֍Chemistry Challenge֍
PART A
Choose only ONE answer for each question.
1.
An atom M has seven valence electrons and forms a stable M2+ ion in an aqueous
solution. Identify electronic configuration of atom M.
A.
B.
C.
D.
2.
1s22s22p63s23p5
1s22s22p63s23p63d6
1s22s22p63s23p63d54s2
1s22s22p63s23p63d14s2
The properties of P, Q, R and S are given below.
(i) P and Q are conductors whereas R and S are insulators,
(ii) P has higher electrical conductivity than Q,
(iii) R has lower boiling point than S.
What could P, Q, R and S be?
A.
B.
C.
D.
3.
P
Mg
Al
K
Pb
Q
Na
Na
Ca
Si
R
Ne
H2O
Br2
HBr
S
Ar
NH3
Cl2
HCl
The Lewis structures of molecules HF, H2O and NH3 are shown respectively below.
Choose the correct statement.
A.
B.
C.
D.
4.
HF and H2O molecules are planar.
The boiling points of the molecules increase in the order of H2O, HF, NH3.
The repulsion of electron pairs in NH3 molecule is stronger than in H2O molecule.
The hydrogen bonds formed by the molecules decrease in the order of HF, H2O,
NH3.
The atomic number of several elements represented by letters which are not the usual
symbols for the element concerned in the Periodic Table is shown in the table below.
Select the element that has the strongest metallic bond.
A.
B.
C.
D.
W
X
Y
Z
Self-Assessment and Review Questions
֍Chemistry Challenge֍
5.
Which statement about the Lewis structure of CO32- and NO3- ions is true?
A.
B.
C.
D.
6.
Choose one of the following that explains why boron has a lower first ionization energy
than beryllium.
A.
B.
C.
D.
7.
Both ions are trigonal-planar in shape.
Both ions have a formal charge on the central atom.
Both ions form two double bonds and one single bond.
Both ions have central atom with one pair of unpaired electron.
A boron atom is smaller than a beryllium atom.
In beryllium all the electrons are paired in full sub-shells.
A beryllium atom has fewer protons than a boron atom.
In boron the 2p electron occupies a higher energy level than a 2s electron.
The selected enthalpy changes of certain thermochemical equations are shown
below.
Choose the statement that is true about the data above.
A.
B.
C.
D.
8.
The bond energy of Cl2 is +121 kJ mol-1.
The lattice energy of PbCl2 is +2264 kJ mol-1.
The standard enthalpy of sublimation of Pb is +195 kJ mol-1.
The standard enthalpy of formation of PbCl2 is -131 kJ mol-1.
The standard enthalpy of formation of C2H2 is +226.7 kJ mol-1. The standard enthalpies
of combustion of C and H, are -393.5 kJ mol-1 and -285.9 kJ mol-1, respectively.
Determine the standard enthalpy of combustion of C2H2.
A.
B.
C.
D.
-119.1 kJ mol-1
-452.1 kJ mol-1
-906.1 kJ mol-1
-1299.6 kJ mol-1
Self-Assessment and Review Questions
֍Chemistry Challenge֍
9.
The lattice energy of YCl2 is -2524 kJ mol-1 and the thermochemical equations for the
formation of gaseous Cl- and Y2+ ions are shown below.
Calculate the standard enthalpy of formation for YCl2.
A.
B.
C.
D.
10.
-418 kJ mol-1
-646 kJ mol-1
-2106 kJ mol-1
-2562 kJ mol-1
The table below shows the standard enthalpy of combustion, ΔHºc for the four
hydrocarbons ethyne, propyne, propene and propane.
MM
−ΔHºc
(g mol−1)
(kJ mol−1)
ethyne
26
1300
HC≡CCH3
propyne
40
1940
H2C=CHCH3
propene
42
2060
CH3CH2CH3
propane
44
2220
Compound
Name
HC≡CH
The complete combustion of 2.0 g of one of the above hydrocarbons releases
exactly 100 kJ of heat energy.
This hydrocarbon is
A.
B.
C.
D.
11.
ethyne.
propyne.
propene.
propane.
Calculate the rms speed of carbon dioxide molecules at STP.
A.
B.
C.
D.
1.24 x101 m/s
1.55 x102 m/s
3.93 x102 m/s
1.55 x105 m/s
Self-Assessment and Review Questions
֍Chemistry Challenge֍
12.
At what temperature is the root mean square speed of helium, He atoms equal to that
of oxygen, O2 molecules at 300 K?
A.
B.
C.
D.
13.
At moderate pressures (~ 200 atm), the measured pressure exerted by CO2 gas is less
than that predicted by the ideal gas equation. This is mainly because
A.
B.
C.
D.
14.
such high pressures cannot be accurately measured.
CO2 will condense to a liquid at 200 atm pressure.
gas phase collisions prevent CO2 molecules from colliding with the walls of the
container.
of attractive intermolecular forces between CO2 molecules.
An unknown liquid is vaporized in a 273-mL flask by immersion in a water bath at 99°C.
The barometric pressure is 753 torr. If the mass of the vapor retained in the flask is
1.362 g, its molar mass is
A.
B.
C.
D.
15.
37.5 K
75 K
106 K
292 K
20.4 g/mol.
40.9 g/mol.
112 g/mol.
154 g/mol.
Consider the set of quantum number for the added electrons in L atom below;
(4, 1, 0, - ½ ) , (4, 1, +1, - ½ )
A.
B.
C.
D.
24W
+
29X
3+
31Y
3+
39Z
Self-Assessment and Review Questions
֍Chemistry Challenge֍
PART B
Answer ALL questions.
QUESTION 1
Ozone, O3, may be used as a bactericide in the treatment of waste water. The amount of
ozone in water may be determined using the following equation:
O3 (g) + 3 I– (aq) + 2 H+ (aq) → O2 (g) + I3- (aq) + H2O (l)
In an experiment, 500.0 cm3 of a waste water sample was treated with an excess of iodide
ions. The volume of oxygen gas collected from the reaction at 25.0 °C and 101.3 kPa was
10.0 cm3. Calculate the mass of ozone in the waste water sample.
(4.09 x 10-4 mol, 0.0193 g)
QUESTION 2
A sample of gases contains an equal amount of ammonia, helium and nitrogen. Determine
the density, in g dm-3, of this sample under atmospheric pressure of 1.01 x 105 Pa and a
temperature of 30 °C.
(1.97 g dm-3)
QUESTION 3
The first seven ionisation energies of element X are given in the table below.
By using the above data, deduce the group for element X in the Periodic Table and draw
its partial orbital diagram.
QUESTION 4
The reaction between an acid and a base produces salt and water. A mixture of 100.0 cm 3
of 0.431 M HCl solution and 100.0 cm3 of 0.216 M Ba(OH)2, solution is added into a
constant-pressure calorimeter. Determine the final temperature of the mixture if the initial
temperature of both solutions is 20.5 ºC. Given, specific heat capacity of water is
4.18 J g-1 ºC-1, heat of neutralisation is -56.2 kJ mol-1 and density of solution is 1.0 g cm-3.
(23.4 ºC)
Self-Assessment and Review Questions
֍Chemistry Challenge֍
QUESTION 5
9.45 g of liquid hexane (C6H14) is introduced into a 10.0 L vessel containing 13.15 atm of
oxygen gas at 21ºC and ignited, yielding carbon dioxide and water. If the vessel is then
cooled to –10.0ºC, calculate the gas pressure inside the vessel.
(10.9 atm)
QUESTION 6
A method of removing CO2 from a spacecraft is to allow the CO2 to react with sodium
hydroxide that produces sodium carbonate and water. Determine volume of carbon dioxide
at 25°C and 749 mmHg can be removed per kilogram of sodium hydroxide that reacts.
(310 L)
QUESTION 7
The mole fraction of oxygen molecules in dry air is 0.2095. Calculate volume of dry air at
1.00 atm and 25°C is required for burning 1.00 L of hexane, C6H14 completely. Given, the
density of C6H14 is 0.660 g/ml.
(8514 L)
QUESTION 8
Calculate the mass of cinnamaldehyde must be added to 175 g of ethanol to give a solution
that boils at 82.7°C. Given, Kb = 1.22°C/m, boiling point of pure ethanol = 78.5°C.
(79.6 g)
QUESTION 9
Determine the freezing point of a solution which contains 0.31 mol of sucrose in 175 g of
water. Kf = 1.86°C/m
(°C)
QUESTION 11
Explain the following observation:
Methane, CH4 (16 g/mol) has lower boiling point than propane, C3H8 (44 g/mol) whereas,
water, H2O (18 g/mol) has higher boiling point than H2S (34 g/mol).
Self-Assessment and Review Questions
֍Chemistry Challenge֍
QUESTION 12
The complete combustion of 0.021 mol benzoic acid, C6H5COOH raises the temperature of
815 g water from x°C to 35.5°C. The standard enthalpy of combustion for C6H5COOH is
given below:
C6H5COOH (s) + 15/2 O2 (g) → 6 CO2 (g) + 3 H2O (l)
ΔHºc = -2586.9 kJ/mol
Determine the value of x. Given, heat capacity of calorimeter is 923 J/°C and specific heat
capacity of water is 4.18 J/g°C.
(23 °C)
QUESTION 13
Phosphine, PH3, reacts to form phosphonium ions, PH4+. Name the type of bond formed
when phosphine reacts with an H+ ion. Explain how this bond is formed.
QUESTION 14
If 0.750 L of argon at 1.50 atm and 177°C and 0.235 L of sulfur dioxide at 95.0 kPa and
63.0°C are added to a 1.00-L flask and the flask's temperature is adjusted to 25.0°C.
Determine the resulting pressure in the flask.
(0.946 atm)
QUESTION 15
A 0.305 mol of magnesium metal and a volume of aqueous hydrochloric acid that contains
0.535 mol of HCl are combined and react to completion. Calculate the volume of hydrogen
gas produced and measured at RTP. The reaction is as follows:
Mg(s)
+
2HCl(aq)
→
MgCl2(aq)
+
H2(g)
(6.55 L)
QUESTION 16
Hydrogen peroxide, H2O2 was catalytically decomposed and 75.3 mL of oxygen, O2 gas
was collected over water at 25°C and 742 torr. Determine the mass of oxygen was collected.
(Pwater = 24 torr at 25°C)
(0.0931 g)
Self-Assessment and Review Questions
֍Chemistry Challenge֍
QUESTION 17
Explain the formation of formaldehyde, CH2O molecule by using hybridization theory and
orbital overlapping.
QUESTION 18
Explain the following observations regarding ionization energy:
a) Helium gases have the highest first ionization energy of all the elements.
b) The first ionization energy of oxygen less than that of nitrogen.
QUESTION 19
Hydrogen is burned in oxygen to release heat as shown in equation below. Determine the
mass of hydrogen must be burned to release enough heat to warm 50 g block of iron from
21°C to 225°C. Iron has a specific heat of 0.449 J g-1°C-1.
2H2 (g)
+
O2 (g)
→
2H2O(g)
ΔHc = -484 kJ
( 0.04 g)
QUESTION 20
Construct a Born-Haber cycle for the formation of CaCl2 ionic compound.
Self-Assessment and Review Questions