ANACHEM FINALS

Gravimetric Analysis

Quantitative method that measures the amount of a substance through mass.

Analyte

Substance being measured or analyzed in a sample.

Pure Compound

Stable form of analyte suitable for weighing in gravimetric analysis.

Advantages Of Gravimetric Analysis

Accurate and precise when using modern analytical balances.

Absolute Method

Method involving direct measurement without calibration.

Inexpensive Apparatus

Uses relatively inexpensive equipment such as muffle furnace and crucibles.

Precipitation Gravimetry

Method where analyte is converted into an insoluble precipitate for measurement.

Precipitate

Solid formed from a solution during a chemical reaction.

Basic Steps In Precipitation Gravimetry

Convert analyte to insoluble precipitate, filter, wash, dry or ignite, weigh, and calculate concentration.

Precipitating Agent

Reagent that reacts with analyte to form a precipitate.

Specificity

Ability of reagent to react only with a particular analyte.

Selectivity

Ability of reagent to react preferentially with a specific analyte.

Ideal Precipitate

Easily filtered, low solubility, free of contaminants, stable, and of known composition.

Particle Size

Size of precipitate particles affecting filtration and purity.

Large Particles

Preferred due to easier filtration, less contamination, and higher purity.

Colloidal Suspension

Very tiny particles that do not settle and are difficult to filter.

Crystalline Suspension

Large particles that settle easily and are easy to filter.

Factors Affecting Particle Size

Solubility, temperature, reactant concentration, rate of addition, mixing, and supersaturation.

Relative Supersaturation (Von Weimarn Ratio)

Measure of how much solute exceeds its solubility in a solution.

Q Value

Concentration of solute.

S Value

Equilibrium solubility of solute.

Supersaturation

Condition where solution contains more dissolved solute than it can hold at equilibrium.

Nucleation

Formation of new particles where molecules aggregate to form small clusters.

Particle Growth

Enlargement of particles by addition of more molecules to nuclei.

Adsorption (Impurity)

Attachment of impurities to the surface of precipitate particles.

How To Get Large Particles

Use dilute solutions, add reagent slowly, stir well, use higher temperature, control pH.

General Applications Of Gravimetric Analysis

Used for standard analysis, calibration, and high-accuracy determinations.

Gravimetric Calculation

Use mass of precipitate and molar relationships to determine analyte concentration.

Precipitation Method

Separation method based on forming insoluble solid.

Volatilization Method

Separation method based on converting analyte to gas.

Electroanalytical Method

Separation using electrical properties.

Extraction Method

Separation based on solubility differences.

Chromatographic Method

Separation based on interaction with stationary and mobile phases.

Spectrophotometry

Technique for measuring light intensity absorbed or transmitted by a solution.

Transmitted Light

Light that passes through a solution and is detected.

Absorbed Light

Light taken in by a substance in solution.

Visible Light Spectrum

White light composed of colors violet, indigo, blue, green, yellow, orange, and red with different wavelengths.

Color Of Solution

Determined by wavelengths transmitted, not absorbed.

Concentration Effect

Higher concentration results in darker color and more light absorbed.

Absorptimetry

Measurement based on absorption of radiant energy.

Colorimetry

Uses visible light to measure concentration based on color intensity.

Percent Transmittance (%T)

(Transmitted light / Incident light) × 100.

Absorbance (A)

Measure of light absorbed calculated from transmittance.

Absorbance-Transmittance Relationship

Absorbance increases as transmittance decreases.

Beer-Lambert Law

States that absorbance is directly proportional to concentration.

A = Ebc

Mathematical expression of Beer's Law.

Molar Absorptivity (E)

Constant for a compound at a given wavelength.

Path Length (B)

Distance light travels through sample in cm.

Concentration (C)

Amount of substance in solution.

Calibration Curve

Graph of absorbance versus concentration used to determine unknown concentration.

Linearity

Relationship where absorbance is directly proportional to concentration.

Light Source

Provides radiant energy for measurement.

Tungsten Lamp

Used for visible and near-infrared light.

Deuterium Lamp

Used for ultraviolet light.

Mercury Arc Lamp

Produces sharp spectral lines for UV and visible regions.

Monochromator

Device that isolates a narrow band of wavelengths.

Bandpass

Range of wavelengths transmitted at more than 50% intensity.

Colored Glass Filter

Simple filter passing broad wavelength ranges with low precision.

Interference Filter

Uses constructive and destructive interference to isolate narrow wavelengths.

Prism Monochromator

Separates light by refraction into continuous spectrum.

Diffraction Grating

Uses diffraction to produce linear and well-dispersed spectrum.

Cuvette

Sample holder where light passes through solution.

Round Cuvette

Requires alignment due to non-uniform shape.

Square Cuvette

More accurate with plane-parallel sides.

Glass Cuvette

Used for visible light only.

Quartz Cuvette

Used for ultraviolet measurements.

Photodetector

Converts light into electrical signal.

Photocell

Simple detector generating its own current but less linear.

Phototube

Uses external voltage to produce measurable current.

Photomultiplier Tube (PMT)

Highly sensitive detector with amplified signal.

Photodiode

Fast and linear detector with no internal amplification.

Photodiode Array

Multiple photodiodes measuring full spectrum simultaneously.

Single-Beam Instrument

Uses one light path and requires manual blanking.

Double-Beam Instrument

Splits light into sample and reference for automatic correction.

Blank

Reference solution used to set baseline measurement.

Wavelength Accuracy

Ensures correct wavelength is used for measurement.

Stray Light

Unwanted wavelengths that affect accuracy.

Linearity Test

Ensures proportional relationship between absorbance and concentration.

Didymium Filter

Used to check wavelength accuracy.

Holmium Oxide Filter

Standard for wavelength calibration.

Mercury Vapor Lamp

Provides known spectral lines for calibration.

Cutoff Filter

Blocks specific wavelength ranges to test stray light.

Neutral Density Filter

Used to test linearity across wavelengths.

Spectrophotometer Validation

Process to ensure accuracy, reliability, and proper instrument performance.

Chromatography

A set of techniques used to separate a complex mixture into its individual components.

Stationary Phase

The material that stays in place and interacts with the compounds being separated.

Mobile Phase

The phase that carries the mixture through the stationary phase; may be a gas or liquid.

Column

The container that holds the stationary phase and provides a path for the mobile phase to travel through.

Eluate

Separated compounds that come out of the column at different times.

Adsorption

Separates compounds based on how strongly they stick to a solid stationary phase.

Adsorption Equilibrium

Continuous process where solute molecules are adsorbed to and desorbed from the stationary phase.

Desorption

Release of solute molecules from the stationary phase into the mobile phase.

Partition

Separates substances based on how well a solute dissolves in two different liquids.

Normal Phase (Partition)

Mode where mobile phase is less polar than stationary phase.

Reversed Phase (Partition)

Mode where mobile phase is more polar than stationary phase.

Partition Coefficient

Ratio of concentration of a solute in two liquids showing its distribution between phases.

Steric Exclusion

Separation based on size and shape of molecules rather than chemical interaction.

Pores

Tiny holes in the packing material where small molecules can enter.

Gel Filtration

Early steric exclusion method using hydrophilic gel beads in water.

Modern Steric Exclusion

Uses rigid inorganic materials like silica or glass as packing material.