Investigating the effect of different temperatures on the amount of magnesium ions (Mg 2+) in sesame

seeds (Sesamum indicum)

Research Question
How does exposure to different temperatures (120, 150, 180, 210, 250 °C) effect the content
of magnesium ions (Mg2+) found in Sesamum indicum, determined by EDTA complexometric
titration with the use of Eriochrome Black T indicator?

I. Introduction
Magnesium plays an important role in assisting enzymes to carry out various chemical
reactions in the body such as building proteins, regulating blood sugar and blood pressure
while also acting as an electrical conductor that contracts muscles and makes the heart beat
steadily (Harvard T.H. Chan School of Public Health, 2023). The recommended dietary
allowance of magnesium can be achieved by taking supplements or including appropriate
food sources in ones diet such as nuts, beans, rice, pumpkin seeds or sesame seeds.
In this Internal Assessment I will be focusing on the magnesium content available in sesame
seeds as it is a food that is often used in my house for cooking meals. In order to bring out the
flavors from the seeds it is necessary to roast them, what in return can affect the nutritional
content within the seed. For example, Rizki et al. (2015) found that roasted sesame seeds had
higher levels of antioxidants and total phenolic, flavonoids, sugar, and protein contents,
compared to not roasted or boiled seeds. Moreover different temperatures of roasting could
have distinct effects on the content of the sesame seeds, therefore possibly on the magnesium
content. Arab et al. (2022) discovered that changing the temperatures in an oven used for
roasting sesame seeds, resulted in, for instance different amounts of phenolic, sesamine or
content of phytosterols.

Background information
EDTA complexometric titration is a type of complexometric titrimetry, which is used mainly
for determining metal ions by use of complex-forming reactions. Ethylenediaminetetraacetic
acid (EDTA) is most commonly used as a complexometric titrant due to its ability to form
stable complexes with most metal ions, where all the complexes have a 1:1 stoichiometry.
This method of titrimetry is also advantageous because of the rapidity of the reaction (Miró et
al. 105-113).
Figure 1. Deprotonated EDTA molecule on the left and six-coordinate metal-EDTA complex with
magnesium ion on the right (Harvey, 2014).

As seen in Fig. 1, EDTA donates electrons from its lone pairs to the magnesium ion and forms
coordinate covalent bonds with Mg2+. The reaction between a metal ion (Men+) and EDTA
(H4Y) can be written as a competition between the metal ion and hydrogen ion for binding
with Y2-:

(1)

where the stability of the binding can be measured by the equilibrium constant. Additionally,
since this reaction creates protons (H+), to avoid pH changes during the next step of titration it
is important to first buffer the solution (Miró et al. 105-113).

Organic dyes, such as Enchriome Black T (EBT), are most commonly used as metallochromic
indicators in complexometric titrations. EBT forms a colored complex with the metal ion,
which during the reaction is replaced by EDTA in order to form a more stable complex with
the metal and after the reaction is completed a change in color can be observed. Since EDTA
in itself is colorless when all magnesium ions are bound to it, the addition of the EBT
indicator allows for a blue color of the solution. In order to allow EBT to bind the magnesium
ions excess moles of EDTA need to be added and the solution needs to be back titrated with a
solution of magnesium chloride (MgCl2), which can bind to EDTA instead of the magnesium
ions. Enchriome Black T reacts with magnesium ions as seen in equation (3) (Miró et al. 105-
113). Back titration reaction can be seen in equation (2) (University of Canterbury). Then
based on the amount of MgCl2 titrated, the amount of magnesium ions can be determined.

(2)

(3)

II. Investigation

Hypothesis

In thermodynamics heated particles have an increased kinetic energy compared to non-heated

particles. If the amount of energy is sufficient the bonds in compounds will start to break
allowing ions or other molecules to form. The higher the temperature the greater the kinetic
energy, allowing more bond breakage to occur (Libretexts, 2022). Therefore, increasing the
temperature subjected to Sesamum indicum will increase the mass of available magnesium
ions.

Variables
Independent variable: roasting temperature (120, 150, 180, 210, 250 °C)

Dependent variable: mass of magnesium ions (Mg2+)

Controlled variables

Variable How was it controlled? Why was it controlled?

Type of seeds All seeds were bought Different types of
from the same store and Sesamum indicum can be
the same brand. bought (e.g different color,
brand) and they can differ
in contents.
Roasting time of seeds The sesame seeds were all The amount of time the
roasted in the same oven seeds are exposed to
for 10 minutes measured effects the amount of
with a stopwatch. kinetic energy provided,
therefore changing the
number of magnesium
ions released from
compounds within the
seeds.
Mass of sesame samples Each sample of sesame The mass of the seeds had
seeds was the same, to be controlled since it
measured by a scale(± ?) influences the amount of
magnesium ions and could
skew the results.
EDTA concentration and The same volume and EDTA in the solution has
volume concentration of EDTA to be in excess to allow it
was used for all existing to bind with the
samples. magnesium ions. Its
volume and molar
concentration also need to
be the same for all samples
in order to obtain accurate
results.
pH The pH was controlled EDTA and EBT molecules
using a buffer (?). need a basic pH in order to
bind with magnesium ions.
Moreover, a pH of 7-11 is
needed for the EBT
indicator to change its
color.
Volume of EBT indicator The same amount of EBT The same amount of EBT
was added to all samples. indicator is needed to
achieve a similar color
intensity in all of the
samples.
Type and volume of water The same volume of Distilled water is not
distilled water was used mineralized and therefore
for all samples. will not influence the
 results of the experiment.
Volume and concentration The volume and molar A different MgCl2
of MgCl2 concentration used was the concentration added to the
same in all trails. samples would result in
different endpoints of the
back titration.

III. Methodology

Materials and apparatus

Risk assessment and ethical issues

 There were no ethical considerations in this experiment.

 A laboratory coat and gloves were worn during the experiment


Arab, Radia, et al. “Effects of Seed Roasting Temperature on Sesame Oil Fatty Acid
Composition, Lignan, Sterol and Tocopherol Contents, Oxidative Stability and
Antioxidant Potential for Food Applications.” Molecules, vol. 27, no. 14, 2022, p. 4508,
doi:10.3390/molecules27144508. [Accessed 31 Aug. 2023]

College of Science, University of Canterbury. Determination of Total Calcium and

Magnesium Ion Concentration. [Accessed 3 Sept. 2023]

Harvard T.H. Chan School of Public Health. “Magnesium.” The Nutrition Source, 7 Mar.
2023, www.hsph.harvard.edu/nutritionsource/magnesium/. [Accessed 31 Aug. 2023]

Harvey, David. “Complexation Titration.” Chemistry LibreTexts, Libretexts, 2014,

chem.libretexts.org/Bookshelves/Ancillary_Materials/Demos,_Techniques,_and_Experi
ments/General_Lab_Techniques/Titra tion/Complexation_Titration. [Accessed 31 Aug.
2023]

Kozak, Joanna, and Alan Townshend. “Titrimetry | Overview.” Encyclopedia of Analytical

Science (Third Edition), by Manuel Miró et al., Academic Press, 2019, pp. 105–113.
[Accessed 31 Aug. 2023]

Rizki, Hajar, et al. “Effects of Roasting Temperature and Time on the Physicochemical
Properties of Sesame (Sesamum Indicum .L) Seeds.” International Journal of
Innovation and Applied Studies, vol. 11, no. 1, Apr. 2015, pp. 148–155. [Accessed 31
Aug. 2023]
“7.2: Heat Changes during Chemical Reactions.” LibreTexts Chemistry, LibreTexts,
chem.libretexts.org/Courses/Saint_Francis_University/CHEM_113%3A_Human_Chem
istry_I_(Zovinka)/07%3A_Chemical_Reactions_-_Energy_Rates_and_Equilibrium/
7.02%3A_Heat_Changes_during_Chemical_Reactions. [Accessed 3 Sept. 2023]