genchemii ch16

What is an Arrhenius acid?

A substance that increases H₃O⁺ concentration in water.

What is an Arrhenius base?

A substance that increases OH⁻ concentration in water.

What is a Brønsted–Lowry acid?

A proton (H⁺) donor.

What is a Brønsted–Lowry base?

A proton (H⁺) acceptor.

What is a Lewis acid?

An electron-pair acceptor.

What is a Lewis base?

An electron-pair donor.

What is a conjugate acid–base pair?

Two species that differ by one H⁺.

When does a conjugate acid–base pair form?

When a Brønsted–Lowry acid donates H⁺ or a base accepts H⁺.

What is a monoprotic acid?

An acid that can donate one proton per molecule.

What is a diprotic acid?

An acid that can donate two protons per molecule.

What is a polyprotic acid?

An acid that can donate more than one proton per molecule.

What is an amphiprotic species?

A species that can both donate and accept a proton.

What is water autoionization?

Two water molecules react to form H₃O⁺ and OH⁻: 2H₂O ⇌ H₃O⁺ + OH⁻.

What is Kw at 25 °C?

Kᵥ = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C.

What defines a neutral solution?

[H₃O⁺] = [OH⁻]. At 25 °C, each is 1.0 × 10⁻⁷ M.

What defines an acidic solution?

[H₃O⁺] > [OH⁻].

What defines a basic solution?

[OH⁻] > [H₃O⁺].

What is the pH equation?

pH = −log[H₃O⁺].

What is the pOH equation?

pOH = −log[OH⁻].

What is the pH–pOH relationship at 25 °C?

pH + pOH = 14.00.

How do you find hydronium concentration from pH?

[H₃O⁺] = 10⁻ᵖᴴ.

How do you find hydroxide concentration from pOH?

[OH⁻] = 10⁻ᵖᴼᴴ.

What does a one-unit pH change mean?

A tenfold change in hydronium concentration.

What determines acid or base strength?

Its tendency to donate or accept a proton; strength also depends on the solvent and conditions.

How do strong acids and bases behave in water?

They ionize essentially completely in water.

How do weak acids and bases behave in water?

They ionize partially and establish an equilibrium.

What does a larger Ka indicate?

A stronger acid and greater acid ionization.

What does a larger Kb indicate?

A stronger base and greater base ionization.

How does acid strength relate to conjugate-base strength?

A stronger acid has a weaker conjugate base.

How does base strength relate to conjugate-acid strength?

A stronger base has a weaker conjugate acid.

What is the Ka expression for HA + H₂O ⇌ H₃O⁺ + A⁻?

Ka = [H₃O⁺][A⁻]/[HA]. Pure liquid water is omitted.

What is the Kb expression for B + H₂O ⇌ BH⁺ + OH⁻?

Kb = [BH⁺][OH⁻]/[B]. Pure liquid water is omitted.

How are Ka, Kb, and Kw related for a conjugate pair at 25 °C?

Ka × Kb = Kw = 1.0 × 10⁻¹⁴.

How do you calculate Kb from Ka?

Kb = Kw/Ka for the conjugate base at the same temperature.

How do you calculate pH for a monoprotic strong acid?

Assume complete ionization: [H₃O⁺] is approximately the initial acid concentration, then pH = −log[H₃O⁺].

How do you calculate pH for a strong base?

Find [OH⁻] using complete dissociation and stoichiometric coefficients; calculate pOH, then pH = 14.00 − pOH at 25 °C.

Why can’t you always set [H₃O⁺] equal to the initial weak-acid concentration?

A weak acid only partially ionizes; equilibrium [H₃O⁺] must be calculated.

What does ICE stand for in an equilibrium table?

Initial, Change, Equilibrium.

In an ICE table, what do the change signs mean?

Reactants consumed have negative changes; products formed have positive changes.

For HA ⇌ H₃O⁺ + A⁻, what are the usual ICE changes?

−x for HA; +x for H₃O⁺ and +x for A⁻, assuming initially negligible products.

For B + H₂O ⇌ BH⁺ + OH⁻, what does x represent?

Usually the equilibrium concentrations [BH⁺] and [OH⁻] formed, if initial products are negligible.

What is the weak-acid Ka equation after an ICE table?

Ka = x²/([HA]initial − x) for a 1:1 acid reaction with initially negligible products.

What is the weak-base Kb equation after an ICE table?

Kb = x²/([B]initial − x) for a 1:1 base reaction with initially negligible products.

When can you use the small-x approximation?

When x is negligible compared with the initial concentration; verify with the 5% rule.

What is the small-x approximation for a weak acid?

If x is negligible: x ≈ √(Ka × [HA]initial), where x ≈ [H₃O⁺].

What is the small-x approximation for a weak base?

If x is negligible: x ≈ √(Kb × [B]initial), where x ≈ [OH⁻].

What is the 5% rule?

Calculate (x/[initial concentration]) × 100%. If below 5%, the small-x approximation is usually acceptable.

What if the 5% check is 5% or greater?

Do not use the small-x approximation; solve the full equilibrium equation, usually with the quadratic formula.

Does the quadratic formula apply because x is very small?

No. Use it when x cannot be neglected in the equilibrium expression.

How do you calculate percent ionization of a weak acid?

% ionization = (x/[HA]initial) × 100%, where x is the amount ionized.

For a weak acid, what does x usually equal?

[H₃O⁺] at equilibrium, if initial hydronium is negligible.

For a weak base, what does x usually equal?

[OH⁻] at equilibrium, if initial hydroxide is negligible.

How do you calculate pH after solving a weak-acid ICE table?

Use x = [H₃O⁺], then pH = −log(x).

How do you calculate pH after solving a weak-base ICE table?

Use x = [OH⁻], calculate pOH = −log(x), then pH = 14.00 − pOH at 25 °C.

What is the hydrolysis of a salt?

A reaction of a salt’s cation or anion with water that can affect solution pH.

What is the approximate pH behavior of NaCl in water?

Approximately neutral: Na⁺ and Cl⁻ have negligible acid–base hydrolysis.

Why is NH₄Cl solution acidic?

NH₄⁺ is the conjugate acid of the weak base NH₃ and can donate a proton to water.

Why is NaF solution basic?

F⁻ is the conjugate base of weak acid HF and reacts with water to form OH⁻.

How do you classify a salt if both ions affect pH?

Compare the acidic and basic strengths of the ions; don’t classify from the formula alone.

How does adding oxygen affect chlorine oxyacid strength?

For oxyacids with the same central atom, more oxygen atoms generally means a stronger acid.

Rank chlorine oxyacids by acid strength.

HClO₄ > HClO₃ > HClO₂ > HClO.

What is the general relationship between acid strength and Ka?

Stronger acid → larger Ka.

What is the general relationship between base strength and Kb?

Stronger base → larger Kb.

What must you account for when a strong base releases multiple OH⁻ ions?

Use the balanced equation’s stoichiometric coefficient; e.g., 1 mol Ba(OH)₂ produces 2 mol OH⁻.

Why is the second ionization of H₂SO₄ treated separately?

The first ionization is essentially complete, but the second is not complete and requires equilibrium treatment.

What does the pH scale measure?

The negative logarithm of hydronium concentration: pH = −log[H₃O⁺].