Final answer:
When substances are added to a buffer of ammonia and ammonium nitrate, the concentration of ammonia, hydroxide ion, and ammonium ion change accordingly to maintain the buffer's pH. The Henderson-Hasselbalch equation is used to calculate the pH of a buffer given its components and their concentrations.
The correct answer is A.
Step-by-step explanation:
Effects on Buffer Components When Substances are Added:
When various substances are added to a basic buffer solution of ammonia (NH3) and ammonium nitrate (NH4NO3), the concentrations of ammonia, hydroxide ion (OH-), and ammonium ion (NH4+) are affected as follows:
- Adding ammonia (NH3): Increases the concentration of ammonia and hydroxide ion due to the equilibrium shifting to the right to accommodate the additional NH3. The concentration of ammonium ion remains relatively unaffected.
- Adding nitric acid (HNO3): Reacts with the ammonia present in the buffer to form more ammonium ion and water, thereby decreasing the ammonia and hydroxide ion concentrations while increasing the ammonium ion concentration.
- Adding sodium hydroxide (NaOH): Reacts with ammonium ion to form ammonia and water, thus decreasing the concentration of ammonium ion and increasing the concentration of ammonia and hydroxide ion.
- Adding ammonium chloride (NH4Cl): Increases the concentration of ammonium ion and consequently decreases the concentration of ammonia and hydroxide ion. The buffer's capacity to maintain pH upon the addition of acid or base is also influenced by these additions.
pH of the Buffer Solution:
To calculate the pH of a buffer solution prepared from 0.20 mol NH3, 0.40 mol NH4NO3, and 1.00 L of water, we use the Henderson-Hasselbalch equation:
pH = pKa + log([Base]/[Acid])
The pKa value for the conjugate acid of ammonia (NH4+) is needed to proceed with the calculation. With that information, the pH can be computed using the molar ratios provided.