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AP Chemistry: Equilibrium, Acids and Bases — quiz

15 multiple-choice questions covering Equilibrium Expressions, Kp and Kc Relationship, Q vs K, Le Chatelier's Principle, Ksp and Solubility. One answer each; you get a score at the end and the explanation for every question. No account needed.

Updated 2026-11-04. Keys 1–4 pick an answer, Enter moves on. Redo it any time, in order or shuffled.

The questions

Answers and explanations are shown after you finish.

1. Equilibrium Expressions

   For the heterogeneous equilibrium CaCO3(s) ⇌ CaO(s) + CO2(g), which expression correctly represents Kc?

   • Kc = [CaO]/[CaCO3]
   • Kc = [CaO][CO2]/[CaCO3]
   • Kc = [CO2]
   • Kc = [CaCO3]/([CaO][CO2])
2. Kp and Kc Relationship

   For 2SO2(g) + O2(g) ⇌ 2SO3(g) at 500 K, Kc = 3.0×10^2. Using R = 0.0821 L·atm/(mol·K), what is Kp?

   • 0.072
   • 300
   • 1.2×10^4
   • 7.3
3. Q vs K

   At a certain point during a reaction, Q = 15 and Kc = 4. Which way must the system shift to reach equilibrium?

   • No shift; already at equilibrium
   • Cannot be determined without temperature
   • Toward reactants (reverse)
   • Toward products (forward)
4. Le Chatelier's Principle

   For N2(g) + 3H2(g) ⇌ 2NH3(g), which change would shift the equilibrium toward more NH3 formation?

   • Increasing the container volume
   • Adding more N2
   • Adding more NH3
   • Removing some H2
5. Le Chatelier's Principle

   For 2NO2(g) ⇌ N2O4(g), compressing the container (decreasing volume) shifts the equilibrium toward which side, and why?

   • Toward NO2, because compression favors reactants
   • Toward NO2, because higher pressure speeds up the reverse reaction only
   • No shift, because pressure doesn't affect equilibrium position
   • Toward N2O4, because it has fewer moles of gas
6. Le Chatelier's Principle

   An inert gas like argon is added to an equilibrium mixture at constant volume. What happens to the equilibrium position?

   • It shifts toward the side with more gas moles
   • It shifts toward the side with fewer gas moles
   • It does not shift, since partial pressures of reactants and products are unchanged
   • It shifts to reduce the increased total pressure
7. Le Chatelier's Principle

   A forward reaction is exothermic. If the temperature is raised, what happens to the value of K?

   • K stays the same, only the rate changes
   • K becomes negative
   • K increases
   • K decreases
8. Ksp and Solubility

   PbI2 has Ksp = 7.1×10^−9 for PbI2(s) ⇌ Pb2+(aq) + 2I−(aq). What is its molar solubility, s?

   • 8.4×10^−5 M
   • 1.2×10^−3 M
   • 7.1×10^−9 M
   • 2.7×10^−5 M
9. Ksp and Solubility

   Solid AgCl is placed in 0.10 M AgNO3 solution instead of pure water. How does its solubility compare, and why?

   • More soluble, because Ag+ reacts with Cl− to remove it from solution
   • More soluble, because increased ionic strength helps dissolve more solid
   • The same, because Ksp is constant regardless of other ions present
   • Less soluble, because the added Ag+ shifts the dissolution equilibrium left
10. Strong Acids & Bases

    Which of the following acids is NOT considered a strong acid and therefore does not ionize completely in water?

    • HCl
    • HF
    • HClO4
    • HNO3
11. Ka, Kb, Kw Relations

    A weak acid HA has Ka = 1.0×10^−5. What is the Kb of its conjugate base, A−, at 25°C?

    • 1.0×10^−19
    • 1.0×10^−9
    • 1.0×10^5
    • 1.0×10^−14
12. pH and pOH

    A solution at 25°C has [OH−] = 1×10^−4 M. What is its pH?

    • 10
    • 14
    • 6
    • 4
13. Percent Ionization

    As a weak acid solution is diluted with water, what happens to its percent ionization and its [H+]?

    • Percent ionization increases while [H+] decreases
    • Percent ionization decreases while [H+] increases
    • Both percent ionization and [H+] increase
    • Both percent ionization and [H+] decrease
14. Buffers

    A buffer contains equal moles of a weak acid HA (pKa = 5.2) and its conjugate base A−. If more A− is added to this buffer, what happens to the pH?

    • pH stays at 5.2 and does not change
    • pH jumps to 7, becoming neutral
    • pH increases above 5.2
    • pH decreases below 5.2
15. Salt Hydrolysis

    Is an aqueous solution of NH4Br expected to be acidic, basic, or neutral, and why?

    • Basic, because Br− hydrolyzes water to form OH−
    • Acidic, because NH4+ is the conjugate acid of the weak base NH3 and hydrolyzes to form H+
    • Neutral, because both ions are spectator ions
    • Basic, because NH4+ releases OH− directly into solution