Redox Reactions and Ligands Quiz

Introduction to Analytical Pharmaceutical Chemistry

• Analytical chemistry is the separation, identification, and determination of the relative amounts of the components making up a sample.

Definition of Analytical Chemistry

• Analytical chemistry is the separation, identification, and determination of the relative amounts of the components making up a sample.

Applications of Analytical Chemistry in Pharmacy Sciences

• Pharmaceutical chemistry
• Pharmaceutical industry (quality control)
• Analytical toxicology is the detection, identification and measurement of drugs and other foreign compounds.
• Natural products detection, isolation, and structural determination.

Chemical Analysis

• Chemical analysis is the chemical characterization of matter involving both qualitative and quantitative analysis.
• Qualitative analysis determines the identity of constituent species in a sample.
• Quantitative analysis determines the quantity of constituent species in a sample.

Steps in Chemical Analysis

• Define the problem
• Select a method
• Sampling (obtain sample)
• Sample preparation (prepare sample for analysis)
• Perform any necessary chemical separations
• Analysis (perform the measurement)
• Calculate the results and report.

Precision & Accuracy

• Precision: If multiple measurements of a quantity closely agree, the measurement is precise. Widely varying values indicate a lack of precision.
• Accuracy: How close a measured value is to the true value; a known standard may be used for comparison.

Types of Errors

• Determinate (systematic): Errors that affect accuracy; these errors are often knowable or can be determined later.
• Indeterminate (random): Errors affecting precision; these errors are often unknown causes.

Types of Systematic Errors

• Instrumental: Imperfections in measuring devices or instabilities in components.
• Method: Non-ideal chemical or physical behavior of analytical systems.
• Personal: Carelessness or inattention in measurements.

Types of Indeterminate Errors

• Due to unknown causes, not specifically identified.
• Affect the precision of measurement.
• Can be addressed through increasing the number of readings and using statistical methods (averaging).

Physical Analysis

• Methods to examine a substance that do not change the composition.
• Methods involve seeing, hearing, feeling, smelling, and measuring.
• Examples of physical properties include melting point, boiling point, density, viscosity, optical rotation, disintegration, dissolution, and particle size.

Melting Point

• A characteristic physical property of a pure solid organic compound.
• Determination aids in compound identification and purity assessment.
• Measured using a Mel-Temp apparatus and a capillary tube to hold the sample.
• Melting point is the temperature at which a substance transitions from a solid to a liquid state.

Boiling Point

• A characteristic physical property of a pure liquid compound.
• Determination does not reliably indicate purity due to impurities having less effect on boiling points.

Density

• Represents the ratio of an object's mass to its volume, an essential physical property.
• SI units are kg/m³, though g/cm³ is frequently used in lab settings.
• Higher temperatures generally result in lower densities.

Viscosity

• Describes the resistance of a fluid to flow.
• For liquids, this corresponds to their perceived "thickness".
• Viscosity depends on factors such as particle size and shape.

Optical Rotation

• The angle through which polarized light is rotated as it passes through a layer of a liquid.
• Used in pharmacopoeia to identify and assess purity.
• Described as dextrorotatory (+) or levorotatory (-) depending on the direction of rotation.

Disintegration and Dissolution

• Tablets/capsules/suppositories disintegrate to facilitate good absorption of active ingredients.
• Disintegration is the breakdown of tablets into smaller particles in water or simulated gastric/intestinal fluid.
• Measurements take place at 37°C and usually involve passing smaller particles through a mesh screen.

Dissolution Test

• Ensures the release of the drug from the tablet is close to 100%.
• Validates uniform rate of drug release.
• Often used for products with solubility or absorption issues.

Particle Size Analysis

• Particle size can affect factors like performance, appearance, stability, and pharmacological behavior.
• Sieving analysis involves using stacked sieves with progressively smaller apertures to separate particles by size.

Complexometric Titration

• A chemical analysis method involving the reaction of metal ions with a ligand to form a complex.
• Metal ions disappear during complex formation.
• If a colored complex is formed, it can indicate the endpoint without needing an indicator.
• Commonly referred to as EDTA titrations.

Chelation

• The process of forming chelates, ring-structured complexes between ligands and metals.
• Chelates are usually insoluble in water but soluble in organic solvents.
• Chelating agents are organic molecules with multiple donor groups that form complexes with metals.
• Sequestering agents are ligands that form water-soluble chelates.

EDTA

• Ethylene diamine tetraacetic acid (EDTA) is a critical sequestering agent for soluble metal ions.
• Its ability to solubilize metal ions is important in various applications.
• Its stable structure—six ligand atoms forming a strainless five-membered ring—is a crucial factor.

Types of Complexing Agent/Ligand

• Classifications of ligands (e.g., monodentate, bidentate, tridentate, multidentate) based on the number of attachment sites to the metal ion.
  • Monodentate: attaches at only one site.
  • Bidentate: attaches at two sites.
  • Tridentate: attaches at three sites.
  • Multidentate: attaches at multiple sites.

Metal Ion Indicator (PM Indicators)

• A dye used as a chelating agent to form a dye-metal complex.
• The appearance of the dye-metal complex differs from that of the dye itself.
• Dye-metal complexes show lower stability than chelate-metal complexes.
• Decomposition into free dye, resulting in color change, signals the titration endpoint.

Redox Titration

• involves reduction and oxidation reactions.
• Changes in the valence of reacting elements or ions.
• Oxidation is loss of electrons.
• Reduction is gain of electrons.
• LEO the lion says GER (Loss of Electrons is Oxidation, and Gain of electrons is Reduction).
• Terms and definitions of oxidation and reduction reactions.

Redox Indicator

• A compound that changes color as it transitions between oxidation and reduction states.
• Often used to determine endpoint during redox titrations. Types include self-indicators (e.g. permanganate) and external indicators (e.g. ferricyanide).

Precipitation Titration

• A titrimetric procedure for determining an analyte through the formation of a precipitate.
• Titrant reacts with analyte to form an insoluble material, continuing until the last quantity of the analyte is consumed.
• An indicator may react with excess titrant, signaling the end of the titration.

Argentometry

• Precipitation titrations involving silver nitrate solutions. Criteria for successful argentometric titrations include:
  • Insoluble precipitates for reliable formation.
  • Rapid and quantitative precipitation reactions.
  • Avoidance of precipitate interference with endpoint detection.
  • Minimal co-precipitation effects.

Types of Argentometry

• Commonly used methods (Mohr, Fajans, and Volhard) that are based on color indicators for endpoint detection.

Mohr Method

• Titration of chloride ions with silver nitrate using a soluble chromate salt indicator.
• Precipitate of silver chloride forms.
• Endpoint is identified when the first excess of silver reacts with the indicator to form a red silver chromate precipitate.

Fajans Method

• Titration method for halide ions or thiocyanate ions utilizing adsorption indicators, specifically dichlorofluorescein, on the silver halide or silver thiocyanate precipitate.

Volhard Method

• Indirect titration for anions that precipitate with silver in strongly acidic conditions, often HNO3.
• Excess silver is titrated with a standard thiocyanate solution.
• Endpoint determined by adding a ferric indicator, forming a colored complex. This indirect technique has advantages for certain anions.

Acid-Base Titration

• A titration technique involving acid-base reactions to determine the concentration of an unknown acid or base. Essential properties of acids and bases are:
  • Taste: Acids are sour, bases are bitter.
  • Color change of indicators (e.g., litmus paper): Acids turn blue litmus paper to red, bases turn red litmus paper to blue.
  • pH values for acids: lower than 7 (<7).
  • pH values for bases: greater than 7 (>7).

Brønsted-Lowry Acid-Base Theory

• Acid is a proton (H+) donor.
• Base is a proton (H+) acceptor.
• Conjugate acid of a base is the species that results after the base accepts a proton.
• Conjugate base of an acid is the species that results after the acid donates a proton

Autoionization of Water

• Water self-ionizes into hydronium (H3O+) and hydroxide (OH-) ions; this reaction is a reversible equilibrium. The autoionization constant of water (Kw) is the equilibrium constant for the process.

pH Scale

• pH is defined as the -log of hydrogen ion concentration ([H⁺]).
• pOH is defined as the -log of hydroxide ion concentration ([OH⁻]).
• The sum of pH and pOH equals 14.

lonization Constant

• The ionization constant (K) for acids or bases quantifies the degree of ionization in water.
• Ka is for acids.
• Kb is for bases.

Ionization constant (Ka)

• For acid ionization
• Ka = [H⁺][A⁻] / [HA].
  • [HA] - amount of undissociated acid
  • [H⁺] - amount of H+ ions
  • [A⁻] - amount of conjugate base
• pKa = -logKa
• Smaller pka = stronger acid

lonization constant (Kb)

• For base ionization
• Kb = [HB⁺][OH⁻] / [B]
  • [B] - amount of undissociated base
  • [HB⁺] - amount of conjugate acid
  • [OH⁻] - amount of OH⁻ ions
• pKb = -logKb, larger pKb = stronger base