MCAT Chem- Acid/Bases Definitions

Bronsted-Lowry Acid

A proton donor

Bronsted-Lowry Base

a proton acceptor

Lewis acid

electron pair acceptor

Lewis base

electron pair donor

what is a buffer?

An aqueous solution that can resist pH change

how do you prepare a buffer?

combine a weak/weak acid and base or 1 part strong to one part weak acid/CB pair

What changes the buffering capacity?

The concentrations of A- and H3O+

What concentration of acid and base makes the best buffer?

1:1 (when pH = pKa)

What is Ka?

acid ionization constant

what is Kb?

base dissociation constant

what does a large Ka or Kb signify?

the larger the Ka/Kb the stronger the acid/base

what is the formula for Ka?

Ka= ( \[H30+\] \[A-\] ) / \[HA\]

what is the formula for Kb?

Kb= ( \[OH-\] \[HA\] ) / \[A-\]

what does amphoteric mean?

Can act as an acid or base (h2o)

what is the formula for Kw

Ka \* Kb = Kw

What is Kw?

autoionization constant (1.0 \* 10^-14)

how to solve for pH

\-log(\[H3O+\]

what is the formula for pOH

pH + pOH = 14

What are the strong acids?

HCl, HBr, HI, HNO3, HClO4, H2SO4

What are the strong bases?

KOH, LiOH, NaOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

How to find the pH of an acid or base solution

ICE chart

How do you know if a salt will change the pH of a solution?

Check if any of the ions will react with water (if they form a strong acid/base they won’t react), and then use ICE chart

What is the common ion effect?

if you add a product, the equilibrium will shift toward reactants thus changing pH, if you add a reactant the equilibrium will shift right thus changing the pH

How do buffers work?

They give the additive something to react with instead of water

What is the henderson-hasselbach equation?

pH = pKa + log( \[A-\] / \[HA\] ) (using conjugate pairs)

how to solve for pKa?

pKa = -log(Ka)

how to solve for pKb?

pKb = -log(Kb)

how to solve for pH of a buffer solution with an additive?

Use BAA chart (in moles)