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Fundamentals of pH and pOH in Chemistry

Understand the concepts of pH and pOH, the acidity or basicity of solutions, pH scale, calculations, and examples in this comprehensive guide.

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Fundamentals of pH and pOH in Chemistry

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  1. pH and pOH Chem 332 – O’Dette

  2. pH (Potential of Hydrogen) • Measures the degree of acidity or basicity of an aqueous solution • Corresponds to the hydrogenion concentration, [H+] • Measured on a scale from 0-14 - pH < 7 → Acid [H+] > 10-7 - pH ≈ 7 → Neutral [H+] = 10-7 - pH > 7 → Base [H+] <10-7

  3. pH Scale Strong Acids Weak Acids Weak Bases Strong Bases Neutral

  4. pH of Different Solutions Acids: • Urine = 6 • Black Coffee = 5 • Tomato Juice = 4 • Orange Juice = 3 • Lemon Juice = 2 • Gastric Acid =1 Bases: • Bleach = 13 • Soapy Water = 12 • Ammonia Solution = 11 • Milk of Magnesia = 10 • Baking Soda = 9 • Sea Water = 8 Neutral: - Distilled Water = 7

  5. Calculating pH pH = - log [H+] Memorize • Based on a log scale • From [H+] → pH • From pH → [H+] [H+] = 10-pH

  6. Step-Through Example • Find pH of 0.2 M of Hydrochloric Acid HCl(aq) → H+(aq) + Cl-(aq) 1 mole 1 mole 1 mole [0.2 M] → [0.2 M] + [0.2 M] pH = - log [H+] = - log [0.2M] pH = 0.7

  7. pOH (Potential of Hydroxide) • Similar to pH except pOH measures the hydroxideion concentration, [OH-]

  8. Calculating pOH pOH = - log [OH-] Memorize • From [OH-] → pOH • From pOH → [OH-] [OH-] = 10-pOH

  9. Relationship between pH and pOH Memorize • pH + pOH = 14 • [H+] x [OH-] = 10-14

  10. Ex: Find the pH of 0.1 M of sulfurous acid, H2SO3 H2SO3 (aq) → 2 H+ (aq) + SO3-2 (aq) 1 mole 2 moles 1 mole [0.1 M] → [0.2 M] + [0.1 M] pH = - log [H+] = - log [0.2M] pH = 0.7

  11. Ex: Find the pH of 0.005 M of Calcium Hydroxide, Ca(OH)2 Ca(OH)2 (aq) → Ca+ (aq) + 2OH- (aq) 1 mole 1 mole 2 moles [0.005 M] → [0.005 M] + [0.01 M] pOH = - log [OH-] = - log [0.01M] pOH = 2 pH + pOH = 14 pH = 14 – pOH = 14 - 2 pH = 12

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