1. A bit more on the pH scale

2. (molar concentrations of H + and OH - ions) ACIDS BASES 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. [H + ] x [OH - ] = 1 x 10 -14 mol/L (FORMULA For H + and OH - Ions) 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. H + ions (concentration) OH - ions (concentration)) pH 1. 0.1 mol/L of HCl 1.0 x 10 -1 1.0 x 10 -13 mol/L 1 2. 0.001 mol/L of HCl 1.0 x 10 -3 1.0 x 10 -11 mol/L 3 3. 0.1 mol/L of NaOH 1.0 x 10 -13 1.0 x 10 -1 mol/L 13 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 pH is always the positive value of the exponent for the H + ions

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

7. 0.5 L To find the pH we use the H + ion concentration The hydrogen ion concentration [H+] of a solution is 1 x 10 -5. What is the pH of this solution? [H+] = 1x10 -5 Change into pH value by taking the positive exponet of the H + concentration 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.  Worksheet #4  Study guide, Module 3, page 32 and 33