Animal Histology
Chem 1252, General Chemistry I Lab Johnson
Acid-Base Titrations
Introduction Titration is a convenient quantitative method for accurately determining unknown concentrations of solutions. A necessary requirement for its use is that a standard solution (a solution of known concentration) reacts chemically with the solution whose concentration is being determined. The standard solution is added to a solution of unknown concentration until all of the unknown solution has reacted. From the known quantity and molarity (or normality) of the standard solution and the measured volume of unknown solution used, the unknown concentration can be calculated. For example, standard base solution (NaOH) is added from a burette to an accurately known volume of the acid solution (HCl). HCl(aq) + NaOH(aq) ------------> H 2 O(l) + NaCl(aq) This reaction (neutralization) can be written as a NET IONIC equation as follows: H+(aq) + OH-(aq) ----------> H 2 O(l) (2) (1)
When sufficient NaOH has been added to react with all of the acid, the titration is complete -- the equivalence point has been reached. Most acid-base solutions are colorless and determining when one reactant has been totally consumed is difficult by simple observations. To allow us to visually determine this point, we use compounds called acid-base indicators to tell us when a reaction is complete. Dyes (usually weak organic acids) whose colors depend upon pH are often used to signal the completion of acidbase reactions. Indicators must be carefully chosen based on the pH of the equivalence point of the titration. In this experiment, a strong base (NaOH) is being added to a strong acid (HCl). An indicator that changes color when the pH becomes greater than 7 (more base is added than necessary) is used. Titrations involving a strong acid and a strong base commonly employ phenolphthalein as an indicator. Phenolphthalein changes from colorless to red at a pH of ≈ 8-10. At the point when the indicator changes color (also
Acid-Base Titrations
Introduction Titration is a convenient quantitative method for accurately determining unknown concentrations of solutions. A necessary requirement for its use is that a standard solution (a solution of known concentration) reacts chemically with the solution whose concentration is being determined. The standard solution is added to a solution of unknown concentration until all of the unknown solution has reacted. From the known quantity and molarity (or normality) of the standard solution and the measured volume of unknown solution used, the unknown concentration can be calculated. For example, standard base solution (NaOH) is added from a burette to an accurately known volume of the acid solution (HCl). HCl(aq) + NaOH(aq) ------------> H 2 O(l) + NaCl(aq) This reaction (neutralization) can be written as a NET IONIC equation as follows: H+(aq) + OH-(aq) ----------> H 2 O(l) (2) (1)
When sufficient NaOH has been added to react with all of the acid, the titration is complete -- the equivalence point has been reached. Most acid-base solutions are colorless and determining when one reactant has been totally consumed is difficult by simple observations. To allow us to visually determine this point, we use compounds called acid-base indicators to tell us when a reaction is complete. Dyes (usually weak organic acids) whose colors depend upon pH are often used to signal the completion of acidbase reactions. Indicators must be carefully chosen based on the pH of the equivalence point of the titration. In this experiment, a strong base (NaOH) is being added to a strong acid (HCl). An indicator that changes color when the pH becomes greater than 7 (more base is added than necessary) is used. Titrations involving a strong acid and a strong base commonly employ phenolphthalein as an indicator. Phenolphthalein changes from colorless to red at a pH of ≈ 8-10. At the point when the indicator changes color (also