Non-Aqueous Titrations Overview
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Questions and Answers

What happens to a substance if it is more acidic than the solvent?

  • It remains neutral.
  • It behaves as a base.
  • It reacts violently.
  • It behaves as an acid. (correct)

Water has a high dissociation constant (Ks) and a high autoprotolysis.

False (B)

What should a substance be to be effective in a solvent?

soluble

Acetic acid has a ______ dissociation constant and ______ autoprotolysis.

<p>low, low</p> Signup and view all the answers

What type of titrant is used for standardization of acetic HCIO?

<p>Potassium Acid Phthalate (A)</p> Signup and view all the answers

Match the following samples with their corresponding titrants:

<p>Loratadine = HClO4 in glacial acetic acid Amino acids = HClO4 in glacial acetic acid Methyldopa = HClO4 in glacial acetic acid Acetic acid = Potassium acid phthalate</p> Signup and view all the answers

The presence of a strong acid titrant allows the suppression of the carboxylic group.

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

What indicator is used for titration with HClO4 in glacial acetic acid?

<p>Crystal violet</p> Signup and view all the answers

Formic acid is characterized by having ______ dissociation and ______ autoprotolysis compared to acetic acid.

<p>high, high</p> Signup and view all the answers

What is the role of the solvent when the substance is more basic?

<p>It behaves as an acid. (D)</p> Signup and view all the answers

What is the purpose of refluxing with acetic anhydride in the analysis of tertiary amines?

<p>To acylate primary and secondary amines (A)</p> Signup and view all the answers

In the reaction of salicylaldehyde, secondary amines react similarly to primary amines.

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

What is the role of sodium methoxide in the titration of acidic samples?

<p>It acts as a titrant.</p> Signup and view all the answers

The indicator used for titration with sodium methoxide is __________.

<p>thymol blue</p> Signup and view all the answers

Match the following compounds with their respective properties:

<p>Allopurinol = Weak acid + water insoluble Barbiturates = Weak acids + water insoluble Sulphonamides = Weak acid + low water solubility Acetic anhydride = Used for acylating amines</p> Signup and view all the answers

Which amine classification is determined by titration with standard acetous HClO4?

<p>Tertiary amines (C)</p> Signup and view all the answers

The endpoint detection in the titration of a mixture of mineral and carboxylic acids is conducted using potentiometry.

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

What differentiating effect does methyl isobutyl ketone have when used as a solvent?

<p>It differentiates between mineral and carboxylic acids.</p> Signup and view all the answers

E1 represents the total amines, while E2 represents the __________ amines.

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

Which of the following is NOT a property of weak acids in the given analysis?

<p>High water solubility (C)</p> Signup and view all the answers

What is a primary reason for using non-aqueous titrations?

<p>To determine very weak acids or bases accurately (D)</p> Signup and view all the answers

Non-aqueous titrations can only be performed in water.

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

What is the leveling effect in non-aqueous titrations?

<p>The ability of solvent to increase strength of weak acids/bases to become strong acids/base.</p> Signup and view all the answers

In non-aqueous titrations, the conjugate base is formed when the acid loses a ______.

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

Match the acids/bases with their definitions:

<p>Conjugate Acid = Species created when the base accepts a proton Conjugate Base = Ion remaining after the acid has lost a proton Weak Acid = An acid that does not fully dissociate in solution Strong Acid = An acid that completely dissociates in solution</p> Signup and view all the answers

Which of the following is NOT an advantage of non-aqueous titrations?

<p>Lower costs than aqueous titrations (A)</p> Signup and view all the answers

The differentiating effect refers to a solvent's ability to make all acids behave the same way.

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

Name one disadvantage of using non-aqueous titrations.

<p>Expensive, volatile, or toxic.</p> Signup and view all the answers

Bronsted theory relates the _____ of a substance to the solvent used.

<p>acidity/alkalinity</p> Signup and view all the answers

Which solvent is mentioned as having a differentiating effect in non-aqueous titrations?

<p>Acetic Acid (D)</p> Signup and view all the answers

Flashcards

Non-Aqueous Titrations

Titrations performed in solvents other than water. These solvents are chosen to increase the dissociation of weak acids and bases, allowing for more accurate measurements.

Leveling Effect

The ability of a solvent to enhance the strength of a weak acid or base, making it behave like a strong acid or base.

Differentiating Effect

A non-aqueous solvent can differentiate between the strengths of acids or bases within a mixture, enabling stepwise titration.

Titration

The act of determining the concentration of a substance by reacting it with a solution of known concentration (the titrant).

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Base (Bronsted Theory)

A substance that accepts a proton (H+) in a chemical reaction.

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Acid (Bronsted Theory)

A substance that donates a proton (H+) in a chemical reaction.

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Conjugate Base

The ion that remains after an acid has lost a proton.

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Conjugate Acid

The species formed when a base accepts a proton.

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Dissociation Constant

A measure of the strength of an acid or base in a given solvent.

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Relative Acidity/Alkalinity (Bronsted Theory)

The relative acidity or alkalinity of a substance is dependent on the solvent it is dissolved in.

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Acid-Base Behavior in Solvents

A substance acts as an acid when its acidity is stronger than the solvent's basicity. Conversely, it acts as a base when its basicity is stronger than the solvent's acidity.

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Dielectric Constant (D)

The dielectric constant (D) of a solvent is a measure of its ability to reduce the strength of electrostatic interactions. Higher D values indicate a solvent's ability to screen charges.

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Autoprotolysis Constant (Ks)

The autoprotolysis constant (Ks) is a measure of the extent to which a solvent can donate protons (H+). Lower Ks values indicate less proton donation.

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Acidimetric Titration for Weak Bases

A strong acid titrant is used in a titration where the analyte is a weak base, e.g., loratadine, amino acids, or methyldopa.

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Glacial Acetic Acid as a Solvent

Glacial acetic acid is a commonly used solvent for acidimetric titrations of weak bases because it levels their strengths and promotes dissolution.

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Crystal Violet Indicator

Crystal violet acts as a suitable indicator in glacial acetic acid titrations, changing color from violet to bluish green at the endpoint.

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Perchloric Acid (HClO4) Titrant

Perchloric acid (HClO4) is a common choice for titrating weak bases in glacial acetic acid due to its strength and stability in this solvent.

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Benzoic Acid for Titrant Standardization

Benzoic acid is a common standard for standardizing titrants like sodium methoxide (NaOCH3) or tertiary-butyl ammonium hydroxide, used in basic titrations.

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Determination of Amines Mixture

A technique used to analyze mixtures of primary, secondary, and tertiary amines by selectively reacting each type of amine with specific reagents. This allows for the determination of the individual concentrations of each type.

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Tertiary Amine Determination

Tertiary amines (R3N) are determined by reacting a sample with acetic anhydride, which specifically acetylates primary and secondary amines. The unreacted tertiary amine can then be titrated with standard acetous perchloric acid.

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Secondary and Tertiary Amine Determination

The reaction of primary amines with salicylaldehyde forms a Schiff base, allowing for the selective determination of secondary and tertiary amines.

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Non-Aqueous Solvent

A non-aqueous solvent that increases the dissociation of weak acids and bases, leading to more accurate titration results.

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Non-Aqueous Titration of Acid Mixtures

A non-aqueous titration technique used to analyze mixtures of mineral and carboxylic acids. The solvent methyl isobutyl ketone differentiates between the acids, allowing for sequential titration with tertiary butyl ammonium hydroxide.

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Potentiometry

A technique used to determine the endpoint of a non-aqueous titration by measuring changes in electrical potential. This method is particularly useful when visual indicators are not suitable.

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Solvent Selection for Titration

The ability of a solvent to dissolve both a substance and the titrant, ensuring a homogeneous reaction medium for accurate titration results.

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Titrant in Non-Aqueous Titration

A reagent used in non-aqueous titrations to neutralize weak acids or bases. Common examples include sodium methoxide and tertiary butyl ammonium hydroxide.

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Study Notes

Non-Aqueous Titrations

  • Titrations performed in a medium without water, utilizing non-aqueous solvents.

Reasons for Non-Aqueous Titrations

  • Solubility: Some substances insoluble in water are soluble in non-aqueous solvents.
  • Weak Acids/Bases: Determination of very weak acids or bases is not accurate in aqueous solutions due to a lack of distinct endpoints.

Aim of Non-Aqueous Titrations

  • Increase Dissociation: To increase the dissociation of weak acids and bases, facilitating their behavior as strong acids and bases.
  • Solvent Selection: Non-aqueous solvents are used instead of water.
  • Acid-Base Concepts: Study of acid-base concepts (e.g., Brønsted) using non-aqueous solvents is important.

Advantages of Non-Aqueous Titrations

  • Pharmacopeial Methods: Many pharmaceutical methods rely on non-aqueous titrations.
  • Insoluble Substances: Useful for substances that are not soluble in water.
  • Weak Species: Applicable for determining very weak acids or bases.
  • Mixed Samples: Useful with mixtures of weak acids or bases with similar dissociation constants.

Disadvantages of Non-Aqueous Titrations

  • Cost: Non-aqueous titrations are typically more expensive.
  • Volatility: Some non-aqueous solvents are volatile.
  • Toxicity: Certain solvents are toxic.

Acid-Base Theories

  • Arrhenius Theory: Acids dissociate to produce H+ ions, and bases dissociate to produce OH- ions.
  • Brønsted-Lowry Theory: Acids donate protons (H+), and bases accept protons.
  • Lewis Theory: Electron-pair acceptors are acids, and electron-pair donors are bases.

Solvent Properties Affecting Titration

  • Autoprotolysis Constant (Ks): The smaller the Ks, the more complete the reaction. Solvents with smaller Ks are usually better for complete reactions.
  • Dielectric Constant (D): The ability of a solvent to separate ions; higher D values result in more complete reactions.
  • Acidic/Basic Character of Solvent: The solvent's character will have an effect on the behavior of acids or bases.

Types of Solvents used in Non-Aqueous Titration

  • Aprotic: Do not have H atoms on O or N, cannot accept or donate protons. Examples: carbon tetrachloride, benzene.
  • Protogenic: Can accept protons, do not undergo autoprotolysis. Examples: formic acid, glacial acetic acid.
  • Protophilic: Can donate protons, do not undergo autoprotolysis. Examples: ammonia, ethylene diamine.

Indicators in Non-Aqueous Titrations

  • Crystal Violet, Azo Violet, and Thymol Blue are common indicators used. Their colors change with the pH of the solution (basic or acidic medium).

Standardization of Titrants

  • Acidic titrants are often standardized against potassium acid phthalate or other suitable materials.
  • Basic titrants such as sodium methoxide are standardized against benzoic acid.

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Non-Aqueous Titrations PDF

Description

Explore the principles and applications of non-aqueous titrations. This quiz covers the reasons for choosing non-aqueous solvents, their advantages, and their relevance in acid-base chemistry. Understand how these titrations play a crucial role in various pharmaceutical methods.

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