DIT VOMP3003 Chemistry Assignment: Problem Sheet Solution

This document provides a comprehensive solution to a chemistry assignment from the School of Chemical & Pharmaceutical Sciences, focusing on the fundamentals of chemistry for active pharmaceutical ingredients. The assignment covers key concepts including the Brønsted-Lowry definition of acids and bases, structural isomerism, and homologous series. It also includes a discussion on the amphoteric nature of water, acting as both an acid and a base. Furthermore, the solution provides structural formulas for various organic compounds such as pentane, propane, ethene, 3-hexene, and 4-decene. Finally, the document includes a short note on the pH scale and its significance in determining the acidity or alkalinity of aqueous solutions. The solution is well-structured, providing detailed explanations and examples to aid understanding of the concepts.

e-(Bio)PharamChem
School of Chemical
& Pharmaceutical
Sciences
Fundamentals of Chemistry for
Active Pharmaceutical Ingredients
DIT Course Code: VOMP3003
Problem Sheet
Student Name:____________________________________
VOMP3003 Problem
Sheet
Lesson 4
and 5
Rev. 001 Page 1

e-(Bio)PharamChem
Answer all Questions
1. Explain in your own words, giving suitable examples the Brønsted- Lowry
definition of acids and bases [25 marks]
The Brønsted–Lowry theory of acids and bases was proposed in the year 1923.
The definition for acids and bases was based on their way of interaction with each
other. An equilibrium expression is used to express the rection between acids and bases.
According to this theory, a Brønsted-Lowry acid is a specieis that is a proton donor. On
the other hand, a Brønsted-Lowry base is a species that is a proton acceptor. While the
acids are capable of donating an H+ ion, the bases are capable of accepting the H+ ion,
with the help of lone pairs of electrons (Stoyanovich, Gandhi and Flynn 2014).
2. Write a note on structural isomerism in Organic Chemistry [25 marks]
Isomerism refers to the phenomenon, exhibited by several compounds that have
similar molecular formula and contain similar number of atoms, however differ in the
spatial arrangement of the atoms. Structural isomerism, also known as constitutional
isomerism usually refers to the condition where molecules with similar molecular
formula have different atomic organisation and patterns of bonding. This differs from
stereoisomerism in the context that the latter differs only in the spatial arrangement of
atoms. Structural isomerism can therefore arise due to differences in the arrangement of
the carbon skeleton, cyclic and acyclic molecules, functional groups, or position of the
functional groups (Li et al. 2012).
3. Write a short note describing a homologous series in Organic Chemistry.
[10 marks]
Homologous series refers to series of compounds that have similar general formula,
which usually varies on the basis of a single parameter. This concept of homologous
series was proposed by Charles Gerhardt in the year 1843. The parameters can be
length of a carbon chain or the number of monomers in the context of straight-chain
alkanes like paraffin and amylase respectively. Thus, alkenes, alkanes and cycloalkanes
belong to the homologous series. The compounds listed as homologous series are
generally categorised on the basis of their increasing size. These compounds have fixed
functional groups that impart similar physical and chemical properties (Brescia 2012).
4. Water can act as both and Acid and a Base – discuss this, giving examples
[25 marks]
Water molecules function as both bases and acids. Water molecules are capable
of donating a proton (H+) to the neighbouring water molecules, thereby forming
hydroxyde and hydronium ions.
H2O+H2O⇌H3O++OH−
Under certain circumstances, water molecules accept proton, thereby acting as
Brønsted-Lowry bases. This can be explained by the fact that upon dissolving a
molecule of hydrogen chloride in water, HCl donates a proton that is accepted by the
water molecule, which acts as a Brønsted-Lowry base.
VOMP3003 Problem
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e-(Bio)PharamChem
HCl(g)+H2O(l)⇌H3O+(aq)+Cl−(aq)
On the other hand, water acts as a Brønsted-Lowry acid by donating a proton to
ammonia, thereby helping in the formation of ammonium ions (Gschwend 2016).
NH3(aq)+H2O(l)⇌NH4+(aq)+OH−(aq)
5. Write a structural formula showing Carbon and Hydrogen bonds for the
following: [ 5 marks]
i. Pentane- This organic compound contains the general formula
C5H12 and is a component of fuels.
CH3-CH2-CH2-CH2-CH3
ii. Propane- It is a 3-carbon alkane and has the general formula
C3H8.
CH3-CH2-CH3
iii. Ethene- Ethene or ethylene is a colourless flammable gas with
the molecular formula C2H4.
H2C=CH2
iv. 3-Hexene- It has the molecular formula C6H12.
CH3-CH2-CH=CH-CH2-CH3
v. 4-Decene- It has the general formula C10H20.
CH3-CH2-CH2-CH2-CH2-CH=CH-CH2-CH2-CH3
6. Write a short note on the pH scale [10 marks]
This is a numerical scale that is basically used for determining the alkalinity or
acidity of an aqueous solution. pH refers to the negative logarithm to the base of 10 of
the molar concentration, and is usually measured in units of moles per litre of hydrogen
ions. Thus, pH can be defined as the negative logarithm to the base of 10, of the activity
of hydrogen ions. The pH scale ranges from the value of 0 to 14. A pH value of 7.0 is
considered neutral. Pure water has a neutral pH at 25 °C, owing to its amphoteric
nature. Mixing certain chemicals with water can make it acidic or alkaline by lowering
or increasing its pH. A pH less than 7 is considered acidic and that greater than 7 as
basic. Thus, pH values lower than 7 are usually 10 times more acidic than the higher
value next to it (Perrin 2012).
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e-(Bio)PharamChem
References
Brescia, F., 2012. Fundamentals of Chemistry: A Modern Introduction (1966). Elsevier,
pp.437-461.
Gschwend, P.M., 2016. Environmental organic chemistry. John Wiley & Sons, pp.35-
39.
Li, H., Giles, K., Bendiak, B., Kaplan, K., Siems, W.F. and Hill Jr, H.H., 2012.
Resolving structural isomers of monosaccharide methyl glycosides using drift tube and
traveling wave ion mobility mass spectrometry. Analytical chemistry, 84(7), pp.3231-
3239.
Perrin, D.D., 2012. Buffers for pH and metal ion control. Springer Science & Business
Media, pp.10-15.
Stoyanovich, C., Gandhi, A. and Flynn, A.B., 2014. Acid–base learning outcomes for
students in an introductory organic chemistry Course. Journal of Chemical
Education, 92(2), pp.220-229.
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