CHE 110: PRACTICAL INTRODUCTORY ORGANIC CHEMISTRY Questions and answers part 1
QUESTIONS
1. a) Define boiling point and Distillation
b) List any FOUR() types of distillation
C) What is the function of the boiling chip in the distilling flask during distillatio?
d) Cyclolhexane and cyclohexene has the boiling points 81.4°C and 83.0PC respectively.
i) How would you separate a mbture of the two liquids?
ii) Describe a simple chemical test to distinguish between the two liquids
2. Using a flow chart diagram, show how you would separate a mixture of Benzoic acid,
Naphthalene and Aniline. [HINT: Benzoic acid is acidic, Naphthalene is neutral and
Aniline is basic]
3. a ) As a Forensic chemist, explain the results of the following errors during TLC
analysis:
i) polarity of the solvent system is too high
ii) too much solvent in the developing jar
iii ) forgetting to mark the solvent front immediately after the removal of the plate from
the developing chamber
b) Namne the TWO (2) most common adsorbents that serves as stationary phase in
Thin-layer and column chromatography.
c) State THREE (3) different ways of visualizing colorless spots in analysis.
d) State FOUR (4) applications of Thin-layer chromatography in an organic chemistry.
SOLUTIONs
1. a) Boiling Point: The boiling point is the temperature at which the vapor pressure of a liquid becomes equal to the external pressure, resulting in the formation of vapor bubbles within the liquid. At this temperature, the liquid turns into vapor.
Distillation: Distillation is a separation process that involves the use of heat to separate components of a liquid mixture based on their differences in boiling points. It involves boiling the mixture and then condensing the vapor formed into a separate container to collect the desired components.
b) Four types of distillation are:
1. Simple distillation
2. Fractional distillation
3. Steam distillation
4. Vacuum distillation
c) The function of boiling chips in the distilling flask during distillation is to promote controlled and even boiling by providing nucleation sites for the formation of bubbles, which prevents superheating and violent boiling (bumping) of the mixture.
d) i) To separate a mixture of cyclohexane (boiling point 81.4°C) and cyclohexene (boiling point 83.0°C), fractional distillation would be used, as it is a technique well-suited for separating components with close boiling points.
ii) A simple chemical test to differentiate between cyclohexane (an alkane) and cyclohexene (an alkene) is the bromine water test. When added to cyclohexene, the bromine water (orange) would undergo decolorization due to the formation of a dibromide, while there will be no color change in the case of cyclohexane.
2. Flowchart for the separation of Benzoic acid, Naphthalene and Aniline:
[START]
|
\/
(Mixture of Benzoic acid, Naphthalene, and Aniline)
|
\/ (Add dilute HCl)
(Mixture of Benzoic acid salt, Naphthalene, and Aniline)
|
\/ (Filter out the salt)
(Benzoic acid salt)
|
\/ (Add dilute NaOH)
(Benzoic acid)
Meanwhile, from the filtrate of Benzoic acid salt:
(Naphthalene and Aniline mixture)
|
\/ (Add dilute NaOH)
(Mixture of sodium naphthalene, Aniline + water)
|
\/ (Extract with ether)
(Naphthalene, ether layer) (Aniline, water layer)
|
\/ (Evaporate ether)
(Naphthalene)
|
\/ (Add dilute HCl)
(Aniline)
3. a) Errors during TLC analysis:
i) If the polarity of the solvent system is too high, the spots will move too quickly, possibly reaching the solvent front, making separation and analysis difficult.
ii) Too much solvent in the developing jar can cause poor separation, as it may cause the spots to become less concentrated or diffuse.
iii) Forgetting to mark the solvent front immediately after removing the plate may lead to inaccurate measurements of Rf values, as the solvent might evaporate, and the location of the solvent front can be lost.
b) The two most common adsorbents that serve as stationary phases in thin-layer and column chromatography are:
1. Silica gel (SiO2)
2. Aluminum oxide (Al2O3)
c) Three different ways of visualizing colorless spots in analysis are:
1. Using a UV lamp to detect fluorescent spots.
2. Iodine vapor staining, which forms colored complexes with the analyte.
3. Chemical staining, for instance, using a potassium permanganate solution or ninhydrin.
d) Four applications of thin-layer chromatography in organic chemistry are:
1. Identification of components in a mixture.
2. Monitoring the progress of a chemical reaction.
3. Determining the purity of a compound.
4. Comparing the components of different samples to establish similarity or difference.
