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Level 7 HL Chemistry IA (Moderated 23/24) - Complexometric determination of the calcium content in chickpeas at different time intervals of simmering

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This HL chemistry IA was predicted perfect score (24/24) but was marked down through moderation. For such a high-scoring IA the practical work was actually quite simple. This high-quality example will surely guide you through your own IA and will help you cater to each of the criteria.

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ib chemistry hl
level 7 hl chemistry ia
moderated
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international baccalaureate ib
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, jfx415
Complexometric determination of the calcium content in chickpeas at different time
intervals of simmering
Research Question:
How does the calcium content change over simmering durations of 15, 25, 35, 45, and 55 minutes, when measured
using complexometric titration with Eriochrome Black T indicator?

Introduction:
Recent studies have indicated that cooking is likely to reduce a vegetable's nutritional content, which has led to a
rise in the popularity of raw food diets. After boiling chickpeas and observing how the broth changed in colour, I
wondered whether that meant the chickpeas were losing their nutritional value. Raw food diets are frequently criticised
with claims that the amount of nutrients lost is inconsequential. Nevertheless, malnutrition-related illnesses continue to
plague developing nations, therefore, it would be valuable to have a precise quantitative understanding of how our
cooking habits influences the nutrition of our food.
Chickpeas are a staple of Middle Eastern cuisine, known for their role in the iconic dip hummus, these legumes are
packed with flavour and calcium containing approximately 1 mg per gram of chickpeas1. Since chickpeas are typically
cooked for an hour before consumption, they make the ideal research subject for examining how our cooking culture
influences their nutrient quality. Chickpeas are usually brought to a boil and then left to simmer, therefore examining
the impact of simmering periods on their calcium content seems to be more relevant than doing so for cooking
temperatures. This will yield relevant findings for applications in the real world. Hence, the following research question
is raised:
How does the calcium content change over simmering times of 15, 25, 35, 45, and 55 minutes, when measured
using complexometric titration with Eriochrome Black T indicator?

Background Information:
Calcium is a mineral essential for humans to maintain healthy bones and teeth. It is also used to spur muscle, in fact
any organism with a distinct musculature depends on calcium to simply move. To maintain a healthy body, the average
adult is recommended a daily intake of 1000mg of calcium2. Calcium is found mostly in dairy products, therefore
lactose intolerant individuals would need to maximise their intake of calcium from other sources, such as chickpeas. As
aforementioned, there is 1mg of calcium per gram of raw chickpeas, however this is likely to decrease after it is
cooked. This would be due to water’s property as a leecher, whereby the constituents of the chickpeas are dislodged by
the water's kinetic energy3. Calcium is also lost through oxalic acids. These molecules are usually bonded to minerals
like calcium, and when they are exposed to heat they release the bound calcium as a result of their heat sensitivity4.
The method used to determine the calcium content of the chickpeas is a complexometric titration which is a type of
volumetric analysis whereby the formation of a coloured complex is used to indicate the endpoint of a titration5. The
molecule Ethylenediaminetetraacetic acid (EDTA) is used for this process and can be seen in Figure 1 below. As a

1
“Fooddata Central Search Results.” FoodData Central, https://fdc.nal.usda.gov/fdc-app.html#/food-details/173756/nutrients.
2
McCallum, Katie. “Should You Be Taking a Calcium Supplement?” Houston Methodist On
Health:https://www.houstonmethodist.org/blog/articles/2021/oct/calcium-supplements-how-much-calcium-is-too-much/#:~:text=How%20much
%20calcium%20do%20you,over%20the%20age%20of%2071.
3
Styles, Serena. “Nutrition of Sprouted Chickpeas.” Healthy Eating | SF Gate, 28 Nov. 2018,
https://healthyeating.sfgate.com/nutrition-sprouted-chickpeas-1991.html
4
Beck, Leslie. “What Is the Healthiest Way to Cook Vegetables to Maximize Their Nutritional Value?” The Globe and Mail, The Globe and
Mail, 28 Nov. 2022,
https://www.theglobeandmail.com/life/health-and-fitness/health/leslie-beck-how-to-keep-the-vitamins-in-your-veggies/article23900957/?scrlybr
kr=032302a2#.
5
Vedantu. “Introduction to Complexometric Titrations.” VEDANTU, Vedantu, 29 Nov. 2022,
https://www.vedantu.com/chemistry/complexometric-titration.

1

, jfx415

polydentate ligand, nitrogen and oxygen atoms act as donors for coordinate bonding and form complex ions with other
metal ions, namely calcium and magnesium6.

Ca2+(aq) + EDTA4-(aq) → [Mg-EDTA]2-(aq)
Mg2+(aq) + EDTA4-(aq) → [Mg-EDTA]2-(aq)

Initially, an excess amount of EDTA4- is introduced into a sample solution so that all the calcium ions present would
transform into complexes7. The solution, now blue, will be unaffected after the Eriochrome Black T indicator (EBT) is
introduced as EDTA4- metal complexes are preferred. A magnesium solution is then titrated so that the additional
magnesium ions would bond with the excess EDTA4-. After the fact, EBT complexes will begin to form instead,
resulting in the solution changing to a pink colour, indicating the endpoint of the titration7.
H2In(aq) + Mg2+(aq) ⇋ MgIn(aq) + 2H+(aq)
(Blue) (Pink)
Magnesium ions and EDTA4- bind in a known 1:1 ratio, therefore with the amount of moles of magnesium ions, the
excess amount of EDTA4- can be determined. A 1:1 ratio is also found between the bonds of calcium and EDTA4- and
with the knowledge of how much EDTA4- is present in the solution we are able to deduce the amount of [Ca-EDTA]2-
complexes.

Hypothesis:
The kinetic energy of simmering water is extremely
high, therefore the calcium content on the chickpeas surface
will be prone to being dislodged and leached. As the
cooking time increases the leaching effect will only be more
potent as more layers of the chickpeas will be exposed.
Moreover, as heat is continuously exposed to the chickpeas,
the heat sensitive oxalic acids bonded to the calcium ions
are increasingly more likely to react and release the bound
ions. Therefore, it is predicted that the calcium content in
chickpeas will decrease as simmering time increases, this is
demonstrated in Figure 2. However, there is a point in which calcium content will stop declining. This is because there
are calcium ions that will have been bonded very strongly to other substances in the chickpeas which are not affected
by heat (i.e not oxalic acid). This is why the line curves and flattens towards a higher simmering time in Figure 2,
representing that of an inverse exponential function.

6
Libretexts. “Ligands.” Chemistry LibreTexts, Libretexts, 14 July 2020,
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Coordination_Che
mistry/Structure_and_Nomenclature_of_Coordination_Compounds/Ligands#:~:text=Polydentate%20ligands%20range%20in%20the,central%2
0metal%20atom%20or%20ion.
7
Determination of Calcium Ion Concentration - University of Canterbury.
https://www.canterbury.ac.nz/media/documents/science-outreach/calcium.pdf.

2

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Level 7 HL Chemistry IA (Moderated 23/24) - Complexometric determination of the calcium content in chickpeas at different time intervals of simmering

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