Two 25.0-mL samples, one 0.100 M HCl and the other 0.100 M HF, are titrated with 0.200 M KOH. b. Is the pH at the equivalence point for each titration acidic, basic, or neutral?

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insert step 1> Determine the nature of the reaction for each titration. HCl is a strong acid, and HF is a weak acid. Both are being titrated with KOH, a strong base.

insert step 2> For the HCl titration, since HCl is a strong acid, it will completely dissociate in water. The reaction with KOH will produce water and KCl, a neutral salt.

insert step 3> At the equivalence point of the HCl titration, the solution will be neutral because the strong acid and strong base completely neutralize each other, resulting in a pH of 7.

insert step 4> For the HF titration, HF is a weak acid and does not completely dissociate in water. The reaction with KOH will produce water and KF, a salt that can hydrolyze to form a basic solution.

insert step 5> At the equivalence point of the HF titration, the solution will be basic because the conjugate base (F-) from the weak acid (HF) will react with water to form OH- ions, increasing the pH above 7.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Strong vs. Weak Acids

Strong acids, like HCl, completely dissociate in solution, while weak acids, such as HF, only partially dissociate. This difference affects the pH at the equivalence point during titration. At the equivalence point, the strong acid will yield a neutral solution, while the weak acid will result in a solution that is more acidic due to the presence of undissociated acid molecules.

Titration and Equivalence Point

Titration is a technique used to determine the concentration of an acid or base by neutralizing it with a base or acid of known concentration. The equivalence point is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance being titrated. This point is crucial for determining the resulting pH of the solution, which varies depending on the strength of the acid or base involved.

pH and Its Interpretation

pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or basicity. A pH less than 7 is considered acidic, a pH of 7 is neutral, and a pH greater than 7 is basic. Understanding how the pH changes at the equivalence point of different acid-base titrations is essential for predicting the nature of the resulting solution.

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Textbook Question

The graphs labeled (a) and (b) show the titration curves for two equal-volume samples of monoprotic acids, one weak and one strong. Both titrations were carried out with the same concentration of strong base.

(i) What is the approximate pH at the equivalence point of each curve?

Textbook Question

(ii) Which graph corresponds to the titration of the strong acid and which one to the titration of the weak acid?

Textbook Question

Two 25.0-mL samples, one 0.100 M HCl and the other 0.100 M HF, are titrated with 0.200 M KOH. c. Which titration curve has the lower initial pH?

Textbook Question

Two 25.0-mL samples, one 0.100 M HCl and the other 0.100 M HF, are titrated with 0.200 M KOH.

d. Sketch each titration curve.

Textbook Question

Two 20.0-mL samples, one 0.200 M KOH and the other 0.200 M CH₃NH₂, are titrated with 0.100 M HI. a. What is the volume of added acid at the equivalence point for each titration?