Distillation is a significant commercial technique that is used to purify a wide range of materials. It is the procedure of selective boiling and condensation to separate the components or compounds from a liquid combination.
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Distillation can produce an almost complete separation (almost pure components) or a partial separation (increased concentration of selected components in the mixture). The technique uses changes in the relative volatility of the mixture’s components in each situation. Distillation is a unit operation of virtually universal importance in industrial applications, although it is a physical separation process, not a chemical reaction.
Distillation Chemistry Questions with Solutions
Q1: Porcelain pieces are put into the distillation flask to avoid ____________
a) Overheating
b) Bumping of the solution
c) Uniform boiling
d) None of the mentioned options
Answer: b) Bumping of the solution
Explanation: To prevent the solution from bumping due to uneven heating, porcelain pieces are placed in the distillation flask.
Q2: What are the two processes in distillation?
a) Distilling and condensation reflux
b) Distilling and freezing
c) Freezing and condensation reflux
d) Only condensation reflux
Answer: a) Distilling and condensation reflux
Explanation: Distillation is a two-step process that includes distillation and condensation reflux. The gas-liquid two-phase flow over the countercurrent contact is commonly carried out in a distillation column.
Q3: How aniline and chloroform can be separated?
a) Sublimation
b) Condensation
c) Distillation
d) Evaporation
Answer: c) Distillation
Explanation: The distillation technique can be used to separate aniline and chloroform. The toxic organic molecule aniline has the formula C6H5NH2. The organic compound chloroform has the formula CHCl3. It’s a colourless, sweet-smelling, thick liquid that’s used as a precursor to PTFE and refrigerants on a huge scale.
Q4: Which of the following is not separated through the distillation process?
a) Acetone and water
b) Milk and water
c) Impurities in Sea water
d) Aniline and chloroform.
Answer: c) Impurities in Sea water
Explanation: The distillation technique does not separate milk from water. A distillation procedure can separate all of the other options.
Q5: The process of distillation is used for the liquids having ____________
a) Sufficient difference in their solubility
b) Sufficient difference in their melting point
c) Sufficient difference in their boiling point
d) None of the mentioned
Answer: c) Sufficient difference in their boiling point
Explanation: The distillation method is employed for liquids with a significant difference in boiling points. Distillation also allows you to separate the components of air.
Q6: Which salt is obtained as a result of the chemical reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH)? Which method will you use to separate it from the solution?
Answer:
The chemical reaction between HCl and NaOH gives rise to common salt (NaCl). The following is a representation of the chemical reaction:
HCl + NaOH → NaCl + H2O.
The salt is separated from the solution using the distillation process.
Q7: Draw a labeled diagram showing the process of distillation.
Answer:
The distillation process is depicted in the diagram below.
Q8: Match the following:
Answer:
(a) Melting point – 4. Change of state from solid to liquid.
(b) Boiling point – 3. Change of state of a liquid into a gas.
(c) Fractional distillation – 2. Obtaining diesel from crude oil
(d) Distillation – 1. Separating common salt and water from their mixture.
Q9: Answer the following questions.
- What will you do to find out the boiling point of water?
- What changes do you see in the appearance of a candle after you have lit it?
- Can a solid and a solvent be separated from their solution by distillation?
Answer:
- To determine the boiling point of water, we will use the following apparatus:
Experiment: We’ll put water in a flask with a round bottom and a single holed rubber stopper. We’ll put a thermometer in the hole and start heating the flask by placing it on iron gauze on a tripod stand.
Observation: The increase in temperature in the thermometer will be observed. When the mercury within the thermometer reaches 100°C., water begins to boil, and the temperature falls.
Conclusion: The boiling point of water is defined as the temperature at which the temperature stops rising and the water begins to boil. As a result of the experiment, the boiling point of water is 100°C.
- When we light the candle, the following changes occur
(i) State change: The candle’s wax melts and then vaporises to generate wax vapours.
(ii) Combustion: Heat and flame are produced when wax vapors burn.
- Yes, distillation can separate components of a solution made up of a dissolved nonvolatile solid (solute) and a liquid (solvent).
Q10: What is the difference between distillation and fractional distillation?
Answer:
The following table summarises the differences between distillation and fractional distillation:
Q11: Mention the various uses of Distillation.
Answer:
Some of the uses of Distillation are as follows:
- It can be used in a laboratory to do experiments. The results aren’t immediately utilised, although they can help with chemical and medicinal research.
- Distillation may remove numerous pollutants from water, making it beneficial for purification. Desalination plants use the seawater distillation process to obtain pure water. When making infant food, parents use distilled water.
- Distilling ferment material (a mixture of fruit and animal components) creates ethyl alcohol, which is used to make alcoholic beverages.
- When crude oil is distilled, various compounds such as gasoline, wax, fuel oil, lubricating oil, and other petrochemical products separate at different boiling points.
- Distillation produces the perfumes we use today. We extract essential oil and aroma from many plants and herbs using this method. Simple distillation is not used because plants begin to disintegrate at higher temperatures. As a result, steam distillation is beneficial.
- Food flavour is created by steam distillation. Citrus oils, for example.
- Acetone and methyl alcohol are separated via fractional distillation.
- Oxygen, nitrogen, carbon dioxide, argon, and other gases are found in the air. Cryogenic distillation can be used to remove these gases.
- The sugarcane industry uses vacuum distillation to concentrate sugarcane juice.
Q12: Fractional distillation can be used to separate miscible liquids having a boiling point difference of less than 25 K. What part of the fractional distillation equipment makes it efficient and superior to a normal distillation process? Use a diagram to explain.
Answer:
Fractional Distillation of Miscible Liquids
- A fractionating column improves the efficiency of fractional distillation over simple distillation by increasing the possibility of liquid condensation.
- A fractionating column with glass beads or glass helices provides a vast surface area for the vapours to collide and lose energy, allowing them to be quickly condensed and distilled.
- Fractional distillation efficiency could be improved by increasing the length of the fractionating column.
Q13: Which tubes in Fig. 2.1 (a) and (b) will be more effective as a condenser in the distillation apparatus?
Answer:
As a condenser in the distillation equipment, tube (a) will be more effective. The presence of marbles enhances the surface area of the vapours’ contact area. This gives the vapours more time to condense, making the first column more effective than the second column without marbles.
Q14: Give an example of each mixture having the following features. Suggest a suitable method to separate the components of these mixtures
a) A volatile and a non-volatile component.
b) Two volatile components with appreciable differences in their boiling point.
c) Two immiscible liquids.
d) Two or more coloured constituents soluble in some solvents.
Answer:
(a) Example: Mixture of acetone and water.
A mixture of volatile and non-volatile components can be separated by simple distillation.
(b) Example: Mixture of kerosene and petrol.
Simple distillation can be used to separate two volatile components with significant boiling point differences.
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(c) Example: Mixture of mustard oil and water.
Separating funnel is used to separate a mixture of immiscible liquids.
(d) Example: A mixture of different pigments from an extract of flower petals.
Two different compounds present in the same solution can be separated using the chromatography method.
Q15: Briefly describe Vacuum Distillation.
Answer:
- Vacuum distillation is ideal for separating mixtures of liquids with extremely high boiling points.
- Heating these chemicals at high temperatures is an ineffective technique for boiling them. As a result, the pressure in the environment is reduced.
- Because the pressure is reduced, the component can boil at lower temperatures. The component is transformed into a vapour when its vapour pressure equals the ambient pressure.
- The fumes are then condensed, and the distillate is collected. High-purity samples of chemicals that degrade at high temperatures are also obtained using the vacuum distillation method.
Practise Questions on Distillation
Q1: What are the basic methods of distillation?
a) Fractional distillation and simple distillation
b) Steam distillation and destructive distillation
c) Steam distillation, simple distillation, and gas distillation
d) Fractional distillation, destructive distillation, and simple distillation
Q2: Define the following terms.
(a) Melting point
(b) Boiling point
(c) Distillation.
Q3: Give scientific reasons.
(a) A condenser has two taps.
(b) At dawn, in winter, we see dewdrops on the leaves of trees
Q4: Salt is dissolved in seawater. You’re probably aware that you can distill pure water from seawater. This approach, however, is not used to obtain drinking water from seawater. What do you believe the reason is?
Q5: Two water samples, labeled ‘A’ and ‘B,’ are given to you. Sample “A” boils at 100°C, while sample “B” boils at 102°C. Which water sample will not freeze at 0°C? Comment.
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Recommended Videos
Distillation Theory
Example of a Typical Experiment
Practical Lab Tips
FAQ: When using the condenser, which hose connector is water-in and which is water-out?
FAQ: Why does it matter whether water enters the condenser at the top or from the bottom?
FAQ: How fast should the water run through the condenser?
FAQ: How far down the stillhead should the thermometer bulb be placed when setting up the distillation apparatus?
FAQ: How do you know when the distillation is complete?
FAQ: Why are no drops coming over eventhough the distillate is boiling?
FAQ: Can I use a bunsen burner for reflux and distillation?
FAQ: When setting up the distillation apparatus, can I use an Erlenmeyer flask as the receiving vessel?
FAQ: How much does the boiling point vary with atmospheric pressure?
FAQ: If the atmospheric pressure today is 695 torr, does that mean the actual boiling point of this liquid is listed in the literature at a higher value than the temperature I saw, even after I corrected the temperature for my thermometer?
Theory: Distillation
Distillation is a purification technique. It can be used for the separation of a low boiling solvent from a solid or a high boiling liquid. The liquid vaporizes in one vessel (the distillation pot) and then condenses into another vessel (the receiving flask).
Heat Sources:
Steam Bath - Use with flammable liquids that have a boiling point below 100 oC.
Heating Mantle with Powermite - Use with round bottom flasks during distillation or reflux. The Powermite allows heat regulation.
Hot Plate - Use with Erlenmeyer flasks containing non-flammable or high boiling liquids. Can also be used with beakers containing water (for a water bath).
Boiling Point:
Boiling point is the temperature at which the vapor pressure of a liquid is equal to that of the surrounding atmosphere.
Boiling point varies with atmospheric pressure and is corrected to the temperature that would be observed at sea level (760 Torr).
The higher the altitude, the lower the atmospheric pressure and the lower the boiling point.
Boiling point is measured during distillation when the temperature is constant (at the stillhead).
Corrected boiling point can be measured using a nomograph or the following equation:
Boiling Point Correction Factor = [(760 torr - atmospheric pressure) / 10 torr x 0.5 oC]
Corrected Boiling Point = Observed Boiling Point + Correction Factor
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Typical Experiment
Student A left approximately 20mL of a liquid mixture for his partner, Student B, to work up. Student B was to remove and identify the solvent as well as retain the residue and distillate. Student B decided to use simple distillation to remove the solvent. He placed a lab jack in position and set up a heating mantle with a Powermite control. He clamped the distillation flask in place and added boiling stones followed by his unknown liquid. A stillhead was then attached and a thermometer was inserted into the thermometer adapter. The receiving flask was clamped in position and the condenser was connected between the receiving flask and distillation flask. Student B then attached the water tubing to the condenser and turn the water tap on full. The tubing popped off and sprayed the student's TA (who was not impressed). The student reconnected the tubing and this time used the hose clamps and turned on the water tap slowly. The student set the Powermite to 25 and after a few minutes, the liquid in the distillation flask began to boil. The solvent began to boil and the temperature of the distillate was observed to be 38 oC at ~700 torr. When no more solvent distilled over, the heating mantle was slowly lowered and the apparatus allowed to cool before disassembly.
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Practical Lab Tips
When connecting the water tubing to your condenser, remember that water enters from the bottom of the condenser and exits from the top.
Add boiling stones to your distillation flask BEFORE you start heating.
Distillation is complete when: a) no more liquid collects in the receiving vessel, b) when the temperature of the thermometer starts to drop or c) when the distillation flask is empty.
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Q: When using the water condenser, which hose connector is water-in and which is water-out?
Water goes in from the BOTTOM of the condenser.
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Q: Why does it matter whether the water enters the condenser at the top or from the bottom?
If water enters from the bottom of the condenser, it will always be completely filled with cold water which ensures efficient cooling. During distillation, vapors are formed in the heated distillation flask. The condenser cools these vapors condensing them back to liquid droplets that flow down the condenser into the receiver flask. A completely filled condenser provides maximum cooling therefore allowing for maximum recovery of the purified liquid during distillation.
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Q: How fast should the water run through the condenser?
A continuous flow of water through the condenser is necessary; however, the lower the flow rate, the lower the pressure and the lower the chance of having the tubing pop off (resulting in you spraying yourself or others).
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Q: How far down the stillhead should the thermometer bulb be placed when setting up the distillation apparatus?
The mercury bulb of the thermometer should be positioned so that vapors condense readily on it. The tip of the bulb should be in line with the lowest part of the connecting tube of the stillhead.
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Q: How do you know when distillation is complete?
Distillation is complete when: a) you notice a drop in temperature, b) no more distillate is being formed or c) the distillation pot is empty.
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Q: Why are no drops coming over eventhough the distillate is boiling?
There could be two reasons for this:
If this happens at the beginning of the distillation, there is insufficient energy input to cause adequate vaporization of the liquid. In this case, you should increase the heat.
If this happens at the end of the distillation, almost all of the low boiling liquid has been removed. Solvent vapors trapped in the boiling stone pores will continue to be an ebullition source, causing bubbling.
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Q: Can I use a bunsen burner for reflux and distillation?
It is safer to use a heating mantle with a Powermite control for flammable vapors. The Powermite also makes it easier to control the temperature.
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Q: When setting up the distillation apparatus, can I use an Erlenmeyer flask for the receiving flask?
Yes, but there are less organic vapors if you use a small round bottom flask.
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Q: How much does boiling point vary with atmospheric pressure?
For most organic liquids, there is a decrease of 0.5 oC with every 10 torr difference from 760 torr
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Q: If the atmospheric pressure is 695 torr today, does that mean the actual boiling point of this liquid is listed in the literature at a higher value than the temperature I saw, even after I corrected the temperature for my thermometer?
Yes. Boiling points are usually recorded as the temperature at 760 torr. Given that, observed boiling point is lowered by 0.5 oC for every 10 torr difference below 760 torr. This means that at 695 torr, the boiling point of your liquid is actually 3.3 oC higher than the temperature you observed during distillation.
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