Pourya Masoudian
SCH4U1-02
Formation and Treatment of Kidney and Gall Stones:
1. Kidney Stones
Background information:
Kidney stone is defined as, solid accumulation of chemical
deposits that are formed inside the urinary tract. Kidney stones are
made of different types of crystals. They vary in size and compositions
depending on the concentration of ions present in the urine.
Patients are treated depending on the severity of the stones in their body. 90% of the stones are
passed out through uterus by drinking a lot of fluids, which increases the solubility of the urine in
kidneys. Other treatments involve the use of Extracorporeal Shockwave Lithotripsy (ESWL), which
uses non-electrical shock waves to break the stones into small pieces to make it easier for kidney to
pass them out.
Connection #1: The common-ion effect and solubility (an application of Le Châtelier's
principle) in formation of calcium oxalate and calcium phosphate stones
Consider the reactions below:


CaC2O4(s) ⇔ Ca2+(aq) + C2O42-(aq)
Ksp = 1.5x10-8 = [Ca2+][C2O42-]
2+
3Ca3(PO4)2 (s)⇔ 3Ca (aq) + 2PO4 (aq), Ksp =2.07x10-33 = [Ca2+]3 [PO43-]2
The solubility of both calcium oxalate and calcium phosphate is very low
because of the small value of Ksp. When the concentrations of calcium, oxalate,
and/or phosphate ions are high, Qsp > Ksp. As a result, the equilibrium will shift
to the left and precipitation forms.
An increase in water consumption will lead to a rise in the volume of urine. As a result, the
concentration of ions decreases and equilibrium shifts to the right, producing more dissolved ions.
Diet can also be crucial in prevention and treatment of stones. Consumption of certain foods can
increase the concentration of certain ions in urine and stimulate the formation of stones.
Connection #2: Weak acid and conjugate base equilibrium and the pH level of the urine
a. An interesting indication of the presence of calcium phosphate stone is the alkaline level of
urine, with pH usually above 7.2. This is because phosphate ions act as the conjugate base of the
hydrogen phosphate ions:
 HPO42-(aq) + H2O(l) ⇔ PO43-(aq)+H3O+(aq)
 Kb = 1x10-14/4.8x10-13 = 2.08x10-2
Ka = 4.8x10-13
Since the value of Ka is much smaller than Kb, the phosphate ions tend to react with water to
produce hydrogen phosphate and hydroxide ions:

PO43-(aq) + H2O(l) ⇔ HPO42-(aq) +OH-(aq)
As a result, the formation of calcium phosphate stones, which is due to the high concentration of
phosphate ions, is indicated by the basic level of urine.
Pourya Masoudian
SCH4U1-02
b. The formation of uric acid stones is favoured in acidic conditions. Consider the acid
dissociation reactions of this weak polyprotic acid:
 C5H4N4O3(s) ⇔ C5H3N4O3-(aq) + H+(aq)
 C5H3N4O3-(aq) ⇔ C5H2N4O32-(aq)+ H+(aq)
Ka1= 1.78x10-6
Ka2=5.01x10-11
The first dissociation constant is much bigger that the second one. As a result, under normal
conditions, the production of hydrogen urate (C5H3N4O3-(aq)) is favoured. When the pH decreases,
the concentration of hydrogen ions is high. Therefore, both first and second reactions shift to the left
and uric acid stone is formed.
2. Gallstone
Background information:
Gallstones are pieces of solid materials that form in gallbladder.
They form when bile stored in gallbladder hardens into crystal-like
particles. They contain cholesterol and a low percentage of bile pigments
(which contain calcium bilirubinate.) Gallstone usually forms when too
much cholesterol is present in gallbladder.
One of the most common non-surgical treatments is consumption of Urisodiol. It is a secondary
bile acid that reduces cholesterol absorption in the intestine and helps dissolving cholesterol.
Moreover, Gallstone can be broken up using Extracorporeal Shockwave Lithotripsy (ESWL).
Similar to Kidney stones, gallstones are broken into tiny pieces and passed. Surgical treatment
which involves the complete removal of gallbladder is used in severe cases.
Connection #3: The role of intermolecular forces and polarity in solubility and formation of
cholesterol gallstones
Cholesterol is made of 3 parts. A hydrocarbon tail, four hydrocarbon
rings, and a hydroxyl (OH) attached to the hydrocarbon ring. Since the ΔEN
of C–H is 0.35 it is mostly covalent. However, H-O bond with ΔEN of 1.24
is polar covalent. An interesting property of cholesterol molecule is that it is
amphopathic. It means that a part of the molecule is soluble in water while
the other part is insoluble. In cholesterol, the hydrocarbon tail and rings are
insoluble. The only soluble part is the hydroxyl head. Since it is polar, it can
form hydrogen bonds with water molecules and therefore it is soluble in water.
insoluble
Bile salts give rise to interesting microstructures that serve as cholesterol
transport vehicles. These microstructures are called “Micelles”. These micelles
consist of phospholipids, which are molecules with phosphate polar heads to
help them transport better in water. Cholesterols are surrounded by the non-polar hydrocarbon tails
of phospholipids inside the micelle. Deficiency of the production of micelles can result in formation
of solid cholesterol crystals in gallbladder.
Pourya Masoudian
SCH4U1-02
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