G Chem Unit 5 - Acids and Bases

What is a bronsted base/acid?

Base: accepts H+ (proton)

Acid: donates H+ (proton)

What is a lewis base/acid?

Base: donates electrons, nucleophiles

Acid: accepts electrons, electrophiles

What is special about lewis bases?

They are ligands and chelates

Donate the electrons in a coordinate bond

How do you recognize lewis acids?

More electronegative atoms bonded to H

Atoms without H can be acids if electron deficient or large positive charges

How do you recognize lewis bases?

Less EN atom with lone pair

Atoms without lone pairs are not usually basic

What are amphoteric compounds?

Have both acid and base characteristics

What are rules for acid/base strength?

More positive charge = more acidic

More electronegative = more acidic

Larger atoms = more acidic

More negative charge = more basic

Less EN = more basic

Small atom = more basic

What are strong acids?

H₂SO₄, HClO₄, HClO₃, HNO₃, HCl, HBr, HI

What are strong bases?

O^2-, OH^-, OR^-, NH₂^-, NR₂^-, H^-, R^-

How do acids dissociate?

HA (acid) dissociates into H+ and A- (conjugate base)

How do bases dissociate?

A- (base) associates with water into HA (conjugate acid) and OH-

What is Ka for strong acids?

> 1

Usually produce salts upon dissociation (not bases)

What is Kb for strong bases?

> 1

Conjugate acids are usually salts, not acids

What is Kw? pKw?

1.00 × 10^-14 = Kw

14.00 = pKw

What is the relationship between Kw, Ka, and Kb? pKa, pK, and pKw?

Kw = Ka*Kb

pKw = pKa + pKb

What is the equation for Kw?

[H3O+][H+]

What is ph and pOH?

pH = - log [H+]

pOH = - log [OH-]

How are pH and pOH related to pKw?

pOH + pH = pKw = 14

How do you find pH or pOH of strong acids/bases (or do logs in general)?

1. Convert to scientific notation

2. Separate terms and take -log of each

3. log 10^x = x

4. log 1 = 0, log 10 = 1 → estimate the remaining term

How do you find pH and pOH of weak acids/bases?

Use ICE table

1. Initial

2. Change

3. Equilibrium

Plug into Ka equation

• x is negligible in the denominator

What is the pH of a weak acid? Found using Ka

pH = - ½ log (Ka[WA])

No difference for diprotic acids

Use pOH, Kb, and WB for bases

What are buffers?

Mix of conjugate acid/base pairs

What is the pH of a buffer?

pH = pKa + log [WB]/[WA]

What buffer should you use?

Equal concentrations on WA and WB

With pKa ± 1 from pH

Larger net concentrations of WA and WB

When is an acid protonated/deprotonated?

pH > pKa → deprotonated

pH < pKa → protonated

What is a neutralization reaction?

Exothermic

Form salt and water

Complete if moles OH- = moles H+

What is equivalence point?

Moles OH- = moles H+

If at 7 → strong base and strong acid

What are indicators?

Used to determine concentrations

Weak acids of one color when protonated and another when deprotonated

Changes color when pH of solution = pKa of indicator

Change color at equivalence point

What will a titration curve of a weak acid and strong base look like?

Equivalence point with pH > 7

What is the half equivalence point?

Where pH = pKa of weak acid or weak base

Volume of titrant needed to reach equivalence point / 2

The flat part

What will a titration curve of a weak base and strong acid look like?

Equivalence point with pH < 7

What are acidic and basic salts?

Contain an ion that is a weak acid/base

For acid → look at cation → group I or II will never be acidic

For bases → look at anion → Cl-, Br-, and I- are never basic

How do you make a titration curve of a diprotic acid?

1st equivalence point = pH = average of pK1 and pK2 = isoelectric point

2nd ep = find like normal

Must fully titrate one proton before moving on to the second