Water Structure, Hydrogen Bonding, pH, and Buffers (Lecture Notes)

Vocabulary flashcards covering water structure, hydrogen bonding, solvent properties, solution concepts, pH, acids/bases, buffers, and the carbonic acid/bicarbonate system as described in the notes.

Bent water molecule

Water has a bent (V‑shaped) geometry due to the two lone pairs on oxygen, giving it polarity.

Polarity of water

Water’s electrons are shared unequally because oxygen is highly electronegative, resulting in partial negative and partial positive charges.

Hydrogen bond

A weak noncovalent attraction between a hydrogen atom bonded to an electronegative atom (O or N) and another electronegative atom with lone pairs (often another O or N in water or biomolecules).

Cohesion

Attraction between like molecules (water–water) due to hydrogen bonding, contributing to surface tension.

Density difference between water and ice

Liquid water is denser than ice; ice’s hydrogen-bond network forms an open lattice that lowers density.

High specific heat

Water can absorb or release a lot of heat with only modest changes in temperature.

High heat of vaporization

A large amount of energy is required to convert water from liquid to gaseous form.

Water as a solvent

Water’s polarity and hydrogen-bonding ability allow it to dissolve many charged or polar substances.

Aqueous solution

A solution in which water is the solvent.

Molarity (M)

1 mole of solute per liter of solution (1 M = 1 mol/L).

Micromolar (μM)

Concentration of 10^-6 moles per liter; a common unit in biology.

Dissolution of salts in water

Salts dissolve because both cations and anions interact with water (hydration); uncharged or nonpolar molecules do not dissolve well.

Autoionization of water

Water can act as both an acid and a base; 2 H2O ⇌ H3O+ + OH− (simplified as H2O ⇌ H+ + OH−).

pH

A measure of hydrogen ion concentration; pH = -log[H+]. Pure water at 25°C has pH = 7.

Acids

Substances that donate protons (H+); Arrhenius definition: produce H+ in solution.

Bases

Substances that accept protons; Arrhenius or general concept: remove H+ from solution.

Buffers

Chemically, a weak acid and its conjugate base that resist changes in pH by neutralizing added acids or bases.

Carbonic acid/bicarbonate buffer (blood)

H2CO3/HCO3− system that buffers blood by accepting or donating protons to maintain pH.