MCAT Acids and Bases Flashcards
Arrhenius acids v. Arrhenius base
Arrhenius acids releases H+ in aqueous solutions forming hydronium.
Arrhenius bases accepts H+ in aqueous solutions.
Bronsted - Lowry acids v. Bronsted- Lowry bases
B-L acids donate H+ and B-L bases accepts H+. Definition doesn’t require aqueous solutions.
Lewis acids v. Lewis basis
Lewis acids accepts electrons whereas Lewis bases donate electrons.
In organic chemistry:
- Electrophiles tend to be Lewis acids (electron deficient, accepts electrons)
- Nucleophiles- tend to be lewis bases (electron rich, donates electrons)
Autoionization of water
Water spontaneously ionizes forming hydronium and hydroxide ions.
pH
Measures the acidity or basicity of a solution.
There is a 10- fold different between subsequent pHs
Acidic solutions- high H+ concentration, low pH.
Basic solutions - low H+ concentration , high pH.
Weak- acid dissociation constant ( Ka)
Value that represents the equilibrium of the dissociation of weak acids.
Ka = [ H+] [A-]/[HA]
When Ka is large more products at equilibrium.
When Ka is small more reactants at equilibrium.
Weak- base dissociation constant ( Kb)
Same thing as Ka excepts represents dissociation of weak bases.
Kb = [ HB][OH]/ [B]
What happens when we take the -log of Ka and Kb?
We get pKa and pKb respectively.
They each are inverse to Ka and Kb.
Describe the relationship between acid or base and its conjugate acid or base?
They’re inverse.
How do we Kw (dissociation constant for water)?
Ka x Kb = Kw
Which equation relates Pka and Pkb?
PKa + PKb = 14
Henderson- Hasselbach equation
Equation that allows us to calculate the concentration of buffer solutions which is made up of an acid and it’s conjugate base.
pH = pKa + log [A-]/ [HA]
What effect does EWGs and EDGs have on acidity?
EWGs increases it because it withdraws electron density.
EDG decreases it because it pushes electron density into the system.
Describe how S character influences acidity?
Alkanes has 25% s character.
Alkenes has 33% character
Alkynes has 50% S character.
The more S character they’re held more closely to the nucleus.
Sp3 ( most acidic hybridized orbital), SP2, SP ( least acidic).
