1604_L9_Properties of water_AY25-26

The polar nature of the water molecule allows it to form hydrogen bonds, which are responsible for water's unique properties such as high surface tension, high specific heat, and solvent capabilities. These properties are crucial for biological functions, including temperature regulation and nutrient transport.

Cohesion and adhesion are essential for biological functions such as:

1. Capillary action - allows water to move through plant vessels.
2. Lubrication - reduces friction in bodily fluids.
3. Flow of bodily fluids - facilitates circulation and nutrient transport in organisms.

Water regulates body temperature primarily through the endothermic nature of evaporation, which absorbs heat from the body, leading to a cooling effect. This is vital for maintaining homeostasis in living organisms.

The components of a solution include:

• Solute: the substance dissolved.
• Solvent: the substance that dissolves the solute (usually water).
• Aqueous solution: a solution where water is the solvent.

Electrolytes dissociate into ions in solution (e.g., sodium chloride), while nonelectrolytes do not (e.g., glucose). This distinction is important in biological contexts, such as cellular function and fluid balance.

Solute concentration can be calculated using:

1. Mass/volume percent (m/v): grams of solute per 100 mL of solution.
2. Volume/volume percent (v/v): mL of solute per 100 mL of solution.

In clinical contexts, these values are crucial for understanding the concentrations of IV fluids and disinfectants, ensuring proper dosage and effectiveness.

The effects of different solutions on cell volume are:

• Isotonic: no net movement of water; cell volume remains stable.
• Hypotonic: water enters the cell, causing it to swell and potentially burst.
• Hypertonic: water leaves the cell, causing it to shrink.

Understanding these effects is essential in clinical scenarios such as IV therapy and managing fluid balance disorders.

Cohesion refers to the attraction between water molecules, which allows for surface tension and the formation of droplets. Adhesion is the attraction between water molecules and other substances, enabling water to climb up surfaces (capillary action).

Water has a high specific heat capacity, meaning it can absorb a lot of heat without a significant change in temperature. This property helps regulate temperature in the environment and within organisms, providing a stable habitat.

Water is known as the 'universal solvent' because it can dissolve many substances due to its polar nature. This property is crucial for biological processes, as it allows for the transport of nutrients and waste in living organisms.

Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process is vital for maintaining cell turgor and overall homeostasis in organisms.

Water is the predominant body component for both men and women, comprising 59% of a male's body composition and 52% of a female's body composition.

Atoms can form Ionic and Covalent bonds to create molecules.

A covalent bond is determined to be polar or nonpolar based on Electronegativity.

The four main types of organic molecules are:

1. Carbohydrates
2. Nucleic acids
3. Proteins
4. Lipids

Water molecules stick together due to Hydrogen bonds.

In a water molecule (H₂O), the oxygen atom has a partial negative charge (8-) because it attracts electrons more strongly than the hydrogen atoms, which carry partial positive charges (6+). This charge distribution occurs due to the polar nature of the water molecule.

A hydrogen bond is the attraction between the partial positive charge of a hydrogen atom in one water molecule and the partial negative charge of an oxygen atom in another water molecule. This interaction leads to the formation of hydrogen bonds between adjacent water molecules.

In liquid water, many water molecules are interconnected through hydrogen bonds, which causes them to stick to one another. This results in unique properties of water, such as cohesion and adhesion.

The polar nature of the water molecule, characterized by its partial positive (δ+) and partial negative (δ-) charges, allows it to form extensive hydrogen bonding networks. This is crucial for the unique properties of water, such as its cohesive and adhesive abilities, its role as a solvent, and its thermal effects.

The key properties of water include:

1. Cohesive & Adhesive
2. Solvent
3. Density
4. Thermal effects

Cohesion is the property of water that allows it to stick to itself due to hydrogen bonds. Its primary functions in the human body include:

• Creating surface tension in the lungs (regulated by surfactant)
• Aiding in the smooth, continuous flow of fluids (e.g., blood, water in xylem of plants)
• Contributing to the viscosity of lubricating fluids.

Adhesion is the property of water that allows it to stick to other substances due to its polarity. Its primary functions in the human body include:

• Enabling capillary action for nutrient/waste exchange
• Allowing water to act as the universal solvent for metabolic reactions
• Providing lubrication by coating surfaces (e.g., mucus, saliva).

Water helps regulate body temperature by transporting heat from the body's core to the skin's surface, where it is released through the evaporation of sweat. This process involves:

1. Heat Transport: Water in blood carries heat to the capillaries at the skin surface.
2. Heat Release: Heat is released at the skin surface, and the evaporation of sweat cools the skin.
3. Return of Cooled Blood: The cooled blood then returns to the body core, helping to maintain a stable internal temperature.

Evaporation is the process where water molecules transition from a liquid state to a gas (water vapor). This occurs when:

• Water molecules at the surface of sweat move fast enough to overcome hydrogen bonds and escape into the air.
• To break these hydrogen bonds, water molecules must absorb energy from their surroundings, such as the skin and blood, which helps cool the body.

Water is a good solvent for salt because its polar nature allows it to surround and interact with the sodium (Na+) and chloride (Cl-) ions. The slight negative charge on water molecules attracts the positive sodium ions, while the slight positive charge attracts the negative chloride ions, facilitating the dissolution process.

A solution is a homogeneous mixture of two or more substances with uniform composition, such as blood plasma or cytosol.

A solute is the substance that is dissolved in a solution, for example, glucose in blood or oxygen in plasma.

A solvent is the substance that does the dissolving; in biological systems, this is typically water.

An aqueous solution is a solution where water is the solvent, which includes all major bodily fluids like blood, lymph, urine, and saliva.

The concentration of Sodium Chloride in the solution is 0.9% w/v (weight/volume).

The Sodium Chloride injection is typically used for medical purposes, such as rehydration or as a diluent for medications.

The Isopropyl Alcohol solution is labeled with several safety precautions: it is highly flammable, should be kept well-closed, and is for external use only.

The formula for Mass/Volume % (m/v) is (mass solute (g) / volume solution (mL)) × 100%. It is used in clinical solutions and IV drips.

Volume/Volume % (v/v) is calculated using the formula (volume solute (mL) / volume solution (mL)) × 100%. It is typically applied in dilute liquid solutes such as alcohol and acids.

Molarity (M) is calculated as moles of solute per liters of solution. It is commonly used in most chemical calculations and reactions.

An example of a solution that uses Mass/Volume % (m/v) is 0.9% saline, which consists of 0.9 g NaCl in 100 mL of solution.

An example of a solution that uses Volume/Volume % (v/v) is 70% rubbing alcohol, which consists of 70 mL isopropanol in 100 mL of solution.

An example of a solution that uses Molarity (M) is 1.0 M Glucose, which contains 1 mole of glucose (180 g) per liter of solution.

A 5% (m/v) dextrose solution means there are 5 grams of dextrose in 100 mL of solution.

In a 500 mL bottle of a 10% (v/v) isopropyl alcohol solution, there are 50 mL of pure isopropyl alcohol.

Electrolytes are solutes that dissociate into ions in water and can conduct electricity (e.g., NaCl → Na+ + Cl-), essential for nerve impulses, muscle contraction, and fluid balance. Nonelectrolytes do not dissociate into ions and do not conduct electricity (e.g., glucose, urea).

Body fluids such as blood plasma, lymph, cytosol, and interstitial fluid are aqueous solutions that contain electrolytes, gases, nutrients, and wastes, which are crucial for various physiological processes.

In a hypertonic solution, red blood cells shrink or become shriveled because water moves out of the cells into the surrounding solution. This occurs due to the higher concentration of solutes outside the cell, creating an osmotic pressure that draws water out.

In an isotonic solution, red blood cells maintain their normal shape because water moves in and out of the cells at equal rates. This balance prevents any net movement of water, keeping the cell volume stable.

In a hypotonic solution, red blood cells swell because water moves into the cells from the surrounding solution. This happens due to the lower concentration of solutes outside the cell, leading to osmotic pressure that drives water into the cell.

Osmosis is the diffusion of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process continues until equilibrium is reached, where both sides have the same osmolarity but may have different volumes depending on the permeability of the membrane to solute molecules.

When osmosis occurs in a U-shaped tube with a permeable membrane to both solute and water, the water moves from the left compartment (lower osmolarity) to the right compartment (higher osmolarity). After equilibrium, both sides have the same osmolarity, but the volume remains unchanged as solute can also move.

In a U-shaped tube with a membrane impermeable to solute molecules but permeable to water, water moves from the left compartment (lower osmolarity) to the right compartment (higher osmolarity). After equilibrium, both solutions have identical osmolarity, but the volume of the solution on the right is greater because only water is free to move.

In an isotonic solution, the solute concentration is the same as inside the cell, resulting in stable cell volume. Water movement is balanced, with equal amounts entering and leaving the cell.

In a hypotonic solution, the solute concentration is lower than inside the cell, causing water to enter the cell. This can lead to the cell swelling and potentially bursting (lysing).

In a hypertonic solution, the solute concentration is higher than inside the cell, leading to water leaving the cell. This causes the cell to shrink and become crenated.

0.9% NaCl is classified as isotonic. This means it has the same osmotic pressure as plasma, making it suitable for fluid resuscitation without causing cellular swelling or shrinkage.

Ringer's lactate has an osmolarity of 273 mOsmol/L, while Plasma-Lyte 148 has an osmolarity of 294 mOsmol/L. This indicates that Plasma-Lyte 148 is slightly more concentrated than Ringer's lactate, which may influence fluid shifts in the body.

Hartmann's solution is isotonic and contains the following key components:

• Na+: 131 mmol/L
• K+: 5 mmol/L
• Cl-: 111 mmol/L
• Ca: 2 mmol/L
• Lactate: 29 mmol/L This composition helps in maintaining electrolyte balance during fluid therapy.

Hypotonic solutions, such as 0.45% NaCl + 5% dextrose, have a lower osmolarity (406 mOsmol/L) compared to plasma. They are used to hydrate cells and can help in conditions where cellular dehydration is present, but caution is needed to avoid cellular swelling.

Plasma-Lyte 148 + 5% glucose costs approximately HK$20/L more than 0.9% NaCl + 5% dextrose. This cost difference should be considered when selecting intravenous fluids for treatment.

B. They will swell and potentially lyse (burst) as water enters the cells.

C. Hypertonic; to draw water out of brain cells into the bloodstream.