Chemistry 200 Answers to Ex 2 Review
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1) What is the frequency of light associated with a photon of energy equal to 7.26 x 10
1.10 x 1015 Hz
- 19
J?
2) What is the wavelength of the radiation described in 1) ? 274 nm
3) a) What is the photoelectric effect? see text / notes
b) What conclusions did Einstein draw from the photoelectric effect? see text / notes
4) The energies of electrons in an atom are said to be quantized. Explain what this means. text / notes
5) Write the ground state electron configurations for the following:
c) O 1s22s22p2
a) Mg 1s22s22p63s2 b) Zn [Ar] 4s23d10
6) Write the electron configurations for the following using noble gas core notation:
a) Na [Ne] 3s1
b) S
[Ne] 3s23p4
c) I [Kr] 5s24d105p5
7) Given:
N2 (g) + 3H2(g)  2NH3 (g)
ΔH = -92 kJ exothermic
92 kJ is the quantity of heat which is:
a. gained from the surroundings when 1 mol of ammonia is formed.
b. gained from the surroundings when 2 mol of ammonia are formed.
c. lost to the surroundings when 1 mol of ammonia is formed.
d. lost to the surroundings when 2 mol of ammonia are formed.
e. none of the above.
8) What are line spectra? Where do they come from? see text / notes
9) a. Explain what is happening inside an atom when it emits light. see text / notes
9) b. Explain what is happening inside an atom when it absorbs light. see text / notes
10) An excited hydrogen atom emits light with a frequency of 1.141 x 10 14 Hz for its electron to reach the n=4
energy level. In which energy level did the electron begin? n=6
11) Calculate the wavelength of the light emitted when an electron in the hydrogen atom undergoes a transition
from the n = 5 to the n = 3 level. What part of the spectrum is this light in? 1280 nm; IR
For the following reactions give the correct products including all phase labels. If no reaction occurs write NR.
Then balance the molecular equation and give the total and net ionic equations.
12)
2AgNO3(aq) +
MgCl2(aq) 
2AgCl(s) + Mg(NO3)2(aq)
2Ag+ + 2 NO3 - + Mg2+ + 2Cl-  2AgCl(s) + Mg2+ + 2 NO3 2Ag+ + 2Cl-  2AgCl(s) (net ionic)
note: on all these, assume no phase label = aq
13)
Pb2+
Pb2+
Pb(NO3)2 (aq)
+ 2 NO3
+
SO42-
-
+
Na2SO4(aq) 
+
2Na+ +
 PbSO4(s)
SO42-
PbSO4(s) + 2NaNO3(aq)
 PbSO4(s) + 2Na+ + 2 NO3 -
Na2CO3(aq) +
2HNO3(aq)  H2O(l) + CO2(g) + 2NaNO3(aq)
2Na+ + CO32- + 2H+ + 2 NO3 -  H2O(l) + CO2(g) + 2Na+ + 2 NO3 CO32- + 2H+  H2O(l) + CO2(g)
14)
15)
NaOH(aq)
+
HNO2(aq)
 NaNO2(aq) + H2O(l)
Na+ + OH- + HNO2(aq)  Na+ + NO2- (aq) + H2O(l)
OH- + HNO2(aq)  NO2- (aq) + H2O(l) (Remember: nitrous acid is a weak acid.)
Classify the following as strong acid, strong base, weak acid or weak base:
16) Ca(OH)2 strong base
21) HClO weak acid 22) NH3 weak base
17) Give oxidation numbers for each element in the compound HClO H +1; Cl +1; O -2
18) Give oxidation numbers for each element in the ion Cr2O72-
Cr +6; O -2
19) Decide whether the following reactions will occur or not, give products if appropriate:
a)
Ag + CuCl2  NR
b)
Ni + 2HCl
 H2(g) + NiCl2(aq) Ni: oxidized; H reduced; Ni: reducing agent; HCl: oxidizing agent
c)
3Ca + 2FeCl3  2Fe(s) + 3CaCl2(aq) Ca: oxidized; Fe reduced Ca: reducing agent; FeCl3:
oxidizing agent
20) For each reaction in 19 that occurs, state which element is oxidized and which is reduced. )
21) If 0.203 g of KHP (potassium hydrogen phthalate) is titrated with 10.7 mL of
NaOH (aq) , what is the molarity of the NaOH solution? (molar mass KHP = 204.22)
KHP
+
NaOH
--------->
H2O
+
salt
Ans: 0.0929 M
22) Given the following equation:
3 NiSO4 (aq) +
2 Na3PO4 (aq)
---->
Ni3(PO4)2 (s)
+
3 Na2SO4 (aq)
How many mL of 0.375 M NiSO4 (aq) are needed to react completely with 35.6 mL of
0.265 M Na3PO4 (aq)? 37.74 mL
True or False:
23) In an exothermic reaction, the sign of q is positive. F
24) A joule is a kg m 2/s2
T
25) In an endothermic process, heat flows from the system into the surroundings.
26) Red light has lower energy than blue light. T
27) If the color of an object is red, that means the material is absorbing red light. F
28) KCl and HClO are both strong electrolytes. F
F
29. Assign all four quantum numbers to the valence electrons in the ground state of argon.
Valence e- of Ar are: 3s23p6
n
l
ml
ms
3
0
0
1/2
3
0
0
-1/2
3
1
-1
1/2
3
1
-1
-1/2
3
1
0
1/2
3
1
0
-1/2
3
1
1
1/2
3
1
1
-1/2
30 What phenomenon was Max Planck able to explain and what new assumption did he use in his
explanation? see text / notes
31 What are the n and l quantum numbers for a 4d electron? n = 4, l = 2
32. Is the following set of quantum numbers allowed? why or why not? n=4 l =1 ml = 2 ms= 1/ 2
no, if l=1, m2 = -1, 0 or 1 only
33. Describe the Bohr model of the atom. Why was this revolutionary? What was the main limitation
of Bohr's model? see text / notes
34. Draw a sketch of an s orbital, a p orbital and a d orbital. What is an orbital? What is a node? see
text / notes
35. Give the ground state electron configurations for Cr and Cu (using noble gas core notation) hint:
they're weird, you may need to look them up. Explain why the actual configuration does not match the
expected configuration for these two elements.
Cr: expect: [Ar] 4s23d4 but actual is: [Ar] 4s13d5 this is because a half filled d sublevel is a more
stable (lower energy) configuration.
Cu: expect: [Ar] 4s23d9 but actual is: [Ar] 4s13d10 this is because a filled d sublevel is a more
stable (lower energy) configuration.
36) What did Max Planck change about Maxwell’s equations? Why was this revolutionary? What phenomenon
was he trying to explain? see text / notes
37) A ground state H atom absorbs a photon of wavelength 94.91 nm, and its electron attains a higher energy
level. The atom then emits two photons: one of wavelength 1281 nm to reach an intermediate level, and a
second to reach the ground state. a) What higher level (n=?) did the electron reach?
b) What intermediate level (n=?) did the electron reach? c) What was the wavelength of the second photon
emitted? HINT: DRAW A PICTURE OF THE ELECTRON JUMPS. a) 5 b) 3
c) 103 nm
38) Enormous numbers of microwave photons are needed to warm macroscopic samples of matter. A portion
of soup containing 252 g of water is heated in a microwave oven from 20.ºC to 98 ºC, with radiation of
wavelength 0.0155 m. How many photons are absorbed by the water in the soup? (Hint: What’s the definition
of a calorie? How are calories related to Joules?) 6.4 x 1027
39. Cl- : [Ar]; Sr2+ : [Kr]; Zn2+ : [Ar]3d10; Fe2+ : [Ar]3d6
40. aluminum
41. Li, because its smaller (see notes for def)
42. Na, atomic radius decreases as you go across the table because effective nuclear charge increases.
43. Rb, atomic radius increases as you go down the table because you are adding entire shells of electrons and
increasing shielding of the nucleus.
44. Na, due to loss of the valence shell in the ion.
45.
a) K2O + H2O --> 2KOH(aq)
b) SO3 + H2O --> H2SO4(aq)
c) 2Na + 2H2O -->
2NaOH(aq) + H2(g)