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Questions and Answers
What is the purpose of titration methods in Analytical Chemistry?
What is the purpose of titration methods in Analytical Chemistry?
What is the purpose of a standard solution in a titration?
What is the purpose of a standard solution in a titration?
When is back-titration used in titration methods?
When is back-titration used in titration methods?
What is the equivalence point in a titration process?
What is the equivalence point in a titration process?
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Why are volumetric titrations also known as direct titrations?
Why are volumetric titrations also known as direct titrations?
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What does the end point in a titration signify?
What does the end point in a titration signify?
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Why does Ag+1 in Mohr method not react firstly with CrO4-2 instead of Cl-1?
Why does Ag+1 in Mohr method not react firstly with CrO4-2 instead of Cl-1?
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Why does Mohr method not use for determination of I -1?
Why does Mohr method not use for determination of I -1?
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Why must the pH of Mohr method be (6.5-9)?
Why must the pH of Mohr method be (6.5-9)?
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Why is the Mohr method now rarely used?
Why is the Mohr method now rarely used?
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Why does Volhard method not use for determination of SCN-1?
Why does Volhard method not use for determination of SCN-1?
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Why must AgCl ppt. in Volhard method be filtered before undertaking the back titration while AgBr and AgI are not required filtration process?
Why must AgCl ppt. in Volhard method be filtered before undertaking the back titration while AgBr and AgI are not required filtration process?
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What is the purpose of an indicator in a titration process?
What is the purpose of an indicator in a titration process?
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Why are weak acids and bases never used as standard reagents in acid-base titrations?
Why are weak acids and bases never used as standard reagents in acid-base titrations?
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In acid-base titrations, what is the pH at the equivalence point for a weak acid + strong base titration?
In acid-base titrations, what is the pH at the equivalence point for a weak acid + strong base titration?
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What is a chelating agent in complexometric titration?
What is a chelating agent in complexometric titration?
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What determines the coordination number of a metal ion?
What determines the coordination number of a metal ion?
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Which type of ligand has two groups available for covalent bonding?
Which type of ligand has two groups available for covalent bonding?
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What is the function of EDTA in complexometric titrations?
What is the function of EDTA in complexometric titrations?
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Study Notes
Titration Methods
- Titration methods are quantitative methods that measure the quantity of a reagent of known concentration required to react completely with the analyte.
- The reagent may be a standard solution of a chemical or an electric current of known magnitude.
Volumetric Titrations
- Volumetric titrations involve measuring the volume of a solution of known concentration needed to react completely with the analyte.
- The analyte is a solution of unknown concentration but known volume.
- The standard solution (titrant) is a reagent of known concentration and volume.
- Back-titration is a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution.
Key Concepts
- Equivalence point: the point in a titration when the amount of added standard reagent is equivalent to the amount of analyte.
- End point: the point in a titration when a physical change occurs that is associated with the condition of chemical equivalence.
- Titration error: the difference in volume between the equivalence point and the end point.
Indicators
- Indicators are added to the analyte solution to produce an observable physical change (detect end point) at or near the equivalence point.
- Indicator changes include the appearance or disappearance of a color.
Types of Standard Solutions
- Primary standard solutions (ex. Na2CO3 and H2C2O4): high purity, stability, rapid reaction with analyte, complete reaction, and selective reaction with analyte.
- Secondary standard solutions (ex. HCl and NaOH): less pure and less stable than primary standards.
Types of Volumetric Titrations
- Neutralization titration (acid-base titration)
- Complexometric titration
- Precipitation titration
- Oxidation-reduction titration
Neutralization Titration
- Standard reagents are always strong acids or strong bases.
- Acid-base indicators are weak organic acids or bases whose color changes according to pH value.
- Types of acid-base titrations:
- Strong acid + strong base (equivalence point pH = 7)
- Strong acid + weak base (equivalence point pH < 7)
- Weak acid + strong base (equivalence point pH > 7)
Complexometric Titration
- Method based on complex formation due to reaction between metal ion (M2+) and ligand (L).
- Ligands: H2O, NH3, Cl-, Br-, I-, and F-.
- Coordination number: the number of covalent bonds a metal forms with electron donors.
- Chelate: a metal ion coordinates with two or more donor groups of a single ligand to form a five- or six-membered heterocyclic ring.
- Types of ligands:
- Unidentate: a ligand with a single donor group (ex. NH3)
- Bidentate: a ligand with two donor groups (ex. glycine)
- Tridentate, tetradentate, pentadentate, and hexadentate
- EDTA (Ethylene Diamine Tetraacetic Acid) is a widely used complexometric titrant that analyzes metal ions as a hexadentate ligand.
Precipitation Titration
- Method based on the formation of a slightly soluble precipitate.
- Standard reagent is a precipitating agent (ex. AgNO3).
- Methods of detection of end point:
- Mohr Method: uses chromate ion (CrO4 -2) as an indicator.
- Fajans Method: uses adsorption indicators (ex. Fluorescein-).
- Volhard Method: uses iron III (Fe+3) as an indicator.
Oxidation-Reduction Titration
- Oxidation: an increase in oxidation number resulting from loss of electrons or increase in oxygen content or decrease in hydrogen content.
- Reduction: a decrease in oxidation number resulting from gain of electrons or decrease in oxygen content or increase in hydrogen content.
- Oxidizing agent (oxidant): a substance that accepts electrons and gets oxidized.
- Reducing agent (reductant): a substance that donates electrons and gets reduced.
- Reaction where a transfer of electrons is involved is called an oxidation-reduction reaction.
- Types of redox indicators:
- Self-indicators: standard reagents with oxidized and reduced forms that differ in color.
- Specific indicators: form a colored compound with a specific oxidized or reduced form of the analyte or standard reagent.
- True redox indicators: have oxidized and reduced forms that differ in color.
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Description
Test your knowledge on titration methods used in analytical chemistry to determine the quantity of an analyte. Learn about volumetric titrations and the concept of analyte (titrand).
