Strong Titrate-Strong Titrant Curves: Videos & Practice Problems

In strong acid-strong base titrations, the titration curve exhibits a characteristic sigmoidal shape, indicating a sharp pH change at the equivalence point where the amount of titrant equals that of the titrate. When titrating a strong acid with a strong base, the pH starts low and increases sharply until reaching the equivalence point, marked by a pH of 7, signifying neutralization. Beyond this point, excess titrant causes the pH to rise gradually until it levels off. Conversely, titrating a strong base with a strong acid starts with a high pH that decreases until the equivalence point, also at a pH of 7, after which excess titrant lowers the pH until it plateaus. In both scenarios, the equivalence point pH reflects the neutralization of the strong acid or base, demonstrating the strength and complete reaction of the titrants.

Strong Acid-Strong Base Titration Curve

In a titration involving a strong acid and a strong base, the titration curve exhibits a characteristic sigmoidal shape. Initially, the pH of the solution is significantly below 7, indicating the presence of a strong acid as the titrate. As a strong base is gradually added as the titrant, the pH begins to rise. This increase is particularly steep around the equivalence point, which occurs when the amount of strong base added completely neutralizes the strong acid.

At approximately 60 mL of strong base added, the curve shows its steepest ascent, marking the equivalence point, where the pH reaches 7. Beyond this point, all the strong acid has been neutralized, and any additional strong base results in a further increase in pH due to the presence of excess base. The pH levels off at just under 13, indicating a highly basic solution.

This titration curve effectively illustrates the relationship between the titrate and titrant, showcasing how the pH transitions from acidic to neutral and finally to basic as the titration progresses. Understanding this curve is crucial for interpreting the results of acid-base titrations and for determining the equivalence point accurately.

Strong Titrate-Strong Titrant Curve

In a titration involving a strong base and a strong acid, the resulting pH curve exhibits a sigmoidal shape, but in contrast to other titration curves, it starts at a pH well above 7. This initial high pH indicates that the titrate is a strong base. As the titrant, which is a strong acid, is added, the pH decreases sharply. The most significant change in pH occurs at the equivalence point, marked by a steep drop in the curve. At this point, the pH reaches 7, demonstrating that when both the titrate and titrant are strong, the equivalence point will always yield a neutral pH of 7, regardless of which is which.

After reaching the equivalence point, the strong base has been completely neutralized, and any additional strong acid leads to a further decrease in pH. This results in a leveling off of the curve at a pH around 1, indicating the presence of excess strong acid. The key takeaway is that the sigmoidal shape of the titration curve is characteristic of strong species, and the equivalence point remains at pH 7 due to the complete neutralization of the strong base by the strong acid.

Strong Titrate-Strong Titrant Curve Example

In a titration scenario involving 100 mL of 0.500 M hydrobromic acid (HBr) and 120 mL of 0.450 M potassium hydroxide (KOH), determining which species is in excess can be approached in two effective ways. The first method involves calculating the equivalence volume of the titrant, which in this case is KOH. The relationship between the moles of acid and base at the equivalence point can be expressed using the formula:

m_{acid} \cdot V_{acid} = m_{base} \cdot V_{base}

Here, m represents molarity and V represents volume. By rearranging the equation to find the equivalence volume of KOH, we can substitute the known values:

V_{base} = \frac{m_{acid} \cdot V_{acid}}{m_{base}}

Substituting the values gives:

V_{base} = \frac{0.500 \, \text{mol/L} \cdot 0.100 \, \text{L}}{0.450 \, \text{mol/L}} \approx 111.1 \, \text{mL}

Since the actual volume of KOH used (120 mL) exceeds the calculated equivalence volume (111.1 mL), it indicates that KOH is in excess.

The second method involves calculating the moles of each reactant. The number of moles can be determined using the formula:

moles = \text{volume (L)} \times \text{molarity (mol/L)}

Converting the volumes from mL to L, we find:

moles \, HBr = 0.100 \, \text{L} \times 0.500 \, \text{mol/L} = 0.0500 \, \text{mol}

moles \, KOH = 0.120 \, \text{L} \times 0.450 \, \text{mol/L} = 0.0540 \, \text{mol}

Comparing the moles, we see that KOH (0.0540 mol) is greater than HBr (0.0500 mol), confirming that KOH is in excess.

In summary, both methods—calculating the equivalence volume and determining the moles—lead to the conclusion that KOH is the species in excess in this titration scenario.

Which combination would give a pH = 7.0 at the equivalence point?
a) HNO₃ and NH₃                      b) HCl and NH₄⁺                        c) HC₂H₃O₂ and NaOH               d) HBr and NaH

• A. HNO₃ and NH₃
• B. HCl and NH₄⁺
• C. HC₂H₃O₂ and NaOH
• D. HBr and NaH

Answer: (D)

Here’s what students ask on this topic:

Which titration curve corresponds to the titration of a strong monoprotic acid (analyte) with a strong base (titrant)?

A titration curve that corresponds to the titration of a strong monoprotic acid with a strong base typically shows a very steep and rapid increase in pH as the equivalence point is approached. This is because both the acid and base fully dissociate in water, leading to a complete neutralization reaction.

At the beginning of the titration, the pH starts out low due to the presence of the strong acid. As the strong base is added, the pH gradually increases. As you get closer to the equivalence point, where the amount of acid initially present has been almost neutralized by the base added, the pH rises more sharply.

At the equivalence point, the solution contains only the salt and water, and the pH will be around 7, indicating a neutral solution. After the equivalence point, adding more base will cause the pH to rise rapidly again, this time due to the excess strong base in the solution.

The curve will be relatively symmetrical around the equivalence point, reflecting the rapid change in pH that occurs in a small volume of titrant addition. The vertical section of the curve is much steeper compared to titrations involving weak acids or bases, which have more gradual slopes due to incomplete dissociation.

What is the characteristic pH-titrant curve for the titration of a strong acid by a strong base?

The pH-titrant curve for the titration of a strong acid by a strong base typically features a very steep and distinct vertical section, representing a rapid pH change, which occurs at the equivalence point. This is where the amount of the strong base added is stoichiometrically equivalent to the amount of strong acid present in the solution.

At the beginning of the titration, the pH starts out low due to the strong acid's high concentration. As the strong base is added, the pH gradually increases until it nears the equivalence point. At this juncture, the pH rises very sharply with the addition of a very small volume of base. Once the equivalence point is passed, the curve levels out again, showing a slower increase in pH as the solution becomes increasingly basic.

The equivalence point for a strong acid-strong base titration typically occurs at a pH of about 7, indicating a neutral solution, because the products of the reaction are water and a salt that does not affect the pH. The curve is symmetrical around the equivalence point in this type of titration.

Which graph best represents the titration of a strong base by a strong acid?

The titration of a strong base by a strong acid is best represented by a graph showing the pH of the solution as a function of the volume of acid added. On this graph, you would see a sharp, vertical rise in the pH at the equivalence point, where the amount of acid added is stoichiometrically equivalent to the amount of base present.

At the beginning of the titration, the pH starts high because the solution is basic. As you add the strong acid, the pH decreases gradually. However, as you approach the equivalence point, the pH drops very rapidly. Once you've added just enough acid to neutralize the base, any additional acid will cause a more gradual decrease in pH again.

The resulting graph will have a characteristic "L" shape, with the vertical part of the "L" representing the rapid change in pH at the equivalence point and the base of the "L" showing the initial and final gradual changes in pH.