Acid-base reactions Flashcards
What is a Brønsted-Lowry acid?
A proton donor.
What is a Brønsted-Lowry base?
A proton acceptor.
What is meant by a conjugate acid-base pair?
A pair where the acid donates a proton to form its conjugate base, and the base accepts a proton to form its conjugate acid.
What does it mean when we say equilibrium is dynamic?
Both forward and reverse reactions occur simultaneously at equal rates.
What is the Law of Mass Action?
The rate of a reaction is proportional to the product of the concentrations of the reactants, each raised to the power of their stoichiometric coefficients.
How do you write an equilibrium constant expression?
For A + B ⇌ C + D, K = [C][D]/[A][B]
What does it mean when K > 1?
The products are favored at equilibrium.
What does it mean when K < 1?
The reactants are favored at equilibrium.
What is Le Chatelier’s Principle?
If a stress is applied to a system at equilibrium, the system shifts to oppose the change and reestablish equilibrium.
How does concentration affect equilibrium position?
Adding reactants shifts equilibrium toward products; adding products shifts it toward reactants.
How does pressure affect equilibrium?
In gaseous systems, increasing pressure shifts equilibrium toward the side with fewer gas molecules.
How does temperature affect equilibrium?
It depends on whether the reaction is exothermic or endothermic; equilibrium shifts to absorb added heat.
What is an acid dissociation constant (Ka)?
A measure of the strength of an acid in solution; high Ka = strong acid.
What is a base dissociation constant (Kb)?
A measure of the strength of a base in solution; high Kb = strong base.
How are Ka and Kb related?
Ka × Kb = Kw (the ionization constant of water = 1.0 × 10⁻¹⁴ at 25°C)
What is pH?
pH = -log₁₀[H₃O⁺]
What is pOH?
pOH = -log₁₀[OH⁻]
How are pH and pOH related?
pH + pOH = 14
What is the pKa?
pKa = -log₁₀Ka; lower pKa = stronger acid
What is the pKb?
pKb = -log₁₀Kb; lower pKb = stronger base
How do strong acids behave in water?
They completely dissociate, so [H₃O⁺] = initial acid concentration.
How do strong bases behave in water?
They completely dissociate, so [OH⁻] = initial base concentration.
How is pH calculated for strong acids?
pH = -log₁₀[acid]
How is pH calculated for strong bases?
pOH = -log₁₀[base], then pH = 14 - pOH
How is pH calculated for weak acids?
Use Ka = [H₃O⁺]² / [HA]; assume [HA]eq ≈ [HA]initial.
How is pH calculated for weak bases?
Use Kb = [OH⁻]² / [B]; then find pOH, then pH = 14 - pOH.
What is a salt solution?
A solution formed from the neutralization of an acid with a base.
Can salt solutions be non-neutral?
Yes, depending on the strength of the acid and base that formed them.
What’s the pH of a strong acid + strong base salt?
Neutral, pH ≈ 7
What’s the pH of a weak acid + strong base salt?
Basic, pH > 7 (due to conjugate base)
What’s the pH of a strong acid + weak base salt?
Acidic, pH < 7 (due to conjugate acid)
What are ampholytes?
Substances that can act as both acid and base; e.g., amino acids.
What is a buffer solution?
A solution of a weak acid and its conjugate base, or vice versa, that resists changes in pH.
How do buffers work?
They neutralize added H⁺ or OH⁻ by reversible reactions with the weak acid/base pair.
What equation is used to calculate buffer pH?
Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA])
What’s buffer capacity?
The amount of acid or base the buffer can neutralize before a significant pH change.
What is the ideal ratio for buffer capacity?
When [A⁻] = [HA], pH = pKa, and buffering is most effective.
What happens when a strong acid is added to a buffer?
The base component of the buffer neutralizes the acid, minimizing pH change.
What happens when a strong base is added to a buffer?
The acid component of the buffer neutralizes the base, minimizing pH change.
What is a titration?
A technique to determine the concentration of an unknown acid or base by neutralizing it with a known solution.
What is the endpoint of a titration?
The point at which equivalent moles of acid and base have reacted.
What is the equivalence point for strong acid–strong base titration?
pH = 7
What is the equivalence point for weak acid–strong base titration?
pH > 7 (due to basic salt)
What is the equivalence point for strong acid–weak base titration?
pH < 7 (due to acidic salt)
What is an indicator?
A compound that changes color depending on the pH of the solution, used to detect titration endpoints.
How do you choose an indicator?
Choose one whose pKa is close to the expected equivalence point pH.
