Acid, Base, and pH/pOH Calculations

pH and Acidity/Basicity

  • pH scale:

    • Below 7: Acidic

    • Above 7: Basic

  • pOH scale (opposite of pH):

    • Below 7: Basic

    • Above 7: Acidic

  • Neutrality: A pH or pOH of 7 is neutral.

  • Strength: The further away from 7, the stronger the acid or base.

  • Weakness: Closer to 7 indicates a weaker acid or base.

Calculations

  • pH Calculation: To find the pH, take the negative log of the hydrogen ion concentration [H+][H^+]. Expressed as: pH=−log[H+]pH = -log[H^+]

  • pOH Calculation: To find the pOH, take the negative log of the hydroxide ion concentration [OH−][OH^-].. Expressed as: pOH=−log[OH−]pOH = -log[OH^-]

Important Considerations

  • Significant Figures: Ensure correct significant figures in calculations.

  • Converting pH to Concentration: If given the pH and need to find the hydrogen ion concentration [H+][H^+], use the formula: [H+]=10−pH[H^+] = 10^{-pH}.

  • Converting pOH to Concentration: If given the pOH and need to find the hydroxide ion concentration [OH−][OH^-], use the formula: [OH−]=10−pOH[OH^-] = 10^{-pOH}.

Relationship Between pH and pOH

  • Formula: pH + pOH always equals 14: pH+pOH=14pH + pOH = 14.

    • Example: If pH = 3, then pOH = 11.

Concentrations of Hydrogen and Hydroxide Ions

  • The product of the concentration of hydrogen ions [H+][H^+] and the concentration of hydroxide ions [OH−][OH^-] is a constant.

Practice and Assessment

  • Practice: Practice problems are essential for mastering these concepts.

  • Progress Check: Next class.

  • Assessment: Next Tuesday.