operation oaxaca: pre-lab jargon.

technical material (009)

Carlos Manuel Jarquín Sánchez
4 min readFeb 6, 2024

this is carlos.

time to explain some research i’ve been going over before entering the lab.


’cause failing to prepare leads to failure.

normally, i review material my past self wrote for this moment:

but this is serious.

ppl gave me money to pull it off.

so now, i got something to lose.


onto the material.

i’ll define each term, explain it, and why it’s relevant.


edit: next time, i’ll go over isotherms and the desorption process. some things to consider when making the next update.

and as always, answer the big question: what is the problem?


the glue.

esterification → the process of combining an organic acid (R-COOH) with an alcohol (R-OH) to form an ester (R-COOR) and water…

or a chemical reaction resulting in the formation of at least one ester product.

R-COOH is a carboxylic acid.

they are anionic groups that can adsorb heavy metal ions.

fyi: metal ions are cationic.

anionic → an ion with a negative electrical charge, more electrons than protons for its respective isotope

cationic → an ion with a positive electrical charge, more protons than electrons for its respective isotope

the anions gotta form when they gain an electron that’s not bonded to an atom/molecule or other methods (i.e., ion exchange).

same thing for cations, but it must be protons.

the “R” in R-COOH stands for one of these molecules/compounds:

  • alkyl (most likely) || (i.e. CH2, CH3, methyl, ethyl, and more)
  • alkenyl (a hydrogen atom is removed from an alkene (H2C=CH2)
  • aryl
  • aromatic group
  • something else lol

why do i care?

this is what i will add to the surface area of the mango peel. so that it can adsorb the metal ions onto the peel.

adsorb → make molecules ‘stay’ on the surface of a material.

surface area: why i care.

for the mango peels:

imma use centimeters squard as the unit of measurement for length (or how small to cut the pieces).

these pieces will come from the original mango peel.

and from that peel, those pieces will be torn into chunks ranging from 0.02 – 0.06 cm² in size.

why tho?

i’m attempting to maximize surface area to obtain more bonding sites on the surface of the peel…

so that there are more chances of heavy metal ions binding to the peel.

for this purpose, here’s the explanation:

take a mango. it has a certain surface area and a certain volume.

let’s say area is 150 cm² & volume is 200 cm².

now, cut the entire mango into pieces. including the peel.

the volume is still the same. you didn’t add “more mango” into the original mango. (you could squish the cut pieces back together, if you wanted to.)

but the amount of surface area that exists did change.

the original surface area of the mango is still there. but you also exposed the inside surface of the mango (aka the part of the mango u eat).

that inner, juicy surface of the mango is now added/tallied onto the original surface area (before we theoretically started cutting the mango).


the volume stayed the same.

the total surface area went up.

so, smaller pieces of mango have a larger surface-area-to-volume ratio than a whole, uncut mango.

picture the box as the mango (or the mango peel).

pH power.

another thing to consider:

i bought Na-OH (or hydroxyl groups) to manipulate the acidity of the water…

to see how well the previous beads would form.

and they can also be used to test the ideal acidity (or pH) of the water to adsorb ions.

but how does the pH of the water affect the properties of the mango peel?

mango is somewhat acidic. it can range from pH 5.8 – 6.1


mango can accept acidic molecules at lower pH values. (pH 3)

the problem?

it may not adsorb as many ions as it possible can.

note this:

surface area expands as the mango is cut, as you expose more surface to the air/water.

but at pH values lower than seven, the water is “acidic”…

meaning there is a surplus of positively charged ions (hydrogen ions, H+), if we’re being exact.

guess what?

heavy metal ions are also positviely charged.

so the metal ions and the H+ will “fight” each other for the right to bond to the mango peel. (aka protonation).

(once we add carboxylate, carboxyl, and/or hydroxyl groups to the mango surface area peel, of course)

but what if we don’t want that?


crank up the pH… deprotonate the peel.

less H+ ions to fight for adsorption.

but how to change the pH?

typically, we add hydroxide ions (OH-).

they’re negatively charged, and can make the free H+ bond to the hydroxide ion and make one water molecule.

H+ & OH- is like a math problem that says (73e²– 73e²)…

they “cancel” each other out. (what does get “cancelled” is their positive/negative electrical charge.)

just to get an idea for the visual ppl

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