Sketch the titration curve for the titration of a generic weak base B with a strong acid. The titration reaction is $$\mathbf{B}+\mathbf{H}^{+} \rightleftharpoons \mathbf{B H}^{+}$$ On this curve, indicate the points that correspond to the following: a. the stoichiometric (equivalence) point b. the region with maximum buffering c. \(\mathrm{pH}=\mathrm{p} K_{\mathrm{a}}\) d. \(\mathrm{pH}\) depends only on \([\mathrm{B}]\) e. \(\mathrm{pH}\) depends only on \(\left[\mathrm{BH}^{+}\right]\) f. \(\mathrm{pH}\) depends only on the amount of excess strong acid added

Short Answer

Expert verified
To sketch the titration curve of a weak base (B) with a strong acid, follow these steps: 1. Draw the initial curve that represents the pH change as a function of the added strong acid's volume. 2. Identify point "a" as the stoichiometric (equivalence) point, where moles of B equal moles of the strong acid added. 3. Label region "b" as the maximum buffering region, where B and its conjugate acid (BH⁺) are in equal amounts. 4. Identify point "c" (inside region "b") as the pH = pKa point, where moles of B equal moles of BH⁺. 5. Label point "d" on the left end, where pH depends only on [B] with no strong acid added yet. 6. Identify point "e" immediately after the equivalence point, where pH depends only on [BH⁺]. 7. Label point "f" on the far right end, where pH depends only on the amount of excess strong acid added.

Step by step solution

01

Draw the initial curve

Begin by sketching a generic titration curve that rises slowly at first, then rapidly in the middle, and finally levels off gradually. This curve represents the pH change as a function of the volume of added strong acid.
02

Identify the stoichiometric (equivalence) point

The stoichiometric (equivalence) point occurs when the moles of the weak base B equate the moles of the strong acid added. At this point, the curve shows the most significant change (usually a steep slope). Label this point as "a" on the curve.
03

Identify the region with maximum buffering

The region with maximum buffering occurs when the weak base (B) and its conjugate acid (BH⁺) are present in equal amounts. In this region, the system is highly resistant to pH changes and the slope of the curve is relatively flat. Label this region as "b" on the curve.
04

Identify the pH = pKa point

The point where pH = pKa occurs when the moles of the weak base (B) equal the moles of the conjugate acid (BH⁺). This is also the same point in the buffering region that you labeled in Step 3. Label this point as "c" on the curve, inside the region "b."
05

Identify the point where pH depends only on [B]

At the beginning of the titration, the pH depends only on [B] because the strong acid has not been added yet. Locate the point at the left end of the curve before any acid has been added, which represents the highest pH value. Label this point as "d" on the curve.
06

Identify the point where pH depends only on [BH⁺]

At the stoichiometric (equivalence) point (point "a"), all weak base (B) has been consumed, and only the conjugate acid (BH⁺) remains. Locate the point on the curve immediately after the equivalence point when the curve starts to level off. Label this point as "e" on the curve.
07

Identify the point where pH depends only on the amount of excess strong acid added

When the acid addition significantly surpasses the stoichiometric (equivalence) point (point "a"), the pH of the solution mainly depends on the concentration of the excess strong acid added. Locate the point at the extreme right end of the curve where the pH is lowest. Label this point as "f" on the curve.

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Most popular questions from this chapter

A sample of a certain monoprotic weak acid was dissolved in water and titrated with 0.125 \(M\) NaOH, requiring \(16.00 \mathrm{mL}\) to reach the equivalence point. During the titration, the pH after adding \(2.00 \mathrm{mL}\) NaOH was \(6.912 .\) Calculate \(K_{\mathrm{a}}\) for the weak acid.

A friend asks the following: "Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH - to form A Thus the amount of acid (HA) is decreased, and the amount of base \(\left(\mathrm{A}^{-}\right)\) is increased. Analogously, adding HCl to the buffered solution forms more of the acid (HA) by reacting with the base \(\left(\mathrm{A}^{-}\right)\). Thus how can we claim that a buffered solution resists changes in the pH of the solution?" How would you explain buffering to this friend?

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