Exam 1: Acid/Base Chemistry

A proton donor

What is an acid?

A proton acceptor

What is a base?

A strong acid totally dissociates; a weak acid only partially dissociates

What is the difference between a strong acid and a weak acid?

Acid dissociation constant

What does Ka mean?

Ka = [H+][A−]/[HA]

What is the equation for Ka?

A stronger acid

What does a larger Ka indicate?

A weaker acid

What does a smaller Ka indicate?

−log(Ka); the pH at which equal amounts of protonated acid and conjugate base are present

What is pKa?

Lower pKa = stronger acid; higher pKa = weaker acid

How does pKa relate to acid strength?

−log[H+]

What does pH mean?

pH = −log[H+]

What equation defines pH?

[H+] = 10^(−pH)

How do you calculate [H+] from pH?

−log[OH−]

What does pOH mean?

pOH = −log[OH−]

What equation defines pOH?

[OH−] = 10^(−pOH)

How do you calculate [OH−] from pOH?

Ion product constant of water

What does Kw mean?

Kw = [H+][OH−] = 1 × 10^−14

What is Kw at 25°C?

−log(Kw)

What does pKw mean?

pH + pOH = 14

What relationship connects pH and pOH at 25°C?

pH = 14 − pOH

How do you calculate pH from pOH?

pOH = 14 − pH

How do you calculate pOH from pH?

A proton / hydrogen ion

What does H+ represent?

Hydroxide ion

What does OH− represent?

Concentration of that species

What do brackets [ ] around a chemical species mean?

Molarity; moles per liter

What does M mean when describing concentration?

Millimolar; 10^−3 moles per liter

What does mM mean?

Normality; concentration based on equivalents of the reactive ion

What does N mean when describing concentration?

pH = pKa + log([Base]/[Acid])

What is the Henderson–Hasselbalch equation?

Base / deprotonated form

Which form goes in the numerator of the Henderson–Hasselbalch ratio?

Acid / protonated form

Which form goes in the denominator of the Henderson–Hasselbalch ratio?

[Base]/[Acid] = 10^(pH − pKa)

How do you solve Henderson–Hasselbalch for the Base:Acid ratio?

[Acid] = [Base]

When pH = pKa, what is the relationship between acid and base concentrations?

50% acid and 50% base

When pH = pKa, approximately what percentage is acid and what percentage is base?

10:1

When pH = pKa + 1, what is the Base:Acid ratio?

1:10

When pH = pKa − 1, what is the Base:Acid ratio?

The protonated form

Which form predominates when pH < pKa?

The deprotonated form

Which form predominates when pH > pKa?

The half-equivalence point

At what point on a titration curve does pH = pKa?

A solution that resists significant changes in pH when acid or base is added

What is a buffer?

Approximately pKa ± 1 pH unit

What is the effective buffering range of a weak acid/conjugate base system?

Near its pKa

At what pH does a buffer work best?

Buffering capacity decreases

What happens to buffering capacity as pH moves farther away from pKa?

H2PO4− / HPO4^2−

What phosphate buffer pair is used in the lecture?

pKa ≈ 6.8

What pKa is used for the phosphate buffer pair in the lecture?

pH = pKa + log([HCO3−]/[CO2])

What blood bicarbonate Henderson–Hasselbalch equation is used in the lecture?

Bicarbonate

What does HCO3− represent?

Carbonic acid

What does H2CO3 represent?

The acid-related denominator used in the lecture’s blood buffer equation

What does CO2 represent in the blood bicarbonate equation?

pKa = 6.1

What pKa is used for the blood bicarbonate buffer system in the lecture?

pH < pKa → mostly protonated; pH > pKa → mostly deprotonated

What rule predicts protonation state from pH relative to pKa?

Multiple titratable groups

Why can amino acids have more than one buffering region or equivalence point?

Blowing off CO2 shifts the bicarbonate equilibrium left and raises pH

How does rapid deep breathing help compensate for acidic blood in diabetic ketoacidosis?

Water can donate and accept protons

Why can water act as both an acid and a base?

pH decreases

What happens to pH as [H+] increases?

pH increases

What happens to pH as [H+] decreases?