practical techniques Flashcards
What is reduced pressure filtration and what equipment is required? Give an example.
Technique which separates a solid from a solid or reaction mixture which requires a Buchner flask and Buchner funnel.
For example in the synthesis of aspirin
How do you use a Buchner funnel?
1) Place a filter paper inside the Buchner funnel and wet this with the wet solvent
2) Pour the reaction into the filter paper
3) Rinse out the beaker with the solvent so that all the solid crystals collect in the Buchner funnel
4) Rinse the crystals in the Buchner funnel with solvent and leave them to dry
How do you recrystallise impure crystals to produce SOLID pure products?
1) Dissolve in a minimum volume of hot solvent to dissolve the impure sample
2) Allow the solution to cool
3) Filter the crystals
4) Leave to dry
What do titrations do?
Accurately measures the volume of one solution that reacts exactly with another solution.
+Find the concentration of a solution
+Identify the unknown chemicals
+Find the purity of a substance
How do you prepare a standard solution?
1) Weight the solid accurately
2) Dissolve in a beaker and transfer to volumetric flask
3) Fill the volumetric flash to the bottom of the meniscus line with distilled water
4) Slowly invert the flash to mix the solution thoroughly
What is the purpose of reflux?
Reflux is conducted to increase the rate of reaction by overcoming the activation energy without boiling the solvent , reactants or products.
What is the purpose of distillation?
A common method to separate a purple liquid from its impurities and reactants left over from reflux.
How do you separate organic liquids?
1) Pour the organic liquids into a separating funnel
2) Invert the funnel to mix the contents
3) Place a funnel underneath the stopper and open the tap until the lower layer is removed.
How can you remove acid impurities?
Add sodium carbonate to react with the gas and release carbon dioxide.
What is the stationary and mobile phase of chromatography?
Stationary: Does not move and is normally a solid or a liquid supported on a solid
Mobile: Does move and is usually a liquid or gas
What is the purpose of thin layer chromatography?
Indicates how many components there are in a mixture my determining the affinities with the relative adsorptions with the stationary phase.
How do you calculate retention factor?
Distance moved by component / Distance moved by solvent
What is the purpose of gas chromatography?
Separates and identifies volatile components present in a mixture which depends on their solubility during the stationary phase. The more soluble, the slower it will move during the stationary phase.
The retention time is taken for how long it takes for the component to move through.
How do you interpret a gas chromatogram?
Each component is shown as a peak,
You can compare retention times with known components and peak integrations can be used to interpret the concentrations of components in the sample.
