Key to Final Review Worksheet
Chem 101, Summer 2006
1. Indicate whether the following are exact or measured numbers:
a) 1 L = 1000 mL
Exact
b) The atomic mass of oxygen is 16.00 amu
Measured
c) The mass number of one isotope of nitrogen is 14
Exact
d) A solution of NaCl has a concentration of 2 M
Measured
e) The percent yield of a reaction was 70.0%
Measured
2. Write the following numbers in scientific notation:
a) 0.00432
4.32 x 10-3
b) 95000
9.5 x 104
c) 602
6.02 x 102
d) 0.300
3.00 x 10-1
3. Complete the following equalities:
a) 1 m =
0.001
b) 1 cm =
10
c) 1000 mg
d) 1 L =
km
mm
1
g
1 x 10-6
e) 1 Mbyte =
L
1 x 106
bytes
4. Complete the following statements regarding accuracy and precision:
a) The average value for 10 experiments was close to the true value, so it was
accurate .
b) The values obtained for the 10 experiments had a wide range, so the average value
was not precise .
c) Another class did the experiment and their average value was far from the true
value, but the 10 values had a narrow range, so the average value was
precise but not accurate .
5. Water is 11.2% by mass hydrogen and 88.8% by mass oxygen.
a) How many grams of water would contain 5.0 g of hydrogen?
g H  g H2O
5.0 g H x 100 g H2O/11.2 g H = 45 g H2O
b) How many grams of water would contain 2.25 kg of oxygen?
2.25 kg x 1000 g/1kg = 2250 g
2250 g x 100 g/88.8 g = 2530 g
6. If 10.0 mL of water and 10.0 mL of olive oil are placed in a 100 mL graduated
cylinder and then stirred vigorously,
a) What kind of mixture do they form?
Suspension
b) Some time later the mixture has separated. Which substance is on top and why?
The olive oil is on top because it is less dense than water.
c) If a 3.00 g piece of aluminum, which has a density of 2.70 g/mL, is placed in the
cylinder, what is the new volume that you would read?
d = m/V
V = m/d
Vmetal = 3.00 g/2.70 (g/mL) = 1.11 mL
Vfinal = Vliquid + Vmetal = 20.0 mL + 1.11 mL = 21.1 mL
7. Give the name of the element represented by each of the following symbols:
a) Si
Silicon
b) B
Boron
c) Ag
Silver
d) Pb
Lead
e) Ca
Calcium
f) Br
Bromine
8. Write the symbol for each of the following elements:
a) Potassium
K
b) Argon
Ar
c) Tin
Sn
d) Phosphorus
P
e) Gold
Au
f) Iron
Fe
9. Complete the following statements about metals and nonmetals:
a)
Metals
are good conductors of heat.
b)
Nonmetals
typically have low densities.
c) When they form ions, metals typically
d) Metals usually form
ionic
lose
bonds with nonmetals.
e) A covalent bond is usually formed between a
10. Make a sketch of an atom.
neutrons.
electrons.
nonmetal
and a
nonmetal
.
Show the locations of the electrons, protons and
Nucleus (contains protons and neutrons)
Electron cloud (where electrons are most likely found)
11. If the atomic number is 17 and the mass number is 37,
a) What is the element?
Cl
b) How many electrons does it have?
17
c) How many neutrons does it have?
20
12. The three isotopes of silicon have the following abundances:
4.70% and 30Si = 3.10%. What is the atomic mass of silicon?
28S
= 92.2%,
(0.922 x 28 g) + (0.0470 x 29 g) + (0.0310 x 30 g) = 28.1 g
13. Write the electron configuration for arsenic:
1s22s22p63s23p64s23d104p3
14. Indicate the element that meets the following conditions:
a) Has 5 electrons in shell 3
b) Has four 3p electrons
P
S
c) Is in group 7A and electrons in shell 5
I
29Si
=
d) Has 5 electrons, 3 of which are valence electrons
B
15. Why can the 3p subshell have a maximum of 6 electrons, while the 3s subshell can
only have a maximum of 2 electrons?
The 3p subshell has 3 orbitals, each of which can have a maximum of 2 electrons, while
the 3s subshell has only one orbital.
16. Complete the following nuclear equations:
a) 210Po 
206Pb
+ 
c)
235U
+ n
143Xe
e)
88Br

+ n
87Br
+
90Sr
+ 3 1n
b)
140La

d)
196At
 4He +
f)
131I

138La
131Xe
+ 2 1n
192Bi
+ 
17. Complete the following statements regarding alpha, beta and gamma emitters:
a)
Gamma
emitters travel the farthest through tissue.
b) Gloves, safety glasses and a labcoat are generally sufficient protection for
working with
alpha
emitters.
c) Plexiglass provides good protection from
beta
emitters.
18. If the half-life of 131I is 8 days, how long will it take for a 300 Ci dose given to a
patient take to decay to a safe level (say less than 40 Ci)?
((300/2)/2)/2 = 37.5 Ci = 3 half-lifes = 24 days
19. Write the electron-dot structures for the following atoms, ions, ionic compounds
and covalent compounds:
a)
N
b)
e)
Cl
Ca2+ Cl
Br
P
c)
Li
f)
H
O
H
O
H
d)
I
g)
H
Cl
H
O
K
Br
h)
O
C
O
H
i)
Br
j)
H
C
Br
H
k)
l)
H
C
N
20. The dots in electron-dot structures represent
valence
electrons.
21. What is the octet rule?
The tendency of elements of Groups 1-7A to form ionic or covalent bonds with other
atoms in order to obtain a full octet (or full outer shell of electrons).
22. Positive ions are formed when atoms
negative ions are formed when atoms
lose
gain
electrons and
electrons.
23. Classify each of the following as an ionic or a covalent compound:
a) Li2S
b) CCl4
c) MgO
d) HCl
e) C4H10
Ionic
Covalent
Ionic
Covalent
Covalent
24. For each of the following compounds, give the name and the molecular geometry
(shape), and classify each as polar or nonpolar overall:
a) H2S
b) CO2
Dihydrogen sulfide, bent, polar Carbon dioxide, linear, nonpolar
c) BF3
Boron trifluoride, trigonal planar,
Nonpolar
d) PF3
Phosphorus trifluoride,
pyramidal, polar
e) SiCl4
f) HCl
Silicon tetrachloride, tetrahedral, nonpolar
Hydrogen chloride, linear, polar
25. Identify the type of attractive force that would occur between molecules of the
following substances:
a) Na2S
b) Br2
c) CH3OH
d) HF
e) CHCl3
Ionic
Dispersion
H-bonding
H-bonding
Dipole-dipole
26. Identify which of each of the following pairs of compounds would have a higher
boiling point:
a) HCl or HF
b) K2SO4 or H2SO4
c) PH3 or BH3
d) CS2 or H2S
e) C2H6 or C4H8
g) Br2 or HBr
h) CO2 or COS
f) CCl4 or CH2Cl2
27. The melting point of benzene is 5.5C and its boiling point is 80.1C. Draw a
heating curve for benzene as it goes from 0C to 100C. Label the x and y axes, physical
states and melting and boiling point on the graph.
100
Temp.
gas
b.p. (liquid + gas)
80.1
( C)
liquid
5.5
0
solid
m.p. (solid + liquid)
Heat Added
28. If an ice cube tray holds 325 g of water, and the water is initially at 25C, how much
heat (in kcals) must be removed in order to cool the water to 0C and then freeze it?
(Given that for water: specific heat = 1.00 cal/g ºC, heat of fusion = 80 cal/g and heat of
vaporization = 540 cal/g)
325 g x 25C x (1.00 cal/g C) = 8125 cal
325 g x (80. cal/g) = 26000 cal
Total heat removed = (8125 cal + 26000 cal) x (1 kcal/1000cal) = 34 kcal
29. Balance the following chemical equations and identify the type, or types, or
reaction:
a) 3Mg(s) + N2(g)  Mg3N2(s)
Combination, redox, exothermic
+
Heat
b) Cl2(g) + 2KI(aq)  2KCl(aq)
Single replacement, redox, precipitation
+
I2(s)
c) NaHCO3(s) + HCl(aq)
Acid/base, decomposition
d) 3H2SO4(aq) + 2Al(OH)3(s)
Acid/base, double replacement


NaCl(aq)
+
Al2(SO4)3(aq)
CO2(g)
+
+
H2O(l)
6H2O(l)
30. For the following redox reactions, identify what is being oxidized and what is being
reduced:
a) 2K + Br2  2KBr
K is oxidized, Br is reduced
b) 2AgNO3 + Cu  Cu(NO3)2 + 2Ag
Cu is oxidized, Ag is reduced
31. Draw an energy diagram for a reaction that is endothermic and slow.
a) Label the diagram with the following: x-axis (what does it represent?), y-axis (what
does it represent?), reactant(s), product(s), transition state, activation energy (E A) and
heat of reaction.
Transition State
Curve for added catalyst
EA
E
Products
Heat of reaction (absorbed)
Reactants
Reaction Progress
b) Is heat
released
or
absorbed ?
c) What would happen if you added a catalyst to the reaction?
The activation energy would be lowered and the reaction would go faster.
d) Draw a line on the diagram to show how addition of a catalyst would change the
diagram.
e) If the reaction represented in the diagram were reversible, would the equilibrium
favor reactants or products?
Reactants
f) If reversible, which way would the equilibrium shift if heat was added?
Towards products
32. According to LeChâtelier’s principle, which way will the equilibrium of the reaction
shown below be shifted under the following conditions?
N2 (g) + 3H2 (g)  2NH3 (g) + 22 kcal
a) NH3 is added
Towards reactants
b) heat is removed
Towards products
c) H2 is added
Towards products
33. 1.00 mol of Ca(OH)2 contains:
a) How many moles of hydrogen?
1.00 mol Ca(OH)2 x (2 mol H/1 mol Ca(OH)2) = 2.00 moles H
b) How many atoms of oxygen?
1.00 mol Ca(OH)2 x (2 mol O/1 mol Ca(OH)2) x (6.02 x 1023) = 1.20 x 1024 atoms O
c) How many grams of calcium?
1.00 mol Ca(OH)2 x (1 mol Ca/1 mol Ca(OH)2) x (40.08 g/1 mol) = 40.1 g Ca
34. Consider the following reaction: Pb(NO3)2 + 2KCl  PbCl2 + 2KNO3
a) If 3.00 grams of Pb(NO3)2 is reacted with sufficient KCl, how many grams of PbCl2
will be formed?
Molar mass Pb(NO3)2 = 207.2 g + (2 x 14.01 g) + (6 x 16.00 g) = 331.22 g
Molar mass PbCl2 = 207.2 g + (2 x 35.45 g) = 278.1 g
3.00 g x (1 mol/331.22 g) x (1 mol/1 mol) x (278.1 g/1 mol) = 2.52g PbCl2
b) How many grams of KCl are required to react with 3.00 g of Pb(NO3)2?
Molar mass KCl = 39.10 g + 35.45 g = 74.55 g
3.00 g x (1 mol/331.22 g) x (2 mol/1 mol) x (74.55 g/1 mol) = 1.35 g KCl
c) If 2.0 moles each of Pb(NO3)2 and KCl are reacted, which is the limiting reactant?
2.0 mol Pb(NO3)2 x (1 mol PbCl2/1 mol Pb(NO3)2) = 2.0 mol PbCl2
2.0 mol KCl x (1 mol PbCl2/2 mol KCl) = 1.0 mol PbCl2
KCl is the limiting reactant
d) If the percent yield of the reaction in part (a) is 85%, what is the actual yield?
% yield = (actual yield/theoretical yield) x 100%
actual yield = (% yield/100%) x theoretical yield = 0.85 x 2.52 g = 2.1 g PbCl2
35. Consider the following reaction:
PCl5  PCl3 + Cl2
a) Write the equilibrium expression:
Keq = [PCl3][Cl2]/[PCl5]
b) If Keq = 2 x 10-2, does the equilibrium favor reactants or products? Reactants
c) If Cl2 is removed from the reaction, does the Keq get larger or smaller? Larger
36. Complete the following statements regarding gases:
a) At constant T and n, the pressure ___decreases__ when V is increased.
b) At STP, the moles of gas have to __increase__ for V to increase.
c) At constant V and n, the pressure ___increases__ when T is increased.
d) At constant P and n, the density ___decreases___ when T is increased.
37. If T and n are constant, what will be the new V of a balloon that is initially at 1.0 L
and 1.0 atm if the P is increased to 10.0 atm?
P1V1 = P2V2 V2 = P1V1/P2 = (1.0 atm)(1.0 L)/10.0 atm = 0.10 L
38. A balloon with a volume is filled with 50.0 g of He gas at 25.0ºC and 1.00 atm. What
is the volume of the He gas in the balloon? (R = 0.0821 L atm/mol K)
T = 25.0 + 273 = 298 K
n = 50.0 g He x (1 mol/4.003 g) = 12.5 mol
PV = nRT
V = nRT/P = (12.5 mol)(0.0821 L atm/mol K)(298 K)/1.00 atm = 306 L
39. In a lab experiment, a 0.280 L glass container is filled with CO2 gas at 22.0ºC and 762
mmHg, and the mass of the CO2 in the container is measured to be 0.508 g, what is the
experimentally determined molar mass of CO2? (R = 62.4 L mmHg/mol K)
T = 22.0 + 273 = 295 K
PV = nRT
n = PV/RT = (762 mmHg)(0.280 L)/(62.4 mmHg/mol K)(295 K) = 0.0116 mol
molar mass = 0.508 g/0.0116 mol = 43.8 g/mol
40. What is the density (g/L) of hydrogen gas at STP?
At STP, 1 mol H2 = 22.4 L = 2.016 g
d = m/V = 2.016 g/22.4 L = 0.0900 g/L
41. A scuba diving tank with a volume of 10.0 L contains 10.0 moles He gas and 20.0
moles O2 gas at 25.0ºC.
a) What is the total pressure (in atm) in the tank? (R = 0.0821 L atm/mol K)
Ptotal = PHe + PO2 (And, since V, R and T are the same for both gases, we can just add
the moles and plug the total into our equation)
T = 25.0 + 273 = 298 K
n = 10.0 mol + 20.0 mol = 30.0 mol
PV = nRT
P = nRT/V = (30.0 mol)(0.0821 L atm/mol K)(298 K)/10.0 L = 73.4 atm
(or, you could calculate each pressure individually this way and add them up)
b) What is the partial pressure of each gas in the tank?
PHe = (10.0 mol)(0.0821 L atm/mol K)(298 K)/10.0 L = 24.5 atm
PO2 = (20.0 mol)(0.0821 L atm/mol K)(298 K)/10.0 L = 48.9 atm
(or, PO2 = 73.4 atm – 24.5 atm = 48.9 atm)
(or, PHe = 73.4 atm x 10.0 mol/30.0 mol = 24.5 atm, etc.)
42. Indicate whether each of the following substances are soluble in water:
a) SiH4
No
e) Cu(NO3)2
Yes
i) CaS
No
b) HF
Yes
f) KOH
Yes
j) PbCl2
No
c) CH3CO2H
Yes
g) CaSO4
No
k) Pb(CH3CO2)2
Yes
d) C3H8
No
h) NaH2PO4
Yes
l) KBr
Yes
43. Write a balanced equation for the dissociation of the following strong electrolytes in
water:
a) CaCl2
CaCl2  Ca2+ + 2Cl-
b) K2SO4
K2SO4  2K+ + SO42-
44. NaCl has a solubility of 36.0 g/100 g H2O at 20ºC. How many grams of NaCl are
needed to prepare a saturated solution using 250.0 mL of H2O? (density of H2O = 1.00
g/mL)
250.0 mL H2O x (1.00 g/1 mL) x (36.0 g NaCl/100 g H2O) = 90.0 g NaCl
45. KCl has a solubility of 42.6 g/100 g H2O at 50.0ºC and 34.0g/100 g H2O at 20.0ºC. If
a saturated solution of KCl is made using 0.500 L of H2O at 50.0ºC and then cooled to
20.0ºC, how many grams of KCl will precipitate out of the solution?
At 50C, 0.500 L H2O x (1000 mL/1 L) x (1.00 g/1 mL) x (42.6 g KCl/100 g H2O = 213 g
At 20C, 0.500 L H2O x (1000 mL/1 L) x (1.00 g/1 mL) x (34.0 g KCl/100 g H2O = 170 g
Grams KCl that precipitate = 213 g – 170 g = 43 g
46. How many liters of 10.0% (v/v) ethanol solution (such as wine) would provide 175
mL of ethanol?
175 mL ethanol x (100 mL wine/10.0 mL ethanol) x (1 L/1000 mL) = 1.75 L
47. If 10.0 g of KCl is dissolved in water to a total volume of 0.500 L, what is the
molarity of the solution?
10.0 g x (1 mol/74.55 g) = 0.134 mol
0.134 mol/0.500 L = 0.268 M
48. If you were in the laboratory, how would you prepare 250.0 mL of a 0.100 M
solution of NaOH?
250.0 mL x (1 L/1000 mL) x (0.100 mol/L) x (39.998 g/1 mol) = 1.00 g NaOH needed
1. Weigh out 1.00 g NaOH and add to 250.0 mL volumetric flask
2. Add some water to dissolve NaOH
3. Add water to a total volume of 250.0 mL
49. If you were in the laboratory, how would you prepare 1.0 L of a 5.0% (m/v)
solution of NaCl?
1.0 L solution x (1000 mL/1 L) x (5.0 g NaCl/100 mL solution) = 50. g NaCl needed
1. Weigh out 50. g NaCl and add to 1.0 L volumetric flask
2. Add some water to dissolve NaCl
3. Add water to a total volume of 1.0 L
50. Consider the following reaction:
Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)
a) How many grams of Mg are required to react with 50.0 mL of 2.00 M HCl?
mL HCl  L HCl  mol HCl  mol Mg  g Mg
50.0 mL x (1 L/1000 mL) x (2.00 mol HCl/1 L) = 0.100 mol HCl
0.100 mol HCl x (1 mol Mg/2 mol HCl) x (24.31 g/1 mol) = 1.22 g Mg
b) How many L of H2 gas will be produced when 0.100 L of a 6.0 M HCl solution reacts
with sufficient Mg at STP?
L HCl(aq)  mol HCl(aq)  mol H2(g)  L H2(g)
0.100 L HCl x (6.0 mol/1 L) x (1 mol H2/2 mol HCl) = 0.30 mol H2
0.30 mol x (22.4 L/1 mol) = 6.7 L H2
c) If 0.500 L of HCl solution reacts with sufficient Mg to produce 10.0 L of H2 gas at
STP, what is the molarity of the HCl solution?
L H2(g)  mol H2(g)  mol HCl(aq)  M HCl(aq)
10.0 L H2 x (1 mol/22.4 L) x (2 mol HCl/1 mol H2) = 0.893 mol HCl
0.893 mol/0.500 L = 1.79 M
51. State whether the salt formed in each of the following reactions would make a
neutral, basic or acidic solution when dissolved in water:
a) KOH + HCl  KCl + H2O
Neutral
b) NH3 + HBr  NH4Br
Acidic
c) NaOH + CH3CO2H  NaCH3CO2 + H2O
Basic
52. What would happen to a red blood cell that was placed into each of the following
types of solution?
a) hypotonic
Cell swells and bursts (water flows in due to osmosis)
b) isotonic
Nothing happens (inside and outside cell are same)
c) hypertonic
Cell shrivels (water flows out due to osmosis)
53. If you were in the laboratory, how would you isolate the NaCl from a mixture
containing the following substances: water and small amounts of NaCl, CaCO 3 and
starch? (Hint: requires 3 steps)
1. Filter out CaCO3, which is insoluble in water and so forms a suspension.
2. Use dialysis to remove the starch (starch stays inside the bag and NaCl flows out).
3. Evaporate the water to obtain the solid NaCl.
54. Give the conjugate base for each of the following Brønstead-Lowry acids:
a) HNO3
NO3-
b) H3O+
H2O
c) H2PO4HPO42-
d) NH3
NH2-
55. Give the conjugate acid for each of the following Brønstead-Lowry bases:
a) HCO3H2CO3
b) SO42HSO4-
56. For the following reaction:
c) NH3
NH4+
d) H2O
H3O+
CH3CO2H + H2O  CH3CO2- + H3O+
a) Identify which reactant is the acid and which is the base.
Acid = CH3CO2H, Base = H2O
b) Identify the conjugate acid and conjugate base.
Conjugate acid = H3O+, Conjugate base = CH3CO2c) Write the equilibrium expression for the reaction.
Ka = [CH3CO2-][H3O+]/[CH3CO2H]
d) Ka = 1.8 x 10-5 for CH3CO2H. Does the equilibrium favor
reactants or products ?
e) Could you make a buffer with CH3CO2H? If so, what would you add besides
CH3CO2H and H2O?
Yes, CH3CO2H is a weak acid, so can be used to make a buffer. You would need to add
a salt that contains its conjugate base, such as NaCH3CO2.
57. Will the conjugate base of H2SO4 be a
strong base or a weak base ?
58. If 1.0 g of HCl is dissolved in H2O to a total volume of 250 mL, what is the pH of the
solution?
HCl + H2O  H3O+ + Cl1.0 g HCl x (1 mol/36.458 g) x (1 mol H3O+/1 mol HCl) = 0.0274 mol H3O+
[H3O+] = 0.0274 mol/0.250 L = 0.11 M
pH = - log (0.11) = 0.96
59. Since H2O can act as either a weak acid or a weak base, it can react with itself.
a) Write a balanced chemical equation for the reaction.
2H2O  H3O+ + OHb) Write the expression and give the value for Kw.
Kw = [H3O+][OH-] = 1.0 x 10-14
c) Write the expression and give the value for pKw.
pKw = pH + pOH = 14.00
60. What is the pH of a neutral aqueous solution?
7.00
61. What is the concentration of OH- if the concentration of H3O+ = 1.0 x 10-5 M?
[OH-] = 1.0 x 10-14/1.0 x 10-5 = 1.0 x 10-9 M
62. What is the pH of a solution that has a pOH of 5.50?
pH = 14.00 – 5.50 = 8.50
63. What is the pH of a solution that has an OH- concentration of 1.0 x 10-3 M?
[H3O+] = Kw/[OH-] = 1.0 x 10-14/1.0 x 10-3 = 1.0 x 10-11 M
pH = -log[H3O+] = -log(1.0 x 10-11) = 11.00
64. Complete and balance the following reactions:
a) Ca + 2HNO3  Ca(NO3)2 + H2
b) KHCO3 + HCl  KCl + CO2 + H2O
c) CH3CO2H + NaOH  CH3CO2Na + H2O
65. A phosphate buffer is made by dissolving H3PO4 and NaH2PO4 in water.
a) Write the equation that shows how the buffer would neutralize a small amount of
added HCl (remember HCl + H2O  H3O+ + Cl-):
CH3CO2- + H3O+  CH3CO2H + H2O
(added acid is neutralized by acetate to form acetic acid and water)
b) Write the equation that shows how the buffer would neutralize a small amount of
added NaOH (remember NaOH  Na+ + OH-):
CH3CO2H + OH-  CH3CO2- + H2O
(added base is neutralized by acetetic acid to form acetate and water)
c) Calculate the theoretical pH of a buffer that is 0.15 M H3PO4 and 0.20 M H2PO4- (Ka
for H3PO4 = 7.5 x 10-3).
[H3O+] = Ka x [H3PO4]/[H2PO4-] = (7.5 x 10-3) x (0.15/0.20) = 5.625 x 10-3 M
pH = -log[H3O+] = -log(5.625 x 10-3) = 2.25
66. How much H2O is needed to dilute 10.0 mL of 2.00 M NaOH to 0.500 M?
M1V1 = M2V2
V2 = M1V1/M2 = (2.00 M x 0.0100 L)/0.500 M = 0.0400 L = 40.0 mL
40.0 mL – 10.0 mL = 30.0 mL
67. If it takes 25.0 mL of 0.250 M KOH to titrate 10.0 mL of HBr solution to the
endpoint, what is the molarity of the HBr solution?
Balanced neutralization equation: HBr + KOH  H2O + KBr
0.0250 L KOH x (0.250 mol/1 L) x (1 mol HBr/1 mol KOH) = 6.25 x 10-3 mol HBr
6.25 x 10-3 mol HBr/0.0100 L = 0.625 M HBr
68. If it takes 15.0 mL of NaOH to titrate 20.0 mL of a 0.100 M solution of H2SO4 to the
endpoint, what is the molarity of the NaOH?
Balanced neutralization equation: H2SO4 + 2NaOH  2H2O + Na2SO4
0.0200L H2SO4 x (0.100 mol/L) x (2 mol NaOH/1 mol H2SO4) = 0.004 mol NaOH
0.004 mol/0.0150 L = 0.267 M NaOH