A bit more on the pH scale

(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))

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

[H + ] x [OH - ] = 1 x 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

H + ions (concentration) OH - ions (concentration)) pH mol/L of HCl 1.0 x x mol/L mol/L of HCl 1.0 x x mol/L mol/L of NaOH 1.0 x x mol/L 13 The product of [H+] ions and [OH]- ions is always = 1.0 x mol/L The Concentration of H+ ions for water is always = 1.0 x mol/L pH is always the positive value of the exponent for the H + ions

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 What is the pH of this solution? [H+] x [OH-] = 1 x mol/L [H+] X 1x = 1x [H+] = 1x10 -2 Change into pH value pH of 2

0.5 L To find the pH we use the H + ion concentration The hydrogen ion concentration [H+] of a solution is 1 x 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

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

 Worksheet #4  Study guide, Module 3, page 32 and 33