CLAB 2670: Organic Chemistry I Lab Midterm Study Guide

Vocabulary practice flashcards covering equipment, principles, operational rules, and formulas for organic chemistry lab midterm preparation.

Erlenmeyer Flask

A conical heating container used in recrystallization to minimize solvent evaporation; beakers should never be used for hot recrystallization.

Hirsch / Büchner Funnel

A filtration funnel designed for collecting solids via vacuum (suction) filtration, which requires the correct diameter filter paper to properly seal the filter bed.

Vigreux Column

A specialized fractionating column containing internal glass indentations that optimize condensate reflux and provide increased surface area for fractional distillation.

Boiling Chips / Stir Bar

Inert materials added to liquids prior to heating to prevent superheating and violent bubbling ("bumping"); they must never be added to an already hot liquid.

Capillary Tube

A narrow glass tube used to hold micro-samples for Mel-Temp melting point testing, which must be packed tightly to a height of $2\text{--}3\,\text{mm}$.

TLC Developing Chamber

An enclosed glass vessel used for thin-layer chromatographic separations that must remain sealed with the developing solvent level kept strictly below the sample spot line.

Mother Liquor

The remaining liquid filtrate after crystals have been separated by filtration, containing soluble impurities and residual dissolved solute.

Recrystallization

A primary purification technique for impure organic solids based on differential solubility in a solvent at hot versus cold temperatures.

Ideal Recrystallization Solvent

A solvent that dissolves solute poorly at room temperature, dissolves it completely near its boiling point, is chemically unreactive, is easily evaporated (volatile), and keeps impurities either permanently insoluble or permanently soluble.

Hot Gravity Filtration

A recrystallization procedure used to separate insoluble solid debris and activated charcoal while keeping the desired compound fully dissolved in hot solvent.

Fluted Filter Paper

Pleated filter paper used during hot gravity filtration to maximize surface area and increase the rate of filtration before the solution cools.

Pre-Warming Equipment (Filtration)

The step of pre-heating the funnel and receiving flask with hot solvent before hot gravity filtration to prevent premature crystallization and stem clogging.

Ice-Cold Solvent Wash

The procedure of washing isolated crystals on a vacuum filter with ice-cold solvent to remove adhering mother liquor without dissolving the purified solid product.

Melting Point (mp)

The temperature range at which the liquid and solid phases of a substance coexist in thermodynamic equilibrium at $1\,\text{atm}$, used for compound identification and purity assessment.

Melting Point Depression

The decrease in the onset melting temperature ($T_{\text{onset}}$) of a solid caused by soluble impurities disrupting the crystalline lattice.

Melting Range Broadening

The widening of the melting temperature interval ($\Delta T > 3\text{--}10\,^\circ\text{C}$) resulting from lattice disruptions caused by impurities.

Eutectic Point

The specific unique composition mixture of two solids that possesses the lowest possible melting temperature and melts sharply over a narrow range as if it were a pure compound.

Mixed Melting Point Analysis

An identification method in which an unknown compound is mixed with a known standard: an unchanged, sharp melting point confirms identity, whereas a depressed, broadened range indicates non-identity.

Thermal Lag

A temperature discrepancy between the heating block and thermometer caused by heating too quickly ($> 2\,^\circ\text{C/min}$ near the MP), leading to artificially broad or depressed melting points.

Thin-Layer Chromatography (TLC)

An analytical separation technique based on differential distribution of analytes between a polar solid stationary phase ($\text{SiO}_2$) and a moving liquid mobile phase.

Retention Factor ($R_f$)

A chromatographic ratio defined as $R_f = \frac{\text{Distance traveled by spot}}{\text{Distance traveled by solvent front}}$, with values ranging strictly between $0.0$ and $1.0$.

Fluorescence Quenching ($254\,\text{nm}$ UV)

A TLC visualization method where conjugated or aromatic molecules absorb $254\,\text{nm}$ light and quench the green glow of an embedded fluorescent indicator, appearing as dark spots.

Iodine ($\text{I}_2$) Staining

A non-destructive TLC visualization method where iodine vapors reversibly form colored brown inclusion complexes with organic compounds.

Normal-Phase Silica Elution Order

A separation behavior on silica gel where non-polar compounds elute first (higher $R_f$) and polar compounds elute last (lower $R_f$) due to strong dipole-dipole interactions with stationary silanol groups.

Column Chromatography

A preparative, scaled-up chromatographic method that purifies mixtures by passing a liquid mobile phase down a vertical glass column packed with a solid adsorbent.

Slurry Packing

The technique of suspending dry silica gel in the running solvent before loading it into a column, preventing air pocket entrapment and bed cracking.

Distillation

A purification technique based on boiling point differences used to separate volatile liquids from one another or from non-volatile impurities.

Boiling Point

The exact temperature at which the vapor pressure of a liquid equals the external atmospheric pressure.

Raoult's Law

A thermodynamic law for ideal solutions stating that the partial vapor pressure of component $A$ is proportional to its mole fraction: $P_A = P^\circ_A \times X_A$.

Dalton's Law of Partial Pressures

The principle stating that the total vapor pressure of an ideal mixture is equal to the sum of the partial pressures of its individual components: $P_{\text{total}} = P_A + P_B$.

Theoretical Plate

A hypothetical single cycle of vaporization and condensation during distillation, equivalent in separation efficiency to one complete simple distillation.

Azeotrope

A constant-boiling liquid mixture (such as $95\%$ ethanol and $5\%$ water) whose vapor composition matches its liquid composition, preventing separation via fractional distillation.

Simple Distillation

A distillation method used for separating liquids with a large boiling point difference ($\Delta\text{bp} > 40\text{--}50\,^\circ\text{C}$) or for separating a volatile liquid from a non-volatile solid.

Fractional Distillation

A distillation technique employing a fractionating column to separate volatile liquids with narrow boiling point differences ($\Delta\text{bp} < 25\,^\circ\text{C}$) through multiple sequential theoretical plates.

Thermometer Bulb Position (Distillation)

The proper placement of the thermometer bulb just below the distillation head sidearm to ensure accurate measurement of distilling vapor rather than superheated gases.

Condenser Water Flow Direction

The rule requiring water to enter the condenser through the lower inlet and exit via the upper outlet to ensure complete filling without air pockets.

Gas Chromatography (GC)

An instrumental method for separating and quantifying volatile organic mixtures in the vapor phase using an inert carrier gas and a stationary liquid polymer film.

Carrier Gas (GC Mobile Phase)

An unreactive gas (typically helium or nitrogen) that carries vaporized organic analytes through a chromatographic column without interacting chemically.

GC Stationary Phase

A high-boiling liquid polymer film coated uniformly on the inner walls of a long capillary column that selectively retards analytes based on polarity.

Retention Time ($t_R$)

The time elapsed between sample injection and the point of maximum detector response (peak apex) for a given analyte under specified operating conditions.

Chromatographic Resolution ($R_s$)

The degree of separation between two adjacent peaks, defined as $R_s = \frac{2(t_{R2} - t_{R1})}{w_1 + w_2}$, where $R_s > 1.5$ indicates baseline separation.

Peak Triangulation (GC)

A geometric method for calculating the area of a chromatographic peak using the formula $\text{Area} = h \times w_{1/2}$, where $h$ is height and $w_{1/2}$ is width at half-height.