C7.5 Chromatography Flashcards
- What happens in chromatography?
-substances are separated by movement of a mobile phase through a stationary phase
- What is chromatography?
- an analytical method used to separate substances in a mixture
- can identify substances
- What does mobile phase mean in chromatography?
- liquid or gas
- molecules can move
- What does stationary phase mean in chromatography?
- solid or thick liquid
- molecules can’t move
- What happens to chemicals in chromatography regarding phases?
- components in mixture separate as mobile phase moves across stationary phase
- molecules of chemical constantly move between phases
- move different speeds depending on attraction to different phase (stationary= slower, mobile= faster)
- What affects the amount of time molecules spend in each phase?
- how soluble they are to the solvent (mobile phase/higher= more)
- how attracted the are to the paper (mobile phase/higher= less)
- What is there between the stationary and mobile phases for each component in a sample?
- for each component in a sample there is a dynamic equilibrium between the stationary and mobile phases
- stationary phase→mobile phase = mobile phase→stationary phase
- What does a separation by chromatography depend on?
-the distribution of the components in the sample between the mobile and stationary phases
- What is the use of standard reference materials in chromatography?
- to check the identities of substances
- they have carefully controlled concentration and purities
- What happens in paper chromatography?
- substance put on baseline of paper
- placed in beaker of solvent
- solvent moves up paper
- chemicals in sample dissolve in solvent and move between solvent and paper= equilibrium between solvent an paper
- mobile phase= chemicals move up paper with solvent
- paper removed from beaker before solvent reaches top of paper
- chemicals form different spots on paper (mobile phase>stationary phase= further up)
- What are the mobile phases and stationary phases in paper chromatography?
- mobile phase: solvent e.g. ethanol, water
- stationary phase: chromatography paper e.g. filter paper
- What is the difference between paper and thin-layer chromatography?
Paper chromatography
- mobile phase: solvent e.g. ethanol, water
- stationary phase: chromatography paper e.g. filter paper
Thin layer chromatography
- mobile phase: solvent e.g. ethanol, water
- stationary phase: thin layer of solid e.g. silica gel spread on a glass plate
- What are Rf values?
-the ratio between the distance travelled by dissolved substances (the solute) and the distance travelled by the solvent
- What is the use of locating agents in paper and thin-layer chromatography? (and example)
- in case the spots on the chromatogram are colourless
- e.g. spray chromatogram with reagent
- What is gc?
-gas chromatography
- What are the different phases in gas chromatography?
- mobile phase: unreactive gas e.g. nitrogen
- stationary phase: viscous (thick) liquid e.g. oil
- What is the process of gas chromatography?
- unknown substances vaporised if not already gases
- mixture injected into tube coated with stationary phase
- mixture moves along mobile phase
- substances are distributed between phases
- time taken to travel through tube= retention time
- different chemicals= different retention times
- What does the term retention time mean regarding gas chromatography?
-retention time is the time it takes for a chemical to travel through the tube
- What is a chromatogram from gc?
-graph made in gc for retention times
- What information can we get from chromatograms for gc?
- distance across y axis= retention time (identifies substance)
- peak height= how much of chemical was in sample (y axis)
- What is a solvent?
-a substance that a solute dissolves in to form a solution
- How is an aqueous solution formed?
-if solvent is water
- How is a non-aqueous solution formed?
-if solvent is not water
- What are examples of non-aqueous solvents?
-alcohol, acetone
