Acid-Base Titration Curves in Analytical Chemistry

Acid-Base Titration Curves

• Acid-base titration curves show the progress of titration as a function of the volume of titrant added, providing a visual picture of how a property, such as pH, changes during the titration.
• The equivalence point is characterized by a pH level that is a function of the acid-base strengths and concentrations of the analyte and titrant.

Titration of Strong Acids and Strong Bases

• When titrating a strong acid (HCl) with a strong base (NaOH), the only equilibrium reaction of importance is H3O+ (aq) + OH- (aq) → 2H2O (l).
• At the equivalence point, the moles of HCl and NaOH are equal, and the pH is determined by the dissociation of water, resulting in a pH of 7.00.
• Before the equivalence point, the pH is determined by the concentration of unreacted HCl, and after the equivalence point, the pH is determined by the excess OH-.

Construction of Titration Curves

• To construct a titration curve, calculate the volume of titrant needed to reach the equivalence point, and then calculate the pH at various points before and after the equivalence point.
• Use the equilibrium calculations described in previous lectures to determine the pH at each point.

Acid-Base Applications

• Acid-base titrations are used in the analysis of inorganic and organic compounds, with an emphasis on applications in environmental and clinical analysis.
• Inorganic analysis uses acid-base titrations to determine the concentration of inorganic acids and bases, such as H3PO4, H3BO3, and H3AsO4, and inorganic bases, such as Na2CO3, NaHCO3, and mixtures of both.
• Environmental analysis uses acid-base titrations to determine the alkalinity (OH-, HCO3-, and CO32-), acidity (HCl, HNO3, and H2SO4), and free CO2 in waters and wastewaters.

Determination of Carbonate in a Mixture

• Acid-base titrations can be used to determine the concentration of carbonate in a mixture of carbonate and bicarbonate using two indicators and a standard HCl solution.
• The volume of HCl required for ½ of the carbonate can be determined, and then the volume of HCl required for the entire carbonate can be calculated.

Organic Analysis

• Acid-base titrations are used in the analysis of organic compounds, particularly in the Kjeldahl analysis for organic nitrogen.
• Examples of analytes determined by a Kjeldahl analysis include caffeine and saccharin in pharmaceutical products, proteins in foods, and nitrogen in fertilizers, sludges, and sediments.

Kjeldahl Analysis

• The Kjeldahl analysis is a quantitative method for determining the %w/w N in a sample, which is then converted to %w/w protein using a conversion factor.
• The method involves oxidizing the nitrogen in the sample to NH4+, and then distilling the ammonia into a flask containing a known amount of standard strong acid, followed by back titration with a standard strong base titrant.
• The benefits of the Kjeldahl method include high precision and reproducibility, high productivity, and affordability.

Acid-Base Titration Curves

• Acid-base titration curves show the progress of titration as a function of the volume of titrant added, providing a visual picture of how a property, such as pH, changes during the titration.
• The equivalence point is characterized by a pH level that is a function of the acid-base strengths and concentrations of the analyte and titrant.

Titration of Strong Acids and Strong Bases

• When titrating a strong acid (HCl) with a strong base (NaOH), the only equilibrium reaction of importance is H3O+ (aq) + OH- (aq) → 2H2O (l).
• At the equivalence point, the moles of HCl and NaOH are equal, and the pH is determined by the dissociation of water, resulting in a pH of 7.00.
• Before the equivalence point, the pH is determined by the concentration of unreacted HCl, and after the equivalence point, the pH is determined by the excess OH-.

Construction of Titration Curves

• To construct a titration curve, calculate the volume of titrant needed to reach the equivalence point, and then calculate the pH at various points before and after the equivalence point.
• Use the equilibrium calculations described in previous lectures to determine the pH at each point.

Acid-Base Applications

• Acid-base titrations are used in the analysis of inorganic and organic compounds, with an emphasis on applications in environmental and clinical analysis.
• Inorganic analysis uses acid-base titrations to determine the concentration of inorganic acids and bases, such as H3PO4, H3BO3, and H3AsO4, and inorganic bases, such as Na2CO3, NaHCO3, and mixtures of both.
• Environmental analysis uses acid-base titrations to determine the alkalinity (OH-, HCO3-, and CO32-), acidity (HCl, HNO3, and H2SO4), and free CO2 in waters and wastewaters.

Determination of Carbonate in a Mixture

• Acid-base titrations can be used to determine the concentration of carbonate in a mixture of carbonate and bicarbonate using two indicators and a standard HCl solution.
• The volume of HCl required for ½ of the carbonate can be determined, and then the volume of HCl required for the entire carbonate can be calculated.

Organic Analysis

• Acid-base titrations are used in the analysis of organic compounds, particularly in the Kjeldahl analysis for organic nitrogen.
• Examples of analytes determined by a Kjeldahl analysis include caffeine and saccharin in pharmaceutical products, proteins in foods, and nitrogen in fertilizers, sludges, and sediments.

Kjeldahl Analysis

• The Kjeldahl analysis is a quantitative method for determining the %w/w N in a sample, which is then converted to %w/w protein using a conversion factor.
• The method involves oxidizing the nitrogen in the sample to NH4+, and then distilling the ammonia into a flask containing a known amount of standard strong acid, followed by back titration with a standard strong base titrant.
• The benefits of the Kjeldahl method include high precision and reproducibility, high productivity, and affordability.

Acid-Base Titration Curves

• Acid-base titration curves show the progress of titration as a function of the volume of titrant added, providing a visual picture of how a property, such as pH, changes during the titration.
• The equivalence point is characterized by a pH level that is a function of the acid-base strengths and concentrations of the analyte and titrant.

Titration of Strong Acids and Strong Bases

• When titrating a strong acid (HCl) with a strong base (NaOH), the only equilibrium reaction of importance is H3O+ (aq) + OH- (aq) → 2H2O (l).
• At the equivalence point, the moles of HCl and NaOH are equal, and the pH is determined by the dissociation of water, resulting in a pH of 7.00.
• Before the equivalence point, the pH is determined by the concentration of unreacted HCl, and after the equivalence point, the pH is determined by the excess OH-.

Construction of Titration Curves

• To construct a titration curve, calculate the volume of titrant needed to reach the equivalence point, and then calculate the pH at various points before and after the equivalence point.
• Use the equilibrium calculations described in previous lectures to determine the pH at each point.

Acid-Base Applications

• Acid-base titrations are used in the analysis of inorganic and organic compounds, with an emphasis on applications in environmental and clinical analysis.
• Inorganic analysis uses acid-base titrations to determine the concentration of inorganic acids and bases, such as H3PO4, H3BO3, and H3AsO4, and inorganic bases, such as Na2CO3, NaHCO3, and mixtures of both.
• Environmental analysis uses acid-base titrations to determine the alkalinity (OH-, HCO3-, and CO32-), acidity (HCl, HNO3, and H2SO4), and free CO2 in waters and wastewaters.

Determination of Carbonate in a Mixture

• Acid-base titrations can be used to determine the concentration of carbonate in a mixture of carbonate and bicarbonate using two indicators and a standard HCl solution.
• The volume of HCl required for ½ of the carbonate can be determined, and then the volume of HCl required for the entire carbonate can be calculated.

Organic Analysis

• Acid-base titrations are used in the analysis of organic compounds, particularly in the Kjeldahl analysis for organic nitrogen.
• Examples of analytes determined by a Kjeldahl analysis include caffeine and saccharin in pharmaceutical products, proteins in foods, and nitrogen in fertilizers, sludges, and sediments.

Kjeldahl Analysis

• The Kjeldahl analysis is a quantitative method for determining the %w/w N in a sample, which is then converted to %w/w protein using a conversion factor.
• The method involves oxidizing the nitrogen in the sample to NH4+, and then distilling the ammonia into a flask containing a known amount of standard strong acid, followed by back titration with a standard strong base titrant.
• The benefits of the Kjeldahl method include high precision and reproducibility, high productivity, and affordability.