Acid-Base Equilibria, Buffers, Indicators, and Solubility Practice Flashcards

A set of practice Q&A flashcards covering Arrhenius/Bronsted-Lowry/Lewis concepts, buffer theory, indicators, titration, and solubility equilibria.

What is the Arrhenius definition of acids and bases?

Acids release H+ (as H3O+) in water; bases release OH− in water.

What is the Bronsted–Lowry definition of an acid and a base?

An acid is a substance that donates a proton (H+); a base is a substance that accepts a proton.

What is a conjugate acid–base pair?

Two species related by the transfer of one proton; e.g., NH3 and NH4+, H2O and H3O+, Cl− and HCl.

Why is HCO3− considered amphiprotic?

Because it can donate a proton (acid behavior) and accept a proton (base behavior) in solution.

What does a Lewis acid do, and what does a Lewis base do?

Lewis acid: accepts a lone pair of electrons; Lewis base: donates a lone pair of electrons.

What is the Common Ion Effect?

Addition of a solute bearing an ion common to a weak electrolyte reduces its degree of dissociation.

Define the ionic product of water, Kw, and its temperature dependence.

Kw = [H+] [OH−]. Kw increases with temperature; at 25°C, Kw ≈ 1.0×10−14.

What is pH and pOH, and how are they related to Kw?

pH = −log[H+], pOH = −log[OH−], and at 25°C pH + pOH = 14 (pKw). Kw = 10^(−pKw).

What is the relationship between Ka, Kb, and Kw?

Ka × Kb = Kw; pKa + pKb = pKw.

How do you estimate the pH of a weak acid solution with concentration C and dissociation constant Ka?

[H+] ≈ √(Ka C); pH ≈ 1/2(pKa − log C).

How do you estimate the pOH of a weak base solution with concentration C and dissociation constant Kb?

[OH−] ≈ √(Kb C); pOH ≈ 1/2(pKb − log C).

What is buffer capacity?

The ability of a buffer to resist pH change; maximum capacity occurs when the concentrations of salt (conjugate base) and acid are in a favorable ratio (often 1:1 for maximum net buffering).

What is Henderson–Hasselbalch equation for an acidic buffer?

pH = pKa + log([A−]/[HA]), where A− is the conjugate base and HA is the weak acid.

What is Henderson–Hasselbalch equation for a basic buffer?

pOH = pKb + log([BH+]/[B]), where B is the weak base and BH+ is its conjugate acid.

What is the equivalence point in titration?

The point at which the amount of titrant added is chemically equivalent to the amount of analyte initially present.

What is the difference between Q (ionic product) and Ksp (solubility product)?

Q is the current product of ion concentrations; Ksp is the equilibrium value. If Q > Ksp, precipitation occurs; if Q < Ksp, solution is unsaturated.

How does common ion effect influence solubility of a sparingly soluble salt like AgCl?

Solubility decreases in the presence of a common ion (e.g., Cl− from NaCl) due to Le Chatelier’s principle.

What effect does complex formation have on solubility?

Formation of complex ions (e.g., Ag+ with NH3 to form [Ag(NH3)2]+) can increase solubility by shifting dissolution equilibrium.

Give an example of a salt whose hydrolysis makes the solution acidic or basic.

Salt of a weak acid with a strong base (e.g., NaHCO3) can be basic due to hydrolysis of the anion; salt of a weak base with a strong acid (e.g., NH4Cl) can be acidic due to hydrolysis of the cation.

Why is H2O amphiprotic and how is this used to estimate pH in amphiprotic species?

Some species can both donate and accept protons (amphiprotic). For amphiprotic salts like HCO3−, pH can be estimated using pH ≈ 1/2(pKa1 + pKa2) for appropriate systems.

Which indicator is best for a weak acid–strong base titration?

Phenolphthalein (pH range ~8.3–10) is typically suitable for weak acid–strong base titrations.

What is the general approach to selecting an indicator for a titration curve?

Choose an indicator whose color change range brackets the pH at the equivalence point of the titration curve.

What is the effect of temperature on the pH of pure water at neutrality?

As temperature increases, Kw increases, so neutral water (where [H+] = [OH−]) has a higher [H+] and lower pH than 7; neutral pH moves below 7 with rising temperature.

What is the pH trend for a salt of weak acid and weak base?

The pH depends on the relative strengths (Ka vs Kb) of the weak acid and weak base; it can be acidic, basic, or neutral depending on Ka and Kb values and concentrations.

What is a buffer solution and what indicates a good buffer capacity?

A buffer resists pH change upon addition of small amounts of acid/base. A good buffer has [salt] ≈ [acid] (for acidic buffers) and sufficient absolute concentrations for capacity.

What is a polyprotic acid, and how are Ka1, Ka2, Ka3 treated in pH calculations?

Polyprotic acids have multiple dissociations. In many pH calculations, only the first dissociation constant (K1) is significant; higher Ka values are often neglected if much smaller than K1.