Chemistry Titration and Precipitation Reactions

Titration and Precipitation Reactions

• In acid-base titrations, the original solution should be made almost neutral by adding sodium hydroxide, ammonium hydroxide, or dilute acid before adding the buffer solution.
• When neutralizing an acid solution containing a metallic ion with alkali, care must be taken to avoid precipitating the metal hydroxide.

Concentration of Metal Ion and Indicator

• Most titrations are successful with 0.25 millimole of the metal ion in 50-150 mL of solution.
• If the metal ion concentration is too high, the end point may be difficult to discern, and it may be necessary to start with a smaller portion of the test solution and dilute it before adding the buffering medium and indicator.
• Too much indicator should be avoided, as it can intensify the color during titration and exhibit dichroism, making it difficult to discern the end point.

Attainment of End Point and Solubility

• To ensure complete precipitation, a common ion can be used in the wash liquid to diminish solubility.
• The diverse-ion effect causes precipitates to show increased solubility when salts containing no ions in common with the precipitate are present.
• Solubility of the salt of a weak acid depends on the pH of the solution.

Hydrolysis, Complexation, and Precipitation Titration

• Hydrolysis and complexation can affect solubility.
• Precipitation titration involves reacting a substance with a standard solution of a precipitating agent, and the end point is marked by a color change with an indicator.

Methods of Precipitation Titration

• Volhard's method is used for determining anions like halides, phosphate, and chromate in acidic medium using silver ions.
• In Volhard's method, the leftover silver nitrate reacts with potassium thiocyanate solution, and the excess thiocyanate reacts with an indicator to form a complex.

Equivalents, Normalities, and Oxidation Numbers

• Equivalent weights and normalities are traditional concepts used in titrimetric analysis, especially in reduction-oxidation titrations.
• Oxidation numbers are required to understand the equivalent weights of substances involved in redox reactions.
• Examples of equivalent weights are provided for various substances, including FeSO₄.7H₂O, SnCl₂, H₂C₂O₄.2H₂O, KHC₂O₄.H₂O, H₂S, Na₂S₂O₃.5H₂O, and H₂O₂.

Learn about acid-base titrations and precipitation reactions in chemistry, including tips for neutralizing acid solutions and avoiding metal hydroxide precipitation.