Section 6- Whats in a medicine? Flashcards
(19 cards)
How would you produce an aldehyde from a primary alcohol?
How would you separate it from the solution and why?
You would oxidise the primary alcohol with aicidified potassium dichromate whilst gently heating it.
You would need to immediately seperate it from the solution because the oxidising agent will further oxidise it to form a carboxylic acid. This can be done by distilling the solution, as the aldehyde has a lower boiling point than the carboxylic acid, and it will evaporate instantly, where it can be condensed in the condenser and it can be collected in a flask.
How would you produce a carboxylic acid?
You would obtain a solution of aldehyde and you would require vigorous oxidation of it to produce the carboxylic acid. To do this you would require a reflux apparatus, which would allow for you to increase the temperature of the reaction, and for any volatile reactants to condense on the apparatus and rejoin the reaction mixture, so that no materials are lost.
Can ketones be oxidised easily?
No.
They cannot therefore be oxidised even with prolonged reflux.
Alcohols can be dehydrated to form ______
What are the two ways this can occur?
Alkenes
Using hot pumice stone, and ceramic wool coated in ethanol. This wool will release ethanol as a vapour and it will pass over the pumice stone catalyst where is will be dehydrated to form ethene. This can be collected in a bung and can be fed into an inverted volumetric tube.
Alternatively, refluxing with sulfuric acid at 170 degrees can be used as a dehydrating agent to produce ethene from ethanol. There is a mechanism for this
What do acid anhydrides and alcohols react together to form?
Carboxylic acids and esters.
What is the test for phenol?
Iron (III) Chloride turns purple when you shake it with phenol.
Phenols are weak acids, what strength of alkali do they react with?
Only strong alkalis, like NaOH. They can very partially dissociate to make a phenoxide ion, so Ka is applicable for them.
What type of reactants are reflux apparatus particularly useful for?
Reactants which are highly flammable and volatile. If these reactants were to be placed in a conventional beaker, they would simply evaporate and become ignited before they could react. The reflux apparatus uses its condenser to condense such reactants and ensure that they can be returned back into the reactant mixture. This allows the reactants to be returned where they can have time to react, due to constant evaporation and condensation.
One thing which is important about this reaction is to use electronic heaters, especially in the case where the reactants are highly flammable.
What is distillation useful for?
Separating substances which aren’t volatile but have different boiling points. Steadily increase the boiling point until the thermometer shows the temperature is around that of the substances boiling point which you’re trying to separate, and then ease off the heat, and keep this temperature the same to allow for the substance to evaporate. It will travel up towards and into the condenser, where it will condense from a gas to a liquid, and it will proceed to drip into a beaker where it will be collected, and a pure distillate product will be collected.
How to remove water soluble impurities without buchner apparatus?
Place a product mixture into a seperating funnel. Add water and shake. This should form an organic product layer and an aqueous layer. The aqueous layer will be more dense, and therefore will sit on the bottom of the separating funnel. The organic layer will include any useful products. Simply open the funnels stopper and allow the aqueous layer to run off.
How would you remove water from a purified product?
You would place a drying agent such as MgSO4 into the solution. It will bind to the water and will make it become hydrated. The water will then become fully binded to it, and you will have a hydrated magnesium sulfate solid sitting in a solution of the product you desire. Simply filter the solid product from the liquid to leave the desired liquid.
How would you separate a solid product from a both solid and liquid mixture?
Buchner apparatus. The decreased pressure inside the flask will force the air through, leaving just the solid.
Describe the process of recrystallisation.
Dissolve an impure solid in a minimum of hot solvent. This will form a saturated solution, containing the desired product soluble product (while hot), as well as both soluble and insoluble impurities. You then carry out hot filtration with a buchner apparatus, and doing so remove any insoluble impurities, this should be done straight away to ensure that the soluble desired product remains hot and therefore dissolved, so as to not be seperated as a solid and therefore the yield of the process be reduced. You should then plunge the conical flask into an ice bath, which will cause the solid desired product to recrystallise out of solution. At this point, there will be a desired recrystallised solid in solution with still some soluble impurities. You should then do cold filtration, and pour the remaining solution through a buchner apparatus once again, whilst washing the solid with cold solvent so as to remove the maximum amount of soluble impurities. All buchner apparatus should have filter paper on them. You can now remove the solid product, place on an evaporating basin and allow to dry passively.
What properties would make a solute suitable for recrystallisation?
If it dissolves in hot solvent, but does in cold solvent.
What can a glass cappilary tube be used for?
Analysing the melting point of a sample to determine whether it is pure or not. You would tap the solid into the somewhat bottom of the glass capillary tube and you would then apply heat using a heat controlled environment (such as a water bath). You should then increase the temperature until the solid turns into liquid. You would measure a melting range, which is a range of temperatures in which the solid begins to melt to where it is melted completely. If there is a range of temperatures, the solid is not a pure substance, and this temperature range can be looked up in a data book to determine what substance it lilely is. If there is one distinct temperature the substance fully melts within, it is likely a pure sample.
Describe the process of thin layer chromatography.
Draw a thin pencil line on a silica plate (silicon dioxide, the stationary phase) and place samples of the substance you wish the analyse onto the pencil line. Place the silica plate into a suitable solvent solution (mobile phase), where the solvent is placed below the pencil line/baseline. Allow the solvent to move up the silica plate, and the substances to be separated. Some substances will move up the plate faster than others, and this will result in a chromatogram being produced. Calculate the Rf values of the given substances by calculating the distance travelled by the spot/the distance travelled by the solvent. If it is the case that the chemicals used are colourless, you would need to either add a fluorescent dye to the plate and use UV light to make the spots visible (the silica plate will glow and the spots will not). You could alternatively use iodine vapour, which would turn the spots purple (it is a locating agent).
What are some principles involved in green chemistry?
Use renewable resources, such as plant products to make plastics or solar and wind energy instead of fossil fuels
Use chemicals and processes which are as safe as possible. This includes the use of reactants and products which arent damaging to both humans and the environment. To minimise the risks of disasters such as explosions, methods of safety procedure should be implemented.
Waste should be minimised and products should be biodegradable (they can be naturally decomposed in the environment) or recyclable. The atom economy should be as high as possible, catalysts should be used so that temperatures and pressures and required to be so high, and not so many raegents and needed to be used.
