Lecture Slide Deck-2-1

WATERS AND BUFFERS

Introduction

  • Dr. Krishneel Singh

  • Email: Krishneel.Singh@uts.edu.au

  • University of Technology, Sydney (UTS)UTS:SCIENCE, CRICOS PROVIDER CODE: 00099F

LEARNING OBJECTIVES: WATERS AND BUFFERS

  • List and explain the four properties of water that emerge from hydrogen bonding:

    • Cohesive behavior

    • Temperature moderation

    • Expansion upon freezing

    • Versatility as a solvent

  • Differentiate between:

    • Hydrophobic and hydrophilic substances

    • Solute, solvent, and solution

  • Define acid, base, and pH

  • Explain the function of buffers

WATER: THE MOLECULE THAT SUPPORTS ALL LIFE

  • Water is the biological medium on Earth

  • Living organisms require water more than any other substance

  • Cells are approximately 70-95% water

  • The abundance of water contributes to Earth's habitability

MAJOR FLUID COMPARTMENTS OF THE BODY

  • Total body water volume: 40 L, 60% of body weight

  • Extracellular fluid volume: 15 L, 20% of body weight

  • Intracellular fluid volume: 25 L, 40% of body weight

  • Interstitial fluid volume: 12 L, 80% of ECF

  • Plasma volume: 3 L, 20% of ECF

POLARITY OF WATER

  • Water is a polar molecule with opposite charges at each end

  • Polarity enables water molecules to form hydrogen bonds with one another

HYDROGEN BONDS IN WATER

  • Hydrogen bonds are between the charged regions of polar water molecules

  • Each molecule can interact with multiple partners, creating transient associations

FOUR EMERGENT PROPERTIES OF WATER

  1. Cohesive Behavior

    • Hydrogen bonds hold water molecules together

    • Essential for the transport of water in plants

  2. Moderation of Temperature

    • Water maintains a stable temperature through heat absorption and release

  3. Expansion Upon Freezing

    • Ice is less dense than liquid water due to the ordered hydrogen bonds in ice

  4. Versatility as a Solvent

    • Water dissolves a wide range of substances due to its polarity

COHESION AND ADHESION

  • Cohesion: Attraction between water molecules (helps transport in plants)

  • Adhesion: Attraction between water and other substances (e.g., plant cell walls)

SURFACE TENSION

  • Measure of how hard it is to break a liquid's surface

  • Higher surface tension relates to stronger cohesion

  • Molecules at the surface experience an imbalance of forces, minimizing the surface area

MODERATION OF TEMPERATURE

  • Water can absorb/releases heat with minimal temperature change

  • Specific heat of water is high (1 cal/g/°C)

  • Heat absorption during hydrogen bond breakage

  • Heat release when hydrogen bonds form

EVAPORATIVE COOLING

  • Evaporation transforms liquid to gas; heat absorption occurs, cooling remaining liquid

  • Important for temperature regulation in organisms

WATER IN A SOLID STATE

  • Ice floats due to lower density (water's greatest density at 4 °C)

  • Crucial for life on Earth; prevents bodies of water from freezing solid

WATER: THE SOLVENT OF LIFE

  • Solution: homogeneous mixture of substances

  • Solvent: substance that dissolves another

  • Solute: substance being dissolved

  • Aqueous solution: solution where water is the solvent

WATER AS A VERSATILE SOLVENT

  • Water's polarity facilitates hydrogen bond formation with solutes

  • Ionic compounds dissolve and create hydration shells around ions

HYDROPHILIC AND HYDROPHOBIC SUBSTANCES

  • Hydrophilic: affinity for water

  • Hydrophobic: does not interact with water (e.g., oil)

  • Colloids: stable suspension of fine particles in a liquid

MOLECULAR CONCEPTS

  • Molarity (M): moles of solute per liter of solution

    • M = moles / L

  • Molecular mass: sum of all atom masses in a molecule

ACIDS AND BASES

  • pH scale measures [H+] concentration

  • Strong acids/bases dissociate completely in water

  • Biological systems often contain weak acids/bases which maintain dynamic pH balance

BUFFER SYSTEMS

  • Buffers minimize changes in H+ and OH- concentrations

  • Composed of a reversible acid-base pair

  • E.g., Bicarbonate buffer in blood maintains a constant pH around 7.4

CONCLUSION

  • Importance of water in biochemical reactions (hydrolysis and condensation)

  • Role of pH scale in biological functions and buffers in maintaining homeostasis

  • Contact Dr. Krishneel Singh for further questions at Krishneel.Singh@uts.edu.au