Complexometric Titration Concepts
40 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What type of ligand is EDTA classified as?

  • Tridentate
  • Hexadentate (correct)
  • Unidentate
  • Bidentate

The coordination number refers to the number of ligands attached to a central metal ion.

True (A)

Name one factor that affects the stability of complexes.

Acidity

In complexometric titration, the metal ion acts as the _______ and the ligand acts as the _______.

<p>acceptor</p> Signup and view all the answers

Match the following ligands with their type:

<p>H2O = Unidentate EDTA = Hexadentate Ethylene Diamine = Bidentate Acetate = Unidentate</p> Signup and view all the answers

Which of the following ions has a higher basicity?

<p>N (B)</p> Signup and view all the answers

The size of the central metal ion does not influence the stability of a complex.

<p>False (B)</p> Signup and view all the answers

What is a common application of complexmetric titration?

<p>Determining metal ion concentrations</p> Signup and view all the answers

Which of the following is NOT a reason why EDTA is considered the best titrant in complexometric titration?

<p>It reacts with only certain metals. (A)</p> Signup and view all the answers

The pH at which Mg2+ is titrated with EDTA is 10.

<p>True (A)</p> Signup and view all the answers

What is the stability constant (Kf) used in the titration example?

<p>5.0 x 10^8</p> Signup and view all the answers

At the equivalence point, the pMg of the solution is __________.

<p>5</p> Signup and view all the answers

What happens to the concentration of Mg2+ when 45.0 mL of EDTA is added?

<p>It decreases to 0.0053 M. (C)</p> Signup and view all the answers

Match the pMg values with the corresponding volumes of EDTA added:

<p>10.0 mL = 1.18 30.0 mL = 1.6 45.0 mL = 2.28 0.0 mL = 1.0</p> Signup and view all the answers

What is the pH when H4Y reacts with water to form H3Y-?

<p>2.7</p> Signup and view all the answers

The titration curve does not alter with the value of the stability constant.

<p>False (B)</p> Signup and view all the answers

Which metal ion forms a more stable complex with EDTA when compared to magnesium?

<p>Calcium (B)</p> Signup and view all the answers

At pH 10, EDTA forms complexes with both calcium and magnesium ions.

<p>False (B)</p> Signup and view all the answers

What is the purpose of adjusting the pH when analyzing metal ion mixtures?

<p>To control the stability of various metal-EDTA complexes.</p> Signup and view all the answers

Ascorbic acid is used as a __________ to reduce Fe3+ to Fe2+ during metal ion analysis.

<p>reducing agent</p> Signup and view all the answers

Match the metal ion with its corresponding group in pH titration:

<p>Ca2+ = Third group: pH=10 using ammonia buffer Cu2+ = Second group: pH 4-6 using acetate buffer Fe3+ = First group: pH 1-3 using conc.HNO3 Pb2+ = Second group: pH 4-6 using acetate buffer</p> Signup and view all the answers

What color change occurs when titrating aluminum ions with Zn2+ using EBT indicator?

<p>Blue to wine red (A)</p> Signup and view all the answers

Masking agents are used to enhance the selectivity of EDTA during complexometric titration.

<p>True (A)</p> Signup and view all the answers

Which indicator is used to titrate Bi3+ ions at pH 2?

<p>Xylenol orange</p> Signup and view all the answers

What is the stability constant (kf) for the reaction involving Mg2+ and Y4-?

<p>5.0 x 10^8 (B)</p> Signup and view all the answers

The pH range for Eriochrome black T indicator is from 5.3 to 12.5.

<p>False (B)</p> Signup and view all the answers

Name one characteristic that a metal ion indicator must have.

<p>The indicator must be very sensitive to metal ions.</p> Signup and view all the answers

In direct titration, the solution is buffered to the desired pH using ___ and ___.

<p>NH4Cl, NH4OH</p> Signup and view all the answers

What color does murexide exhibit at a pH of 10?

<p>Yellow-orange (D)</p> Signup and view all the answers

Match the following types of EDTA titrations with their descriptions.

<p>Direct titration = Metal ion solution buffered and titrated directly with EDTA Back-titration = Excess EDTA is added followed by titration to find unreacted EDTA Replacement titration = Metal ion replaces Mg2+ from the complex Indirect titration = Metal is determined by titrating a related species</p> Signup and view all the answers

The color change from colorless to colored indicates the endpoint in complexometric titration.

<p>True (A)</p> Signup and view all the answers

What is one requirement for a metal ion indicator in relation to the metal-EDTA complex?

<p>The metal-indicator complex must be less stable than the metal-EDTA complex.</p> Signup and view all the answers

Which of the following metal ions do not react with EDTA?

<p>Hg (A), Fe2+ (D)</p> Signup and view all the answers

Masking agents are used to enhance the reaction of metal ions with EDTA.

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of a demasking agent?

<p>To release a metal ion from a masking agent.</p> Signup and view all the answers

A solution is titrated to a blue color after adding ____ mL of 0.01 M EDTA solution in a sample fixed at pH 10.

<p>30</p> Signup and view all the answers

Match the following actions with their corresponding definitions:

<p>Masking agents = Prevent certain ions from reacting with EDTA Demasking agents = Release masked metal ions pH adjustment = Control acidity for titration Complexation = Formation of stable metal complexes</p> Signup and view all the answers

In the titration of a water sample containing Ca and Mg, what volume of EDTA is needed to titrate only Ca when the pH is fixed at 12?

<p>28 mL (A)</p> Signup and view all the answers

The total hardness of water can be calculated based only on the volume of EDTA used in the titration.

<p>True (A)</p> Signup and view all the answers

How would you calculate the concentration of Ni2+ in a paint sample using EDTA?

<p>By subtracting the volume of EDTA consumed by Mg2+ from the total volume added to the sample and relating it to the concentration of Ni2+.</p> Signup and view all the answers

Flashcards

Complexmetric Titration

A type of titration that involves the formation of soluble complexes between metal ions (acting as acceptors) and ligands (acting as donors). These complexes are formed through coordination bonds.

Central Metal Atom (M)

The central atom in a coordination compound, usually a metal ion.

Ligand (L)

A molecule or ion that binds to a central metal atom through a coordinate bond.

Complex (Coordination Compound)

The product formed when a metal ion coordinates with a ligand.

Signup and view all the flashcards

Coordination Number

The number of coordination bonds formed between the central metal ion and ligands.

Signup and view all the flashcards

Unidentate Ligand

A type of ligand that binds to a metal ion using a single donor atom.

Signup and view all the flashcards

Bidentate Ligand

A type of ligand that binds to a metal ion with two donor atoms.

Signup and view all the flashcards

Chelating Agent

A type of ligand that binds to a metal ion through multiple donor atoms.

Signup and view all the flashcards

Complexing Agent

A substance that forms a stable complex with a metal ion.

Signup and view all the flashcards

Endpoint Detection

The end point of a titration marked by a color change of the indicator.

Signup and view all the flashcards

Metal Ion Indicator

A substance that changes color in the presence of specific metal ions, indicating the endpoint.

Signup and view all the flashcards

Direct Titration

A titration where the analyte (metal ion) is directly titrated with a standard EDTA solution.

Signup and view all the flashcards

Back Titration

A titration where excess EDTA is added to the analyte, the excess is then back-titrated with a known metal ion.

Signup and view all the flashcards

Replacement Titration

A titration where the analyte reacts with a known metal-EDTA complex, releasing the metal ion which is then titrated.

Signup and view all the flashcards

Indirect Titration

A titration where the analyte is indirectly determined by reacting it with a reagent and then titrating the product.

Signup and view all the flashcards

What is a Complexometric Titration?

The formation of a stable complex between a metal ion (M) and a ligand (L) through coordination bonds. The complex is formed in a 1:1 stoichiometric ratio.

Signup and view all the flashcards

What is a Ligand?

A molecule or ion that binds to a central metal atom through a coordinate bond. It donates electrons to the metal atom.

Signup and view all the flashcards

What is a Central Metal Atom?

The central atom in a coordination compound, usually a metal ion. It accepts electrons from the ligand.

Signup and view all the flashcards

Define Coordination Number

The number of coordination bonds formed between the central metal ion and ligands. It determines the geometry of the complex.

Signup and view all the flashcards

What is a Unidentate Ligand?

A type of ligand that binds to a metal ion using a single donor atom. It forms a simple bond.

Signup and view all the flashcards

What is a Bidentate Ligand?

A type of ligand that binds to a metal ion with two donor atoms. It forms a stronger bond.

Signup and view all the flashcards

What is a Chelating Agent?

A type of ligand that binds to a metal ion through multiple donor atoms. It creates a stable, cage-like complex.

Signup and view all the flashcards

Why is EDTA the best titrant for complexometric titration?

EDTA is a hexadentate ligand that forms very stable complexes with all metals. It's a single-step reaction, has a sharp end point, forms soluble complexes, and is available as a primary standard (disodium salt).

Signup and view all the flashcards

Water Hardness Determination

The process of determining the total amount of calcium and magnesium ions in a sample, usually water.

Signup and view all the flashcards

EDTA

A chelating agent useful in complexometric titration that forms a stable complex with metal ions.

Signup and view all the flashcards

Metal-EDTA Complex

A complex formed by the interaction of EDTA and a metal ion. This is typically formed during complexometric titration.

Signup and view all the flashcards

Control of pH

The ability to selectively analyze metal ions by manipulating the pH of the solution.

Signup and view all the flashcards

Adjustment of Oxidation Number

A chemical reaction used to change the oxidation state of a metal ion to influence its reactivity and make it more suitable for titration.

Signup and view all the flashcards

Masking Agent

Chemical compounds used to temporarily block the reactivity of other metal ions in a mixture, allowing selective titration of the target ion.

Signup and view all the flashcards

Metal Indicator

A chemical indicator used in complexometric titration to signal the endpoint of the reaction, typically by changing color.

Signup and view all the flashcards

Total Hardness

The total concentration of calcium and magnesium ions in a water sample, often expressed as ppm CaCO3.

Signup and view all the flashcards

Back Titration (Compleximetric)

A titration where a known amount of EDTA is added to a solution containing the metal ion. The excess EDTA is then titrated with a standard solution of a metal ion to determine the amount of EDTA that reacted with the analyte.

Signup and view all the flashcards

Replacement Titration (Compleximetric)

A titration where the analyte reacts with a known metal-EDTA complex, releasing the metal ion. The released metal ion is then titrated with EDTA.

Signup and view all the flashcards

Direct Titration (Compleximetric)

A titration where a known amount of EDTA is added to the analyte, and the amount of EDTA that reacts with the analyte is determined by calculating the difference between the initial amount of EDTA and the amount of EDTA that remains unreacted.

Signup and view all the flashcards

Titration

The process of determining the concentration of a component (analyte) by performing a chemical reaction with a reagent of known concentration.

Signup and view all the flashcards

Study Notes

Complexometric Titration

  • Complexometric titration involves the formation of soluble complexes between metal ions (acceptors) and ligands (donors) to produce coordination compounds (complexes).
  • The metal ion is known as the central metal atom (M).
  • The anion or neutral molecule is known as the ligand (L).
  • The central metals must have small size, vacant orbitals, and increasing ability with increasing oxidation state..
  • Ligands (complexing agents) require high basicity and must contain at least one atom with lone pairs or a negative charge.
  • The number of coordination bonds around the central metal ion is called the coordination number.

Types of Complexing Agents (Ligands)

  • Unidentate: These ligands (H₂O, NH₃, CN⁻, Cl⁻, I⁻, Br⁻) attach to the metal ion at one site.
  • Bidentate: These ligands (e.g., ethylenediamine) attach to the metal ion at two sites
  • Tridentate, tetradentate, etc.: These ligands attach to the metal ion at three or more sites, respectively. Chelating agents are examples of these types of ligands. (examples of chelating agents include EDTA, diethylene triamine, triethylenetetramine)

Factors Affecting Complex Stability

  • Central Metal Ion: Ionic size (metal radius), ionic charge (metal charge), and acidity influence the stability.
  • Ligand: Basic character (N > O > S > I > Br > Cl > F−) enhances stability. The degree of chelation and steric effect also affect stability.

EDTA Titration

  • EDTA (ethylenediaminetetraacetic acid) is a hexadentate ligand with 4 oxygen and 2 nitrogen donors.
  • EDTA is not a selective chelating agent
  • Titration involving EDTA is known as complexometric titration.
  • EDTA forms stoichiometric 1:1 complexes with all metals
  • EDTA has very stable complexes with all metals and has a sharp abrupt reaction.
  • The disodium salt of EDTA (Na₂H₂Y.2H₂O) is a primary standard.
  • The end point of the titration can be easily determined using metal ion indicators.

Titration Curve

  • The titration curve changes with the stability constant as the titration is performed at a suitable pH.
  • The concentration of metal ions is calculated via pMg = −log([Mg]).

Detection of End Point: Use of Metal Ion Indicators

  • The color reaction must be sensitive to metal ions and occur before the endpoint.
  • The metal-indicator complex must be less stable than the metal-EDTA complex.
  • There should be high color contrast between the free and complexed indicators.
  • The color reaction should be specific or at least selective.
  • The pH range at which the titration takes place determines the indicator's effectiveness.
  • Examples of metal ion indicators include Eriochrome Black T (H₂In⁻ to In³⁻), pH 5-7.3, red to blue. and Murexide.

Types of EDTA Titration

  • Direct Titration: The metal ion solution is buffered to a desired pH and titrated directly in the presence of an indicator.
  • Back Titration: An excess of EDTA is added to the metal ion solution, and the unreacted EDTA is then titrated with a standard solution.
  • Replacement or Substitution Titration: A metal ion in a complex is replaced by another metal ion, which is then titrated.
  • Indirect Titration: The metal ion is reacted with another substance that is then titrated to determine the original metal ion.

Examples

  • Water Hardness: EDTA is used to determine water hardness due to the presence of Ca²⁺ & Mg²⁺ salts
  • Aluminum Determination: Al³⁺ is heated with excess standard EDTA and then adjusted to pH 10 with an ammonia buffer. The residual EDTA is determined via titration with a standard Zn₂⁺ solution using EBT indicator.
  • Analysis of Metal Ion Mixtures (Selectivity Improvements): Selectivity is improved via pH control, adjusting oxidation numbers, masking and demasking agents, and selective metal indicators.
  • Analysis of Metal Ion Mixtures (Control of pH of the medium): Different metal ions are titrated in various pH ranges using various buffers (examples provided include different metal ions and relevant pH ranges)
  • Analysis of Metal Ion Mixtures (Masking and Demasking Agents): Masking agents prevent reaction of certain metal ions with EDTA, and demasking agents release the metal ion from the masking agent. (examples included titration of Ca and Mg in the presence of Zn or Cd)

Additional Considerations

  • The provided notes outline a variety of complexometric titration applications and considerations for adjusting pH, controlling the reaction, determining the concentration of metal ions, and conducting analyses on mixtures of multiple metals. Using appropriate pH control with indicators, and understanding the various types of titrations, are important for determining endpoint and assessing accuracy.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Lecture 8 Analytical PDF

Description

Explore the essential concepts of complexometric titration, focusing on the formation of soluble complexes and the role of ligands. Understand the classification of different types of ligands and their coordination with metal ions. This quiz will test your knowledge of the principles behind these chemical interactions.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser