Water and Life (Lesson 3)

A vocabulary-focused set of flashcards covering the key concepts from the lecture notes on water’s properties, hydrogen bonding, pH, acids/bases, buffers, and Earth's water-related processes.

Water polarity

Water is a polar molecule with a partial negative charge on oxygen and partial positive charges on hydrogens.

Partial charges

Oxygen carries a partial negative charge; hydrogen carries partial positive charges.

Hydrogen bond

A weak attraction between a slightly positive hydrogen of one water molecule and a slightly negative oxygen of another.

Dynamic hydrogen bonding

Hydrogen bonds form and break rapidly, with water molecules continually forming new bonds.

Cohesion

The attraction between like molecules, notably water molecules sticking to each other.

Adhesion

The clinging of water to other substances, such as cell walls.

Surface tension

The measure of how difficult it is to stretch or break the surface of a liquid, due to hydrogen bonding.

Interfacial water structure

At the air–water interface, water molecules are hydrogen-bonded to each other and to those below.

Emergent properties of water

Cohesion, temperature moderation, ice floating, and solvent power arising from water’s hydrogen bonding.

Cohesion in plants

Hydrogen bonding increases cohesion, aiding water transport; adhesion to cell walls helps counter gravity.

Transpiration transport in plants

Water transport in plants driven by cohesion and adhesion, enabling movement against gravity.

Surface tension (definition)

The resistance of a liquid surface to bending or breaking due to cohesive forces.

Hydration shell

Water molecules surround and stabilize dissolved ions or polar molecules.

Hydrophilic

Water-loving substances that dissolve in water (salts, charged or polar molecules).

Hydrophobic

Water-fearing substances that do not dissolve well in water (nonpolar substances).

Solvent

The dissolving agent in a solution, typically water in biological systems.

Solute

Substance dissolved in a solvent to form a solution.

Aqueous solution

A solution in which water is the solvent.

Dissociation of water

Water autoprolyzes to H+ and OH− ions, a rare event but essential for pH concepts.

H+ (proton)

A hydrogen ion produced when water dissociates; increases acidity.

OH− (hydroxide)

A hydroxide ion produced when water dissociates; increases basicity.

Neutral water concentration

Pure water has [H+] = [OH−] = 1 × 10−7 M.

Acid

A substance that increases hydrogen ion (H+) concentration in solution.

Base

A substance that reduces H+ concentration, often by donating OH− or accepting H+.

pH

The negative logarithm of the hydrogen ion concentration, indicating how acidic/basic a solution is.

pH scale (logarithmic)

Each unit difference represents a tenfold change in H+ concentration.

Neutral pH

pH around 7, where [H+] ≈ [OH−].

Acidic vs basic pH

Acids lower pH; bases raise pH.

Buffers

Solutions that minimize changes in pH by absorbing or releasing H+.,

Carbonic acid (H2CO3)

A weak acid formed from CO2 and water; can release H+ to form bicarbonate.

Bicarbonate (HCO3−)

Conjugate base of carbonic acid; formed when H2CO3 loses a proton.

Carbonate (CO3^2−)

Conjugate base formed after two deprotonations of carbonic acid.

Buffer system in blood

Carbonic acid–bicarbonate system helps maintain blood pH near 7.4.

Buffer reversibility

Buffer reactions can shift back and forth to absorb or release H+ as needed.

Blood pH 7.4

Normal blood pH, maintained by buffering systems; deviations can be harmful.

Ocean acidification

Decrease in ocean pH due to uptake of atmospheric CO2 forming carbonic acid.

CO2 hydration to carbonic acid

CO2 + H2O ⇌ H2CO3, which can dissociate to H+ and HCO3−, increasing acidity.

Carbonic acid dissociation

H2CO3 ⇌ H+ + HCO3−; contributes to buffering and acid–base balance.

Hydration shell in salts

Water molecules surround and stabilize dissolved ions, aiding dissolution.

Solubility of polar molecules

Water dissolves polar and charged molecules due to hydration shells.

Dissociation constant of water

In pure water, [H+] and [OH−] are equal, 1 × 10−7 M each, yielding neutral pH.

Specific heat of water

1 Calorie per gram per degree Celsius (1 cal/g·°C); water’s high heat capacity.

Calories vs kilocalories

Calorie (kcal) is the amount of heat to raise 1 kg of water by 1°C; nutrition uses kilocalories.

Heat vs temperature

Heat is energy transfer; temperature is the average kinetic energy of molecules.

Evaporative cooling

Cooling of a liquid as high-energy molecules escape as vapor, lowering the temperature of the remainder.

Oceans moderating climate

Large bodies of water absorb heat during the day and release it at night, stabilizing temps.

Temperature moderation by water

Water’s high heat capacity helps keep coastal and global temperatures stable.

Ice density anomaly

Ice is less dense than liquid water and floats; this insulates liquid water beneath.

Ice floes and insulation

Floating ice reduces heat loss and protects aquatic life by insulating the water below.

Water as a solvent

Water dissolves many substances, enabling chemical reactions in biological systems.

Solute and solvent definitions

Solute is dissolved; solvent is the dissolving medium, often water.

Hydrophilic vs hydrophobic (recap)

Hydrophilic dissolves in water; hydrophobic does not dissolve well.