VCE-CHEM-U34 9.1 📋 Practice Exam 6: Question Paper

Calculate the pH of a 0.15 mol/L acetic acid solution. Ka = 1.8×10⁻⁵.

A buffer contains 0.200 mol/L CH₃COOH and 0.100 mol/L CH₃COONa. Calculate the pH. (pKa=4.74)

Explain how a buffer of NH₃/NH₄⁺ resists pH change when (i) small amounts of HCl (ii) small amounts of NaOH are added.

Describe the shape of a titration curve for a strong acid vs strong base. Indicate the equivalence point pH and a suitable indicator.

Calculate Ka for a 0.100 mol/L weak acid HA with pH = 3.00.

A solution contains 0.050 mol/L H₂CO₃ (Ka₁=4.3×10⁻⁷, Ka₂=4.8×10⁻¹¹). Calculate the pH, showing that the second dissociation is negligible.

What volume of 0.500 mol/L NaOH must be added to 100 mL of 0.500 mol/L acetic acid to prepare a buffer at pH 5.14? (pKa=4.74)

Explain why the pH at the half-equivalence point of a weak acid titration equals pKa.

Extended Response 1: Titration Curve Analysis

Extended Response 1: Titration Curve Analysis (a)
Sketch and label the titration curve for 25.0 mL of 0.100 mol/L CH₃COOH titrated with 0.100 mol/L NaOH. Mark: initial pH, half-equivalence point, equivalence point, and buffer region.

Extended Response 1: Titration Curve Analysis

Extended Response 1: Titration Curve Analysis (b)
Calculate the pH at the equivalence point. Ka(CH₃COOH)=1.8×10⁻⁵.

Extended Response 1: Titration Curve Analysis

Extended Response 1: Titration Curve Analysis (c)
Justify the choice of phenolphthalein (changes colour at pH 8.2-10.0) as indicator for this titration.

Extended Response 2: Buffer Chemistry

Extended Response 2: Buffer Chemistry (a)
A blood buffer contains [H₂CO₃]=0.00125 mol/L and [HCO₃⁻]=0.0250 mol/L. Ka₁(H₂CO₃)=4.3×10⁻⁷. Calculate blood pH.

Extended Response 2: Buffer Chemistry

Extended Response 2: Buffer Chemistry (b)
Explain what happens to blood pH if a person hyperventilates (breathing rate increases, CO₂ removed rapidly).