11. Which of the following is true about the equilibrium constant (KcKc) for a reaction?
a) It depends on the concentration of reactants and products.
b) It changes with temperature.
c) It changes with pressure.
d) It depends on the initial concentration of reactants.
Answer: b) It changes with temperature.
Explanation:
The equilibrium constant depends only on temperature, not on the concentrations of reactants or products, or pressure. A change in temperature can shift the equilibrium, changing the KcKc.
12. In the dissociation of ammonia in water, NH3+H2O⇌NH4++OH−NH3+H2O⇌NH4++OH−, what is the effect of adding an acid?
a) The concentration of OH−OH− increases.
b) The concentration of OH−OH− decreases.
c) The dissociation of ammonia increases.
d) The dissociation of ammonia decreases.
Answer: b) The concentration of OH−OH− decreases.
Explanation:
Adding an acid increases the concentration of H++ ions, which react with OH−− ions to form water, thereby decreasing the concentration of OH−−.
13. Which of the following conditions will favor the forward reaction in an exothermic equilibrium reaction?
a) Increasing the temperature
b) Decreasing the temperature
c) Increasing the concentration of products
d) Adding a catalyst
Answer: b) Decreasing the temperature
Explanation:
In an exothermic reaction, decreasing the temperature favors the forward reaction, as the system will shift to produce more heat, which is in line with Le Chatelier’s principle.
14. Which of the following statements is correct for a solution of a weak electrolyte?
a) The ionization increases with increasing concentration.
b) The ionization decreases with increasing concentration.
c) The ionization is unaffected by dilution.
d) The ionization is complete at all concentrations.
Answer: b) The ionization decreases with increasing concentration.
Explanation:
According to Ostwald’s dilution law, the degree of ionization of a weak electrolyte decreases as the concentration increases.
15. Which of the following salts will produce a basic solution in water?
a) NaCl
b) KNO33
c) CH33COONa
d) NH44Cl
Answer: c) CH33COONa
Explanation:
CH33COONa is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide). When dissolved in water, it hydrolyzes to form OH−− ions, making the solution basic.
16. In a buffer solution containing a weak acid and its conjugate base, the pH will:
a) Decrease when more conjugate base is added
b) Increase when more conjugate base is added
c) Remain unchanged when acid is added
d) Remain unchanged when base is added
Answer: b) Increase when more conjugate base is added
Explanation:
Adding more conjugate base increases the concentration of the base relative to the acid, which reduces the concentration of H++ ions, raising the pH.
17. For the dissociation of acetic acid, which of the following factors will increase the equilibrium concentration of CH3COO−CH3COO−?
a) Addition of NaOH
b) Addition of HCl
c) Increasing the temperature
d) Decreasing the concentration of acetic acid
Answer: a) Addition of NaOH
Explanation:
NaOH reacts with H++ ions, which decreases the H++ concentration. This causes the equilibrium to shift to the right to replace the lost H++, increasing the concentration of CH3COO−CH3COO−.
18. In the equilibrium N2O4(g)⇌2NO2(g)N2O4(g)⇌2NO2(g), what will happen if the volume of the system is increased?
a) The equilibrium will shift towards the products.
b) The equilibrium will shift towards the reactants.
c) The equilibrium constant will increase.
d) The equilibrium will not shift.
Answer: a) The equilibrium will shift towards the products.
Explanation:
According to Le Chatelier’s principle, increasing the volume (decreasing pressure) shifts the equilibrium towards the side with more gas molecules. In this case, there are more moles of gas on the product side (2 NO22).
19. The solubility of AgCl in water will increase if:
a) NaCl is added to the solution
b) HCl is added to the solution
c) Ammonia is added to the solution
d) The temperature is decreased
Answer: c) Ammonia is added to the solution
Explanation:
Ammonia reacts with Ag++ ions to form a complex ion [Ag(NH3)2]+[Ag(NH3)2]+, which reduces the concentration of Ag++ in solution, thus increasing the solubility of AgCl.
20. Which of the following is an example of a buffer solution?
a) HCl and NaCl
b) NaOH and NaCl
c) NH44OH and NH44Cl
d) HNO33 and NaNO33
Answer: c) NH44OH and NH44Cl
Explanation:
A buffer solution contains a weak acid and its conjugate base or a weak base and its conjugate acid. NH44OH (weak base) and NH44Cl (its conjugate acid) form a buffer solution.
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