I I'IRITIIBIFI UNIVERSITY OF SCIEI'ICE FII'ID TECHNOLOGY FACULTY OF HEALTH AND APPLIED SCIENCES DEPARTMENT OF NATURAL AND APPLIED SCIENCES QUALIFICATION: BACHELOR OF SCIENCE QUALIFICATION CODE: O7BOSC LEVEL: 6 COURSE CODE: APP601$ COURSE NAME: ANALYTICAL PRINCIPLES AND PRACTICE SESSION: JULY 2017 PAPER: THEORY DURATION: 3 HOURS MARKS: 100 SUPPLEMENTARY/SECOND OPPORTUNITY EXAMINATION QUESTION PAPER EXAMINER(S) DrJULIEN LUSILAO MODERATOR: Prof OMOTAYO AWOFOLU INSTRUCTIONS 1. Answer ALL the questions in the answer book provided. 2. Write and number your answers clearly. 3. All written work MUST be done in blue or black ink. PERMISSIBLE MATERIALS Non-programmable Calculators ATTACHMENT List of Useful Tables, formulas and Constants THIS QUESTION PAPER CONSISTS OF 12 PAGES (Including this front page and List of Useful Tables, formulas and Constants)
12
Embed
SUPPLEMENTARY/SECOND QUESTION EXAMINER(S)exampapers.nust.na/greenstone3/sites/localsite...1.15 When conducting analyses of substances that are weak acids by titrating solutions with
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
I e
I'IRITIIBIFI UNIVERSITY
OF SCIEI'ICE FII'ID TECHNOLOGY
FACULTY OF HEALTH AND APPLIED SCIENCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION: BACHELOR OF SCIENCE
QUALIFICATION CODE: O7BOSC LEVEL: 6
COURSE CODE: APP601$COURSE NAME: ANALYTICAL PRINCIPLES AND
PRACTICE
SESSION: JULY 2017 PAPER: THEORY
DURATION: 3 HOURS MARKS: 100
SUPPLEMENTARY/SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S) DrJULIEN LUSILAO
MODERATOR:Prof OMOTAYO AWOFOLU
INSTRUCTIONS
1. Answer ALL the questions in the answer book provided.
2. Write and number your answers clearly.
3. All written work MUST be done in blue or black ink.
PERMISSIBLE MATERIALS
Non-programmable Calculators
ATTACHMENT
List of Useful Tables, formulas and Constants
THIS QUESTION PAPER CONSISTS OF 12 PAGES (Including this front page and List of Useful
Tables, formulas and Constants)
Question 1: Multiple Choice Questions [45]
0 Choose the best possible answer for each question.
1.1 A mass of 5.4 grams of aluminum (Al) reacts with an excess of copper (ll) chloride
(CuClz) in solution, as shown below.
3CuCl2 + 2Al 9 2AlCl3 + 3Cu
What mass of solid copper (Cu) is produced? (3)
(A) 0.65 g
(B) 8.5 g
(C) 13 g
(D) 19 g
1.2 A human patient suffering from a duodenal ulcer may show a hydrochloric acid
concentration of 0.080 mol/liter in his gastricjuice. it is possible to neutralize this
acid with aluminum hydroxide, A|(OH)3, which reacts with HCl according to the
balanced chemical equation
Al(OH)3 + 3HC| 9 AlCl3 + 3H20
If the patient's stomach receives 3.0 liters of gastric juice per day, how much
aluminum hydroxide must he consume per day to counteract the acid? (3)
(A) 6.2 g
(B) 19 g
(C) 26 g
(D) 78 g
1.3 What is the molarity ofthe sulfate ion in a solution prepared by dissolving 17.1 g of
aluminum sulfate, A|2(SO4)3, in enough water to prepare 1.00 L of solution. Neglect
any hydrolysis. (3)
(A) 1.67 x 10'2 M
(B) 5.00 x 10‘2 M
(C) 1.50 x 10'1 M
(0) 2.50 x 10'1 M
1.4 The net ionic equation for the precipitation reaction that occurs when aqueous
solutions of AgNO; and K2CrO4 are mixed is (3)
(A) K+ + N03’ ---> KN03(s)
(B) Ag+ + CrO4' ---> AgCrO4(s)
(C) K2++ N03" ---> K2N03(s)
(D) 2Ag+ + 00.3" ---> AgZCrO4(s)
1.5 A reaction for which AH < 0 and AS < 0 is most likely to have which of these
thermodynamic properties? (3)
(A) The reaction cannot be spontaneous at any temperature.
(B) The reaction will tend to be spontaneous at low temperatures.
(C) The reaction will tend to be spontaneous at high temperatures.
(D) The spontaneity of the reaction will be independent of temperature.
1.6 Consider the equilibrium reaction
4NH3(g) + 302(g) e 2N2(g) + 6H20(g) AH = -1268 kJ
Which change will cause the reaction to shift to the right? (3)
(A) Increase the temperature
(B) Decrease the volume of the container.
(C) Add a catalyst to speed up the reaction.
(D) Remove the gaseous water by allowing it to react and be absorbed by KOH.
1.7 2.00 moles of NO and an undetermined amount of 02 are placed in a 1L container
at 460°C. When the reaction
2NO(g) + 02(g) H 2N02(g)
reaches equilibrium, we find 0.00156 mol of Oz and 0.500 mol of N02. The value of
the equilibrium constant for this system is (3)
(A) 4.42
(B) 40.1
(C) 71.2
(D) 214
1.8 Consider the following reaction at equilibrium in a container of constant volume:
2502(g) + 02(g) H 2503(g) AH = -7.8 kcal
Which of the following would result in a greater concentration of 502? (3)
(A) addition of 02
(B) addition of 303
(C) removal of 503
(D) a decrease in temperature
1.9 In the reaction
6K! + 2KMnO4 + 4H20 9 Biz + 2Mn02 + 8KOH
which atom undergoes oxidation? (3)
(A) K
(B) Mn
(C) 0
(D) |
1.10 Given the standard reduction potentials
Cu2++ 2e” 9 Cu(s) E“ = +0.34 v
AI3+ + 3e" e—> AI(s) E° = —1.66 v
Calculate the standard voltage for the reaction
2Al(s) + 3Cu2+9 2Al3+ + 3Cu(s) (3)
(A) -1.22 V
(B) +2.00 V
(C) +4.34 v
(D) +5.86 v
1.11 Given the standard electrode (reduction) potentials:
Cd2*(aq) + 2e' 9 Cd(s) E" = -0.40 v
Ag+(aq) + e'-> Ag(s) E° = +0.80 V
What would be the E° for a cadmium—silver cell?
(A) 0.4 v
(B) 0.5 v
(C) 1.2 v
(D) 2.0 v
1.12 A reaction has positive values of both AS“ and AH°. From this you can deduce that
the reaction
(A) must be spontaneous at any temperature.
(B) cannot be spontaneous at any temperature.
(C) will be spontaneous only at low temperatures.
(D) will be spontaneous only at high temperatures.
1.13 The equilibrium constant for the below reaction is
Ag+(aq) + l'(aq) <9 Ag|(s) AGO = -91.9 kJ mol'1
(A) 7.78 x 10'17
(B) 1.29 x 1016
(C) 1.24 x 1037
(D) 37.1
1.14 The pH of a solution of vinegar is 3.00. The concentration of OH" ion in this
solution is
(A) 3.00 M
(B) 1 x 10'3 M
(C) 1 x 10'11 M
(D) 17 M
(3)
(3)
1.15 When conducting analyses of substances that are weak acids by titrating
solutions with a standardized strong base, the end-point indicator is chosen so
that (3)
(A) its color change occurs around the neutralization pH of 7.00.
(B) its color change occurs when the pH is about the same as the pKa of the weak acid.
(C) its color change occurs at a pH that is more basic than pH = 7.00.
(D) its color change occurs at a pH that is the same as that of the standardized base
solution.
Question 2 [8]
The Figure below shows a standard additions calibration curve for the quantitative
analysis of Mn2+. Each solution contains 25.00 mL (i.e.Vo) of the original sample and
either of 0; 2.0; 4.0; 6.0; 8.0; or 10.0 mg/L of external standard (Cstd) of an+_
All standard addition samples were diluted to 50.00 mL (Vf) before reading the
absorbance.
0.60,
0.50 :- y—intercept = flC—Avi: Vf
0.40:-
Sspike 0.305-
0202-
0.10}/0:...1...J..|..I...1.,.l...l-4.00
\-2.000 2.00 4,00 6.00 8.00 10.00 12.00
'
AC Vo Cstd x V‘sl—td (mg/L)Vf
fx-intercept =
The equation for the calibration curve in the Figure is
5..., = 0.0425 x cstdwstd/vf) + 0.1478
2.1 What is the concentration of Mn“ (CA in mg/L) in this sample? (5)
2.2 Express the obtained concentration in ppb and in molarity (M) (3)
Question 3 [10]
A researcher at NUST investigated the quantitative determination of Cr in high—alloy
steels using a potentiometric titration of Cr(Vl). A reference steel was analysed to
6
validate the used analytical method and the following results (as %w/w Cr) were