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pH Revisited quiz

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  • What is the formula for calculating pH from the concentration of H+ ions?
    pH = -log[H+], where [H+] is the concentration of hydrogen ions.
  • At 50°C, if the Kw of water is 7.94 x 10^-14, what is the concentration of H+ in pure water?
    The concentration of H+ is the square root of Kw, which is 2.82 x 10^-7 M.
  • Why does the value of Kw change with temperature?
    Kw is temperature dependent because the ionization of water increases with temperature, altering the equilibrium constant.
  • What is the pH of pure water at 50°C when Kw = 7.94 x 10^-14?
    The pH is 6.55, calculated as -log(2.82 x 10^-7).
  • How do free floating ions like Na+ and Br- affect the pH calculation in water?
    They increase the ionic strength, which affects the activity coefficients and slightly alters the effective concentration of H+ used in the pH calculation.
  • What is the role of the activity coefficient in pH calculations?
    The activity coefficient adjusts the effective concentration of ions to account for non-ideal behavior due to ionic strength.
  • How is ionic strength calculated for a solution containing Na+ and Br-?
    Ionic strength is calculated as 0.5 × (concentration of Na+ × charge^2 + concentration of Br- × charge^2).
  • What is the effect on pH when the activity coefficient of H+ is less than 1?
    The effective concentration of H+ decreases, resulting in a slightly lower pH than if the activity coefficient were 1.
  • What is the pH of pure water with Na+ and Br- ions present at 50°C?
    The pH is 6.54, slightly lower than pure water due to the effect of ionic strength and activity coefficients.
  • How does the presence of non-common ions like lithium nitrate affect the solubility of barium hydroxide?
    Non-common ions increase the ionic strength, which increases the solubility of barium hydroxide by affecting activity coefficients.
  • What is the Ksp expression for barium hydroxide dissolving in water?
    Ksp = [Ba^2+][OH^-]^2, but in the presence of ionic strength, it includes activity coefficients: Ksp = [Ba^2+](γ_Ba^2+)[OH^-]^2(γ_OH^-)^2.
  • How do you find the concentration of OH- in a saturated solution of Ba(OH)2 with non-common ions present?
    First, solve for x using the Ksp expression with activity coefficients, then multiply x by 2 to get [OH^-].
  • How is the activity of OH- calculated in these solutions?
    The activity of OH- is the product of its concentration and its activity coefficient.
  • How do you calculate pOH from the activity of OH-?
    pOH = -log(activity of OH-), where activity is concentration times activity coefficient.
  • What is the final pH of a saturated Ba(OH)2 solution in 0.05 M lithium nitrate?
    The pH is approximately 13.41, accounting for increased solubility and activity coefficients due to ionic strength.