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Weak Acid-Base Equilibria quiz

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  • What does a Ka value less than 1 indicate about an acid?
    A Ka value less than 1 indicates that the acid is weak and only partially ionizes in water.
  • How do you calculate [H3O+] from a given pH?
    [H3O+] is calculated by taking 10 to the negative pH, or [H3O+] = 10^(-pH).
  • What is the equilibrium expression for a weak acid HA in water?
    The equilibrium expression is Ka = [A^-][H3O^+]/[HA].
  • Why are liquids and solids not included in the ICE chart for equilibrium calculations?
    Liquids and solids are not included because their concentrations do not change during the reaction.
  • What does the variable 'f' represent in the ICE table for weak acid calculations?
    'f' represents the original or formal concentration of the weak acid before any ionization occurs.
  • If the pH of a weak acid solution is 4.12, what is the [H3O^+]?
    [H3O^+] = 10^(-4.12) = 7.59 × 10^-5 M.
  • How do you set up the equation to solve for the original concentration of a weak acid using Ka and [H3O^+]?
    Set up Ka = x^2/(f - x), where x is [H3O^+], and solve for f, the original concentration.
  • What is the final calculated original concentration of the weak acid in the example provided?
    The original concentration is 7.71 × 10^-5 M.
  • What is the relationship between [A^-] and [H3O^+] at equilibrium for a monoprotic weak acid?
    At equilibrium, [A^-] = [H3O^+] = x, where x is the amount ionized.
  • What is the significance of the ICE table in weak acid equilibrium problems?
    The ICE table helps track the initial, change, and equilibrium concentrations of all species involved.
  • How do you solve for the formal concentration (f) after setting up the equilibrium equation?
    Isolate f by cross-multiplying and rearranging the equation, then solve for f algebraically.
  • What does the term 'formal concentration' mean in the context of weak acid solutions?
    Formal concentration refers to the initial molarity of the acid before any ionization occurs.
  • If given pOH instead of pH, what ion concentration can you calculate directly?
    You can calculate [OH^-] directly from pOH using [OH^-] = 10^(-pOH).
  • Why is it important to recognize whether a substance is a weak acid or weak base in equilibrium problems?
    Recognizing this determines whether you use Ka or Kb and which ion concentrations to focus on.
  • What is the general approach to finding the original molarity of a weak acid solution given Ka and pH?
    Calculate [H3O^+] from pH, substitute into the equilibrium expression with Ka, and solve for the original molarity.