C7: Chromatography

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Why is chromatography an important analytical technique?
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it allows chemists to separate substances in complex mixtures.
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What does Qualitative analysis mean?
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Any method of identifying the chemicals in a sample. It describes properties and characteristics without expressing numbers (colour)
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What does Quantitative analysis mean?
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Working out how much of a particular chemical there is in a sample. Quantitative data has numbers.
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What must analysis be carried out on an why?
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A sample that represents the bulk of a material being tested. This means the results from the analysis can be used to draw conclusions about the rest of the substance.
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What are many analytical techniques based on?
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Samples in solution.
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What do standard procedures cover?
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-Collecting samples -Storing samples -Preparing samples for analysis.
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What is Chromatography used for?
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To find out what unknown mixtures are made up of. Done by comparing the mixture to a known reference sample.
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What happens in chromatography?
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Substances are separated as they travel in a mobile phase which passes through a stationary phase.
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What are the stationary and mobile phases in paper chromatography?
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-Stationary phase is paper -Mobile phase may either be an aqueous (water-based) liquid or a non-aqueous organic (carbon-based) solvent.
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What is an example of an organic solvent
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Propanone
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What is there for each chemical in the sample?
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There is a dynamic equilibrium between the stationary phase and the mobile phase.
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What does separation by chromatography depend on?
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Components being distributed between the mobile and stationary phases. (How strongly attracted the chemicals are to the mobile and the stationary phases)
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What does Thin Layer Chromatography use for the stationary and mobile phases?
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-Stationary phase: A plate of glass (flat, unreactive surface). -Mobile Phase: Silica/Aluminia (thin layer of an inert substance)
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What are the advantages of TLC over paper chromatography?
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-mobile phase moves more quickly through stationary -mobile phase moves more evenly through stationary -there is a range of absorbencies for the stationary phase -TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the components in the mixture – easier to analyse.
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When and what are locating agents used for?
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Locating agents are used in thin layer and paper chromatography to show test materials if they’re colourless.
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How do locating agents work?
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They bind to the chemicals in the spots. Sometimes, another chemical is then added, which reacts with the locating agent to produce a coloured spot, or the chromatogram is put under ultraviolet light and the locating agent glows to show where the spots are.
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What is the movement of a substance during chromatography, relative to the movement of the solvent, measured by?
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calculating its retardation factor (Rf)
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What is the equation for the Rf?
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Rf= Distance travelled by substance/distance travelled by solvent
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What are the stationary and mobile phases in Gas Chromatography?
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-Stationary Phase: very thin layer of an inert liquid on an inert solid support (beads of silica packed into a long thin tube) -Mobile Phase: An inert gas (helium)
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What is GC used for?
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It is used to separate complex mixtures. It is much better at this than thin-layer or paper chromatography.
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Why is GC better at separating comple mixtures than thin-layer or paper chromatography?
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It is more sensitive – allowing the determination not only of what chemicals are in the mixture, but also how much of each chemical there is.
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How is Gas Chromatography carried out?
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1.Mixture to be analysed injected in stream carrier gas. 2.As it passes along the long thin tube it separates into the different substances. Substances with a greater attraction for mobile phase reach the detector at the end of the tube more quickly. Substances with a greater attraction for stationary phase move more slowly through column.
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What is an example of where GC is used?
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Gas chromatography is used to detect banned substances in urine samples from athletes.
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What is the retention time?
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The amount of time that a substance takes to pass through the column (tube).
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What is the number of compounds in a mixture represented by?
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The number of peaks.

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