Part B-2 and Part C
Questions 2011 Exam
Part B-2 Questions 2011 Exam
51 Explain, in terms of protons and neutrons, why U-235
and U-238 are different isotopes of uranium. [1]
Isotopes of an element have the same number of
protons but different number of neutrons.
(Recall atomic number = # of protons;
mass number = ( # of protons + neutrons)
U-235 versus
U-238
Base your answers to questions 52 through 54 on the information below.
The bright-line spectra for three elements and a mixture of elements are shown below.
52 Explain, in terms of both electrons and energy, how the bright-line spectrum
of an element is produced. [1]
53 Identify all the elements in the mixture. [1]
54 State the total number of valence electrons in a cadmium atom in the
ground state. [1]
52 Explain, in terms of both electrons and
energy, how the bright-line spectrum of an
element is produced. [1]
Possible Answers:
Bright line spectra are produced when
electrons in an excited state return to a lower
energy state; specific amounts of energy are
emitted and these energies are associated
with specific wavelengths of light that are
characteristic of the bright-line spectrum of
an element.
Or
Energy is emitted when excited electrons fall
back to lower shells.
Base your answers to questions 52
through 54 on the information
below.
The bright-line spectra for three
elements and a mixture of elements
are shown below.
53 Identify all the elements in the mixture. [1]
Answer: lithium and strontium (Sr and Li) Match spectral lines of unknown with the
reference spectra.
54 State the total number of valence electrons in a cadmium atom in the ground state.
[1] Answer: 2 valence electrons.
(Cd has a 2-8-18-18-2 electron configuration so 2 valence electrons).
Base your answers to questions 55 through 59 on the information below.
The ionic radii of some Group 2 elements are given in the table below.
Base your answers to questions 55 through 59 on the information below.
The ionic radii of some Group 2 elements are given in the table below.
55 and 56 On the grid in your
answer booklet, mark an
appropriate scale on the axis
labeled “Ionic Radius (pm).” [1]
On the same grid, plot the data
from the data table. Circle and
connect the points. [1]
(57) Estimate the ionic radius of strontium. [1] Answer: 117 pm ± 2 pm
Use P table to find Atomic # of Sr (38) and then use your graph
58 State the trend in ionic radius as the elements in Group 2 are considered in
order of increasing atomic number. [1]
Answer: As the atomic number of elements in Group 2 increases, the ionic radius
increases (Recall periodic trends.)
59 Explain, in terms of electrons, why the ionic radius of a Group 2 element is
smaller than its atomic radius. [1]
Answer: A Group 2 ion has two fewer electrons than the atom from which it was
formed.
Base your answers to questions 60 and 61 on the information below.
The balanced equation below represents the decomposition of
potassium chlorate.
2KClO3(s) → 2KCl(s) + 3O2(g)
60 Determine the oxidation number of chlorine in the reactant in the
equation. [1]
Answer: Oxidation number is +5 .
(Recall: use the sum rule to determine the oxidation number of chlorine
in KClO3 )
61 State why the entropy of the reactant is less than the entropy of the
products.
Answer: The gaseous product is more disordered than the solid
reactant or The solid reactant is more ordered than the products
(which are gas and solid).
Base your answers to questions 62 and 63 on the information below.
At 550°C, 1.00 mole of CO2(g) and 1.00 mole of H2(g) are placed in a 1.00-liter
reaction vessel. The substances react to form CO(g) and H2O(g). Changes in the
concentrations of the reactants and the concentrations of the products are shown in
the graph below.
62 Determine the change in the
concentration of CO2(g)
between time t0 and time t1. [1]
63 What can be concluded from
the graph about the
concentrations of the reactants
and the concentrations of the
products between time t1 and
time t2? [1]
Base your answers to questions 62 and 63 on the information below.
At 550°C, 1.00 mole of CO2(g) and 1.00 mole of H2(g) are placed in a 1.00-liter reaction vessel.
The substances react to form CO(g) and H2O(g). Changes in the concentrations of the reactants
and the concentrations of the products are shown in the graph below.
62 Determine the change in the
concentration of CO2(g) between
time t0 and time t1.
Answer: the concentration
decreases by 0.27 mol/L
63 What can be concluded from the
graph about the concentrations of
the reactants and the
concentrations of the products
between time t1 and time t2?
Answer: The concentrations of
reactants and products do not
change ( the concentrations
become constant)
Base your answers to questions 64 and 65 on the information below.
A reaction between bromine and a hydrocarbon is represented by the
balanced equation below.
64 Identify the type of organic reaction.
Br2 + C3H6
C3H6Br2
Answer: This is an addition reaction. (This is one of the types of organic
reactions that you need to know)
65 Write the name of the homologous series to which the hydrocarbon belongs.
Answer: Use Table Q to help you identify the answer as alkenes.
• Q 66-68 are based on the following Unbalanced Equation
electricity
O2 (g)
O3 (g)
66. Balance the equation using the smallest whole-number coefficients
67. Identify the type of Bonding between the atoms of oxygen
68. Identify , in terms of electron configuration, why an oxygen molecule
is more stable than an oxygen atom.
• Q 66-68 are based on the following Unbalanced Equation
O2 (g)
O3 (g)
(“electricity” written over the arrow)
66. Balance the equation using the smallest whole-number coefficients
3 O2
2 O3
(Balance for Mass; 6 O atoms on each side)
67. Identify the type of Bonding between the atoms of oxygen
Ans: Oxygen has 6 valence electrons and is a nonmetal; bonding will be covalent
68. Identify , in terms of electron configuration, why an oxygen molecule is more
stable than an oxygen atom.
Ans. A single O atom has six valence electrons and so does not have a stable octet
Q 69-70 are based on data for four components of natural gas
Components of Natural Gas
Boiling Point at Standard
Pressure ( oC )
Butane
-0.5
Ethane
-88.6
Methane
-161.6
Propane
-42.1
Q69. Identify a process used to separate the components
of natural gas.
Q70. List the four components of natural gas in order of
increasing strength of intermolecular forces.
Components of Natural
Gas
Boiling Point at Standard
Pressure ( oC )
Butane
-0.5
Ethane
-88.6
Methane
-161.6
Propane
-42.1
69. Ans: Distillation
(You want a separation technique based on differences in
boiling points/condensation points).
Distillation or selective condensation are possible processes).
Q70.
List in order of increasing strength of intermolecular forces.
( recall: the weaker the forces of attraction between molecules, the lower the
boiling pts)
Answer:
methane
ethane
propane
butane
Photos from POGIL on Distillation and Wikipedia
Typical lab Distillation Apparatus
www.chemheritage.org
Q 71-73 are based on the following reaction
NaCl + NH3 + CO2 + H2O
NaHCO3 + NH4Cl
71. Write the chemical formula for one compound in the equation
that contains both ionic bonds and covalent bonds.
72. Explain, in terms of electronegativity difference, why the bond
between hydrogen and oxygen in a water molecule is more
polar than the bond between hydrogen and nitrogen in an
ammonia molecule.
73. In the space in your answer booklet, draw a Lewis dot diagram
for the reactant containing nitrogen in the equation.
NaCl + NH3 + CO2 + H2O
NaHCO3 + NH4Cl
71. Either NaHCO3 or NH4Cl are acceptable answers
Compounds that contain polyatomic ions (HCO3 - or NH4 +will
have both ionic bonds and covalent bonds (Table E: Selected
Polyatomic Ions)
72. ANS: The electronegativity difference between oxygen and hydrogen (3.4-2.2 =
1.2) is greater than the electronegativity difference between nitrogen and
hydrogen (3.0-2.2 = 0.8) and so the bond between oxygen and hydrogen in
water is more polar than the bond between nitrogen and hydrogen in
ammonia. (Use table S for Electronegativity values)
73. Ans: Draw a dot diagram for NH3
(N has 5 valence electrons and each H atom has 1 valence
electron; atoms will bond in order to achieve the same
electron configuration as a noble gas)
73. Ans: Draw a dot diagram for NH3
•
•
•
•
•
•
N has 5 valence electrons (2-5 is the electron configuration listed in P. Table)
H atoms have 1 valence electron
Atoms will bond to achieve the same electron configuration as a noble gas.
Start by drawing the dot structures of each atom
Make shared pairs where needed
Tidy up dot diagram
Questions 74 – 76 are based on the following Data Table
Mixture 1
Mixture 2
composition
NaCl in H2O
Fe filings in H2O
Student observations
•Colorless liquid
•No visible solid in bottom of
beaker
•Colorless liquid
•Black solid on bottom of
beaker
Other data
Mass of dissolved NaCl (s) = 2.9 g
•Mass of Fe (s) = 15.9 g
•Density of Fe(s) = 7.87 g/cm3
74. Classify each mixture using the term “homogeneous” or
the term “heterogeneous”.
75. Determine the volume of the Fe filings used to produce
mixture 2.
76. Describe a procedure to physically remove the water from
mixture 1.
Mixture 1
Mixture 2
composition
NaCl in H2O
Fe filings in H2O
Student observations
•Colorless liquid
•No visible solid in bottom of
beaker
•Colorless liquid
•Black solid on bottom of beaker
Other data
Mass of dissolved NaCl (s) = 2.9 g
•Mass of Fe (s) = 15.9 g
•Density of Fe(s) = 7.87 g/cm3
74. Mixture 1 is homogeneous, Mixture 2 is heterogeneous.
75. Density = 7.87 g/cm3 so 7.87 g in 1 cm3
1 cm3
2.02
15.9 g x ________ = ______
cm 3
7.87 g
(You are given mass and density and need to find the volume. Solve with dimensional analysis
or use density formula in table T to solve for missing variable)
74. Water can be removed by…………..
Heating Salt Water removes the H2O from the Salt Water Mixture leaving NaCl behind.
(Pictures from Wikipedia (http://upload.wikimedia.org/wikipedia/commons/4/43/Image-Zigong_Salt.jpg and
http://upload.wikimedia.org/wikipedia/commons/9/9f/SaltCrystaUSGOV.jpg )
Other ways of removing water include” :
(1) Just allowing the water to evaporate at room temperature
(2) Removing water by distillation since Water and NaCl will have very different
boiling points
Salt Crystal NaCl (s)
Q 77-79 involve a lab experiment with Aluminum foil and
Copper(II) chloride solution. The reaction equation is given
and student observations are listed in a table.
2 Al (s) + 3 CuCl2 (aq)
3 Cu (s) + 2 AlCl3 (aq)
Procedure
Observation
In a beaker, completely dissolve 5.0 g of
CuCl2 in 80.0 mL of water.
•The solution is blue green
Cut 1.5 g of Al (s) foil into small pieces. Add
all the foil to the mixture in the beaker. Stir
the contents for 1 min.
•The surface of the Al(s) foil appears
partially black.
•The beaker feels warm to the touch.
Observe the beaker and contents after 10
minutes
•The liquid in the beaker appears colorless
•A reddish-brown solid is seen at the
bottom of the beaker
•Some pieces of Al(s) with a partially black
coating remain in the beaker
http://www.youtube.com/watch?v=zg-gsLEGk2A&feature=related for youtube video
for this experiment
Procedure
Observation
In a beaker, completely dissolve 5.0 g of
CuCl2 in 80.0 mL of water.
•The solution is blue green
Cut 1.5 g of Al (s) foil into small pieces. Add
all the foil to the mixture in the beaker. Stir
the contents for 1 min.
•The surface of the Al(s) foil appears partially
black.
•The beaker feels warm to the touch.
Observe the beaker and contents after 10
minutes
•The liquid in the beaker appears colorless
•A reddish-brown solid is seen at the bottom
of the beaker
•Some pieces of Al(s) with a partially black
coating remain in the beaker
77. State one observation that indicates Cu+2 ions became Cu
atoms.
Possible Answers:
The solution is no longer blue or blue green (characteristic of
Cu+2 ions in aqueous solution) .
Or
A reddish-brown solid is formed (corresponds to color of copper)
Q 77-79 continued
2 Al (s) + 3 CuCl2 (aq)
3 Cu (s) + 2 AlCl3 (aq)
78. Describe one change in the procedure that would cause the
reaction to occur at a faster rate.
Possible Answers:
• Increase the concentrations of the CuCl2 solution
• Cut the aluminum into even smaller pieces
• Use a catalyst
• Use heated solutions
79. State one safety procedure the student should perform after
completing the laboratory activity.
Possible answers: wash hands before leaving the lab or dispose of
chemicals as teacher instructs or wash and return equipment to
cabinets, etc.
Base your answers to questions 80 through 82 on the
information below.
Some carbonated beverages are made by forcing
carbon dioxide gas into a beverage solution. When a
bottle of one kind of carbonated beverage is first
opened, the beverage has a pH value of 3.
80. State, in terms of the pH scale, why this
beverage is classified as acidic.
Ans: beverage is acidic because its pH is less than than 7
What happens when CO2 (g)
is bubbled through water ?
(Hint; See table K Common Acids
81 Using Table M, identify one indicator that is yellow in a solution
that has the same pH value as this beverage.
Use Table L, Possible Answers = bromthymol blue, bromcresol green or thymol blue
82 After the beverage bottle is left open for several hours, the
hydronium ion concentration in the beverage solution decreases to
1/1000 of the original concentration. Determine the new pH of the
beverage solution.
Started at pH = 3 ( so H + ion concentration = 10 –pH = 1 x 10-3 M (mol/L)
New H+ concentration = 1 x 10-3 ÷ 1000 = 1 x 10-6 M
Remember pH = -log (H+) so the new pH = 6
• Base your answers to questions 83 through 85 on the information below.
Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily
used in devices designed to eliminate static electricity in machinery. It is also
used in brushes to remove dust from camera lenses.
Polonium-210 can be created in the laboratory by bombarding bismuth209 with neutrons to create bismuth-210. The bismuth-210 undergoes
beta decay to produce polonium-210. Polonium-210 has a half-life of 138
days and undergoes alpha decay.
83. State one beneficial use of Po-210.
(Extract answer from reading passage above)
• Base your answers to questions 83 through 85 on the information
below.
Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily used in devices
designed to eliminate static electricity in machinery. It is also used in brushes to remove dust from
camera lenses.
Polonium-210 can be created in the laboratory by bombarding bismuth-209 with neutrons to
create bismuth-210. The bismuth-210 undergoes beta decay to produce polonium-210.
Polonium-210 has a half-life of 138 days and undergoes alpha decay.
84. Complete the nuclear equation in your answer booklet for the
decay of Po-210, by writing a notation for the missing
product.
(Use ref table O, N and periodic table)
Ans booklet:
210 Po
84
4He
2
+ ________
• Base your answers to questions 83 through 85 on the information
below.
Polonium-210 occurs naturally, but is scarce. Polonium-210 is primarily used in devices
designed to eliminate static electricity in machinery. It is also used in brushes to remove dust from
camera lenses.
Polonium-210 can be created in the laboratory by bombarding bismuth-209 with neutrons to
create bismuth-210. The bismuth-210 undergoes beta decay to produce polonium-210.
Polonium-210 has a half-life of 138 days and undergoes alpha decay.
84. Complete the nuclear equation in your answer booklet for the
decay of Po-210, by writing a notation for the missing
product. (Use ref table O, N and periodic table)
Ans booklet:
210Po
84
4He
2
+
206Pb
82
85. Determine the total mass of an original 28.0-milligram sample of Po210 that remains unchanged after 414 days.
Steps: (1) determine the number of half-lives during
the elapsed time period
# of half-lives = total elapsed time ÷ half-life of isotope
414 days ÷ 138 = 3 half-lives
(2) Setup figure to predict the remaining mass
28.0 mg
85. Determine the total mass of an original 28.0-milligram sample of Po210 that remains unchanged after 414 days.
Steps: (1) determine the number of half-lives during
the elapsed time period
# of half-lives = total elapsed time ÷ half-life of isotope
414 days ÷ 138 = 3 half-lives
(2) Setup figure to predict the remaining mass
28.0 mg
14.0 mg
7.0 mg
3.5 mg