Introductory Chemistry — Mid-term Exam
Name:________________________________
Student number:_______________________
Autumn Semester
Basic Chemistry for Engineering/
Fundamental Inorganic Chemistry
Mid-term Exam
05 December 2011
Time: 45 minutes
Instructions:
Answer any 4 questions out of 6 possible questions.
You may answer more than 4 questions if you wish.
Your marks will be taken from your top 4 questions.
Show all relevant working.
Write all answers and final working in pen.
10 pages including: 1 top page, 1 data page, 1 periodic table, 6 question pages, 1
page for rough working
Hand in all pages at the end of the exam.
Permissible materials:
Calculator.
English or English bilingual Dictionary.
Course text book.
Mobile phones and/or devices with internet connectivity are NOT allowed.
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Introductory Chemistry — Mid-term Exam
Equations and Data
pV = nRT where p = pressure, V = volume, n= no. of moles, R = 8.3144 J K–1mol–1 or R =
0.082057 L atm K–1mol–1, T = temperature
Avagadro number 6.022 x 1023
Heat of fusion of H2O at 0°C: 334 J g–1
Heat of vapourisation of H2O at 100°C: 2.26 x 103 J g–1
Specific heat capacity of H2O(s) (ice): 2.09 J g–1 K–1
Specific heat capacity of H2O(l) (liquid water): 4.184 J g–1 K–1
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Introductory Chemistry — Mid-term Exam
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Introductory Chemistry — Mid-term Exam
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Question 1
A)
i) Which element has an atomic number of 40? ______
ii) Which element has a relative atomic mass of approximately 40? ______
iii) Which of these elements has the highest total number of electrons? ______
iv) Which of these elements has the most valence electrons? ______
[2]
B) Label the following substances as being ‘mixture’, ‘compound’ or ‘element’.
i) wood:
___________________
ii) copper:
___________________
iii) air: ___________________
iv) iron chloride:
___________________
[2]
C) i) Label the following diagram of an atom. The atom is neutral and all particles are visible.
ii) Identify the element: ___________________
iii) This element easily forms ions. What charge (oxidation state) is this element most likely to form
in ions? ___________________
iv) This diagram is a simplification of an atom. Name one way this diagram is simplified, when
compared to a real atom.
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[6]
Introductory Chemistry — Mid-term Exam
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Question 2
A) Determine the relative molecular mass of the following compounds:
i) CH3CH2CO2H
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ii) KMnO4
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[2]
B) How many atoms of oxygen would be found in 5 g of Na2CO3?
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[3]
C) i) Balance the following equation:
__NH3(g) + __O2(g)
__NO(g) + __H2O(g)
(‘(g)’ means ‘gas’)
[1]
ii) This reaction is conducted in a sealed 200L reaction vessel at an initial pressure of 0.9 atm and a
temperature of 560 ˚C. Assuming the temperature and volume is kept constant over the course of
the reaction, what is the pressure in the reaction vessel once the reaction has completed?
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[1]
iii) A little time after the reaction has finished, the vessel is allowed to cool below 100 ˚C,
whereupon the pressure in the vessel suddenly drops significantly, even though no further reaction
occurs. What is the reason for this sudden drop in pressure?
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[1]
What is the total number of molecules in the reaction vessel at the end of the reaction?
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[2]
Introductory Chemistry — Mid-term Exam
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Question 3
A) i) What mass of sodium hydrogen carbonate (NaHCO3) is required to make 150 ml of a 5M
solution?
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[2]
ii) NaHCO3 reacts with HNO3 according to the following equation:
NaHCO3 + HNO3
NaNO3 + H2CO3
What kind of reaction is this? ___________________________________
[1]
iii) What is the minimum amount of 5M NaHCO3 solution we need to completely react with 18 ml
of 3M HNO3 solution?
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[1]
B) i) Can we easily make O3– ions? Explain why.
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[1]
ii) How does the arrangement of elements in the periodic table, according to periods (rows) and
groups (columns) correspond to the arrangement of electrons in their atoms.
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[2]
C)Draw simple Lewis diagrams of the following compounds/ions:
i) CO32–
iii) AlCl3
ii) PH3
iv) I–
[2]
v) Which compound(s) is/are likely to be a Lewis acid? ___________________________________
[1]
Introductory Chemistry — Mid-term Exam
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Question 4
A) Which equations are correct, which are incorrect? Correct the incorrect equations.
i) NaHCO3 + HNO3
NaNO3 + H2CO3 _________________________________________
ii) CO2 + NaOH
Na2CO3 + H2O ______________________________________________
iii) 2Na + 2H2O
2Na + 2OH– + H2 ____________________________________________
iv) 3NO
H2O + NO2 _______________________________________________________
[2]
B) Classify the following reactions as combination, decomposition or displacement:
i) 2NO2
2NO + O2 ____________________________________
ii) CuO + H2
Cu + H2O ________________________________
iii) N2O2 + Br2
2NOBr _________________________________
–
iv) C4H9Br + OH
C4H9OH + Br– _________________________
[2]
C) Classify the following reactions as being either Bronsted-Lowry (write B-L) or Lewis acid-base
reactions. Identify the acids and bases.
i) 3NH3 + H3PO3
(NH4)3PO3 ________________________________________________
ii) PtCl2 + 4NH3
PtCl2(NH3)4 ________________________________________________
–
iii) B(OH)3 + Cl
iv) CuO + H2O
[B(OH)3Cl]– ________________________________________________
Cu(OH)2 ____________________________________________________
[4]
D) Sodium is an extremely reactive metal that catches fire when it reacts with water and chlorine is
an extremely reactive and toxic gas. Sodium chloride, however, is an unreactive solid that we can
eat in small amounts. Briefly explain why sodium chloride is so different to sodium metal and
chlorine gas.
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[2]
Introductory Chemistry — Mid-term Exam
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Question 5
A) Calculate the formal charge on the indicated atoms. Assume all valence shells are filled.
–O
O
H3C
Br
H
–O
P
C
O–
H
Br
O
–O
O
H
Al
Br
Br
[2]
B) Calculate the formal oxidation states of the indicated elements:
i) PO43– P:__
ii) AlCl3 Al:__
iii) KMnO4 Mn:__
iv) H2Se Se:__
[2]
C) Which of the following statements are true or false? Why?
i) Assuming constant pressure, a sample of gas cooled from 42 ˚C to 21˚C will halve its volume.
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ii) At 1 atm and 25 ˚C, 3.5 moles of SF6 (Mr = 146 g mol–1) will occupy a greater volume than 3.5
moles of F2 (Mr = 38 g mol–1).
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iii) At 35K and a pressure of 10 atm, the ideal gas equation cannot be used to predict the properties
of gaseous H2.
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[3]
D) A researcher drops and breaks a bottle containing 50 ml of liquid chloroform in a corridor. The
corridor has a volume of 187 m3. Assume that all of the chloroform evaporates and disperses evenly
throughout the whole volume. Will the concentration of chloroform vapour pass the acceptable
limit of 240 mg m–3? (Assume the liquid chloroform had a density of 1.5g cm–3 at the time it was
dropped). Show your working.
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[3]
Introductory Chemistry — Mid-term Exam
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Question 6
A) Explain, in terms of vapour pressure, why a visible mist forms over hot cups of coffee.
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[2]
B) A domestic solar panel heats water at a rate of 2.9 kJ s–1. How many hours will it take the solar
panel to heat 273 L of water from 12 ˚C to 65 ˚C?
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[4]
C) i) Ceasium chloride has a crystal lattice made of two interpenetrating simple cubic lattices of Cs+
and Cl– ions. Which of the following diagrams represents the unit cell of CsCl? (Spheres with the
same pattern represent the same element, different patterns represent different elements)
a)
b)
c)
d)
Answer: ________
ii) What is the total sum of Cs+ and Cl– ions inside the unit cell? Cs+: ____ Cl–: ____
iii) Lithium fluoride (LiF), sodium chloride (NaCl) and potassium bromide (KBr) have similar
crystal structures, however, their densities are in the order: KBr (2.75 g cm3) > LiF (2.63 g cm3) >
NaCl (2.61 g cm3).
How can we best explain this order?
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[4]
Introductory Chemistry — Mid-term Exam
Rough Working
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