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Dce0016:Chemistry Question Paper
Dce0016:Chemistry
Course:Diploma In Civil Engineering
Institution: Meru University Of Science And Technology question papers
Exam Year:2013
INSTRUCTIONS: Answers Question one and any other two questions
QUESTION ONE – (30 MARKS)
(a) Give three properties of cathode rays. (3 Marks)
(b) Define the term:
(i) Isotope (1 Mark)
(ii) Mass number (1 Mark)
(c) (i) An electron makes a transition from the n=4 state to the n=2 in a hydrogen atom.
Calculate the wavelength in nanometers of a photon that is emitted when this transition
occurs. (5 Marks)
[RH = 1.9097 x 107m-1 c = 3.0 x 108ms-1]
(ii) State Pauli’s exclusion principle of maximum multiplicity. (2 Marks)
(d) Using the inert gas core, write the electronic configuration of the following elements.
(3 Marks)
(i) K (z = 19)
(ii) P (z = 15)
(iii)Al (z = 13)
(e) Use Lewis symbols to show the bonding between:
(i) Oxygen and hydrogen to form a molecule of water. (2 Marks)
(ii) Oxygen and carbon to form a molecule of Carbon dioxide. (2 Marks)
(iii) Nitrogen and hydrogen to form the ammonium ion (2 Marks)
[H = 1, C = 6, N = 7, O = 8]
(f) Give the properties and nature of
(i) The ?–rays (3 Marks)
(ii) ?? -particles (3 Marks)
(g) The concentration of H+ ions in a solution is 1.92 x 10-5 mole per liter. What is the pH of
the solution? (3 Marks)
QUESTION TWO – (15 MARKS)
(a) Magnesium burns in air to form a white solid.
(i) Identify the products of the combustion of magnesium in air. (2 Marks)
(ii) Write balanced chemical equations to show the reaction of the products in (i)
above with water. (4 Marks)
(b) The element of Lithium, Z = 3 differs from the rest of the alkali metals of group IA and
its properties resemble those of the group IIA elements.
(i) Write the electronic configuration of Lithium. (1 Mark)
(ii) Draw the orbital diagram of the Lithium atom. (1 Mark)
(iii)In what ways do Lithium and Magnesium resemble? (7 Marks)
QUESTION THREE – (15 MARKS)
(a) The autoionization of pure water is written in the form: H2O + H2O ? H3O+ + OH-
(i) Write an expression for the equilibrium constant for water. (1 Mark)
(ii) Given that the expression for the ionic product constant,
Kw = [H+] [OH-] = 1.0 x 10-14. Determine the pH of pure water. (2 Marks)
(b) The mole solution of a solution of HCl is given as 0.001M. calculate:
(i) The concentration of OH- ions (2 Marks)
(ii) The concentration of H+ ions (2 Marks)
(iii)The pOH of this solution. (2 Marks)
(c) (i) What is a buffer solution? (1 Mark)
(ii) Using water, hydrochloric acid and Sodium hydroxide briefly explain the action of a
buffer. (2 Marks)
(iii) A buffer solution is made by adding ethanoic (acetic) acid and sodium ethanoate
(Sodium acetate) until the concentration of each is 0.1 mole per litre. Given that Ka = 1.8
x 10-5. Calculate the pH of the buffer solution formed by mixing both ethanoic acid and
sodium ethanoate. (3 Marks)
QUESTION FOUR – (15 MARKS)
(a) Explain giving examples the following terms as applied in thermodynamics
(i) A system (1 Mark)
(ii) Adiabatic process (1 Mark)
(iii)Exothermic reaction. (1 Mark)
(b) (i) State Hess law of heat summation. (1 Mark)
(ii) Given that the following thermochemical equations:
NO(g) + O3(g) ? NO2(g) + O2(g) ? H = -198.9 KJ mol-1
O3(g) ?
3
2
O2(g) ? H = -142.3KJ mol -1
O2(g) ? 2O(g) ? H = +495 KJ mol-1
Determine the enthalpy change for the reaction:
NO(g) + O(g) ? NO2(g) ?H = ? (5 Marks)
(c) Acetylene (ethyne) is a very useful gaseous hydrocarbon which is used together with
oxygen for welding. Acetylene can be formed from its constituent elements. Using the
following information, determine the standard enthalpy of formation of acetylene (C2H2)
from its constituent elements. (6 Marks)
C(graphite) + O2(g) ? CO2(g) ?H° = -393.5 KJ
H2(g) +
1
2
O2(g) ? H2O(l) ?H° = -285.8 KJ
2C2H2(g) + 5O2(g) 4CO2(g) +2H2O(l) ?H° = -2598.8 KJ
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