Titrations: Strong Acid-Strong Base: Videos & Practice Problems

Understanding the pH during a titration between a strong acid and a strong base is simplified by the fact that either can act as the titrant or titrate, with the strong species typically serving as the titrant. To determine the pH, an ICE (Initial, Change, Final) chart is utilized, which helps track the concentrations of the acid and base throughout the reaction. This process is essential in acid–base titrations, a fundamental concept in chemistry that involves the neutralization reaction between acids and bases, leading to the formation of water and a salt. Mastery of this technique is critical for accurate pH calculations in various chemical applications.

Strong Acid-Strong Base Titration

In the context of acid-base titrations, the interaction between a strong acid and a strong base is particularly straightforward for calculating pH. In these titrations, either the strong acid or the strong base can serve as the titrant, which is the substance added to the solution. The titrant is typically the stronger species in the reaction. Therefore, you can have scenarios where the strong acid acts as the titrant while the strong base is the titrate, or vice versa.

When a strong acid and a strong base are mixed, the process of determining the pH involves using an ICF chart, which stands for Initial, Change, and Final concentrations. This chart helps in systematically tracking the concentrations of the reactants and products throughout the titration process. The initial concentrations of the strong acid and strong base are recorded, followed by the changes that occur as they react. Finally, the resulting concentrations are used to calculate the pH of the solution.

For a strong acid, such as hydrochloric acid (HCl), and a strong base, like sodium hydroxide (NaOH), the neutralization reaction can be represented as:

$$\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$$

In this reaction, the strong acid completely dissociates into hydrogen ions (H⁺) and chloride ions (Cl^-), while the strong base dissociates into sodium ions (Na⁺) and hydroxide ions (OH^-). The resulting solution will typically have a neutral pH of 7 at the equivalence point, assuming equal concentrations of the acid and base are mixed.

Understanding this process is crucial for accurately determining the pH during titrations involving strong acids and bases, as it lays the foundation for more complex titration scenarios.

Strong Acid-Strong Base Titration Example

To calculate the pH of a solution resulting from the titration of 75 mL of 0.100 M perbromic acid (HBrO₄) with 55 mL of 0.100 M sodium hydroxide (NaOH), we first recognize that both substances are strong acid and strong base, respectively. This means they will completely dissociate in solution.

We begin by setting up an ICF (Initial, Change, Final) chart to track the amounts of reactants. The first step is to calculate the moles of each reactant using the formula:

moles = volume (L) × molarity (mol/L)

Converting the volumes from milliliters to liters, we find:

For perbromic acid:

75 mL = 0.075 L

0.075 L × 0.100 mol/L = 0.0075 moles of HBrO₄

For sodium hydroxide:

55 mL = 0.055 L

0.055 L × 0.100 mol/L = 0.0055 moles of NaOH

Next, we fill in the ICF chart. Since NaOH is the limiting reactant (having fewer moles), we subtract its amount from both reactants:

Initial moles:

• HBrO₄: 0.0075
• NaOH: 0.0055

Change:

• HBrO₄: -0.0055
• NaOH: -0.0055

Final moles:

• HBrO₄: 0.0020
• NaOH: 0

Now, we calculate the concentration of the remaining strong acid (HBrO₄) in the total volume of the solution. The total volume is:

75 mL + 55 mL = 130 mL = 0.130 L

Using the final moles of HBrO₄:

Concentration of HBrO₄ = moles/volume = 0.0020 moles / 0.130 L = 0.01538 M

Since we have a strong acid remaining, the concentration of hydronium ions (H⁺) is equal to the concentration of the strong acid:

[H⁺] = 0.01538 M

To find the pH, we use the formula:

pH = -log[H⁺]

Calculating this gives:

pH = -log(0.01538) ≈ 1.81

Thus, the final pH of the solution after the titration is approximately 1.81.

Calculate the pH of the solution resulting from the mixing of 175.0 mL of 0.250 M HNO₃ with 75.0 mL of 0.200 M Ba(OH)₂.

• A. 1.26
• B. 1.86
• C. 1.36
• D. 1.57

Answer: (A)

Calculate the pH of the solution resulting from the titration of 110.0 mL of 0.300 M HCl with 330.0 mL of 0.100 M LiOH.

• A. 1.5
• B. 7.0
• C. 8.5
• D. 10.0

Answer: (B)

Here’s what students ask on this topic:

What will be the pH at the equivalence point for a strong acid-strong base titration?

The pH at the equivalence point for a strong acid-strong base titration will be approximately 7. This is because strong acids and strong bases completely dissociate into their ions in water, producing hydrogen ions ($H^{+}$) and hydroxide ions (${\mathrm{OH}}^{-}$) respectively. At the equivalence point, the number of moles of hydrogen ions equals the number of moles of hydroxide ions, resulting in the formation of water ($H_{2}O$). Since water has a neutral pH of 7, the solution at the equivalence point will also be neutral if the titration is performed at room temperature and there are no other substances in the solution that could affect the pH. Keep in mind that this is true for titrations carried out in aqueous solutions under standard conditions.

When the hydronium concentration equals the hydroxide concentration in a strong acid - strong base titration, then the ______________ has been reached?

When the hydronium concentration equals the hydroxide concentration in a strong acid-strong base titration, then the equivalence point has been reached. This is the point at which the amount of acid equals the amount of base during the titration process. At the equivalence point, the number of moles of hydrogen ions (H⁺) from the acid is equal to the number of moles of hydroxide ions (OH^-) from the base, resulting in a neutral solution, typically with a pH of 7.00 at 25°C. However, the actual pH at the equivalence point can vary depending on the strengths of the acid and base used. In the case of a strong acid-strong base titration, the pH will be neutral at the equivalence point because both the acid and base completely dissociate in water.