Acid Base Equilibrium Flashcards
For Exam 2
What is the concept of Lewis acids and bases?
- It’s in terms of electrons. (Like Lewis structures!)
-
Acid = an electron acceptor
- Hint: Acid accepts electrons
- Includes metal cations with open d orbitals (like iron in hemoglobin)
- Base = an electron donor.
- Neutralization = formation of a coordinate covalent bond
What is the Bronsted-Lowry concept of acids and bases?
- Acid-base reactions are about proton transfers
- Hint: Bro, pro
- Acid = proton donor
- Base = proton acceptor
What is a conjugate acid-base pair?
- Two substances that differ only by ONE proton
- Ex: H3O+ and H2O
- The conjugate acid has one more H+, it’s the proton donor (Ex: H3O+)
- The conjugate base is the proton acceptor (Ex: H2O)
- The stronger a Brønsted-Lowry acid or base is, the weaker its conjugate acid or base. Vice versa.
- Every rxn between a Brønsted acid and a Brønsted base involves two conjugate acid–base pairs, typically on opposite sides of arrows
- Stronger acids and bases tend to react with each other to produce their weaker conjugates

What is an amphoteric substance?
(aka amphiprotic)
- It can behave as either an acid or a base, depending on the other substance
How are the strengths of acids and bases measured?
- The more complete its reaction with water, the stronger the acid or the base
- If Ka or Kb > 1, strong. If Ka or Kb < 1, weak.
- The larger the K, the stronger the species
- The smaller the pKa, the stronger the species
- The strongest base in water is OH-, the strongest acid in water is H3O+
- Pam’s fav weak acid: acetic acid. HC2H3O2
Which side does an acid-base equilibrium favor,
with weak acid + weak base?
- The weaker side.
- Equilibrium lies on the side of the weaker acid and weaker base
- In this case, the left, so K < 1.
- (We don’t deal with equilibrium when there is a strong acid or base involved. Then it just goes that direction.)

What is a coordinate covalent bond?
- When both electrons in the pair came from one species instead of one from each.
- This is associated with the Lewis concept of acids and bases. The base gives an electron pair, the acid accepts it.
- Neutralization = formation of a coordinate covalent bond

What are binary acids and what is the periodic trend for their strength?
- Binary acids - binary compounds between hydrogen and nonmetals. (ex: HCl, H2S)
- Strength of the acid increases as move down same group, and right across the same period.
- Down a group: Think about bond length.
- HF < HCl < HBr < HI. HI is the strongest halide acid. It has the weakest bond because of bigger atomic radius. Since HF has the strongest bond (because F is the most electronegative so HF is the most polar) it’s the weakest acid.
- Across a period: Think about electronegativity. The more electronegative, the higher the partial positive charge on the H, the closer that it already is to being H+.
What are oxoacids, and what is the trend on the periodic table for their strength?
- Acids composed of hydrogen, oxygen, and some other element
- They have O-H groups bonded to some central atom. Ex: H2SO4 sulfuric acid
- Stronger acid if there are more oxygens held by central atom
- Ex: nitric acid (HNO3) is a stronger acid than nitrous acid (HNO2)
- Stronger acid if the central atom is more electronegative
What is the Arrhenius definition of acids and bases?
- Acid: dissociates to increase [H+]
- Base: dissociates to increase [OH-]
What are the equations to find pH?
- pH= -log[H+]
- [H+] = 10-pH
- pOH= -log[OH-]
- [OH-] = 10-pOH
- pH + pOH = 14
- [H+][OH-] = 10-14
What are Ka and Kb
and how can you solve for them?
- Types of equilibrium constants: ionization constants (or dissociation constants)
- Ka: Acid
- Kb: Base
- Weak acids and bases dissociate to an extent that is quantified by their equilibrium constant
- Ka and Kb allows us to compare the relative strengths of weak acids and bases.
- Larger Ka or Kb indicates a stronger acid or base, because more product favored. Smaller Ka or Kb indicates a weaker acid or base
- Kw = 10-14 = Ka * Kb

What are pKa and pKb
and how can you solve for them?
- Just the -log
- pKa= -log(Ka)
- pKb= -log(Kb)
- The smaller the pK value, the stronger it is
What are the relationships between Ka, Kb, and Kw
for conjugate pairs?
- Kw = 10-14at 25oC
- KaKb = KW
- pKa + pKb = 14

Equation for concentrations of H+ and OH-?
(shortcut)
[H+] = √(Ka x M)
[OH-] = √(Kb x M)
- Can use these to calculate pH
What is an amphiprotic substance,
and what are examples?
- It can act as an acid or a base, donate OR accept a proton.
- Ex: Water.
- Polyprotics always have an amphiprotic form. The acid form is the fully protonated form. The base form is the fully deprotonated form. The amphiprotic form is in between, a conjugate of the acid form and the base form.
- Ex: Hydrogen phosphate HPO42- and dihydrogen phosphate H2PO4- are amphiprotic. (H3PO4 is phosphoric acid, weak but only an acid.)
- Ex: bicarbonate HCO3-, hydrogen sulfide HS-, hydrogen oxalate HC2O4-

With polyprotic acids, which form is stronger?
- The fully protonated form is the strongest
- Each successive dissociation produces a weaker acid
- Ex: phosphoric acid is triprotic, and will have a larger K value and smaller pKa value than its children. H3PO4 > H2PO4- > HPO42-
What is the labile hydrogen?
- The hydrogen that is easily removable
What is a carboxylic acid, and what is the trend for strength?
- A carboxylic acid is an organic compound. The general formula is R–COOH, with R referring to the rest of the molecule.
- If there is an electronegative element on the carbon (like chlorine or fluorine) then they hog the electrons, leaving just a partial negative charge on the other side, and it’s easier for the H to be removed.
- So trichloroacetic acid and trifluoroacetic acid are stronger than acetic acid, which just has hydrogens around the carbon.

How does the ammonium ion behave in water?
NH4+
- Ammonium ion is acidic in water
- So NH4Cl would also be weakly acidic. But NH4OH would be basic because hydroxide is stronger.
How does bicarbonate behave in water?
HCO3-
- Amphiprotic, but it acts as a weak base in water, receives a hydrogen
- But if you were to put it in a solution with a stronger base, it would be forced to work as an acid.
- Memorize this, but can also see that tabulated Kb value > Ka value.
What are some ions that make a neutral solution with water?
- Don’t need to memorize. But getting familiar…
- Note that these are the beginnings of the strong acids and some strong bases. When an acid or a base is extremely strong, the conjugate is too weak to affect the pH.
- Metal ions with small charges are nonacids
- Application: CaCl2 and KNO3 are neutral solutions in water because neither the cation nor anion is able to affect the pH

What is an ion that is acidic in water?
- Only one we have to memorize is NH4+
- Hydrated Al3+ , Cr3+, Fe3+, because metal ions with high charge densities are weak acids
- The only time an anion might be acidic is if it is from a partially neutralized polyprotic acid, and has another hydrogen to donate.

What is an ion that is basic in water?
- HCO3- (bicarbonate) acts as a weak base in water
- Don’t need to memorize, but here are some more ions that are basic in water








