Grade 11 Chemistry: Separation Techniques

Comprehensive vocabulary flashcards covering Grade 11 Chemistry separation methods: paper chromatography, fractional distillation of crude oil, filtration, simple distillation, evaporation, and crystallization.

Chromatography

A separation technique used to separate and identify substances in a mixture, derived from the Greek words "chroma" (colour) and "graphein" (to write).

Stationary phase (paper chromatography)

The phase that does not move, consisting of the chromatography paper (cellulose fibres holding a thin layer of water) which holds substances back by attraction.

Mobile phase (paper chromatography)

The phase that moves, consisting of the solvent (such as water, ethanol, or propanone) which travels up the paper by capillary action and carries dissolved substances along.

Capillary action

The movement of a liquid up through tiny spaces, such as between paper fibres.

Tug of war (chromatography principle)

The separation mechanism where the mobile phase pulls a substance up the paper because it dissolves in the solvent, while the stationary phase holds it back by attraction.

Baseline

The pencil line drawn about $2\,\text{cm}$ from the bottom edge of the chromatography paper where sample spots are applied at the start.

Solvent front

The furthest point reached by the solvent moving up the chromatography paper, marked immediately in pencil before it evaporates.

Chromatogram

The dried chromatography paper showing the separated substances as distinct spots.

$\text{R}_\text{f}$ value (Retention factor)

A dimensionless number between $0$ and $1$ calculated as: $\text{distance moved by the substance (baseline to centre of spot)} \div \text{distance moved by the solvent front (baseline to solvent front)}$.

Pure substance (chromatographic identification)

A substance that produces only one single spot on a chromatogram, confirmed if only one spot appears even when repeated with different solvents.

Impure substance (chromatographic identification)

A mixture of two or more substances that separates into two or more distinct spots on a chromatogram.

Locating agent

A chemical spray (such as ninhydrin) or ultraviolet light used to make colourless spots visible on a chromatogram.

Ninhydrin spray

A specific locating agent sprayed onto a chromatogram to reveal colourless amino acid spots.

Solute

The substance that dissolves into a liquid to create a solution.

Solvent

The liquid in which a solute dissolves.

Soluble

The property of being able to dissolve in a particular solvent.

Chromatographic smear

A long streak instead of a distinct spot on a chromatogram, caused by using too much sample or choosing an unsuitable solvent.

Baseline spot retention

A spot remaining entirely on the baseline, which indicates that the substance is completely insoluble in the chosen solvent.

Paper chromatography apparatus setup

An experimental arrangement showing the pencil baseline positioned above the solvent level inside a covered container at the start, yielding separated spots and a marked solvent front at the end.

Chromatogram analysis of dyes and mixture

A calibrated chromatogram where Dye 1 has an $\text{R}_\text{f}$ of $3.6\,\text{cm} \div 9.0\,\text{cm} = 0.40$ and Dye 2 has an $\text{R}_\text{f}$ of $7.2\,\text{cm} \div 9.0\,\text{cm} = 0.80$, proving the mixture contains both dyes.

Forensic science (chromatography application)

The application of paper chromatography to compare and match ink from a questioned note to a suspect pen.

Multi-sample dye chromatogram

A chromatogram showing pure reference dyes A, B, and C alongside unknown ink X and sample Z, showing X contains dyes A ($2.0\,\text{cm}$) and C ($6.0\,\text{cm}$) plus an unknown component ($5.0\,\text{cm}$), while Z is pure ($4.0\,\text{cm}$).

Pencil baseline rationale

The reason for drawing the start line in pencil rather than ink: graphite is insoluble in the solvent and will not dissolve or run.

Container lid rationale (chromatography)

The requirement to cover the chromatography container to keep the surrounding air saturated with solvent vapour, preventing uneven evaporation.

Solvent depth guideline (chromatography)

The requirement that the solvent depth must be kept below the baseline (about $1\,\text{cm}$) so the sample spots do not wash directly into the solvent pool.

Fractional distillation

A separation method used to separate a mixture of miscible liquids with different, relatively close boiling points by vaporization and condensation at different heights.

Crude oil

A complex mixture of hydrocarbons consisting of molecules with different chain lengths, sizes, and boiling ranges.

Fraction (crude oil)

A collected group of hydrocarbons that possess similar boiling ranges, molecular sizes, and physical properties.

Fractionating column (crude oil)

A tall industrial column that separates vaporized crude oil continuously along a temperature gradient, being hottest at the bottom and coolest at the top.

Column temperature gradient

The continuous decrease in temperature inside a fractionating column from the hot base to the cooler top.

Refinery gases

The fraction containing small molecules with very low boiling points that is collected at the very top of the fractionating column and used as LPG for cooking and heating.

Petrol / gasoline

A light fraction consisting of relatively small molecules with a low boiling range, collected near the top of the column and used as fuel for cars.

Naphtha

A light liquid crude oil fraction collected below petrol and used primarily as a chemical feedstock.

Kerosene

A fraction consisting of middle-range hydrocarbons collected in the central part of the column, used as jet fuel and for domestic heating.

Diesel (gas oil)

A fraction containing larger molecules with a higher boiling range than petrol and kerosene, used as fuel for diesel engines.

Fuel oil

A heavy crude oil fraction with a high boiling range collected near the bottom of the column, used for powering large ships and industrial heating.

Bitumen / residue

A very heavy, low-volatility material with extremely high boiling points that remains unvaporized at the base of the column, used for road surfacing and roofing.

Hydrocarbon molecule size trend (distillation)

The principle that as hydrocarbon molecule size increases, boiling point and viscosity increase, while volatility decreases.

Viscosity (hydrocarbon fractions)

The thickness and resistance to flow of a liquid fraction, which increases progressively toward the lower fractions of the column.

Volatility (hydrocarbon fractions)

The tendency of a fraction to vaporize, which is highest for the small molecules collected at the top of the column.

Glass beads (fractionating column)

Packing material in a laboratory column providing a large surface area for repeated evaporation and condensation, yielding vapour richer in the lower-boiling liquid.

Miscible liquids

Liquids that dissolve completely in one another to form a single homogenous layer, such as ethanol and water.

Ethanol collection (fractional distillation)

The separation of an ethanol-water mixture where ethanol boils at about $78\,^\circ\text{C}$ and is collected first because it has a lower boiling point than water ($100\,^\circ\text{C}$).

Filtration

A separation technique used to separate an insoluble solid from a liquid in a suspension.

Suspension

A mixture consisting of large, insoluble solid particles dispersed throughout a liquid, such as sand and water, chalk in water, or flour and water.

Filtrate

The clear liquid or solution that successfully passes through the pores of the filter paper.

Residue (filtration)

The solid material that is trapped and left behind on the filter paper because its particles are larger than the paper's pores.

Filtration apparatus assembly

A laboratory filtration setup composed of a filter funnel (A) lined with filter paper (B) set over a conical flask or beaker (C).

Filter paper pore mechanism

The sieve-like process where liquid particles pass through tiny paper pores while solid suspension particles are physically trapped because they are too large.

Simple distillation

A separation technique used to obtain a pure liquid solvent from a solution containing a dissolved solute.

Solution

A homogenous mixture formed when a soluble solid solute dissolves completely into a liquid solvent, such as salt dissolved in water.

Distillate

The purified liquid collected in the receiving flask after vaporizing and condensing in a distillation apparatus.

Liebig condenser

A piece of distillation glassware consisting of an inner condensation tube cooled by an outer jacket of circulating cold water.

Simple distillation apparatus assembly

A laboratory apparatus comprising a thermometer (A), a Liebig condenser (B), a cold water inlet (C), and a receiving flask (D) collecting pure distillate.

Condenser water inlet placement

The orientation where cold water enters the lowest point (C) of the condenser jacket, ensuring it fills completely and cools counter-currently.

Evaporation (separation technique)

Heating a solution until all the solvent evaporates into vapour, leaving the solid solute behind as a powder or small crystals.

Crystallization

Heating a solution gently to evaporate only part of the solvent until saturated, then cooling slowly so that large, pure crystals form while soluble impurities stay in solution.

Saturated solution

A solution that has dissolved the maximum possible mass of solute at a given temperature, prepared during crystallization prior to slow cooling.

Thermal damage (evaporation)

The decomposition or degradation of sensitive chemical compounds that occurs when heating a solid directly to complete dryness during rapid evaporation.

Commercial salt extraction (sea water)

The rapid and economical production of solid salt on salt farms using total evaporation where crystal size and purity are not critical.