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A bit more on the pH scale

Learn about pH scale, molar concentrations of H+ and OH- ions, and how acidity and basicity are determined by concentration levels of H+ ions. Explore pH calculations with formulas and examples.

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A bit more on the pH scale

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  1. A bit more on the pH scale

  2. CONCENTRATION ACIDS BASES (molar concentrations of H+ and OH- ions) Contain greater number of H+ ions than OH- ions pH of (0-6.9)) Contain less H+ ions than OH- ions pH of (7.1-14) Neutral Solutions Contain an equal number of H+ ions and OH- ions (pH of 7 (water))

  3. IMPORTANT INFORMATION: • Level of acidity and basicity is based on the nature of the acid or base and its concentration • pH is expressed as the positive value of an exponent in H+ ion concentration

  4. CONCENTRATION (FORMULA For H+ and OH- Ions) [H+] x [OH-] = 1 x 10-14 mol/L This formula is used to find the concentrations of H+ ions and OH- ions in various solutions pH is expressed as the positive value of an exponent in H+ ion concentration

  5. pH is always the positive value of the exponent for the H+ ions For example: Remember The product of [H+] ions and [OH]- ions is always = 1.0 x10-14 mol/L The Concentration of H+ ions for water is always = 1.0 x 10-7- mol/L

  6. EXAMPLE # 1 The hydroxide ion concentration (OH-) of a solution is 1 x 10-12. What is the pH of this solution? STEP # 1 To find the pH we must know the concentration of the H+ ions. Use the formula to find this: [H+] x [OH-] = 1 x 10-14 mol/L [H+]X1x10-12 = 1x10-14 [H+] = 1x10-2 0.5 L STEP # 2 Change into pH value [H+] = 1x10-2 pH of 2

  7. EXAMPLE # 2 The hydrogen ion concentration [H+] of a solution is 1 x 10-5. What is the pH of this solution? To find the pH we use the H+ ion concentration SO IF.... [H+] = 1x10-5 THEN... Change into pH value by taking the positive exponet of the H+ concentration 0.5 L pH of 5

  8. KEY POINTS • The formula for concentration of H+ and OH- ions is as follows: [H+] x [OH-] = 1 x 10-14 mol/L • The Concentration of H+ ions for water is always = 1.0 x 10-7- mol/L • pH is always the positive value of the exponent for the H+ ions

  9. PRACTICE PROBLEMS • Worksheet #4 • Study guide, Module 3, page 32 and 33

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