CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2013/14
Module Title:
Chemical Principles (CA)
Module Code:
CHEM 6002
School :
Science
Programme Title:
BSc in Applied Physics & Instrumentation
BSc (Honours) in Instrument Engineering
Programme Code:
SPHYS_7_Y1
SINEN_8_Y1
External Examiner(s):
Internal Examiner(s):
Dr. Carmel Roche
Dr. W. Doherty
Instructions: Answer THREE questions in total.
Answer Question 1 and two other questions.
Show all calculations on the examination script
Duration:
2 Hours
Sitting:
Autumn 2014
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have
received the correct examination.
If in doubt please contact an Invigilator.
Q1
This Question is compulsory. You must attempt this question.
In an experiment to determine the percentage ammonia in “Liquid Ammonia” a
sulphuric acid solution is first standardised by a primary standard, sodium bicarbonate,
which is then used to determine the ammonia. The reactions involved are:
Na2CO3 (aq) + H2SO4 (aq) ⟶
2 NH3 (aq)
(a)
Na2SO4(aq)
+ H2O(l) + CO2(g)
+ H2SO4 (aq) ⟶ (NH4)2SO4(aq)
Explain what is meant by a primary standard. What characteristics are
desirable in a primary standard and why?
(b)
(10 Marks)
A primary standard base, sodium carbonate (Na2CO3) is titrated against a
sulphuric acid solution (H2SO4). The procedure is outlined as follows:
2.6g of Na2CO3 was weighed out and dissolved in deionised water and
made up to the mark in a 250cm3 volumetric flask. Three 20cm3 aliquots
of this Na2CO3 solution were titrated against H2SO4 giving the following
titres:
Titre No
Volume of H2SO4(aq) (cm3)
1
9.9
2
9.8
3
9.7
(i.) The indicator used was methyl orange. What is the colour change
indicating the end-point?
(ii.) Calculate the mol.dm-3 concentration of the Na2CO3 solution prepared.
(iii.) Calculate the number of moles of Na2CO3 solution used in the 20cm3
aliquot.
(iv.) Deduce the number of moles of H2SO4 used in the titration from the
reaction equation above.
(v.) Calculate the mol.dm-3 concentration of the H2SO4 solution.
(15 Marks)
....Continued overleaf
(c)
In a second set of reactions, 10.0g of liquid ammonia was dissolved and
made up to 250cm3 in the usual way. The average H2SO 4 titration value
for a 20cm3 aliquot of liquid ammonia solution was 9.8cm3.
(i.) Draw a labelled diagram showing the apparatus used in this titration,
indicating which solutions are in which pieces of glassware.
(ii.) Calculate the number of moles of H2SO4 used in the titration.
(iii.) Deduce the number of moles of NH3 in the 20cm3 aliquot.
(iv.) Calculate the mol.dm-3 concentration of NH3 in the “Liquid Ammonia”
solution used in the titration
(15 Marks)
Q2.
(a)
Two types of chemical bonding that exist are covalent bonding and ionic
bonding.
(i.) Discuss covalent and ionic bonds, highlighting the differences between
them.
(ii.) What influences whether a group of atoms will form an ionic or covalent
bond?
(iii.) List the following molecules as either covalent of ionic, stating your
reasons:
HCl ; CO2 ; XeCl ; CH4
(15 Marks)
(b)
The following table shows a plot of boiling points of some group 4 and
group 6 hydrogen compounds versus molar mass.
(i.) Discuss this plot explaining any trend(s) that are observed.
(ii.) Explain clearly any deviations to the trend(s) observed, detailing the
mechanism for these deviations, if any.
(15 Marks)
Q3.
(a)
(i)
What is meant by the “Octet Rule”? How does H2 satisfy this rule?
(ii)
Draw the Lewis Structure for the following atoms:
Cl
(iii)
C
O
Be
Draw the Lewis Structure for ozone, O3.
(12 Marks)
(b)
(i)
Describe how VSEPR can be used to determine the shape of a
molecule
(ii)
For ozone, O3, determine the electronic group geometry.
(iii)
For O3, determine the molecular group geometry and draw it.
(18 Marks)
Q4.
(a)
(i)
Explain, using diagrams to illustrate your answer, what is meant by
the Aufbau Principle?
(ii)
What is the Pauli exclusion Principle?
(iii)
What is Hund’s Rule?
(iv)
Give the electronic configuration of the following atoms:
C
N+
O2-
Na
Cu
(15 Marks)
(b)
(i)
Explain concisely the following tems: isotopes, allotropes and
mole.
(ii)
What are the 3 subatomic particles that make up an atom?
(iii)
List the numbers of each of the subatomic particles for the
following atoms:
(iv)
23
13
Mg
C
37
C
From the following table, detrmine the average atomic mass of Si.
Isotope
Mass [amu]
Abundance [%]
28
27.97693
92.23
29
28.97649
4.68
30
29.97377
3.09
Si
Si
Si
(15 Marks)