature in which sublimation of caffeine occurs can be found to
detect the purity of the solution. Further research discovered that Moyé (1972, p.194) have
developed a design of extracting mostly pure caffeine crystals from No-Doz® tablet. The
author also suggests the recrystallization of caffeine to extract pure caffeine from the mixture
crude caffeine and benzene using Büchner funnels.
With more advanced equipment such as Büchner funnels and potentially dangerous chemical
reagents such as chloroform and dichloromethane which is not provided in school laboratory,
it is possible to explore further and develop better method for the experiment. The concept of
this experiment is no doubt worthy of further investigation with more access to advanced
equipment.
Word count: 3979
8
The melting point of caffeine is 238°C (K) see appendix 4

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Bibliography
Atomssa, T & Gholap, A 2011, Characterization of caffeine and determination of caffeine in
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Bansal, R & Goyal, M 2005, Activated Carbon Adsorption, CRC press Francis & Taylor
group, United State of America
Cammack, J 2012, Lab 5: Extraction of caffeine from tea, Chemeketa Community College
http://faculty.chemeketa.edu/jcammack/CH241-
3B%20Lab/CH241B%20Labs/CH241%205%20Caffeine%20Extraction.pdf
Dews, P 1982, Caffeine, Annual Review of Nutrition, Vol. 2, p. 323-341
Guetta, D 2006, Acidity, Basicity and pKa, Columbia University,
http://www.columbia.edu/~crg2133/Files/CambridgeIA/Chemistry/AcidityBasicitykPa.pdf
László, K, Tombácz, E & Novák, C 2007, pH-dependent adsorption and desorption of phenol
and aniline on basic activated carbon, Colloids and Surfaces A: Physicochemical and
Engineering Aspects, vol. 306, no. 1-3, p. 95-101
Long, R 2013, Caffeine Pathway Map (fungal), 19 April, University of Minnesota,
http://umbbd.ethz.ch/caf2/caf2_map.html
Moyé, A 1972, Extraction of Caffeine, Journal of chemical education, vol. 49, no. 3, p. 194
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Carbot Corp.
http://www.norit.com/files/documents/Isotherm_Test_rev2.pdf
[Accessed 17 November 2012]
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http://www.norit.com/files/documents/Pilot_Col_Testing_rev2.pdf
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http://lxsrv7.oru.edu/~alang/onsc/solubility/allsolvents.php?solute=caffeine

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Penn State University Department of Chemistry, 2006, Liquid/Liquid Extraction, Penn State
department of Chemistry, Pennsylvania,
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Appendix I
Apparatus
List of equipment used in the experiment:
Glassware
(36) Beaker (100ml)
(18) Volumetric flask (50 ±0.2ml)
(6) Watch glass
(1) Glass Funnel
(1) Measuring cylinder (100 ±0.10ml)
(1) Separatory funnel (100ml)
(1) Graduated pipette (10 ±0.1ml)
(1) Stirring rod
(2) Burette (50 ±0.05ml) with a stopcock
Electronic supply
(6) Hot plate/magnetic stirrer
(6) Stir bar
(1) Water bath
(1) Pasco® pH probe/laptop
(1) Weighing scale
Other equipment
(33) Standard laboratory filtration paper
(3) Retort stand/boss head/retort clamp
(2) Burette clamp
(2) Spatula
Reagents andChemicals
No-Doz® Caffeine tablet
100mg caffeine per tablet
Powdered Activated Carbon – PAC
Atomic weight: 12.01
Impurities: Water ≤ 4%
Ash ≤ 13%
Particle size: 44μm 9
Ethyl Acetate (CH3COOCH2CH3)
Hydrochloric acid (HCl), 1M
Sodium hydroxide (NaOH), 1%
Distilled water
9 Generally accepted value proposed by Bansal & Goyal 2005

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Appendix II
Rawdata
Theexperimentalrecordingofdataiswrittenhere:

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Appendix III
Propagated uncertainty table
Table 3′: absolute and percentage uncertainty - Percentage removal of caffeine after PAC batch
treatment procedure for different pH
pH ±0.01
Average mass of
caffeine collected /g
±0.002
Average mass of
caffeine removed from
0.017g /g ±0.004
Percentage removal of
caffeine via PAC (%)
2.11 ±0.02 (1%) ±0.001 (7%) ±0.003 (82%) (82%)
3.10 ±0.05 (1%) ±0.002 (12%) ±0.004 (130%) (130%)
6.31 ±0.35 (6%) ±0.002 (12%) ±0.005 (88%) (88%)
9.14 ±0.04 (0%) ±0.001 (12%) ±0.004 (34%) (34%)
11.03 ±0.03 (0%) ±0.002 (21%) ±0.004 (36%) (36%)

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Appendix IV
Information about chemicals
Caffeine
(Silverman & Griffiths 2001, p.209)
Molecular formula: C6H10N4O2
Molecular Weight: 194.2
Sublimation: 178°C at 1 ATM
Melting point: 238°C
pKa: 14.2 at 19°C
(Sigma-Aldrich, 1999)

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