In a titration of 50.00 mL of 1.00 M HC2 H3 O2 with 1.00 M NaOH, a student used bromcresol gree

step 1 So when we titrate, we can titrate a weak acid and a strong base, or we can titrate a weak base

In a titration of 50.00 mL of 1.00 M HC2 H3 O2 with 1.00 M...

In a titration of $50.00 \mathrm{~mL}$ of $1.00 \mathrm{M} \mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$ with $1.00 \mathrm{M} \mathrm{NaOH},$ a student used bromcresol green as an indicator $\left(K_{\mathrm{a}}=1.0 \times 10^{-5}\right) .$ About how many milliliters of $\mathrm{NaOH}$ would it take to reach the end point with this indicator? Is there a better indicator that she could have used for this titration?

Key Concepts

Indicator Selection in Titrations

Indicators are substances that change color at a specific pH range and are used to signal the endpoint of a titration. The color change range of an indicator should be chosen to closely match the pH at the equivalence point of the titration. Inappropriate indicator selection can lead to inaccurate readings of the endpoint. Understanding the pH change during the titration, particularly for weak acid–strong base titrations, is essential for selecting a suitable indicator.

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, provides a measure of the strength of an acid in solution. For a weak acid, a lower Ka indicates that the acid does not fully dissociate, meaning its conjugate base is relatively stronger. This property influences the pH at the equivalence point in a titration involving a weak acid and a strong base, typically resulting in a pH above 7. Understanding Ka helps in predicting the titration curve and determining an appropriate indicator based on the expected shift in pH.

Acid-Base Titration

Acid-base titration is a quantitative analytical method used to determine the concentration of an acid or a base by reacting it with a reagent of known concentration. This process involves gradually adding the titrant to the analyte until the reaction reaches completion, typically signaled by a change in an indicator or a measured pH change. The titration relies on a stoichiometric reaction between hydrogen ions and hydroxide ions to determine the equivalence point, where the amount of titrant exactly neutralizes the analyte.

Equivalence Point

The equivalence point in a titration refers to the moment when the number of moles of titrant added equals the number of moles of the analyte present, resulting in complete neutralization. In titrations involving a weak acid and a strong base, the pH at the equivalence point is typically greater than 7 because the weak acid forms a conjugate base that hydrolyzes, producing hydroxide ions. Identifying the equivalence point accurately is crucial for obtaining a correct determination of the analyte’s concentration.

Transcript

Please give Ace some feedback