Ch. 10: Acids and Bases Flashcards
Define Arrhenius acid and Arrehnius base.
Arrhenius acid: will dissociate to form an excess of H+ in solution
Arrhenius base: will dissociate to form an excess of OH- in solution
Define Bronsted-Lowry acid and base.
Acid: species that donates hydrogen ions
Base: species that accepts hydrogen ions
Define Lewis acid and base.
Acid: electron pair acceptor
Base: electron pair donor
What is the difference between the Arrhenius, Bronsted-Lowry, and Lewis base definitions?
Arrhenius and Bronsted-Lowry focus on producing hydrogen ions. The Lewis definition focuses on electron pair.
What is an amphoteric species?
A species that reacts like an acid in a basic environment and like a base in an acidic environment.
Ex. H2O
What is Kw?
Kw = [H3O+][OH-] = 10^-14
How does Kw change?
Only changes in temperature change Kw.
If [H+] = 10^-3 what is the pH and pOH?
pH = 3 pOH = 11
If Kb = 10^-12 what is the pKb?
12
What are the pH and pOH equations?
pH = -log [H+]
pOH = -log[OH-]
What does a small Ka and small Kb mean (less than 1)?
Small Ka means the acid is weak and will dissociate less.
K = [products]/[reactants]
Small Kb means the base is weak ad will dissociate less.
What is a conjugate base and conjugate acid?
Conjugate acid: formed when a base gains a proton
Conjugate base: formed when an acid loses a proton
Bicarb equilibrium: what is the conjugate base and acid?
HCO3- + H2O CO3 2- + H3O+
Conjugate acid is H3O+
Conjugate base is CO3 2-
How can you determine the equilibrium constant of a conjugate base given the equilibrium constant of the acid that produced it?
K(acid) x K(conjugate base) = Kw = 10^-14
What is the relationship between Ka and Kb?
They are inversely related. If Ka is large then Kb is small, and vice versa
What is the relationship between pKa and Ka?
pKa = -log Ka
High Ka = small pKa = strong acid
Low Ka = large pKa = weaker acid
How does electronegativity affect acid strength?
Electronegative elements positioned near an acidic proton increase acid strength by pulling electron density out of the bond holding the acidic proton.
Define the equivalence point of a titration curve.
When the # of acid equivalents = the # of base equivalents
What are indicators?
Indicators are weak acids or bases that have different colors in their protonated and deprotonated states. Thier small structural change (the binding or release of a proton) leads to a change in the absorption spectrum of the molecule, which we perceive as a color change.
What are indicators used for?
They are used to determine the equivalence point in an acid-base titration.
Should indicators be weaker or stronger than the acid or base being titrated?
WEAKER so they are not titrated first.
How is the ideal indicator determined?
First, find the pH of the reaction at the equivalence point
Next, select the indicator that has the closest pKa value to it.
What is the Henderson-Hasselbalch equation?
pH = pKa + log [A-]/[HA]
What is the log of 1?
zero
When does pH = pKa?
When the concentration of the conjugate base equals the concentration of the acid.
This is the 1/2 equivalence points in a titration.
What is the difference between the half equivalence point and equivalence point?
Half equivalence point: [HA] = [A-}
Equivalence point: equivalents of acid = equivalents of base
What is the endpoint of titration?
The pH at which an indicator turns its final color.
