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Glass Electrodes and pH Measurements quiz

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  • How do you calculate the pH of pure water at 50°C given Kw = 7.94 x 10^-14?
    Take the square root of Kw to find [H+], then calculate pH as -log([H+]); the answer is 6.55.
  • What is the relationship between [H+] and [OH-] in pure water?
    In pure water, [H+] equals [OH-] because water ionizes equally into both ions.
  • How does temperature affect the value of Kw?
    Kw is temperature dependent; as temperature changes, Kw changes from its value at 25°C.
  • What is the effect of adding Na+ and Br- ions to pure water on pH calculation?
    Adding Na+ and Br- increases ionic strength, requiring the use of activity coefficients in pH calculations.
  • What is the ionic strength formula for a solution containing Na+ and Br-?
    Ionic strength = 0.5 × (concentration of Na+ × charge^2 + concentration of Br- × charge^2).
  • How do you use activity coefficients in pH calculations?
    Multiply the ion concentration by its activity coefficient before taking the negative log to find pH.
  • What is the impact of ionic strength on the activity coefficient?
    Higher ionic strength lowers the activity coefficient, affecting the effective concentration of ions.
  • How does the presence of non-common ions affect solubility product (Ksp) calculations?
    Non-common ions increase ionic strength, requiring the use of activity coefficients in Ksp calculations.
  • What is the Ksp expression for barium hydroxide dissolving in solution?
    Ksp = [Ba^2+][OH^-]^2, but with activity coefficients, it becomes Ksp = [Ba^2+](γ_Ba^2+)[OH^-]^2(γ_OH^-)^2.
  • How do you find the pH of a saturated Ba(OH)2 solution in 0.05 M LiNO3?
    Calculate [OH^-] using Ksp and activity coefficients, find pOH as -log(activity of OH^-), then pH = 14 - pOH.
  • Why do you multiply the concentration of OH^- by 2 when calculating from Ba(OH)2?
    Because each Ba(OH)2 produces two OH^- ions for every one Ba^2+ ion dissolved.
  • What is the effect of increasing the concentration or charge of ions on pH?
    Increasing concentration or charge increases ionic strength, which can have a greater impact on pH.
  • How do you determine the activity of an ion in solution?
    Multiply the ion's concentration by its activity coefficient to get its activity.
  • What is the final pH of a saturated Ba(OH)2 solution in 0.05 M LiNO3, given the calculations?
    The final pH is approximately 13.41 after accounting for ionic strength and activity coefficients.
  • Why must activity coefficients be considered in solutions with non-common ions?
    Because non-common ions increase ionic strength, altering the effective concentrations of ions involved in equilibrium.