We normally encounter solutions in chemistry. A solution is defined when it is a mixture of a Solute and Solvent. For example, a Hydrochloric Acid (HCl). It is considered a solution. It mixes a Hydrochloride solid (Solute) with water (Solvent). Forming solution is simple but have you ever thought above the process of separating them?
Well, there are several methods of separating mixtures. They are Distillation, Using of Separating Funnel, Filtration, Evaporation, Fractional Distillation and Chromatography. Please note that Electrolysis is used to separate IONISED compounds.
Distillation is a process of separating
impurities from a solution. For example, impurities from sea water. The whole
solution is been evaporated. The impurities which have higher temperature so,
will remain in the round-bottom flask. Hence, the water, which boils at 100oC,
will be distillated first. The water will flow through the liebig condenser.
Next, it will flow out as a distillate.
Function of the parts.
1. Mantle Heater acts as a Bunsen burner in this case. It will evaporate the liquid which has lowest boiling point.
2. The Round-bottom flask is used to contain the impurities and the liquid which is supposed to be separated.
3. The thermometer is supposed to be positioned at the mouth opening of the Liebig Condenser. It is used to indicate the first evaporating liquid. If the thermometer reading reaches 100oC, it shows that water is currently evaporating and the distillate collected is water.
4. The liebig condenser is sure to condense liquid as the word 'condenser' comes from the root 'condense'. How is it been done? Well, there is a pipe downwards, which is meant for water to pump in. Similarly, there is a pipe closer to the mouth of the liebig condenser, which is meant for water to be pumped out. What are the function of these 2 pipes then? It is used to prevent the liquid from evaporating further. The liquid may evaporate due to the high temperature from the heater. It may as well resemble the Bunsen burner, which has the highest flame point at 600oC. Consider the whole process without a liebig condenser. It will be similar to evaporation process. The liquid will evaporate into gaseous state. That is the reason why we need a liebig condenser here. It will cool down the whole liquid to a cooler temperature. So, the water is pumped in and out to regulate the coolness of the liquid. In such, we will be able to obtain our pure distillate.
5. The distillate is then collected in a conical flask (not shown).
Fractional
Distillation is separation of 2 miscible liquids of two different temperatures,
one of a high and the other liquid of low temperature. Miscible liquids are
liquids which are soluble in one another but an exception is that its components
has 2 different range of temperature. There are many examples which can be
separated by Fractional Distillation. Several examples are separation of Crude
Oil, Ethanol-water mixture and many other more. The diagram on the left shows a
Fractional Distillation Set-up of 2 miscible liquids of Ethanol and Water
mixture. In this set-up you will find a slight difference compared to the above
set-up, which is the presence of Glass Beads. The glass beads in this set-up
play a significant role in this experiment.
According to this set-up, it is obvious that Ethanol Acid (C2H5) has a lower boiling point (78oC) than Water (100oC). In this case, the Ethanol Acid will be distillated first. Let go into the processed steps...
The miscible liquid, C2H5 and H2O, is initially mixed together. The problem faced is to separate the C2H6 and H2O individually. The process of Fractional Distillation comes about here.
The miscible liquid is been filled into the round-bottom flask. Some boiling stones are added into the miscible liquid. A fractional column is linked from the mouth of the round-bottom flask with glass beads. A thermometer is positioned at the mouth of fractional column and the tip of the thermometer is placed at the mouth of the liebig condenser, which will be linked from the fractional column. The liebig condenser has got 2 openings. One is meant for Water-in and the other is meant for Water-out. A conical Flask is placed at the bottom of the condenser to collect the distillate.
The Ethanol acid will be distillated first as it has the lowest boiling point. The vapor that is been evaporated contains high-content of ethane. There will be a continuous evaporation of ethanol acid until the thermometer indicates that the boiling point is rising and that shows the next liquid to be distillated will be water. However, the first distillate that is been distillated will not have FULL content of Ethanol acid due to some water moisture presence during evaporation.
Therefore, Calcium Oxide is been added into the distillate to absorb the water moisture to form Calcium Hydroxide (Ca(OH)2). Calcium Hydroxide is needed as it is an ionic compound which has a property of HIGH BOILING point. The boiling point of Calcium Hydroxide differs very much from the boiling point of the Ethanol Acid. Therefore, the fractional distillation is repeated again to separate Calcium Hydroxide and Ethanol Acid. In this case, Ethanol Acid will be distillated first as it has a lowest boiling point, followed by Calcium Hydroxide. However, there WILL NOT BE ANY water content.
Similarly, if i want to obtain the water content, i will add an acidic solution to Calcium Hydroxide. According to the acid general rule, the product of Salt and Water is formed when Acidic solution mixed together with Alkali Solution. In this case, i will be able to obtain the water. However, calculations are needed to obtain the accuracy of the water concentration. (ACID + BASE --> SALT + WATER)
FAQs
1. Why should there be boiling stones in the miscible liquid?
Boiling stones are needed to regulate the boiling rate. They are used in the boiling flask to reduce the violent heating of the liquid which will cause inaccurateness in the whole evaporating process.
2. What is the use of glass beads in the fractional column?
As stated, the glass beads played a very significant role in this process. The glass beads act as to regulate the temperature and impurities of the mixture. As the temperature rises reaches 75oC and above, steam will be produced and this steam WILL NOT be Ethanol acid as explained in the 5th paragraph. As a result, this steam vaporized and stay on the glass beads. However, when the temperature reaches 79oC, Ethanol acid starts to vaporized too. The glass beads condense the mixture and let the liquid flow down. However, the hot steam at the flask generates energy for the mixture to move up further more. In the result, the liquid can flow into the tubing of the liebig condenser and distillate out.
3. What is the function of liebig condenser and the functions of the 2 different openings?
The liebig condenser is obviously used to condense the liquid from evaporating into gaseous state as some liquid has very low boiling temperature which can be evaporated into gaseous state quickly. The opening below is meant for water to be pumped in whereas the opening at the top is meant for water to be pumped out. People often got confused by asking why is the method of connecting is not the other way. It is true that water pressure transfers from a higher height to a lower height. However, if this statement is the answer, the liquid MAY NOT be cooled completely as it only condenses the top portion of the liebig condenser. The rest of the part of the liebig condenser will not be in contact. Just take the temperature of the surrounding into consideration as well. The surrounding temperature is warm and hot due to the high temperature of the Bunsen burner. Therefore, if the rest of the part of the liebig condenser is not cooled, the liquid may evaporate into gas when it is been condensed out due to the hot temperature.
Therefore, the positioning of the water inlet and outlet is equally important as the glass beads as well! The water is been pumped in from the bottom and pumped out from the upper opening. In this scenario, the liquid in the liebig will be cooled completely. Therefore, it will be cooled down into the room temperature. Hence, the liquid can be distillated out purely.
4. What is the function of the thermometer and why is the positioning of the thermometer at the mouth of the liebig condenser?
The thermometer is used to indicate of what certain liquid will be distillated. If the thermometer reading is at 70oC constant for a moment, it indicates that Ethanol acid is distillated at that moment.
The thermometer is positioned at the mouth of the liebig condenser for the accurate reading. This is done so because the liquid starts to enter the condenser, which has the boiling temperature as stated in the 3rd FAQ pointer. So, if the thermometer is placed somewhere away from the mouth of the liebig condenser, the liquid may be cooled down a little by then and therefore having an inaccurate reading.
5. Why is Calcium Oxide added into the initial distillate of Ethanol Acid?
As mentioned, the initial distillate MAY not be perfectly pure as some water moisture may be evaporated at the same time. Hence, it does not satisfy the solution we want. The solution we want is Ethanol Acid. As we know in a chemistry background, when a basic oxide is been mixed with water, it forms an alkali solution. Hence, alkali salts like NaO, CaO, etc, can form alkali solution. All these are in the form of IONIC COMPOUND. According to the properties of an IONIC COMPOUND, it has HIGH boiling point. Therefore, when it got its ionic compound, Calcium Hydroxide (an alkali solution which is used to reduce the acidic content of crops or agricultures), it has higher boiling point than Ethanol Acid. When this miscible solution is been distillated again, it can be confirmed that Ethanol acid will be distillated first as the Calcium Hydroxide has a boiling temperature of 172oC.
Filtration is a process of separation of a solute that is undissolved in solvent. E.g. CaCO3 with water.
In
filtration, there will only be a separation of 'residue' and 'filtrate'.
Residue is the substance separated from the mixture of 2 insoluble substances.
Filtrate is the separated solvent from the residue. To set up a filtration
process, we will need a filter funnel, a beaker and a filter paper. Filter paper
is a filtering paper with semi-permeable holes which allows small molecular
substances to flow through as a filtrate whereas leave the residue, with bigger
molecular structures. In this case, the CaCO3 is insoluble in water.
Therefore, it can be easily separated by filtration. The mixture is been poured
into a filter funnel with filter paper. The smaller molecular structures, the
water, will flow through as a liquid filtrate. The bigger molecular structures,
the CaCO3, will be left on the filter paper.
There are several examples to separate mixtures with using Filtration. Such Examples are: Sand from sea water, chalk powder from water, etc.
Evaporation is the process to remove solutes from its solution. For example, a salt solution. If we heat up the solution, we will evaporate the water from the salt solution to obtain salt and water vapour. Firstly, the salt (NaCl) solution is an ionised solution. Therefore, at flame point 100oC, as it is the boiling point of the water, water will be evaporated away. This is how we obtained the NaCl crystal. However, if we want to further separate NaCl into its pure form, we have to go through electrolysis. For more information about electrolysis, click here to download.
Chromatography is an important separating technique used in many criminal investigation (Drugs), clinics, food test, etc. Chromatography enables the chemist to separate the colors or the traces of all chemicals of a solvent. Therefore, in chromatography, the testing agent or solvent is inked on the pencil line. After which, it will be placed into a dissolving solvent (water of alcohol), where its solvent level does not reach the pencil line. After that, there will be an observation of solvent level rise. Hence, we will be able to see what the solvent contains. However, there is no mean of Physical separation during the dissolving but it is just an indication.
Black
ink marked along the pencil line.
Solvent
level rise when dissolving with solvent.
To find the Rf value (rate of separation of solvent),
Rf value = Dist. travelled by solvent on pencil line / Dist. travelled by dissolving agent.
