pH review

pH Review

pH Scale

  • Definition: The pH scale (0 - 14) indicates the concentration of H+ and OH- ions in water.

pH Scale Principle

  • Important statements regarding pH scale:

    • a. Increasing pH means the H+ ions are decreasing.

    • b. Decreasing pH means H+ ions are increasing.

    • c. Increasing pH means OH- ions are increasing.

    • d. Decreasing pH means OH- ions are decreasing.

pH of Solutions

  • Identify if the solutions are acidic, basic, or neutral, and compare [H+] concentrations to a solution with pH = 7:

    • pH = 13:

    • Type: Alkaline (basic)

    • [H+]: Lower than [H+] in pH = 7

    • pH = 8:

    • Type: Alkaline (basic)

    • [H+]: Lower than [H+] in pH = 7

    • pH = 2:

    • Type: Acidic

    • [H+]: Higher than [H+] in pH = 7

    • pH = 5.5:

    • Type: Acidic

    • [H+]: Higher than [H+] in pH = 7

    • pH = 9:

    • Type: Alkaline (basic)

    • [H+]: Lower than [H+] in pH = 7

    • pH = 1:

    • Type: Acidic

    • [H+]: Higher than [H+] in pH = 7

    • pH = 3:

    • Type: Acidic

    • [H+]: Higher than [H+] in pH = 7

    • pH = 10:

    • Type: Alkaline (basic)

    • [H+]: Lower than [H+] in pH = 7

    • pH = 14:

    • Type: Alkaline (basic)

    • [H+]: Lower than [H+] in pH = 7

Questions and Solutions Regarding H+ and OH- Ions

  • Most H+ ions: Compare pH 4 vs. pH 5:

    • Answer: pH = 4 has more H+ ions.

  • Most OH- ions: Compare pH 10 vs. pH 13:

    • Answer: pH = 13 has more OH- ions.

  • Least H+ ions: Compare pH 12 vs. pH 13:

    • Answer: pH = 13 has less H+ ions.

  • Least OH- ions: Compare pH 8 vs. pH 9:

    • Answer: pH = 8 has less OH- ions.

Effect of Adding or Removing Acids and Bases

  • If acid is added to a solution of pH 4:

    • pH: Decrease

    • [H+]: Increase

  • If acid is removed from a solution of pH 3:

    • pH: Increase

  • If base is added to a solution of pH 9:

    • pH: Increase

    • [H+]: Decrease

  • If base is added to a solution of pH 2:

    • pH: Increase

  • If acid is added to a solution of pH 13:

    • pH: Decrease

  • If base is removed from a solution of pH 12:

    • pH: Decrease

Short Answer Questions

  1. pH Equation: pH=−extlog(rac1[H+])pH = - ext{log} \bigg( rac{1}{[H^+]} \bigg)

  2. Definition of an Acid: A molecule that releases an H+ when added to a solution.

    • 2a. Effect of an Acid on pH: Decrease.

  3. Definition of a Base: A molecule that either releases OH- or binds H+.

    • 3a. Effect of a Base on pH: Increase.

  4. Reaction of an Acid with a Base: Forms salts.

  5. Function of Chemical Buffer: To minimize changes in pH in a solution.

    • 5a. If a strong base is added: The weak acid component of the buffer releases H+.

    • 5b. If a strong acid is added: The weak base component of the buffer binds the H+ released from the added acid.

  6. Chemical Reaction Explanation:

    • Reaction: H<em>2CO</em>3+OH−<br>ightarrowHCO<em>3−+H</em>2OH<em>2CO</em>3 + OH^- <br>ightarrow HCO<em>3^- + H</em>2O

    • Explanation: When OH- is added to the buffered solution, the weak carbonic acid (H2CO3) dissociates to release H+, which then binds to the OH- to produce a water molecule. As this occurs, the base, HCO3-, is produced.