A 1.0-L buffer solution initially contains 0.25 mol of NH_...

Question

A 1.0-L buffer solution initially contains 0.25 mol of NH₃ and 0.25 mol of NH₄Cl. In order to adjust the buffer pH to 8.75, should you add NaOH or HCl to the buffer mixture? What mass of the correct reagent should you add?

Accepted Answer

First, we need to understand that a buffer solution resists changes in pH when small amounts of an acid or a base are added. In this case, the buffer solution is made up of NH3 (a weak base) and NH4Cl (its conjugate acid).. Next, we need to calculate the pH of the buffer solution before any reagent is added. We can use the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base (NH3) and [HA] is the concentration of the acid (NH4+). Since the molar amounts of NH3 and NH4+ are equal, the log term will be zero, and the pH of the buffer will be equal to the pKa of the NH4+/NH3 system.. Then, we compare the initial pH of the buffer solution with the desired pH. If the initial pH is lower than the desired pH, we need to add a base (NaOH) to increase the pH. If the initial pH is higher than the desired pH, we need to add an acid (HCl) to decrease the pH.. Once we know which reagent to add, we can calculate the amount of reagent needed to adjust the pH to the desired value. We can use the equation n = C*V, where n is the number of moles, C is the concentration, and V is the volume. We can rearrange this equation to find the number of moles of reagent needed, and then convert this to mass using the molar mass of the reagent.. Finally, we add the calculated mass of the reagent to the buffer solution to adjust the pH to the desired value.

A 1.0-L buffer solution initially contains 0.25 mol of NH₃ and 0.25 mol of NH₄Cl. In order to adjust the buffer pH to 8.75, should you add NaOH or HCl to the buffer mixture? What mass of the correct reagent should you add?

Verified video answer for a similar problem:

Key Concepts

Buffer Solutions

Henderson-Hasselbalch Equation

pH Adjustment with Strong Acids and Bases

A 1.0-L buffer solution initially contains 0.25 mol of NH3 and 0.25 mol of NH4Cl. In order to adjust the buffer pH to 8.75, should you add NaOH or HCl to the buffer mixture? What mass of the correct reagent should you add?

Verified video answer for a similar problem:

Key Concepts

Buffer Solutions

Henderson-Hasselbalch Equation

pH Adjustment with Strong Acids and Bases

A 1.0-L buffer solution initially contains 0.25 mol of NH₃ and 0.25 mol of NH₄Cl. In order to adjust the buffer pH to 8.75, should you add NaOH or HCl to the buffer mixture? What mass of the correct reagent should you add?