Acid-base titration problems and solutions

1. What is an acid-base titration? Solution: An acid-base titration is a quantitative analysis of acids and bases; it is used to determine the unknown concentration of an acid or base by neutralizing it with an acid or base of known concentration.

2. What is the purpose of an indicator in a titration? Solution: The purpose of an indicator in a titration is to show the point at which all the reactants have reacted, which is known as the endpoint. The indicator does this by changing color.
3. What is the equivalence point in a titration? Solution: The equivalence point in a titration is the point at which exactly enough titrant has been added to react with all of the analyte. In an acid-base titration, it is the point at which the amount of acid equals the amount of base.
4. How is the endpoint of a titration determined? Solution: The endpoint of a titration is determined by observing the color change of the indicator.
5. How is the concentration of an unknown acid or base determined in a titration? Solution: The concentration of an unknown acid or base can be determined in a titration using the equation M₁V₁ = M₂V₂, where M₁ and M₂ are the molarities of the acid and base, and V₁ and V₂ are the volumes of the acid and base.
6. What is the role of a burette in a titration? Solution: A burette is used to deliver the solution of known concentration into the solution of unknown concentration. It allows for precise measurement of the volume of solution used.
7. How can a strong acid-strong base titration curve be distinguished from a weak acid-strong base titration curve? Solution: In a strong acid-strong base titration, the pH changes abruptly at the equivalence point and the pH at the equivalence point will be 7. In a weak acid-strong base titration, the pH change is more gradual around the equivalence point and the pH at the equivalence point will be greater than 7.
8. What is a half-equivalence point? Solution: The half-equivalence point is the point at which half of the analyte has reacted with the titrant. At this point, the pH equals the pKa of the weak acid or the pKb of the weak base.
9. What is back titration? Solution: Back titration is a method used when the molar concentration of the analyte cannot be determined directly by forward titration. It involves adding an excess of standard reagent to the analyte, and then titrating the remaining unreacted standard reagent with a second reagent.
10. What is the role of the conical (Erlenmeyer) flask in a titration? Solution: The conical or Erlenmeyer flask is used to hold the solution of unknown concentration during a titration. Its narrow neck and wider base allow for swirling of the solution without risk of spillage.
11. Why is distilled water used in titrations? Solution: Distilled water is used in titrations to rinse the equipment and to dilute solutions if necessary. It ensures that no other ions interfere with the reaction.
12. Why is it important not to add excess titrant after reaching the endpoint in a titration? Solution: Adding excess titrant after reaching the endpoint will change the pH of the solution and thus the color of the indicator. This will lead to an overestimation of the volume of titrant used and hence inaccurate results.
13. What is a standard solution in the context of a titration? Solution: A standard solution is a solution of known concentration used in titrations. It is typically the solution added from the burette.
14. Why should a burette be rinsed with the titrant solution before starting a titration? Solution: The burette should be rinsed with the titrant solution to ensure that any water or other solution is removed. This ensures that only the titrant reacts with the analyte, which leads to more accurate results.
15. What is phenolphthalein and how is it used in titrations? Solution: Phenolphthalein is a common indicator used in acid-base titrations. It is colorless in acidic solution and pink in basic solution. When the solution being titrated switches from acidic to basic (or vice versa), the color change of the indicator signals the endpoint of the titration.
16. How does a titration curve of a weak base-strong acid differ from that of a strong base-strong acid? Solution: In a weak base-strong acid titration, the pH changes more gradually around the equivalence point, and the pH at the equivalence point will be less than 7. In a strong base-strong acid titration, the pH changes abruptly at the equivalence point, and the pH at the equivalence point will be 7.
17. What does the term “primary standard” mean in the context of a titration? Solution: A primary standard is a highly pure, stable and non-hygroscopic substance that can be weighed accurately to prepare a solution of known concentration. It is used to standardize or check the concentration of a solution used in a titration.
18. Why is the titrant added slowly in a titration? Solution: The titrant is added slowly in a titration to make sure not to overshoot the endpoint. If the titrant is added too quickly, it could result in an inaccurate determination of the volume of titrant used and hence the calculated concentration of the analyte.
19. What is potentiometric titration? Solution: Potentiometric titration is a type of titration in which the potential difference (voltage) is measured with a pH meter or other potentiometer. It does not require an indicator and can provide more precise results than a titration that relies on visual detection of the endpoint.
20. What is gravimetric titration? Solution: Gravimetric titration is a type of titration in which the endpoint is determined by the mass of the titrant required to react with the analyte. It is used when the reaction produces a precipitate that can be filtered and weighed.