IB Diploma Programme IB-DP-CHEM: Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL) | Tutolia Study Library

Conjugate acid-base pairs, ionic product of water Kw, Ka/pKa calculations for weak acids, buffer action, and salt hydrolysis for IB DP Chemistry.

Subject: Chemistry | Grade Level: Grade 11-12 (IB DP HL/SL) | Curriculum: IB Diploma Programme

IB Diploma Programme: Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL) (Chemistry)

Syllabus Code: IB-DP-CHEM · Topic Code: Reactivity 3.1 · Level: Grade 11-12 (IB DP HL/SL)

Aligned with official IB Diploma Programme examination standards and assessment objectives.

🎯 Official Syllabus Learning Objectives

Candidates should be able to:

• [x] Identify Bronsted-Lowry conjugate acid-base pairs and amphiprotic species
• [x] Calculate pH, pOH, [H+], and [OH-] using Kw = 1.0 x 10⁻¹⁴ at 298 K and weak acid Ka expressions
• [x] Explain how acidic and basic buffer solutions resist changes in pH upon addition of small amounts of acid or base

📐 Essential Formulas & Mathematical Equations

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\text{pH} = -\log_{10}[H^+], \quad K_w = [H^+][OH^-] = 1.0 \times 10^{-14} \text{ at 298 K}

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\text{p}K_a + \text{p}K_b = \text{p}K_w = 14

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\text{pH} = \text{p}K_a + \log_{10} \left(\frac{[\text{A}^-]}{[\text{HA}]}\right)

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💡 Conceptual Breakdown & Core Revision Notes

Mastering Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL) is critical for scoring Grade 9 / A* in IB Diploma Programme Chemistry. When preparing for exam papers, examiners prioritize precise definitions, proper scientific command-word execution (State, Describe, Explain, Evaluate), and dimensional unit consistency.

Methodical Problem-Solving Framework

1. List Given Variables: Write down all given quantities with their respective SI units and identify the target variable.
2. Standardise Units: Always convert non-standard units (e.g. grams to kilograms, centimeters to meters, cm³ to dm³, hours to seconds).
3. State the Base Formula: Always state the general equation explicitly before substituting numbers to secure method marks.
4. State Final Value with Units: Quote your final calculated value to the required number of significant figures (typically 2 or 3 significant figures in Cambridge & IB) followed by the correct unit.

⚠️ Examiner Warnings & Common Student Pitfalls

Chief Examiner Advice:

As temperature increases, the endothermic auto-ionization of water shifts right, so Kw increases and the pH of pure water falls below 7.0—yet the water remains completely NEUTRAL because [H+] = [OH-]!

📝 Worked Exam Exemplar (Mark Scheme Breakdown)

Question:

Calculate the pH of a 0.10 mol dm⁻³ solution of ethanoic acid given pKa = 4.76 at 298 K.

Model Answer & Marking Rubric:

Ka = 10⁻⁴.⁷⁶ = 1.74 10⁻⁵. Assuming [H+] ≈ sqrt(Ka [HA]) = sqrt(1.74 10⁻⁵ 0.10) = sqrt(1.74 10⁻⁶) = 1.32 10⁻³ mol dm⁻³. pH = -log10(1.32 * 10⁻³) = 2.88.

🧠 Rapid Active-Recall Study Deck (Spaced Repetition)

Test your immediate retention before leaving this page:

1. Question: What is the fundamental definition associated with Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL)?

Answer: Check the primary learning objective in the checklist above.

1. Question: Which governing formula links the main physical quantities in this topic?

Answer: `\text{pH} = -\log_{10}[H^+], \quad K_w = [H^+][OH^-] = 1.0 \times 10^{-14} \text{ at 298 K}`.

1. Question: What classic trap do examiners frequently set on this topic?

Answer: As temperature increases, the endothermic auto-ionization of water shifts right, so Kw increases and the pH of pure water falls below 7.0—yet the water remains completely NEUTRAL because [H+] = [OH-]!

Exam Questions & Key Takeaways (FAQ)

Calculate the pH of a 0.10 mol dm⁻³ solution of ethanoic acid given pKa = 4.76 at 298 K.

Ka = 10⁻⁴.⁷⁶ = 1.74 10⁻⁵. Assuming [H+] ≈ sqrt(Ka [HA]) = sqrt(1.74 10⁻⁵ 0.10) = sqrt(1.74 10⁻⁶) = 1.32 10⁻³ mol dm⁻³. pH = -log10(1.32 * 10⁻³) = 2.88.

What is the key examiner tip and common student pitfall for Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL)?

As temperature increases, the endothermic auto-ionization of water shifts right, so Kw increases and the pH of pure water falls below 7.0—yet the water remains completely NEUTRAL because [H+] = [OH-]!

What are the official syllabus learning objectives for IB Diploma Programme IB-DP-CHEM: Proton Transfer Reactions: Bronsted-Lowry Acids, pH & Buffers (HL/SL)?

Identify Bronsted-Lowry conjugate acid-base pairs and amphiprotic species; Calculate pH, pOH, [H+], and [OH-] using Kw = 1.0 x 10⁻¹⁴ at 298 K and weak acid Ka expressions; Explain how acidic and basic buffer solutions resist changes in pH upon addition of small amounts of acid or base