Sample (Mid-term Test) Paper for Chem 1008 <<General Chemistry>>
Multiple choices
(2 marks each, 40 marks in total)
1. A sulfide ion, S2-, has
(a) 16 protons and 16 electrons
(c) 16 protons and 14 electrons
(e) 32 protons and 18 electrons
(b) 32 protons and 16 electrons
(d) 16 protons and 18 electrons
2. To describe an atomic orbital, how many quantum numbers are required?
(a) 4 (b) 3 (c) 2 (d) 1 (e) none of the above
3. An electron in a certain atom is in the n=2 quantum level. Which choice lists
possible values of both l and m that it can have?
(a) l=2 m=2
(b) l=1 m=2 (c) l=0 m=-1 (d) l=0 m=0 (e) l=2 m=1
4. An atom of manganese has
unpaired electrons and is
. Atomic number
of manganese is 25.
(a) 0, diamagnetic
(b) 2, diamagnetic
(c) 3, paramagnetic
(d) 5, paramagnetic
(e) 7, paramagnetic
5. Consider an element with an electron configuration of [Kr]5s24d105p5. How would
you classify this element?
(a) a representative element
(b) a transition metal (c) an alkali metal
(d) an actinide element
(e) a noble gas
6. The electron configuration of a Co3+ ion is:
The atomic number of Co is 27.
5
1
5
2
4
(a) [Ar]3d
(b) [Ar]4s 3d (c) [Ar]4s 3d
(d) [Ar]3d6
(e) [Ar]4s23d9
7. Which element will display an unusually large jump in ionization energy values
between I4 and I5, the 4 rd and 5th ionization energies?
(a) Na
(b) P
(c) Al
(d) Si
(e) S
8. Which of the following statements is true?
(a) The radii of ions are always smaller than the radii of the corresponding atoms of
the same element.
(b) The electron configuration of the outermost electrons of atoms of the halogens is
ns2 np 7.
(c) An electron in a 3p orbital could have a value of 2 for its angular momentum
quantum number l.
(d) Each shell of quantum number n contains n subshells.
9. Each of the three resonance structures of NO3- has how many lone-pairs of electrons?
(a) 7 (b) 8
(c) 9
(d) 10
(e) 13
10. Which molecule has a Lewis structure that does not obey the octet rule?
(a) N2O
(b) CS2
(c) PH3
(d) SiCl4
(e) NO2
11. Which of the following molecule is polar
(a) NO3(b) CO2
(c) PF5
12. The geometry of BrF4+ is best described as:
(a) tetrahedral
(b) trigonal pyramidal
(d) square planar
(e) none of above
(d) ClO3-
(e) BeCl2
(c) a see-saw structure
13. What is the hybridization on the central atom in ClO3(a) sp
(b) sp2
(c) sp3
(d) sp3d
(e) sp3d 2
14. Complete the sentence. The XeO4 molecule has:
(a) nonpolar bonds, and is a nonpolar molecule.
(b) nonpolar bonds, but is a polar molecule.
(c) polar bonds, and is a polar molecule.
(d) polar bonds, but is a nonpolar molecule.
(e) none of above
15. In the coordination compound [Cr(NH3)2(en)Cl2]Br2, where en = ethylenediamine, the
coordination number (C.N.) and oxidation number (O.N.) of the metal atom,
respectively are:
(The atomic number of Cr is 24)
(a) C.N.=6; O.N.=4
(b) C.N.=6; O.N.=3 (c) C.N.=5; O.N.=2
(d) C.N.=5; O.N.=4
(e) C.N.=4; O.N.=3
16. In K4[Fe(CN)6], how many 3d electrons does the iron ion have?
(a) 3
(b) 4
(c) 5
(d) 6
(e) 7]
(The atomic number of iron is 26)
17. The numbers of geometrical isomers and optical isomers of the complex ion
[Co(en)2Br2]+ (en = ethylenediamine) are, respectively:
(a) 2 and 2
(b) 1 and 1
(c) 3 and 2
(d) 1 and 2
(e) 2 and 4
18. Which of the following involve an increase in the entropy of the
system ? (1) Melting of a solid
(2) evaporation of a liquid
(3) Freezing
(4) Precipitation of a solid from a solution
(a) (1) and (3)
(d) (2) and (4)
(b) (1) and (2)
(e) (3) and (4)
(c) (2) and (3)
(f) none of the above
19. Arrange the following reactions according to increasing ∆S
(1) H2O(g) H2O(l)
(2) 2 NO(g) N2(g) + O2(g)
(3) MgCO3(s) MgO(s) + CO2(g)
(a) (3)<(2)<(1)
(b) (1)<(2)<(3)
(c) (2)<(3)<(1)
(d) (3)<(1)<(2) (e) (1)<(3)<(2)
20. A negative sign for ∆G indicates that:
(a) the reaction is exothermic
(b) the reaction is endothermic
(c) the reaction is fast
(d) the reaction is slow
(e) none of above
Short and Long Questions
1. For each of the following pairs of hydrogenic orbitals, indicate which is higher in
energy?
(5 marks)
(a) 4s, 3s
(b) 5s, 4f
(c) 6dxz, 6d xy
(d) 5p, 4f
(e) 5s, 5f
2. The planar N2O5 molecule has six N-O σ bonds and two π bonds, bust has no N-N
bonds and O-O bonds.
(i)
Draw two distinguishable Lewis structures for N2O5 and assign formal charges
to the atom in each Lewis structure.
(6 marks)
(ii)
Which Lewis structure(s) make(s) more important contribution to the
molecular structure.
(2 marks)
(iii)
Explain briefly your choice in (ii)
(2 marks)
3. Consider OSF2Me2 molecule [S is the central atom and all other groups (O, two F and
two Me) are not bonded to each other. Here, Me is CH3).
(a) Give the most stable Lewis structure;
(3 marks)
(b) List all possible three-dimensional structural isomers and point out which
structural isomer is chiral. Assume that Me is an atom. (8 marks)
(c) Based on the VSEPR model, point out the most stable structural isomer.
(3 marks)
(d) For the most stable structural isomer, please give the polarity using
and state the hybridization type of the central atom.
(2 marks)
4. Predict the number of unpaired electrons for in the following complex ions
(a) [Cr(CN)6]4(b) [Fe(CN)6]3(4 marks)
5. (a) The complex ion (i) [Fe(H2O)5NCS]2+ is red and (ii) [Co(H2O)6]3+ is violet.
Which one has a larger crystal field splitting?
(b) In the pair of complexes (i) [CoCl6]3- and (ii) [Co(NH3)6]3+, please
choose the one that absorbs light at a longer wavelength in the visible region?
(5 marks)
6. Ammonium nitrate is dangerous because it decomposes (sometime explosively) when
heated:
(10 marks)
NH4NO3(s) N2O(g) + 2 H2O(g)
(a) Show that this reaction is spontaneous at 25oC.
∆Hof in kJ/mol: -365.6 [NH4NO3(s)]; 82.0 [N2O(g)]; -241.8 [H2O(g)]
So in J/K·mol: 151.1 [NH4NO3(s)]; 219.7 [N2O(g)]; 188.7 [H2O(g)]
(b) How does ∆Go for the reaction change when temperature is raised?
(c) Calculated the equilibrium constant Kp at 25oC. (Here R=8.314 J/K)
(d) Calculate ∆G for the reaction when the partial pressure of each gas is 30 atm.
7. Do you agree with the following statements? Briefly explain your answers.
(10 marks)
(a) Spontaneous reactions are always fast.
(b) In any spontaneous process, the entropy of the system always increases.
(c) An endothermic reaction is always nonspontaneous.
(d) A reaction that is nonspontaneous in the forward direction is always spontaneous in
the reverse direction.
Answer keys:
Multiple choices
1. (d)
2. (b)
3. (d)
4. (d)
5. (a)
6. (d)
7. (d)
8. (d)
9. (b)
10. (e)
11. (d)
12. (c)
13. (c)
14. (d)
15. (a)
16. (d)
17. (a)
18. (b)
19. (b)
20. (e)
Short and Long Questions
1. (a) 4s
(b) 5s
(c) the same
(d) 5p
(e) the same
2.
(i)
0
0
O
O
+1
N
-1
O
+1
+1
O
0
O
N
N
O
N
+1 +1
0
O
O
O
-1
-1
-1
O
-1
(ii)
The Lewis structure shown in the left-hand side makes more important contribution.
(iii)
The charges are more evenly distributed in the Lewis structure shown in the left-hand side.
3.
(a)
F
Me
S
Me
O
F
(b)
F
Me
Me
Me
F
F
S
O
Me
S
O
Me
F
F
S
O
F
Me
This structural
isomer is chiral
O
O
F
Me
S
S
F
Me
F
Me
Me
F
(c) and (d)
F
Me
S
O
Me
F
The hybridisation type of S: sp3d
4. (a) 2
(b) 1
5. (a) (i)
(b) (i)
6.
(a)
(b)
(c)
(d)
∆H0 = -36.0 kcal/mol
∆S0 = 446.0 J/K
∆G = -168.9 kJ
∆G0 becomes more negative when temperature is raised.
Kp = 4.04 ×1029
∆G = ∆G0 + RT ln (30 × 302) = -143.6 kJ
0
7.
(a) Disagree. Whether a reaction is fast or slow is a kinetic problem not a
thermodynamic problem.
(b) Disagree. Spontaneity depends on the entropy of the universe, not on the entropy
of the system.
(c) Disagree. Spontaneity depends on ∆G, not on ∆H.
(d) Agree. The sign of ∆G for the forward reaction is opposite to that of the reverse
reaction.