BIOCHEMISTRY
Notes on Chemical Properties of Water
Rostyslav, M. (2023). Physical and Chemical Properties of Water | Ecosoft Blog. Ecosoft.com. https://www.ecosoft.com/post/physical-and-chemical-properties-of-water
, BIOCHEMISTRY
Properties of Water I
(1st Sem Lecture Notes)
I. Overview: Importance of Water in Life
● Water as a Major Component of Life
Water plays a central role in the chemistry of life. It makes up about 60% to 95% of the mass of living
cells. This makes it the most abundant and essential substance in living organisms.
● Water Distribution in the Human Body
In humans, body water is distributed in two main areas:
○ Intracellular fluid (inside cells): ~55%
○ Extracellular fluid (outside cells): ~45%, which includes:
■ Plasma (blood fluid): ~8%
■ Interstitial fluid and lymph (between cells and in the lymphatic system): ~22%
■ Connective tissue, bone, and cartilage fluids: ~15%
● Water and Metabolism
For cells to perform normal metabolic functions, they must contain at least 65% water. Without this
level of hydration, essential chemical reactions in the body cannot take place efficiently.
Function of Water as Solvent for Biochemical Reactions:
1.Water as a Transport Medium
Water plays a critical role in transporting substances across cell membranes, facilitating the
movement of nutrients into cells and the removal of waste products out of cells.
● Through osmosis and diffusion, water enables the transport of ions, gases (like oxygen and
carbon dioxide), and nutrients such as glucose and amino acids. In multicellular organisms,
fluids like blood and lymph rely on water to carry these substances throughout the body
efficiently.
2. Water Helps Regulate Body Temperature
● Water assists in stabilizing body temperature by absorbing and redistributing heat.
● Thanks to water’s high specific heat capacity, it can absorb a lot of heat without drastically
changing temperature. This helps organisms maintain homeostasis. In humans, sweat (mostly
water) cools the body through evaporative cooling, preventing overheating.
3. Water as a Solvent in Digestion and Waste Removal
, ● Water dissolves and transports nutrients and waste products, playing a key role in digestion
and excretion.
● In the digestive system, water dissolves nutrients so they can be absorbed through the
intestinal walls into the bloodstream. In the excretory system, it helps the kidneys filter waste
from the blood and forms urine, the body’s liquid waste. Water is also a key component of
saliva, gastric juice, and bile, all vital for digestion.
4. Water Determines the Shape and Function of Biomolecules
● Biological molecules rely on the chemical and physical characteristics of water to fold into their
functional forms.
● Proteins, DNA, and enzymes adopt their unique three-dimensional structures in aqueous
environments. Water affects hydrogen bonding, hydrophobic interactions, and ionic
stability, which are critical for molecules to fold properly. If these structures are disrupted (as in
dehydration), the molecules may lose function—a phenomenon known as denaturation.
Water Balance in the Human Body
● The human body constantly gains and loses water throughout the day. To maintain good health
and proper physiological functioning, the body must keep a balance between water intake and
water loss.
● In a healthy individual, water is regularly consumed and lost through processes like urination,
sweating, breathing, and defecation. When the amount of water lost is roughly equal to the
amount taken in, the body is said to be in a state of water balance.
Dehydration
● Occurs when water loss exceeds water intake over a period of time.
● Symptoms include dry mouth, dizziness, fatigue, low blood pressure, and dark yellow urine.
● Causes may include excessive sweating, diarrhea, vomiting, fever, or inadequate fluid intake.
● Severe dehydration can lead to organ failure, heatstroke, or even death if untreated.
Edema (Water Retention)
● Happens when water intake exceeds water loss, or when the body fails to eliminate excess
water properly.
● This leads to the accumulation of fluid in tissues, causing swelling, especially in the hands, legs,
ankles, or feet.
● Common in people with heart, liver, or kidney disorders, or as a side effect of some medications.
● Mild cases may resolve with dietary changes or increased activity; severe cases may require
medical intervention.
, II. PHYSICAL PROPERTIES OF WATER
Water is classified as a hydride of oxygen because it is composed of hydrogen and oxygen
atoms (H₂O). When compared to other similar hydrides—such as ammonia (NH₃), hydrogen fluoride
(HF), and hydrogen sulfide (H₂S)—which are close to it on the periodic table, water stands out for
having significantly higher values in the following physical properties:
● boiling point,
● melting point,
● heat of vaporization, and
● surface tension
These unique characteristics of water are largely due to its strong hydrogen bonding.
– In fact, all of these physical characteristics are unusually high for a molecule of such low molecular
weight, especially one that is neither metallic nor ionic. This indicates that water molecules experience
strong intermolecular attractions.
– Additionally, unlike most substances, water reaches its greatest density in its liquid form rather than in
its solid form. This unique trait explains why ice floats on liquid water.
– These unusual and remarkable features of water can be attributed to its exceptional capacity to form
hydrogen bonds.
Polarity of Water
The 2 hydrogens of water are covalently linked to the oxygen
atom giving a non-linear arrangement. This structure of water is known
as bent structure (See Figure below). In the O–H bonds of H2O,
oxygen is more electronegative than hydrogen, meaning there is a
higher probability that the bonding electrons are closer to the oxygen.
This gives rise to a partial negative charge in the oxygen atom and
partial positive charge in the hydrogen atom. The partial charges are
usually depicted as δ + and δ - , respectively.
-Bonds such as this are called polar bonds. Molecules with polar bonds are polar molecules, that is why
water molecules are polar. - In the case where the electronegativity difference is quite small, such as in
the C–H bond in hydrocarbons, the sharing of electrons is very nearly equal, and the bond is essentially
nonpolar.
Notes on Chemical Properties of Water
Rostyslav, M. (2023). Physical and Chemical Properties of Water | Ecosoft Blog. Ecosoft.com. https://www.ecosoft.com/post/physical-and-chemical-properties-of-water
, BIOCHEMISTRY
Properties of Water I
(1st Sem Lecture Notes)
I. Overview: Importance of Water in Life
● Water as a Major Component of Life
Water plays a central role in the chemistry of life. It makes up about 60% to 95% of the mass of living
cells. This makes it the most abundant and essential substance in living organisms.
● Water Distribution in the Human Body
In humans, body water is distributed in two main areas:
○ Intracellular fluid (inside cells): ~55%
○ Extracellular fluid (outside cells): ~45%, which includes:
■ Plasma (blood fluid): ~8%
■ Interstitial fluid and lymph (between cells and in the lymphatic system): ~22%
■ Connective tissue, bone, and cartilage fluids: ~15%
● Water and Metabolism
For cells to perform normal metabolic functions, they must contain at least 65% water. Without this
level of hydration, essential chemical reactions in the body cannot take place efficiently.
Function of Water as Solvent for Biochemical Reactions:
1.Water as a Transport Medium
Water plays a critical role in transporting substances across cell membranes, facilitating the
movement of nutrients into cells and the removal of waste products out of cells.
● Through osmosis and diffusion, water enables the transport of ions, gases (like oxygen and
carbon dioxide), and nutrients such as glucose and amino acids. In multicellular organisms,
fluids like blood and lymph rely on water to carry these substances throughout the body
efficiently.
2. Water Helps Regulate Body Temperature
● Water assists in stabilizing body temperature by absorbing and redistributing heat.
● Thanks to water’s high specific heat capacity, it can absorb a lot of heat without drastically
changing temperature. This helps organisms maintain homeostasis. In humans, sweat (mostly
water) cools the body through evaporative cooling, preventing overheating.
3. Water as a Solvent in Digestion and Waste Removal
, ● Water dissolves and transports nutrients and waste products, playing a key role in digestion
and excretion.
● In the digestive system, water dissolves nutrients so they can be absorbed through the
intestinal walls into the bloodstream. In the excretory system, it helps the kidneys filter waste
from the blood and forms urine, the body’s liquid waste. Water is also a key component of
saliva, gastric juice, and bile, all vital for digestion.
4. Water Determines the Shape and Function of Biomolecules
● Biological molecules rely on the chemical and physical characteristics of water to fold into their
functional forms.
● Proteins, DNA, and enzymes adopt their unique three-dimensional structures in aqueous
environments. Water affects hydrogen bonding, hydrophobic interactions, and ionic
stability, which are critical for molecules to fold properly. If these structures are disrupted (as in
dehydration), the molecules may lose function—a phenomenon known as denaturation.
Water Balance in the Human Body
● The human body constantly gains and loses water throughout the day. To maintain good health
and proper physiological functioning, the body must keep a balance between water intake and
water loss.
● In a healthy individual, water is regularly consumed and lost through processes like urination,
sweating, breathing, and defecation. When the amount of water lost is roughly equal to the
amount taken in, the body is said to be in a state of water balance.
Dehydration
● Occurs when water loss exceeds water intake over a period of time.
● Symptoms include dry mouth, dizziness, fatigue, low blood pressure, and dark yellow urine.
● Causes may include excessive sweating, diarrhea, vomiting, fever, or inadequate fluid intake.
● Severe dehydration can lead to organ failure, heatstroke, or even death if untreated.
Edema (Water Retention)
● Happens when water intake exceeds water loss, or when the body fails to eliminate excess
water properly.
● This leads to the accumulation of fluid in tissues, causing swelling, especially in the hands, legs,
ankles, or feet.
● Common in people with heart, liver, or kidney disorders, or as a side effect of some medications.
● Mild cases may resolve with dietary changes or increased activity; severe cases may require
medical intervention.
, II. PHYSICAL PROPERTIES OF WATER
Water is classified as a hydride of oxygen because it is composed of hydrogen and oxygen
atoms (H₂O). When compared to other similar hydrides—such as ammonia (NH₃), hydrogen fluoride
(HF), and hydrogen sulfide (H₂S)—which are close to it on the periodic table, water stands out for
having significantly higher values in the following physical properties:
● boiling point,
● melting point,
● heat of vaporization, and
● surface tension
These unique characteristics of water are largely due to its strong hydrogen bonding.
– In fact, all of these physical characteristics are unusually high for a molecule of such low molecular
weight, especially one that is neither metallic nor ionic. This indicates that water molecules experience
strong intermolecular attractions.
– Additionally, unlike most substances, water reaches its greatest density in its liquid form rather than in
its solid form. This unique trait explains why ice floats on liquid water.
– These unusual and remarkable features of water can be attributed to its exceptional capacity to form
hydrogen bonds.
Polarity of Water
The 2 hydrogens of water are covalently linked to the oxygen
atom giving a non-linear arrangement. This structure of water is known
as bent structure (See Figure below). In the O–H bonds of H2O,
oxygen is more electronegative than hydrogen, meaning there is a
higher probability that the bonding electrons are closer to the oxygen.
This gives rise to a partial negative charge in the oxygen atom and
partial positive charge in the hydrogen atom. The partial charges are
usually depicted as δ + and δ - , respectively.
-Bonds such as this are called polar bonds. Molecules with polar bonds are polar molecules, that is why
water molecules are polar. - In the case where the electronegativity difference is quite small, such as in
the C–H bond in hydrocarbons, the sharing of electrons is very nearly equal, and the bond is essentially
nonpolar.
