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Chem 104: Chemical Bonding And Structure Question Paper
Chem 104: Chemical Bonding And Structure
Course:Bachelor Of Science
Institution: Catholic University Of Eastern Africa question papers
Exam Year:2015
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ISO 9001:2008 Certified by the Kenya Bureau of Standards
THE CATHOLIC UNIVERSITY OF EASTERN AFRICA
MAIN EXAMINATION
AUGUST - DECEMBER 2015 TRIMESTER
FACULTY OF SCIENCE
DEPARTMENT OF CHEMISTRY
REGULAR PROGRAMME
CHEM 104: CHEMICAL BONDING AND STRUCTURE
Date: DECEMBER 2015 Duration: 2 Hours
INSTRUCTIONS: Answer Question ONE and ANY OTHER TWO Questions
Q1. a) Classify each statement as an observation, a law or theory
i All matter is made of tiny, indestructible particles called atoms
ii When iron rusts in a closed container, the mass of the container
and its contents does not change.
Iii In chemical reactions, matter is neither created nor destroyed.
Iv When a match burns, heat is released. (2 marks)
b) Determine whether each change is physical or chemical. What kind of property (chemical or physical ) is demonstrated in each case.
i A copper wire is hammered flat.
ii Dry ice sublimes (ie changes from solid to gas) without melting.
iii The bleaching of hair with hydrogen peroxide.
iv The burning of lamp oil / paraffin. (2 marks)
P.O. Box 62157
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A. M. E. C. E. A
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c) Gallium is a solid metal at room temperature, but will melt to a liquid in
your hand. The melting point of gallium is 85.60F. What is this temperature
on;
i The Celsius scale
ii The Kelvin scale. Express final answers in correct significant
figures. (2 marks)
d) Describe Rutherford’s gold foil experiment (draw a sketch to help explain)
How did the experiment show that the plum-pudding model of the atom
was wrong? (3 marks)
e) Arrange these ionic compounds in order of increasing magnitude of lattice
energy: CaO, KBr, SrO, KCl (2 marks)
f) How many protons and neutrons are present in an atom of K
39
19
(1 mark)
g) Sulphuric acid is a component of acid rain formed when gaseous sulfur
dioxide pollutant reacts with gaseous oxygen and liquid water to form
aqueous sulphuric acid. Write a balanced chemical equation for this
reaction.
(2 marks)
h) Titanium metal can be obtained from its oxide according to the following
balanced equation
TiO2(s) + 2C(s) Ti(s) + 2CO(g)
When 28.6kg of C reacts with 88.2kg of TiO2, 42.8kg of Ti is produced. Find the
limiting reactant theoretical yield in (kg) and percent yield. (4 marks)
i) Write complete ionic and net ionic equations for the following reaction
occurring in
2AgNO3(aq) + MgCl2(aq) 2AgCl(s) + Mg(NO3)2(aq)
(2 marks)
j) Determine the wavelength of light absorbed when an electron in a
hydrogen atom makes a transition from an orbital in which n = 2 to an
orbital in which n = 7. Place final answer in appropriate units. (4 marks)
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k) List the quantum numbers associated with all of the 5d orbitals. How many 5d orbitals exist? (2 marks)
l) What is ionization energy? What is the general trend in ionization energy as you move down a column in the periodic table? As you move across a row? Explain the trends. (2 marks)
m) Determine whether NH3 is polar. (2 marks)
Q2. a) What are the atomic number, mass number and symbol for the carbon isotope with 7 neutrons. (2 marks)
b) Magnessium has three naturally occurring isotopes with masses of 23.99 amu 24.00 amu and 25.98 amu and natural abundance of 78.99%, 10.00% and 11.01% respectively. Calculate the atomic mass of magnesium. (4 marks)
c) Arrange the following colors of visible light-green, red and blue in order of increasing
i Wavelength
ii Frequency
iii Energy per photon (4 marks)
d) Define the deBroglie wavelength of an electron. Calculate the wavelength of an electron travelling with speed of 2.65 x 106 m/s (4 marks)
e) Write the electron configuration and orbital diagram for each ion and determine whether it is diamagnetic or paramagnetic
i Al3+
ii Fe3+ (2 marks)
f) Name an element in the fourth period (row) of the periodic table with
a) Five valence electrons
b) Four 4p electrons
c) Three 3d electrons
d) A complete outer shell. (4 marks)
Q3. a) Write a Lewis structure for each of the following NH4+ ion, CO2 and NH3
(3 marks)
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b) Identify the reducing agent and the oxidizing agent in the oxidation reduction reaction below and balance it
Mg(s) + N2 (g) Mg3 N2 (s) (3 marks)
c) Assign formal charges to each atom in the resonance forms of the cyanate ion (OCN-). Which resonance form is likely to contribute most to the correct structure of OCN-? (4 marks)
d) How many ml of 0.155M Kcl solution contains 2.55g KCl? (2 marks)
e) Acetic acid (C2H4O2) is the active ingredient in vinegar. Calculate the mass percent composition of oxygen in acetic acid. (3 marks)
f) A titanium cube contains 2.86 x 1023 atoms. What is the edge length of the cube? The density of titanium is 4.50g/cm3 (5 marks)
Q4. a) What is the hybridization for BrF3 (show the Lewis structure and your work. (2 marks)
b) Use molecular orbital theory to predict the bond order of H2- Is the H-2 bond a stronger or weaker bond than the H2 bond? (4 marks)
c) Order these compounds in order of increasing carbon-carbon bond strength and in order if decreasing carbon-carbon bond length:
HCCH, H2CCH2, H3CCH3. Show your work. (4 marks)
d) Determine whether a bond between each pair of atoms would be pure covalent, polar covalent or ionic
i Br and Br
ii C and Cl (2 marks)
e) Hydrogen gas, a potential fuel, can be made by the reaction of methane gas and steam. Use bond energies to calculate ?H rxn for this reaction.
CH4(g) + 2H20(g) 4H2(g) + C02(g) (8 marks)
See table in the typed print out
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Q5. a) Distinguish between a complex ion and a coordination compound. Give an example of each of these ( a structure or formular should suffice)
(2 marks)
b) Define monodentate ligand, bidentate ligand, polydentate ligand and chelating agent, give an example of each (structure or formular)
(4 marks)
c) In the emission spectra, which transition will result in emitted light with the shortest wavelength? Explain
i n = 5 n = 4
ii n = 4 n = 3
iii n = 3 n = 2 (2 marks)
d) Write the correct formular for
i Hexaamminechromium(III)
ii Potassium hexacyanoferrate(III) (2 marks)
e) What is the Born – Harber cycle? Use the Born – Haber cycle to find the lattice energy of Nacl
Ionization energy of Na to Na+(g) IEI = +496kJ/mol
Ionization energy of Na to Na2+IE2 = +4560kJ/mol (10 marks)
Electron affinity of Cl to Cl-, EA = -349kj/mol
See table in the typed print out
*END*
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