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Questions and Answers
Why is it necessary to make the original solution almost neutral before adding a buffer solution?
Why is it necessary to make the original solution almost neutral before adding a buffer solution?
What happens if the metal ion concentration is too high in a titration?
What happens if the metal ion concentration is too high in a titration?
What is a fault to be guarded against when adding an indicator in a titration?
What is a fault to be guarded against when adding an indicator in a titration?
What is the typical amount of indicator mixture used in a titration?
What is the typical amount of indicator mixture used in a titration?
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What is the consequence of adding too much indicator in a titration?
What is the consequence of adding too much indicator in a titration?
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Why is it important to carefully add alkali to an acid solution containing a metallic ion?
Why is it important to carefully add alkali to an acid solution containing a metallic ion?
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What is the typical volume of solution used in a titration?
What is the typical volume of solution used in a titration?
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What is the purpose of using a buffering medium in a titration?
What is the purpose of using a buffering medium in a titration?
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What is the equivalent weight of the ferrous compound FeSO4.(NH4)2SO4.6H2O?
What is the equivalent weight of the ferrous compound FeSO4.(NH4)2SO4.6H2O?
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What is the oxidation number of Fe2+ in the reaction Fe2+ → Fe3+?
What is the oxidation number of Fe2+ in the reaction Fe2+ → Fe3+?
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What is the purpose of calculating the equivalent weight of a substance?
What is the purpose of calculating the equivalent weight of a substance?
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What is the normality of the ferrous solution containing 1,176g of FeSO4.(NH4)2SO4.6H2O in 30.00 ml?
What is the normality of the ferrous solution containing 1,176g of FeSO4.(NH4)2SO4.6H2O in 30.00 ml?
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What is the equivalent weight of the dichromate K2Cr2O7?
What is the equivalent weight of the dichromate K2Cr2O7?
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What is the purpose of calculating the normality of a solution?
What is the purpose of calculating the normality of a solution?
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What is the oxidation number of Cr2O72- in the reaction Cr2O72- → Cr3+?
What is the oxidation number of Cr2O72- in the reaction Cr2O72- → Cr3+?
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What is the volume of the dichromate solution equivalent to 1.000 ml of the ferrous solution?
What is the volume of the dichromate solution equivalent to 1.000 ml of the ferrous solution?
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Why is it important to perform Volhard's method in an acidic medium?
Why is it important to perform Volhard's method in an acidic medium?
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What is the purpose of adding a common ion to the wash liquid in precipitation reactions?
What is the purpose of adding a common ion to the wash liquid in precipitation reactions?
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What is the effect of pH on the solubility of the salt of a weak acid?
What is the effect of pH on the solubility of the salt of a weak acid?
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What is the principle behind the formation of a colored complex in Volhard's method?
What is the principle behind the formation of a colored complex in Volhard's method?
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What is the role of the indicator in Volhard's method?
What is the role of the indicator in Volhard's method?
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What is the effect of the diverse-ion effect on the solubility of a precipitate?
What is the effect of the diverse-ion effect on the solubility of a precipitate?
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What is the reaction that occurs at the end point of Volhard's method?
What is the reaction that occurs at the end point of Volhard's method?
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What is the purpose of using potassium thiocyanate solution in Volhard's method?
What is the purpose of using potassium thiocyanate solution in Volhard's method?
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Study Notes
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.
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Description
Learn about acid-base titrations and precipitation reactions in chemistry, including tips for neutralizing acid solutions and avoiding metal hydroxide precipitation.