UNIVERSITY OF LIMPOPO
FACULTY OF SCIENCE AND AGRICULTURE
SCHOOL OF PHYSICAL AND MINERAL SCIENCES
DEPARTMENT OF CHEMISTRY
DEGREE AND DIPLOMA EXAMINATION
MAY/JUNE: 2019
MODULE:
PAPER: P
SCHM011
(GENERAL CHEMISTRY 1A)
TIME:
3 HOURS
MARKS:100
INTERNAL EXAMINERS: MS MP MOTHAPO
MR BN MBOKANE
DR LV MULAUDZI
PROF MJ HATO
SECOND EXAMINER:
DR LE MACEVELE
THIS PAPER CONSISTS OF…13…PAGES INCLUDING COVER PAGE
INSTRUCTIONS:
1. Answer all questions.
2. Start each question on a NEW page.
3. Write neatly and legibly using BLUE or BLANK ink ONLY.
4. Answer Section A on Multiple Choice Answer Sheet.
5. Section B and C must be answered on two Separate Answer Books.
6. Use of fluid eraser is prohibited.
7. The Periodic Table and Data Sheets are given.
8. Report your answer to correct number of significant figures with conversion
factors explicitly shown.
SCHM011
MAY/JUNE EXAMINATION
2019
SECTION A
1. There are _____________ cubic inches in 1.0 L. Note: 1 in. = 2.54 cm.
(a)
155
(b)
61.0
(c)
394
(d)
1.64 x 104
(e)
3.83 x 102
2. The SI derived unit for area is_______________.
(a)
Square centimeter
(b)
Square yard
(c)
Square kilometer
(d)
Square meter
(e)
Pascal
(2)
(2)
3. The boiling point of a liquid was measured in the laboratory with the following results:
Trial
Boiling Point
22.0 ºC ∓ 0.1
1
22.1 ºC ∓ 0.1
2
21.9 ºC ∓ 0.1
3
The actual boiling point of the liquid is 28.7 C. Results of the obtained boiling point
are_________________.
(a)
Accurate and precise.
(b)
Precise but inaccurate.
(c)
Accurate and not precise.
(d)
Inaccurate and not precise.
(e)
None of the above.
2|Page
(2)
SCHM011
MAY/JUNE EXAMINATION
2019
4. Which one of the following properties is a chemical property___________.
(a)
Combustibility
(b)
Volatility
(c)
Viscosity
(d)
Malleability
(e)
Ductulity
5. Distillation can readily be used to separate__________________.
(a)
the elements in a compound.
(b)
a heterogenous mixture.
(c)
a homogeneous mixture.
(d)
iron filings.
(e)
a liquid solvent from a dissolved solid.
(2)
(2)
6. What is the mole fraction of hydrogen in a gaseous mixture that consists of 8.00 g of
hydrogen and 12.00 g of neon in a 3.50 L container maintained at 35.20 °C?
(a)
0.150
(b)
0.870
(c)
0.930
(d)
0.660
(e)
0.400
7. In a bomb calorimeter, the reactions are carried out at_____________.
(a)
1 atm and 25 °C
(b)
at constant pressure
(c)
at constant volume
(d)
at constant volume and 0 °C
(e)
None of the above
3|Page
(2)
(2)
SCHM011
MAY/JUNE EXAMINATION
2019
8. A real gas behaves most nearly like an ideal gas under condition of_______.
(a)
(2)
Low temperature and high pressure
(b) Low temperature and low pressure
(c)
High temperature and high pressure
(d) High temperature and low pressure
(e)
Actually it will behave like an ideal gas regardless of the conditions as long as
it remains in the gaseous state.
9. The criterion for a spontaneous chemical reaction is________.
(a)
(2)
∆G = 0
(b) ∆H > 0
(c)
∆S > 0
(d) ∆E > 0
(e)
∆G < 0
10. If a reaction involving a single reactant is first order with a rate constant of
4.50
x 10-2 s-1, how much time is needed for 75.0 % of the initial quantity of reactant to be
used up?
(a)
(2)
16.7 seconds
(b) 30.8 seconds
(c)
23.1 seconds
(d) 25.3 seconds
(e)
11.6 seconds
11. Chemical Equations are balanced to_______________.
(a)
(2)
show the number of atoms in their physical state
(b) show the same number of atoms of each element changing into new
compounds
(c)
show the same number of atoms of each element on each side
(d) show how the number of atoms of each element differ on each side
(e)
4|Page
show the same number of atoms of only elements that form the product
SCHM011
12.
MAY/JUNE EXAMINATION
2019
For the following reaction, AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Give the net reaction__________________.
(a)
(2)
Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq)  AgCl (s) + Na+ (aq) + NO3- (aq)
(b) Ag+ (aq) + NO3- (aq)  NaNO3 (s)
(c)
Ag+ (aq) + Cl- (aq)  AgCl (s)
(d) Ag+ (aq) + NO3- (aq) + Na+ (aq) + Cl- (aq)  AgCl (aq) + Na+ (aq) + NO3-(aq)
(e)
No reaction
13. The calculated hydroxide ion concentration at 25 °C in 1.4 × 10-4 M Mg(OH)2
is_______________.
(a)
(2)
1.4 × 10-4 M
(b) 1.4 × 10-2 M
(c)
0.7 × 10-4 M
(d) 2.8 × 10-4 M
(e)
0.7 × 10-2 M
14. The equivalence point is_________________.
(a)
When stoichiometric balanced moles of base or acid are added.
(b) When equal amounts of acid and base are added.
(c)
When the indicators changes
(d) When the indicator changes colour.
(e)
5|Page
When the indicator can no longer change colour.
(2)
SCHM011
15. All
of
2019
MAY/JUNE EXAMINATION
the
following
statements
about
chemical
equilibrium
except_________________.
(a)
are
true
(2)
At equilibrium, the reactant and the product concentrations show no further
change with time.
(b) A true chemical equilibrium can only be attained starting with reagents from
the reactant side of the equation.
(c)
At equilibrium, the forward reaction rate equals the reverse reaction rate.
(d) The same equilibrium state can be attained starting either from the reactant or
product side of the equation.
(e)
At equilibrium, the reactant and product concentrations are constant.
16. A study of the system, 4NH3 (g)+ 7O2 (g) ↔ 2N2O4(g) + 6H2O (g), was carried out.
A system was prepared with [NH3] = [O2] = 3.60 M as the only components initially. At
equilibrium,
[N2O4]
is
0.60M.
Calculate
NH3___________.
(a)
the
equilibrium
concentration
of
(2)
3.00 M
(b) 2.10 M
(c)
3.30 M
(d) 1.80 M
(e)
2.40 M
17. The cell notation for the reaction, Cu(s) + Zn2(aq)+ ↔ Cu2+(s)+ Zn(s) is_________.
(2)
(a)
Cu(s) | Cu2+(aq) | Zn2+(aq) | Zn(s)
(b) Cu(aq) | Cu2+(s) || Zn2+(aq) | Zn(s)
(c)
Cu(s)2+ | Cu(s)(aq) || Zn2+(aq) | Zn(s)
(d) Cu(s) | Cu2+(aq) || Zn2+(aq) | Zn(s)
(e)
6|Page
Cu(s) || Cu2+(aq) || Zn2+(aq) | Zn(s)
SCHM011
MAY/JUNE EXAMINATION
2019
18. A solute is____________.
(a)
(2)
That component of a solution in greater proportion.
(b) That component of a solution in smaller proportion.
(c)
That component of a solution in a liquid state.
(d) That component of a solution in a solid state.
(e)
That component of a solution in the same state as the solvent state.
19. The oxidation number of Cr in dichromate, Cr2O72- is_____________.
(a)
(2)
2
(b) 2(c)
6
(d) 12
(e)
5
20. AFe (s) + BO2 (g)  C Fe2O3 (s)
When the above equation is balanced, the stoichiometry relationship as
displayed by A:B:C will follow the following pattern___________.
(a)
1:2:1
(b) 4:3:2
(c)
2:3:2
(d) 3:2:1
(e)
3:2:3
[20 x 2 = 40]
7|Page
(2)
SCHM011
MAY/JUNE EXAMINATION
2019
SECTION B (ANSWER ON A SEPARATE ANSWER BOOK)
QUESTION 1
(a) Why is the actual yield in a reaction almost always less than the theoretical yield?
(2)
(b) An element analysis of an organic acid with the molar mass of 136 g/mol exhibits
that it comprises of 5.89% hydrogen, 70.6% carbon and 23.5% oxygen by mass. What
is the molecular formula of the organic acid?
(6)
(c) Nitrogen can be synthesised by passing gaseous ammonia (NH3) over solid
copper(II) oxide (CuO) at high temperatures. The other products of the reaction are
solid copper (Cu) and water vapour? If the sample containing 18.1 g of NH3 is reacted
with with 90.4 g of CuO, determine the limiting reactant in this reaction.
(6)
[14]
QUESTION 2
(a) List the four variables or factors that can affect the rate of a chemical reaction.
(4)
(b) When a student mixes 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH in a coffeecup calorimeter, the temperature of the resultant solution increases from 21.0 to 27.5
°C. Calculate the enthalpy change for the reaction in kJ/mol HCl, assuming that the
calorimeter loses only a negligible amount of heat if the total volume of the solution is
100 mL, its density is 1.0 g/mL and the specific heat is 4.18 J/g.K.
(8)
(c) The standard free energy of formations for NO2 (g) and N2O4 (g) at 25 °C are 51.30
kJ/mol and 97.82 kJ/mol, respectively. Calculate the value of the thermodynmic
equilbrium constant at this temperature for the following reaction.
N2O4 (g)
8|Page
⇌
(4)
2NO2 (g)
[16]
SCHM011
MAY/JUNE EXAMINATION
2019
SECTION C (ANSWER ON A SEPARATE ANSWER BOOK)
QUESTION 1
(a) Explain the following terms.
(i)
Saturated solution
(1)
(ii) Voltaic cell
(1)
(iii) Buffer
(1)
(iv) Le Châtelier’s Principle
(1)
(v) Molality
(1)
(b) Aunt Josephina prepares a solution of sodium chloride in water with a concentration of
0.154 M NaCl to clean a cut in Thabo’s right thumb. The total mass of the solution is
500 g.
(i) How many moles of NaCl are contained in 500.00 mL of physiological saline?
(2)
(ii) How many grams of NaCl are in the 500.00 mL of solution?
(2)
(iii) What is its molality?
(1)
(iv) Is this solution a strong electrolyte?
(1)
(c) At 448 °C, the equilibrium constant Kc for the reaction given below is 50.5.
H2 (g) + I2 (g) ⇌ 2HI (g)
Predict in which direction the reaction will proceeds to reach equilibrium if you
start with 2.0 x 10-2 mol HI, 1.0 x 10-2 mol of H2 and 3.0 x 10-2 mol of I2 in a
2000 mL container.
(5)
[16]
9|Page
SCHM011
MAY/JUNE EXAMINATION
2019
QUESTION 2
(a) Calculate the pOH and the pH of a solution in which 15.5 mL of 0.100 M HCl is added
to 25.0 mL of 0.150 M NaOH.
(6)
(b) For the Zn/Cu2+ voltaic cell and given that the standard reduction potential of Zn2+ to
Zn(s) is - 0.76 V
Zn (s) + Cu2+ (aq, 1 M) Zn2+ (aq, 1 M) + Cu (s) E°cell = 1.10 V
Calculate the standard reduction potential (E° red) for the reduction of Cu2+ to
Cu (Cu2+ (aq, 1.0 M) + 2 e → Cu(s)
(3)
(c) Glycerin (C3H8O3) is a non-volatile nonelectrolyte with a density of 1.26 g/mL at 25
°
C.
Calculate the vapour pressure at 25 °C of a solution made by adding 50.0 mL of
glycerine to 500.0 mL of water. The vapour pressure of pure water at 25 °C is 23.8 torr
and its density is 1.00 g/mL.
(5)
[14]
10 | P a g e
SCHM011
11 | P a g e
MAY/JUNE EXAMINATION
2019
SCHM011
MAY/JUNE EXAMINATION
TABLE 1: Standard entropies at 25 ºC
12 | P a g e
2019
SCHM011
13 | P a g e
MAY/JUNE EXAMINATION
2019