AP Chem titration curves and indicators

Initial pH of a strong acid titration

Low, typically between 1-3, due to high concentration of H⁺ ions.

Shape of a strong acid-strong base titration curve

S-shaped with a steep vertical region near the equivalence point.

Equivalence point in titrations

Point where moles of acid = moles of base, sharp pH change.

Titration curve of weak acid-strong base

Starts higher pH than strong acid, gradual rise, and a buffer region.

pH at equivalence point for weak acid + strong base

Above 7 due to the formation of a basic salt.

Identify the buffer region

Region before the steep rise in the titration curve, where pH changes slowly.

True or False: pH at start is the same for all titrations.

False - varies based on acid/base strength and concentration.

Factors affecting the steepness of the titration curve

Concentration of reactants, strength of acids/bases, presence of buffers.

How to determine the end point of a titration

Use indicators that change color at the equivalence point pH.

Inflection point in titration curve

Indicates the equivalence point; steepest part of the curve.

What is the pH at the equivalence point for strong acid-strong base?

pH = 7, neutral solution.

Role of pH indicators in titrations

Show visual color change to indicate the endpoint of titration.

Expected pH at start of weak base-strong acid titration

Higher than 7, usually around 10-12 depending on concentration.

Calculate pH at equivalence point for a weak acid

Use $\displaystyle K_b$ of the conjugate base to find pH: $\displaystyle pH = 14 - pOH$.

Comparison: strong acid vs. weak acid titration curve

Strong acid: steep rise; Weak acid: gradual rise with buffer region.

Effect of dilution on titration curves

Dilution lowers initial pH, may alter curve shape slightly.

Fill in the blank: The pH at the initial stage of a weak acid titration is ___

Above 3, typically around 4-5 depending on concentration.

How does a strong acid affect pH change near equivalence?

Rapid decrease in pH due to complete dissociation of H⁺ ions.

Identify the characteristic of a pH curve near the equivalence point

Sharp increase in pH indicating quick neutralization.

Key characteristics of titration curves?

- Initial flat region - Buffer region - Sharp rise at equivalence point - Post-equivalence flat region - pH changes markedly at equivalence for weak/strong titrations.

Phenolphthalein pH range

8.2 to 10.0 - Colorless in acid - Pink in base

Methyl orange pH range

3.1 to 4.4 - Red in acid - Yellow in base

Bromothymol blue color change

6.0 to 7.6 - Yellow in acid - Blue in base

True or False: Litmus is only red in acid.

False: Litmus is red in acid and blue in base.

Which indicator is suitable for strong acid-strong base titrations?

Phenolphthalein is suitable due to its clear color change around neutral pH.

Fill in the blank: Methyl red turns ______ in basic solutions.

Yellow

Acid-base indicator definition

A substance that changes color at a specific pH range, indicating acidity or basicity.

Bromothymol blue transition colors

Yellow (acid) ↔ Blue (neutral/base)

Which indicator for weak acid-strong base titration?

Use phenolphthalein for clear color change at endpoint.

True or False: Phenolphthalein is yellow in acidic solutions.

False: It is colorless in acidic solutions.

How does methyl orange behave in different pH?

Red in acid, yellow in neutral/base; transitions at pH 3.1 to 4.4.

Fill in the blank: Litmus turns ______ in alkaline solution.

Blue

Transition color of phenolphthalein

Colorless to pink around pH 8.2 to 10.0.

Which indicator is best for strong acid-weak base titration?

Methyl orange is best due to early transition in acidic pH.

Bromocresol green pH range

3.8 to 5.4 - Yellow in acid - Blue in base

True or False: Indicators can be used outside their pH range.

True, but results may be inaccurate.

What color does bromothymol blue turn in neutral solutions?

Green, as it is a mix of yellow (acid) and blue (base).

pH range of litmus

Approximately 4.5 to 8.3 - Red: Acid - Blue: Base

Strong acid vs. weak acid

Strong acids fully dissociate in water, weak acids partially dissociate. Examples: HCl (strong), CH₃COOH (weak).

Consequences of strong bases

Strong bases like NaOH completely dissociate, producing high pH, leading to rapid neutralization in titrations.

pH of strong acid solutions

pH = -log[H⁺]; for 0.01 M HCl, pH = 2.

True or False: Weak acids have high pKa values.

True: Higher pKa indicates weaker acid strength.

Identify: H₂SO₄

Strong acid: completely dissociates into H⁺ and SO₄²⁻.

Fill in the blank: A strong base like ____ completely dissociates.

NaOH (sodium hydroxide).

Effect of dilution on strong acids

Dilution lowers concentration; pH increases but remains low.

Compare HCl and CH₃COOH in titrations

HCl shows a steep curve; CH₃COOH shows a gradual curve due to partial dissociation.

Ka definition

Acid dissociation constant; measures strength of weak acids. Larger Ka = stronger acid.

Effect of weak base on pH

Weak bases like NH₃ raise pH moderately due to partial dissociation.

Write the dissociation for HNO₃

HNO₃ → H⁺ + NO₃⁻; strong acid, fully dissociates.

Cause → Effect: Strong acid titration

Rapid pH drop at equivalence point due to complete dissociation.

pH range of weak acid solutions

Typically between 4 and 7, depending on concentration.

True or False: Strong acids have low pH and weak acids have high pH.

True: Strong acids have pH < 3; weak acids usually > 4.

Identify: NH₄Cl

Weak acid salt; contributes to acidic solutions when dissolved.

Weak acid example: H₂CO₃

Carbonic acid; partially dissociates in water, weak acid.

Dissociation of a weak base

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻; equilibrium established.

Calculate pH of 0.1 M HCl

pH = -log(0.1) = 1.

Contributions of acetic acid in titration

Acts as a weak acid; gradual pH change near equivalence point.

Identify: pKa = 4.75

Indicates a weak acid; lower pKa = stronger acid.

Molarity (M) formula?

Molarity (M) = \\frac{moles \ of \ solute}{liters \ of \ solution}

Calculate moles of NaOH in 0.5 L of 0.2 M solution.

Moles = Molarity × Volume = 0.2 mol/L × 0.5 L = 0.1 moles.

True or False: Molarity changes with temperature.

True. Molarity can change as temperature affects volume.

Neutralization reaction formula?

HA + BOH → BA + H_2O (HA = acid, BOH = base)

What is the pH at the equivalence point of a strong acid-strong base titration?

pH = 7.0 at equivalence point.

Calculate the concentration of HCl if 25 mL neutralizes 50 mL of 0.1 M NaOH.

C1V1 = C2V2 → C1(25 mL) = 0.1 M(50 mL), C1 = 0.2 M.

What does the equivalence point represent?

The point where moles of acid equals moles of base.

Fill in the blank: pH = -log[___].

pH = -log[H^+].

Compare strong acids and weak acids.

Strong acids fully dissociate in water, while weak acids partially dissociate.

Calculate the dilution of 2 M HCl to 0.5 M.

C1V1 = C2V2 → (2 M)(V1) = (0.5 M)(100 mL). V1 = 25 mL.

Cause → Effect: Adding a strong acid to a strong base.

Cause: Acid and base mix → Effect: Heat and water produced.

What is the endpoint in a titration?

The point where the indicator changes color, signifying completion.

Volume of NaOH needed to neutralize 20 mL of 0.1 M HCl?

V_NaOH = \\frac{(0.1 M)(20 mL)}{0.1 M} = 20 mL.

Calculate the moles in a titration.

Use the formula: Moles = Molarity × Volume (L) Example: For 0.1 M NaOH in 50 mL: Moles = 0.1 mol/L × 0.050 L = 0.005 moles.