Water Dissociation, pH, Acid and Bases

Calculate the pH of a solution of weak acid given its pKa or Ka and its molarity.

- apply Ka = [H+][A-]/[HA] - replace concentrations with variables (x) - check to ignore denominator x *assume x is negligible when:* - [HA]initial > 100*Ka - if agrees, then ignore - complete calculation *ignore when <10% of HA*

Describe the ionization of water and the balance that exists between the concentration of hydrogen and hydroxide ions in aqueous solutions.

- h2o is not inert; it ionizes - only 2 of every 10^9 molecules in h2o are dissociated / ionized at any given time - [H+] really affects biochemistry even tho the ions are relatively rare pure water at 25C at pH7 - [H+] = -log[H+] - [OH-] =-log[OH-]

Discuss weak acids and bases

HA <-> H+ + A- EQUILIBRIUM CONSTANT FOR WEAK ACIDS -acid dissociation constant *Ka = [H+][A-]/[HA]* *pKa = -log[Ka]* - *low pKa = stronger acid* - *high pKa = weaker acid* - *strong acid* has a *high Ka* and a *low pKa* bc it dissociates completely - the stronger the acid, the greater tendency to lose its proton - every acid has tendency to lose proton

Calculate the pH or pOH of a solution of strong acid or base.

STRONG ACIDS AND BASES - acids = proton donor - bases = proton acceptor - strong acids and bases will completely dissociate in h2o pH - apply pH. equation pOH - apply pOH equation - use pH = 14 - pOH

Calculate pH, pOH, [H+], or [OH-] given sufficient data and explain the relationship between these variables.

pH - a property of a solution, not a compound - pH6 is *10x* more acidic than pH7 *pH = -log[H+]* *pOH = -log[OH-]* *[H+][OH-] = 10^-14 M* *pH + pOH = 14*

Calculate pKa given Ka and vice versa.

pKa -use equation pKa = -logKa Ka - Ka = [H+][A-]/[HA]