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laboratory techniques and their application.
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4.3 assignment- Explore manufacturing techniques and testing methods for an organic solid. Grade: Distinction
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UNIT 4 LEARNING AIM C: EXPLORE MANUFCTURING TECHNIQUES AND TESTING METHODS FOR ANORGANIC SOLID.
In this assignment we made aspirin and we tested its purity in three different ways. I am going talking
about reflux, recrystallisation, purification and the two different methods to test purity of a sample. The
descriptions of two industrial methods for aspirin production and testing purity. Also, I am discussing the
advantages and disadvantages of aspirin synthesis and testing methods industrially and laboratory and
compare between them. Finally, I will analyse the methods and explain the relative yield.
SOLUTIONS.
Most of the reaction happen in liquid state to allow the particles to move and react. Solution is formed
when a solute is dissolved in a solvent. An example of solution are water and ethanol. Solute would be
solid, liquid and gas. Saturated solution is when there is a large amount of solute that has been
dissolved. If there is more solute added, then it will stay at the bottom of the liquid. Supersaturated
solution is when a solution has more of the dissolved solute that it can dissolved in room temperature.
The influence of the temperature in the solution is as the temperature increases the amount of the
solute that can be dissolved in it will increase this happen because of the particles which have more
kinetic energy to move quickly. Solubility is temperature dependent, and solids are more soluble at high
temperatures. The particles of a solid state are close together, as they have more energy they can move
and can become in a liquid state this means when a substance is dissolved. If the temperature increases
the solubility of a solid will increase too. Supersaturated means when there is more solute than normal
dissolved in the solvent.
The influence of polarity of solvents depends on their polarity and the
distribution of the electrons that has one part positive and the other part
negative. Molecules like hexane have covalent bonding and they are non-
polar molecules the attraction of the bonds between them are weak
which is van der Waals forces. Polar molecules have a large difference in
electronegativity in their compounds. Water is polar molecules; it has two
hydrogen atoms and one oxygen atom and is highly electronegative. As
the molecules is less polar the polarity of the molecules decreases.
Substance will dissolve in solvent in which the polarity is the same. Non-
polar dissolve with non-polar and polar will dissolve with polar. The
reason why polar needs to be dissolved in polar molecules is that need to
have a strong force of attraction between molecules. As you can see in
the picture the most highly polar is water and the most highly non-polar
is hexane.
CRYSTALLISATION.
Crystallisation is a technique used to separate from a liquid phase into a solid phase forming crystals. In
which the sample forms crystals from liquid or gas state. The molecules of the substance arrange in a
three-dimensional lattice to reduce the energy between them. One factor that affect crystallisation to
, happen is supersaturation. Supersaturation cause crystal nucleation and growth. This means that when
there are more solids dissolved than for a digital solution it starts to form crystals.
Nucleation is the process when the solid starts to form crystals. The formation of the crystals starts to
form when the dissolved substance starts to come out of the solution from a solution in the liquid or gas
state, which have a small quantity of ions, atoms or molecules that become arranged in a crystalline
solid. Crystals growth faster in low saturation because the crystals have a large size distribution in
another way at higher supersaturation results a small size of crystals because the crystals nucleation
rules crystals growth.
RECRYSTALLISATION.
When an organic solid is prepared it need to be purified. Recrystallisation is technique used to remove
impurities of an organic solid. One point to know in recrystallisation ids that different substances have
different solubilities in a solvent at different temperatures. We can separate the substance by differing
solubility of the product and impurity in hot and cold solvent. If a substance is soluble in a solvent in a
cold temperature, then the crystals will not come back out. To get a good recrystallisation you need to
select a good solvent in which the substance is soluble ion hot temperature. The benefit of hot
temperature is to remove impurities. Some of the solvent that are useful and used is water, ethanol,
propanone ethyl ethanoate and cyclohexane.
First, add the impure solid to a conical flask and heat the solvent separately then add it dropping pipette
make sure that no product in not lost through spitting. When the solid is heated and there is some
undissolved solid at the bottom of the conical flask add more solvent and warmer it until the mixture
boils. After the solvent is boiled let it boil for a few minutes then let the solvent to cool down. If you cool
the solvent at room temperature slowly the result of the crystals will be bigger, and you can get more
crystals. When the solvent is cooled use the method of filtration to separate the solid crystals and let it
to dry.
REFLUX.
Reflux is a technique where you heat organic substances for a long period. The reaction needs to be
heated in the flask fitted with reflux condenser. The reflux condenser has two tubes one inside other.
The space between the two tubes allows the water to flow through to cool down the gases causing
condensation. The advantage of reflux is that we can leave it for a long time without fearing the
reaction. In the reflux condenser, the vapours that come from the reaction during the mixture enter the
condenser and change into liquid then the unreacted compound returns to the flask, and they react.
We use a hot water bath to heat the flask, there is another way to heat the flask is using or instead of
water, but it is dangerous. The use of anti-bumping granules is used to avoid large gas bubbles and let
the development of nucleation sites for small bubbles which allow a safety reaction mixture and help
boiling to make it smooth. Nucleation sites are where the anti-bumping granules form a small bubble
and avoid the reaction to boil more quickly. At the bottom of the condenser. cold water flows and cools
and condenses the vapours to return into the flask.
FILTRATION.
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