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Barcode: SCHOOL OF CHEMISTRY & PHYSICS UNIVERSITY OF KWAZULU‐NATAL, HOWARD COLLEGE CAMPUS CHEM 181: CHEMISTRY FOR ENGINEERS 1A JUNE 2013 MAIN EXAMINATION DURATION: 2 HOURS INTERNAL EXAMINER: MODERATING BOARD: Student No. Notes:
TOTAL MARKS: 75 MR A. BISSESSUR DR P. NDUNGU MS G. DAWSON Seat Number: This paper consists of 16 pages including the cover page, periodic table and two data
sheets. Please ensure that you have them all.
The use of non-programmable electronic calculators is permitted.
ANSWER ALL QUESTIONS DIRECTLY ON THE PAPER AND WHERE NECESSARY
OVER THE PAGE.
Examiner
Question 1
Question 2
Total
Internal
External
Students are requested, in their own interest, to write legibly.
Rule 9 (1)(e) WARNING: CANDIDATES WILL BE DISQUALIFIED IF: (a) they introduce, or attempt to introduce, into any place where an examination is about to be conducted or is being conducted, any paper, book, note, document or instrument, the use of which is not authorized by the examiner or the examination officer. (b) they possess, use, or attempt to use during an examination, any paper, book, note, document or instrument the use of which is not authorized by the examiner or the examination officer. (c) they remove or attempt to remove from the examination room, any examination book or writing paper supplied by the University for the purposes of answering an examination. (d) they communicate or attempt to communicate any information relating to the examination to another candidate while the examination is in progress. (e) they use a false name or identity number in an examination. (f) they commit any other fraudulent, deceitful or dishonest practice which would mislead or deceive the examiner or examination officer. IF A STUDENT IS FOUND GUILTY BY A STUDENT DISCIPLINE COURT OF CONTRAVENING THE ABOVE RULE –9(1)(e) – SHE/HE WILL SUFFER ONE OR MORE OF THE FOLLOWING CONSEQUENCES: (i) Disqualification from entry to any examination. (ii) Cancellation or forfeiture of examination results. (iii) Deprivation of a degree, diploma or certificate obtained as a result of the offence. School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 1
QUESTION 1
1.1
(MULTIPLE CHOICE)
48 MARKS
Perform the following mathematical operation expressing your answer to
the correct number of significant figures:
(7.8 m – 0.34 m) ÷ (1.150 s + 0.82 s)
1.2
1.3
1.4
(a)
3.7
m/s
(b)
3.786 m/s
(c)
3.8
(d)
3.790 m/s
m/s
(1)
Determine which one of the following calculations performed to the correct
number of significant figures is incorrect:
(a)
34.00 x 567 ÷ 4.564 = 4.22 × 103
(b)
79.3 ÷ 0.004 x 35.4 = 7 × 105
(c)
89.763 ÷ 22.4581 = 3.997
(d)
(4.32 × 1012) ÷ (3.1 × 10-4) = 1.4 × 1016
(1)
Which one of the following can be classified as a heterogeneous mixture?
(a)
A mixture of oxygen and nitrogen in a tank.
(b)
A mixture of octane and water.
(c)
A mixture of sea water and distilled water.
(d)
A mixture of ethanol and water.
(2)
Which one of the following properties can be classified as an extensive property?
(a)
Beryllium has a density of 1.85 g cm-3
(b)
The enthalpy for the formation of CO2(g) from C(s) is -393.5 kJ mol-1
(c)
The specific heat capacity of CH4(g) is 2.20 J g-1 K-1
(d)
Copper(II) sulfate turns from blue to green when excess HCl is added
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 2
1.5
In which of the following statements are both processes a result of chemical
changes?
1.6
(a)
Melts at 73oC and is soluble in water.
(b)
Sublimation of a solid at room temperature and reacts with oxygen.
(c)
Displaces hydrogen gas and is easily oxidized.
(d)
Tarnishes in air and sublimes at high temperature.
(2)
Characterise each of the following pairs of atoms as containing
(1) same number of neutrons, (2) same number of electrons or (3) same total
number of subatomic particles.
ଶଷ
ଶସ
ଵଵܰܽ and ଵଶ‫݃ܯ‬
1.7
(a)
Same number of subatomic particles (p+, no, e-).
(b)
Same number of neutrons.
(c)
Same number of neutrons and subatomic particles (p+, no, e-).
(d)
Same number of electrons and subatomic particles (p+, no, e-).
(2)
One isotope of a metallic element has a mass number of 65 and 35 neutrons
in the nucleus. The cation derived from the isotope has 28 electrons. The
cation can be identified as:
(a)
Tb2+
(b)
Tc2+
(c)
Zn2+
(d)
Ni2+
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 3
1.8
1.9
The compounds (i) N2O, (ii) P4, are classified as:
(a)
(i) molecular
(ii) atomic element
(b)
(i) ionic
(ii) ionic
(c)
(i) molecular
(ii) molecular element
(d)
(i) molecular
(ii) molecular
(2)
The empirical formula of the compounds formed by combination of
manganese(II) and chlorate is:
(a)
Mn2ClO4
(b)
Mn2ClO3
(c)
MnClO2
(d)
Mn(ClO3)2
(2)
1.10 The correct chemical formula for hydrocyanic acid is:
(a)
HOCN(aq)
(b)
HCN(aq)
(c)
H2CN(aq)
(d)
HCNO3(aq)
(1)
1.11 The correct name for the chemical formula, HOCl(aq), is:
(a)
hypochloric acid
(b)
chlorous acid
(c)
hypochlorous acid
(d)
chloric acid
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 4
1.12 The elements that will not displace H2 (g) from acids but will react with HNO3
and not produce H2(g) are:
(a)
Li, Al, Cu
(b)
Ag, Pt, Au
(c)
Ag, Zn, Ba
(d)
Pt, Cu, Ni
(2)
1.13 Which single displacement reaction shown below, is non-spontaneous?
(a)
Ca(s) + 3H2O(ℓ) → 2 Ca(OH)2(aq) + H2(g)
(b)
2 Al(s) + 3H2O (steam) → Al2O3(s) + 3H2(g)
(c)
Cu(s) + ZnSO4(aq) → CuSO4(aq) + Zn(s)
(d)
Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(ℓ)
(2)
1.14 Using solubility rules, identify the reagent that will separate the following two
ions from a mixture by precipitating one of the cations in the mixture below:
Pb2+ (aq) + Ca2+(aq)
(a)
CH3COOH(aq)
(b)
NaClO3(aq)
(c)
NaI(aq)
(d)
HNO3(aq)
(1)
1.15 Using solubility rules, identify the reagent that will precipitate one of the
anions in the mixture below:
Cl-(aq) + SO42-(aq)
(a)
KNO3(aq)
(b)
NH4Cl(aq)
(c)
Ba(NO3)2(aq)
(d)
NaCl(aq)
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 5
1.16 For liquid state samples of (i) HCl and (ii) Cl2, classify the dominant
intermolecular forces present as London forces, dipole-dipole interactions or
hydrogen bonds
(a)
(i) London dispersion forces
(ii) London dispersion forces
(b)
(i) dipole-dipole
(ii) London dispersion forces
(c)
(i) hydrogen bonds
(ii) London dispersion forces
(d)
(i) dipole-dipole
(ii) dipole-dipole
(2)
1.17 How many H atoms are in 78 g of CH3CH2OH (ethanol) (molar mass = 46.08
g mol-1) ?
(a)
1.0 x 1024
(b)
7.8 x 1024
(c)
6.1 x 1024
(d)
2.8 x 1026
(2)
1.18 An organic compound made up of carbon and hydrogen only, undergoes
combustion producing 3.14 g of CO2 (44.01 g mol-1) and 1.29 g of H2O (18.02
g mol-1). The empirical formula for this organic compound is:
(a)
CH
(b)
C2H4
(c)
CH2
(d)
C2H3
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 6
1.19 In the reaction: 2 NaOH(aq) + Cl2(g) → NaCl + 2 NaOCl(aq) + H2O(ℓ)
(molar masses in g mol-1) : NaOH = 40.0; Cl2 = 70.9; NaOCl =74.44)
The theoretical yield (in grams) of NaOCl that can be obtained from a reaction
mixture containing 75.0 g of NaOH and 50 g of Cl2(g) is:
(a)
52.5 g
(b)
69.8 g
(c)
37.5 g
(d)
49.0 g
(2)
1.20 A mixture contains 75.0 % by mass CS2 and 25.0 % by mass H2S. The
combustion reactions are:
CS2(ℓ) + 3 O2(g) → CO2(g) + 2 SO2(g)
2 H2S + 3O2(g) → 2 SO2(g) + H2O(g)
(molar masses in g mol-1) :
CS2 = 76.14; SO2 = 64.07
H2S =34.09;
CO2 = 44.00
The total number of moles of SO2 produced from the combustion of 75g of the
mixture is:
(a)
2.028 mol
(b)
1.289 mol
(c)
0.5500 mol
(d)
2.722 mol
(2)
1.21 What volume (mL) of deionized H2O must be added to 0.100 L of a 15 M
NaOH to obtain 1.00 M of NaOH?
(a)
1500 mL
(b)
1510 mL
(c)
1000 mL
(d)
1400 mL
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 7
1.22 How much 0.125 M NaOH solution (in mL) is required to completely neutralize
0.225 L of a 0.175 M H2SO4 solution?
Reaction: H2SO4(aq) + 2 NaOH(aq)  Na2SO4(aq) + 2 H2O(ℓ)
(a)
158 mL
(b)
630 mL
(c)
194 mL
(d)
315 mL
(2)
1.23 A quantity of 18.68 mL of a KOH (56.11 g mol-1) solution is needed to
neutralize 0.4218 g of potassium hydrogen phthalate (KHC8H4O4) (204.22 g
mol-1).
KOH(aq) + KHC8H4O4 (aq)  K2C8H4O4 (aq) + H2O
The molarity of the KOH solution is:
(a)
0.4024 M
(b)
0.1106 M
(c)
1.1056 × 10-4 M
(d)
4.024 × 10-4 M
(2)
1.24 The density of HCN(g) at STP (standard temperature and standard pressure)
conditions is:
(a)
22.41 g L-1
(b)
0.830 g L-1
(c)
2.410 g L-1
(d)
1.206 g L-1
(2)
1.25 A 0.276 g sample of a gas occupies a volume of 0.270 L at 739 mmHg and
98oC. The molar mass of the gas is:
(a)
8.27 g mol-1
(b)
32.0 g mol-1
(c)
1225 g mol-1
(d)
323.6 g mol-1
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 8
1.26 Boric oxide is added to soda-lime commonly used in the manufacture of
borosilicate glass (e.g. pyrex) which is used in chemistry labs as a result of the
following important factor:
(a)
The boric oxide replaces CaO and Na2O to increase the refractive index
of the glass providing exceptionally clear glassware to observe chemical
reactions.
(b)
The boric oxide replaces CaO and Na2O to increase the melting point
and improve the glassware resistance to thermal shock.
(c)
The boric oxide replaces CaO and Na2O to increase the ability of
glassware to resist expansion and withstand heat changes without
cracking.
(d)
The boric oxide replaces CaO and Na2O to increase its alkali content
and make it less prone to chemical attack.
(2)
1.27 Which statement on silicones, given below, is false?
(a)
Their commercial uses include: fluids, oils, elastomers (rubbers) and
resins.
(b)
Silicones are organosilicon polymers.
(c)
Silicones are water soluble because a silicone chain is surrounded by
inorganic side groups.
(d)
Hydrolysis of alkyl substituted chlorosilanes led to long-chain polymers
called silicones.
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 9
QUESTION 2
2.1
27 MARKS
Aspirin (C9H8O4) is synthesized in a laboratory by reacting acetic anhydride
(C4H6O3) with salicylic acid (C7H6O3) according to the balanced equation:
C4H6O3 + C7H6O3  C9H8O4 (aspirin) + C2H4O2 (acetic acid)
In a lab synthesis, a student begins with 5.00 mL of acetic anhydride (density
= 1.08 g mL-1) and 2.08 g of salicylic acid. Once the reaction is complete, the
student collects 2.01 g of aspirin.
Calculate:
(a)
The limiting reagent.
(3)
(b)
The theoretical yield
(1)
(c)
Percentage yield.
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 10
2.2
Nitric acid is purchased in concentrated form with a 70.3 % (m/m)
concentration by mass and a density of 1.41 g mL-1. How much of the
concentrated solution in millilitres should you use to make 2.5 L of 0.500 M
HNO3?
(5)
2.3
A gaseous compound containing hydrogen and carbon is decomposed and
found to contain 82.66 % carbon and 17.34 % hydrogen only by mass. The
mass of 158 mL of the gas, measured at 556 mm Hg and 25 oC, is found to be
0.275 g. Determine the molecular formula of the compound.
(5)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 11
2.4
How many grams of hydrogen are collected in a reaction where 1.78 L of
hydrogen gas is collected over water at a temperature of 40 oC and a total of
pressure of 748 torr? (Table of vapour pressures of water versus temp given
in data sheet)
(4)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 12
2.5
A 50 mL aliquot of 0.10 M AgNO3 was mixed with 50 mL of 0.10 M HCl mixed
in a constant-pressure calorimeter, causing the temperature to rise from
22.20oC to 23.11oC. The reaction responsible for the change in temperature is:
AgNO3(aq) + HCl(aq)  AgCl(s) + HNO3(aq)
Calculate H (in kJ mol-1) for the reaction.
(Assume the density of both solutions to be 1.0 g mL-1 and specific heat
capacity = 4.18 J g-1 oC-1 )
2.6
(4)
Given the data:
N2(g) + O2(g)  2 NO(g)
2 NO(g) + O2(g)  2 NO2 (g)
2 N2O(g)  2 N2(g) + O2(g)
H = +180.7 kJ
H = -113.1 kJ
H = -163.2 kJ
Use Hess’s Law to calculate H for the reaction
N2O(g) + NO2(g)  3 NO(g)
(4)
Barcode: SCHOOL OF CHEMISTRY & PHYSICS UNIVERSITY OF KWAZULU‐NATAL, HOWARD COLLEGE CAMPUS CHEM 181: CHEMISTRY FOR ENGINEERS 1A JUNE 2013 MAIN EXAMINATION DURATION: 2 HOURS INTERNAL EXAMINER: MODERATING BOARD: Student No. Notes:
TOTAL MARKS: 75 MR A. BISSESSUR DR P. NDUNGU MS G. DAWSON Seat Number: This paper consists of 16 pages including the cover page, periodic table and two data
sheets. Please ensure that you have them all.
The use of non-programmable electronic calculators is permitted.
ANSWER ALL QUESTIONS DIRECTLY ON THE PAPER AND WHERE NECESSARY
OVER THE PAGE.
Examiner
Question 1
Question 2
Total
Internal
External
Students are requested, in their own interest, to write legibly.
Rule 9 (1)(e) WARNING: CANDIDATES WILL BE DISQUALIFIED IF: (a) they introduce, or attempt to introduce, into any place where an examination is about to be conducted or is being conducted, any paper, book, note, document or instrument, the use of which is not authorized by the examiner or the examination officer. (b) they possess, use, or attempt to use during an examination, any paper, book, note, document or instrument the use of which is not authorized by the examiner or the examination officer. (c) they remove or attempt to remove from the examination room, any examination book or writing paper supplied by the University for the purposes of answering an examination. (d) they communicate or attempt to communicate any information relating to the examination to another candidate while the examination is in progress. (e) they use a false name or identity number in an examination. (f) they commit any other fraudulent, deceitful or dishonest practice which would mislead or deceive the examiner or examination officer. IF A STUDENT IS FOUND GUILTY BY A STUDENT DISCIPLINE COURT OF CONTRAVENING THE ABOVE RULE –9(1)(e) – SHE/HE WILL SUFFER ONE OR MORE OF THE FOLLOWING CONSEQUENCES: (i) Disqualification from entry to any examination. (ii) Cancellation or forfeiture of examination results. (iii) Deprivation of a degree, diploma or certificate obtained as a result of the offence. School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 1
QUESTION 1
1.1
(MULTIPLE CHOICE)
48 MARKS
Perform the following mathematical operation expressing your answer to
the correct number of significant figures:
(7.8 m – 0.34 m) ÷ (1.150 s + 0.82 s)
1.2
1.3
1.4
(a)
3.7
m/s
(b)
3.786 m/s
(c)
3.8
(d)
3.790 m/s
m/s
(1)
Determine which one of the following calculations performed to the correct
number of significant figures is incorrect:
(a)
34.00 x 567 ÷ 4.564 = 4.22 × 103
(b)
79.3 ÷ 0.004 x 35.4 = 7 × 105
(c)
89.763 ÷ 22.4581 = 3.9969
(d)
(4.32 × 1012) ÷ (3.1 × 10-4) = 1.4 × 1016
(1)
Which one of the following can be classified as a heterogeneous mixture?
(a)
A mixture of oxygen and nitrogen in a tank.
(b)
A mixture of octane and water.
(c)
A mixture of sea water and distilled water.
(d)
A mixture of ethanol and water.
(2)
Which one of the following properties can be classified as an extensive property?
(a)
Beryllium has a density of 1.85 g cm-3
(b)
The enthalpy for the formation of CO2(g) from C(s) is -393.5 kJ mol-1
(c)
The specific heat capacity of CH4(g) is 2.20 J g-1 K-1
(d)
Copper(II) sulfate turns from blue to green when excess HCl is added
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 2
1.5
In which of the following statements are both processes a result of chemical
changes?
1.6
(a)
Melts at 73oC and is soluble in water.
(b)
Sublimation of a solid at room temperature and reacts with oxygen.
(c)
Displaces hydrogen gas and is easily oxidized.
(d)
Tarnishes in air and sublimes at high temperature.
(2)
Characterise each of the following pairs of atoms as containing
(1) same number of neutrons, (2) same number of electrons or (3) same total
number of subatomic particles.
ଶଷ
ଶସ
ଵଵܰܽ and ଵଶ‫݃ܯ‬
1.7
(a)
Same number of subatomic particles (p+, no, e-).
(b)
Same number of neutrons.
(c)
Same number of neutrons and subatomic particles (p+, no, e-).
(d)
Same number of electrons and subatomic particles (p+, no, e-).
(2)
One isotope of a metallic element has a mass number of 65 and 35 neutrons
in the nucleus. The cation derived from the isotope has 28 electrons. The
cation can be identified as:
(a)
Tb2+
(b)
Tc2+
(c)
Zn2+
(d)
Ni2+
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 3
1.8
1.9
The compounds (i) N2O, (ii) P4, are classified as:
(a)
(i) molecular
(ii) atomic element
(b)
(i) ionic
(ii) ionic
(c)
(i) molecular
(ii) molecular element
(d)
(i) molecular
(ii) molecular
(2)
The empirical formula of the compounds formed by combination of
manganese(II) and chlorate is:
(a)
Mn2ClO4
(b)
Mn2ClO3
(c)
MnClO2
(d)
Mn(ClO3)2
(2)
1.10 The correct chemical formula for hydrocyanic acid is:
(a)
HOCN(aq)
(b)
HCN(aq)
(c)
H2CN(aq)
(d)
HCNO3(aq)
(1)
1.11 The correct name for the chemical formula, HOCl(aq), is:
(a)
hypochloric acid
(b)
chlorous acid
(c)
hypochlorous acid
(d)
chloric acid
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 4
1.12 The elements that will not displace H2 (g) from acids but will react with HNO3
and not produce H2(g) are:
(a)
Li, Al, Cu
(b)
Ag, Pt, Au
(c)
Ag, Zn, Ba
(d)
Pt, Cu, Ni
(2)
1.13 Which single displacement reaction shown below, is non-spontaneous?
(a)
Ca(s) + 3H2O(ℓ) → 2 Ca(OH)2(aq) + H2(g)
(b)
2 Al(s) + 3H2O (steam) → Al2O3(s) + 3H2(g)
(c)
Cu(s) + ZnSO4(aq) → CuSO4(aq) + Zn(s)
(d)
Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(ℓ)
(2)
1.14 Using solubility rules, identify the reagent that will separate the following two
ions from a mixture by precipitating one of the cations in the mixture below:
Pb2+ (aq) + Ca2+(aq)
(a)
CH3COOH(aq)
(b)
NaClO3(aq)
(c)
NaI(aq)
(d)
HNO3(aq)
(1)
1.15 Using solubility rules, identify the reagent that will precipitate one of the
anions in the mixture below:
Cl-(aq) + SO42-(aq)
(a)
KNO3(aq)
(b)
NH4Cl(aq)
(c)
Ba(NO3)2(aq)
(d)
NaCl(aq)
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 5
1.16 For liquid state samples of (i) HCl and (ii) Cl2, classify the dominant
intermolecular forces present as London forces, dipole-dipole interactions or
hydrogen bonds
(a)
(i) London dispersion forces
(ii) London dispersion forces
(b)
(i) dipole-dipole
(ii) London dispersion forces
(c)
(i) hydrogen bonds
(ii) London dispersion forces
(d)
(i) dipole-dipole
(ii) dipole-dipole
(2)
1.17 How many H atoms are in 78 g of CH3CH2OH (ethanol) (molar mass = 46.08
g mol-1) ?
(a)
1.0 x 1024
(b)
7.8 x 1024
(c)
6.1 x 1024
(d)
2.8 x 1026
(2)
1.18 An organic compound made up of carbon and hydrogen only, undergoes
combustion producing 3.14 g of CO2 (44.01 g mol-1) and 1.29 g of H2O (18.02
g mol-1). The empirical formula for this organic compound is:
(a)
CH
(b)
C2H4
(c)
CH2
(d)
C2H3
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 6
1.19 In the reaction: 2 NaOH(aq) + Cl2(g) → NaCl + 2 NaOCl(aq) + H2O(ℓ)
(molar masses in g mol-1) : NaOH = 40.0; Cl2 = 70.9; NaOCl =74.44)
The theoretical yield (in grams) of NaOCl that can be obtained from a reaction
mixture containing 75.0 g of NaOH and 50 g of Cl2(g) is:
(a)
52.5 g
(b)
69.8 g
(c)
37.5 g
(d)
49.0 g
(2)
1.20 A mixture contains 75.0 % by mass CS2 and 25.0 % by mass H2S. The
combustion reactions are:
CS2(ℓ) + 3 O2(g) → CO2(g) + 2 SO2(g)
2 H2S + 3O2(g) → 2 SO2(g) + H2O(g)
(molar masses in g mol-1) :
CS2 = 76.14; SO2 = 64.07
H2S =34.09;
CO2 = 44.00
The total number of moles of SO2 produced from the combustion of 75g of the
mixture is:
(a)
2.028 mol
(b)
1.289 mol
(c)
0.5500 mol
(d)
2.722 mol
(2)
1.21 What volume (mL) of deionized H2O must be added to 0.100 L of a 15 M
NaOH to obtain 1.00 M of NaOH?
(a)
1500 mL
(b)
1510 mL
(c)
1000 mL
(d)
1400 mL
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 7
1.22 How much 0.125 M NaOH solution (in mL) is required to completely neutralize
0.225 L of a 0.175 M H2SO4 solution?
Reaction: H2SO4(aq) + 2 NaOH(aq)  Na2SO4(aq) + 2 H2O(ℓ)
(a)
158 mL
(b)
630 mL
(c)
194 mL
(d)
315 mL
(2)
1.23 A quantity of 18.68 mL of a KOH (56.11 g mol-1) solution is needed to
neutralize 0.4218 g of potassium hydrogen phthalate (KHC8H4O4) (204.22 g
mol-1).
KOH(aq) + KHC8H4O4 (aq)  K2C8H4O4 (aq) + H2O
The molarity of the KOH solution is:
(a)
0.4024 M
(b)
0.1106 M
(c)
1.1056 × 10-4 M
(d)
4.024 × 10-4 M
(2)
1.24 The density of HCN(g) at STP (standard temperature and standard pressure)
conditions is:
(a)
22.41 g L-1
(b)
0.830 g L-1
(c)
2.410 g L-1
(d)
1.206 g L-1
(2)
1.25 A 0.276 g sample of a gas occupies a volume of 0.270 L at 739 mmHg and
98oC. The molar mass of the gas is:
(a)
8.27 g mol-1
(b)
32.0 g mol-1
(c)
1225 g mol-1
(d)
323.6 g mol-1
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 8
1.26 Boric oxide is added to soda-lime commonly used in the manufacture of
borosilicate glass (e.g. pyrex) which is used in chemistry labs as a result of the
following important factor:
(a)
The boric oxide replaces CaO and Na2O to increase the refractive index
of the glass providing exceptionally clear glassware to observe chemical
reactions.
(b)
The boric oxide replaces CaO and Na2O to increase the melting point
and improve the glassware resistance to thermal shock.
(c)
The boric oxide replaces CaO and Na2O to increase the ability of
glassware to resist expansion and withstand heat changes without
cracking.
(d)
The boric oxide replaces CaO and Na2O to increase its alkali content
and make it less prone to chemical attack.
(2)
1.27 Which statement on silicones, given below, is false?
(a)
Their commercial uses include: fluids, oils, elastomers (rubbers) and
resins.
(b)
Silicones are organosilicon polymers.
(c)
Silicones are water soluble because a silicone chain is surrounded by
inorganic side groups.
(d)
Hydrolysis of alkyl substituted chlorosilanes led to long-chain polymers
called silicones.
(2)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 9
QUESTION 2
2.1
27 MARKS
Aspirin (C9H8O4) is synthesized in a laboratory by reacting acetic anhydride
(C4H6O3) with salicylic acid (C7H6O3) according to the balanced equation:
C4H6O3 + C7H6O3  C9H8O4 (aspirin) + C2H4O2 (acetic acid)
In a lab synthesis, a student begins with 5.00 mL of acetic anhydride (density
= 1.08 g mL-1) and 2.08 g of salicylic acid. Once the reaction is complete, the
student collects 2.01 g of aspirin.
Calculate:
(a)
The limiting reagent.
(3)
(b)
The theoretical yield
(1)
(c)
Percentage yield.
(1)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 10
2.2
Nitric acid is purchased in concentrated form with a 70.3 % (m/m)
concentration by mass and a density of 1.41 g mL-1. How much of the
concentrated solution in millilitres should you use to make 2.5 L of 0.500 M
HNO3?
(5)
2.3
A gaseous compound containing hydrogen and carbon is decomposed and
found to contain 82.66 % carbon and 17.34 % hydrogen only by mass. The
mass of 158 mL of the gas, measured at 556 mm Hg and 25 oC, is found to be
0.275 g. Determine the molecular formula of the compound.
(5)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 11
2.4
How many grams of hydrogen are collected in a reaction where 1.78 L of
hydrogen gas is collected over water at a temperature of 40 oC and a total of
pressure of 748 torr? (Table of vapour pressures of water versus temp given
in data sheet)
(4)
School of Chemistry and Physics, UNIVERSITY OF KWAZULU-NATAL, HOWARD COLLEGE,
JUNE 2013 EXAMINATION
CHEM 181: CHEMISTRY FOR ENGINEERS 1A
Page 12
2.5
A 50 mL aliquot of 0.10 M AgNO3 was mixed with 50 mL of 0.10 M HCl mixed
in a constant-pressure calorimeter, causing the temperature to rise from
22.20oC to 23.11oC. The reaction responsible for the change in temperature is:
AgNO3(aq) + HCl(aq)  AgCl(s) + HNO3(aq)
Calculate H (in kJ mol-1) for the reaction.
(Assume the density of both solutions to be 1.0 g mL-1 and specific heat
capacity = 4.18 J g-1 oC-1 )
2.6
(4)
Given the data:
N2(g) + O2(g)  2 NO(g)
2 NO(g) + O2(g)  2 NO2 (g)
2 N2O(g)  2 N2(g) + O2(g)
H = +180.7 kJ
H = -113.1 kJ
H = -163.2 kJ
Use Hess’s Law to calculate H for the reaction
N2O(g) + NO2(g)  3 NO(g)
(4)