Honors
Chemistry
FINAL
Study
Guide‐
117
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Atomic Concepts: 9 Questions
1. Compared to the charge and mass of a proton, an electron has
a) the same charge and a smaller mass
b) the same charge and the same mass
c) an opposite charge and a smaller mass
d) an opposite charge and the same mass
c- Protons are positively charged and have a mass of 1.00720 amu;
electrons are negatively charged and have a mass of 0.00055 amu.
2. When alpha particles are used to bombard gold foil, most of the alpha
particles pass through undeflected. This result indicates that most of the
volume of a gold atom consists of
a) deuterons
b) neutrons
c) protons
d) unoccupied space
d- Because most of the particles do not hit anything (pass right through),
one can infer the atom is mostly empty space.
3. A proton has approximately the same mass as
a) a neutron
b) an alpha particle
c) a beta particle
d) an electron
a- A proton has the same mass as a neutron. An electron has the same
mass as a beta particle. An alpha particle has a mass of 4: two protons
plus two neutrons.
4. When electrons in an atom in an excited state fall to lower energy
levels, energy is
a) absorbed, only
b) released, only
c) neither released nor absorbed
d) both released and absorbed
b- The ground state is the lowest energy state. To raise the atom to an
excited state, energy must be added. To fall back to the ground state
(lowest energy), the energy it had absorbed must be released.
5. A neutron has approximately the same mass as
a) an alpha particle
b) a beta particle
c) an electron
d) a proton
d- Protons and neutrons each have a mass of 1 amu. Electrons have
negligible mass. Beta particles are electrons that come from the nucleus.
6. Which symbols represent atoms that are isotopes?
a) C-14 and N-14
b) O-16 and O-18
c) I-131 and I-131
d) Rn-222 and Ra-222
b- Isotopes are atoms of the same element (same atomic number) but
with a different number of neutrons (different atomic mass). Only choice
b is correct. Choice A: C and N are not the same elements. Choice C:
both are the same element but there is no difference in mass. Therefore,
they are not isotopes. Choice D: not the same elements.
7. Which atom contains exactly 15 protons?
a) P-32
b) S-32
c) O-15
d) N-15
a- An atom with 15 protons also has an atomic number of 15. Refer to
the Periodic Table for element 15 (phosphorus).
8. An ion with 5 protons, 6 neutrons, and a charge of 3+ has an atomic
number of
a) 5
b) 6
c) 8
d) 11
a- The number of protons is the same as the atomic number. There are 5
protons so the atomic number is also 5.
9. What is the mass number of an atom which contains 28 protons, 28
electrons, and 34 neutrons?
a) 28
b) 56
c) 62
d) 90
c- Atomic mass is found by adding protons plus neutrons. 28 + 34 = 62.
Electrons have a mass of nearly 0, so they are not counted in the formula
for atomic mass.
Periodic Table: 10 questions
1. Which three groups of the Periodic Table contain the most elements
classified as metalloids (semimetals)?
a) 1, 2, and 13
b) 2, 13, and 14
c) 14, 15, and 16
d) 16, 17, and 18
c- Go to the Periodic Table and note the location of the stepped line
dividing metals and nonmetals. Elements next to the left or right of this
line are metalloids. Choice C includes 5 metalloids.
2. Which element has the highest first ionization energy?
a) sodium
b) aluminum
c) calcium
d) phosphorus
d- On the periodic table, ionization energy usually increases from left to
right across a period and up a group. This means that the closer an
element is to fluorine on the periodic table the higher its ionization
energy will be. Electronegativity values follow this same trend.
3. Which of the following elements has the smallest atomic radius?
a) nickel
b) cobalt
c) calcium
d) potassium
a- On the periodic table, atomic radius (size) decreases from left to right
across a period and up a group. This makes fluorine the smallest atom.
The closer an element is to fluorine on the periodic table the smaller it’s
atomic radius will be.
4. Which halogens are gases at STP?
a) chlorine and fluorine
b) chlorine and bromine
c) iodine and fluorine
d) iodine and bromine
a- Iodine is a solid and bromine is a liquid. The gaseous halogens are
chlorine and fluorine.
5. When combining with nonmetallic atoms, metallic atoms generally
will
a) lose electrons and form negative ions
b) lose electrons and form positive ions
c) gain electrons and from negative ions
d) gain electrons and form positive ions
b- Metals tend to lose electrons and form positive ions. A neutral atom
of Li has 3 protons (+) and 3 electrons (-). If it loses an electron, the Li
atom now has +3 and -2 or a net charge of +1. Metals also have low
electronegativities and low ionization energies.
6. Which set of elements contains a metalloid?
a) K, Mn, As, Ar
b) Li, Mg, Ca, Kr
c) Ba, Ag, Sn, Xe
d) Fr, F, O, Rn
a- Go to the Periodic Table and note the location of the stepped line
dividing metals and nonmetals. Elements next to the left or right of this
line are metalloids. As (Arsenic) is a metalloid.
7. Atoms of elements in a group on the Periodic Table have similar
chemical properties. This similarity is most closely related to the atoms'
a) number of principal energy levels
b) number of valence electrons
c) atomic numbers
d) atomic masses
b- Most of the time elements in the same group have the same number
of valence electrons. Valence electrons are involved in bonding and this
effects how elements react and determines their chemical properties.
8. As atoms of elements in Group 16 are considered in order from top to
bottom, the electronegativity of each successive element
a) decreases
b) increases
c) remains the same
a- Electronegativity usually increases from left to right across a period
and from the bottom up to the top of a group. Flourine has the highest
electronegativity, and the closer an element is to fluorine, on the periodic
table, the higher its electronegativity will be.
9. An atom of which of the following elements has the greatest ability to
attract electrons?
a) silicon
b) sulfur
c) nitrogen
d) iodine
d- Electronegativity is a measure of the ability of an atom to attract
electrons. The greater the ability to attract, the higher the
electronegativity. Chlorine has the highest electronegativity of the
choices given.
10. At STP, which substance is the best conductor of electricity?
a) nitrogen
b) neon
c) sulfur
d) silver
d- The best conductors of electricity are metals. Silver is a metal, the
others are nonmetals.
Moles/Stoichiometry: 15 questions
1. Given the unbalanced equation: Al + O2 = Al2O3 When this equation
is completely balanced using the smallest whole numbers, what is the
sum of the coefficients?
a) 9
b) 7
c) 5
d) 4
a4Al + 3O2 2 Al2O3. Add 4+3+2 to get 9.
2. What is the empirical formula of the compound whose molecular
formula is P4O10?
a) PO
b) PO2
c) P2O5
d) P8O20
c- Take P4O10 and reduce it to the smallest whole number ratio of atoms.
In math this would be called reducing to lowest terms. P4O10 reduced by
2 equals P2O5.
3. What is the gram formula mass of K2CO3?
a) 138 g
b) 106 g
c) 99 g
d) 67 g
a- Find the formula mass in grams. K =39 x 2 = 78 g; C =12 x 1 = 12 g;
O =16 x 3 = 48 g. Total is 78 + 12 + 48 or 138 g.
4. What is the total number of atoms contained in 2.00 moles of nickel?
a) 58.9
b) 118
c) 6.02 x 1023
d) 1.2 x 1024
d- By definition one mole is 6.02 x 1023 atoms. Two moles is twice that
amount or 12.04 x 1023 atoms or 1.2 x 1024. (Do not forget to move the
decimal). Answer is 1.2 x 1024 atoms. See the long poster on the wall if
you forget Avogadro's number.
5. What is the percent by mass of oxygen in magnesium oxide, MgO?
a) 20%
b) 40%
c) 50%
d) 60%
b- Solve the problem by first finding the ratio of the mass of oxygen to
the mass of the compound; then multiply by 100.
MgO has a mass of 24 + 16.
Percent by mass of O = 16 / 40
Reduce to lowest terms: 2 / 5 or .4 and multiply by 100. Answer is 40%.
16 / 40 x 100% = 40%
6. Which solution is the most concentrated?
a) 1 mole of solute dissolved in 1 liter of solution?
b) 2 moles of solute dissolved in 3 liters of solution?
c) 6 moles of solute dissolved in 4 liters of solution?
d) 4 moles of solute dissolved in 8 liters of solution?
c- Find the molarity ( moles of solute/liter of solution) for each answer.
#1) 1 mole / 1 liter or 1 M.
#2) 2 moles / 3 liters or 0.67 M.
#3) 6 moles / 4 liters or 1.5 M.
#4) 4 moles / 8 liters or 0.5 M.
Choice C (1.5 M. ) is the most concentrated.
7. What is the total number of moles of hydrogen gas contained in 9.03 x
1023 molecules of H2?
a) 1.5 moles
b) 2.00 moles
c) 6.02 moles
d) 9.03 moles
a- Divide 9.03 x 1023 by 6.02 x 1023 to find the number of moles of
hydrogen gas. 9.02 / 6.02 = 1.5 moles (remember the numerator and
denominator each contain 10 to the 23, so this cancels out. 1 mole equals
6.02 x 1023 molecules).
8. A compound is 86% carbon and 14% hydrogen by mass. What is the
empirical formula for this compound?
a) CH
b) CH2
c) CH3
d) CH4
b- Step 1: change percent to grams.
Step 2: find out how many moles
you have of C and H by: 86 g / 12 g per mole of C = 7 moles of C;
14 / 1 g per mole H = 14 moles of H.
Step 3: find the ratio of moles of C and H to each other: 14 / 7 is 2.
In other words there are 2 H moles for every C mole or CH2. This is the
empirical formula.
9. What is the total number of moles of H2SO4 needed to prepare 5.0
liters of a 2.0 M solution of H2SO4?
a) 2.5
b) 5.0
c) 10
d) 20
c- Molarity = moles of solute / volume of solution (L).
Change the formula to find moles.
Moles = molarity x volume of solution (L) or 2.0 M x 5.0 L = 10 moles
of H2SO4
10. What is the mass in grams of 3.0 x 1023 molecules of CO2?
a) 22 g
b) 44 g
c) 66 g
d) 88 g
a- 1 mole of CO2 has a formula mass of 44 grams and contains 1 mole
of molecules (6.02 x 1023). You are given 3 x 10 23 equals 1/2 the mass
of 1 mole of CO2 or
1/2 x 44 = 22 g.
11. At STP, 32.0 liters of O2 contain the same number of molecules as
a) 22.4 L Ar
b) 28.0 L of N2
c) 32. 0 L of H2
d) 44.8 L of He
c- At the same temperature and pressure, equal volumes of gases have an
equal (the same) number of molecules. This is known as Avogadro's
Law.
12. What is the molarity of a KF (aq) solution containing 116 grams of
KF in 1.00 liter of solution?
a) 1.00 M
b) 2.00 M
c) 3.00 M
d) 4.00 M
b- Molarity = step 1: find the moles of solute using the formula: mass
of solute (g) divided by formula mass of solute
Step 2: divide moles of solute by volume of solution in liters M / V.
Or if you know the moles of solute,
Molarity = moles of solute divided by volume of solution in liters .
KF has a formula mass of 39 + 19 or 58 g/mole. Since 116 grams are
given, 116g / 58g/mole = 2 moles of solute.
To find the Molarity, take 2 moles of solute and divide by 1 L of
solution.
2 moles / 1 L = 2.00 M solution
13. What is the gram formula mass of (NH4)3PO4?
a) 113 g
b) 121 g
c) 149 g
d) 404 g
c- Find formula mass in grams. N =14 x 3 = 42 g; H =1 x 4 x 3 = 12g;
P=31 x 1=31; O =16 x 4 = 64 g.
Total is 42 + 12 + 31 + 64 or 149 g.
14. What is the empirical formula of a compound that contains 85% Ag
and 15% F by mass?
a) AgF
b) Ag2F
c) AgF2
d) Ag2F2
a- First change % to grams. Next convert the grams to moles. The
molecular mass of Ag is 108 g/mol; molecular mass of F is 19 g/mol.
85 g Ag/108 g/mol = 0.79 mol
15 g F/19 g/mol = 0.79 mol
Or the whole number ratio is 0.79 / 0.79 = 1 In other words, 1 Ag mole
for each 1 F mole.
15. Given the reaction CH4 + 2O2  CO2 + 2H2O
What amount of oxygen will completely react with 1 mole of CH4?
a) 2 moles
b) 2 atoms
c) 2 grams
d) 2 molecules
a- The number of moles in a balanced equation is shown by the
coefficients. Hint: when there is no coefficient (the number in front of
the compound), the number 1 is understood. 1 mole of CH4 reacts with 2
moles of 02.
Chemical Bonding: 6 questions
1. Which formula represents a molecular substance?
a) CaO
b) CO
c) Li2O
d) Al2O3
b- Use Ref. Table S THE PERIODIC TABLE to determine the
RELATIVE electronegativity difference of each of the choices. The
difference between C (2.6) and O (3.4) is 0.9 or in the range of covalent
bonding (covalent bonds have electronegativity differences of less than
1.7). The other three compounds have differences in the ionic bond
range.
2. Which sequence of Group 18 elements demonstrates a gradual
decrease in the strength of the Van der Waals forces? All the choices are
elements in the liquid state.
a) Ar, Kr, Ne, Xe
b) Kr, Xe, Ar, Ne
c) Ne, Ar, Kr, Xe
d) Xe, Kr, Ar, Ne
d- Van der Waals forces are weak forces of attraction between
molecules. These forces decrease as the molecule gets smaller and
increase as the molecule increases. Look at the periodic table and notice
how in answer D, the elements are getting smaller. Therefore the Van der
Waals (specifically London dispersion) forces would also be decreasing.
3. Which substance is an example of a network solid?
a) nitrogen dioxide
b) sulfur dioxide
c) carbon dioxide
d) silicon dioxide
d- Only silicon dioxide forms a network solid, a network of covalent
bonds extending throughout the crystal without forming a molecule.
Carbon also forms network solids in its diamond form.
4. Which combination of atoms can form a polar covalent bond?
a) H and H
b) H and Br
c) N and N
d) Na and Br
b- Covalent bonds form between two non-metals (including hydrogen).
Na and Br would form an ionic bond as sodium is a metal. The diatomic
molecules H-H and N≡N are non-polar covalent because the identical
atoms will share electrons equally.
5. A strontium atom differs from a strontium ion in that the atom has a
greater
a) number of electrons
b) number of protons
c) atomic number
d) mass number
a- Strontium has 2 valence electrons in its outer shell. It is easier to lose
these 2 electrons than it is to gain 6 more electrons. Losing 2 electrons
will give the strontium ion a charge of +2. Ions are charged atoms. A
neutral atom has no charge because it has the same number of protons
and electrons. An ion can have more or less electrons than an atom of the
same element does. A strontium atom would have 2 more electrons than
a strontium ion.
6. Which bond has the greatest ionic character?
a) H--Cl
b) H--F
c) H--O
d) H--N
b- The greater the electronegativity difference the more ionic character
a bond will have. Because fluorine is the most electronegative element,
it makes the most polar bonds with other elements.
Physical Behavior of Matter: 27 questions!
1. Which gas is monatomic at STP?
a) chlorine
b) fluorine
c) neon
d) nitrogen
c- The noble gases, group 8A, are the least reactive elements. Look up
Neon on the periodic table and notice that it has a completely filled
energy shell. When an energy shell is completely filled, the element does
not form bonds with other atoms. It is inert or nonreactive. Thus Neon is
a monatomic gas. Cl2, F2, and N2 are diatomic gases (bond with another
atom. Di means two).
2. What Kelvin temperature is equal to 25°C?
a) 248 K
b) 298 K
c) 100 K
d) 200 K
b- Change Celsius to Kelvin by adding 273. 25°C + 273 = 298 K .
3. When the external pressure is 101.3 kPa, water will boil at what
temperature?
a) 12.8°C
b) 14.5°C
c) 100°C
d) 18°C
c- Atmospheric pressure is 1 atm or 101.3 kPa, so the question is asking
for the normal boiling point of water. When the atmospheric pressure
above a liquid equals its vapor pressure, the liquid will boil. At 100°C
the vapor pressure of water is 101.1 kPa. If the external pressure was 50
kPa, water would boil at about 82°C.
4. As ice cools from 273 K to 263 K, the average kinetic energy of its
molecules will
a) decrease
b) increase
c) remain the same
a- By definition, temperature is a measure of the average kinetic energy
of the molecules in matter. As the temperature decreases, the average
kinetic energy also decreases.
5. The phase change represented by the equation I2 (s)  I2 (g) is called
a) sublimation
b) condensation
c) melting
d) boiling
a- Sublimation means to go from the solid to gas phase (without passing
through the liquid phase).
6. The heat of fusion is defined as the energy required at constant
temperature to change 1 unit mass of a
a) gas to a liquid
b) gas to a solid
c) solid to a gas
d) solid to a liquid
d- Heat of fusion is the amount of energy (joules) needed to melt 1 unit
of solid mass to a liquid at constant temperature. It is measured in joules/
gram.
7. Solid X is placed in contact with solid Y. Heat will flow
spontaneously from X to Y when
a) X is 20°C and Y is 20°C
b) X is 10°C and Y is 5°C
c) X is -25°C and Y is -10°C
d) X is 25°C and Y is 30°C
b- Heat flow is always from high temperature to low temperature.
Watch out for negative numbers. In choice c, Y is warmer than X and
heat would flow from Y to X (not what the question asks).
10. A compound differs from a mixture in that a compound always has a
a) homogeneous composition
b) maximum of two components
c) minimum of three components
d) heterogeneous composition
a- By definition compounds are homogenous. They cannot be separated
by physical means. A mixture (salad for example) is not homogenous.
11. Which substance cannot be decomposed into simpler substances?
a) ammonia
b) aluminum
c) methane
d) methanol
b- Elements cannot be decomposed into simpler substances because an
element by definition is one kind of substance, one kind of atom. The
other choices are compounds--composed of two or more elements.
12. How many joules are equivalent to 35 kilojoules?
a) 0.035 joules
b) 0.35 joules
c) 3,500 joules
d) 35,000 joules
d- kilo means 103 or 1000. 35 x 1000 = 35,000 joules.
13. Under the same conditions of temperature and pressure, a liquid
differs from a gas because the particles of the liquid
a) are in constant straight-line motion
b) take the shape of the container they occupy
c) have no regular arrangement
d) have stronger forces of attraction between them
d- Liquids and gases take the shape of the container they occupy and
both have no regular arrangement (solids have a regular arrangement).
Both liquids and gases have particles that are in constant straight-line
motion. Liquids have a constant volume because the forces of attraction
between the particles keep them together. Gases do not have a constant
volume and the forces of attraction between particles are weaker.
14. Which statement describes a chemical property?
a) Its crystals are a metallic gray.
b) It dissolves in alcohol.
c) It forms a violet-colored gas.
d) It reacts with hydrogen to form a gas.
d- While all the answers are true for iodine, only choice D describes a
chemical property. The other choices are physical properties.
15. The volume of a given mass of an ideal gas at constant pressure is
a) directly proportional to the Kelvin temperature.
b) directly proportional to the Celsius temperature.
c) inversely proportional to the Kelvin temperature.
d) inversely proportional to the Celsius temperature.
a- Use combined gas law to figure this out. If the Kelvin temperature
was 50 and doubled to 100, the volume would also double. Another way
to look at this: according to Charles's Law, volume of a gas is directly
proportional to the Kelvin temperature.
8. As the pressure of a gas at 2 atm is changed to 1 atm at constant
temperature, the volume of the gas
a) decreases
b) increases
c) remains the same
b- See the combined gas law. Since the pressure is decreased, the
volume will increase. Another way to look at the problem: at constant
temperature volume is inversely related to pressure (Boyle Law).
16. How are the boiling and freezing points of a sample of water affected
when salt is dissolved in the water?
a) The boiling point decreases and the freezing point decreases.
b) The boiling point decreases and the freezing point increases.
c) The boiling point increases and the freezing point decreases.
d) The boiling point increases and the freezing point increases.
c- In winter salt is put on ice to melt it because the salt makes the ice
melt at a colder (decreased) temperature. Conversely, salt raises the
boiling point of water.
9. What is the total number of joules of heat energy absorbed by 15
grams of water when it is heated from 30°C to 40°C?
a) 10
b) 63
c) 150
d) 630
d- Use q(heat) = mcT (change in temp).
q (heat)= 15 g x 4.2 J/g°C x 10°C or 630 joules.
17. A sample of unknown gas at STP has a density of 0.630 g per liter.
What is the gram molecular mass of this gas?
a) 2.81 g
b) 14.1 g
c) 22.4 g
d) 63 g
b- Remember at STP a mole of gas occupies 22.4 liters. Density =
mass / volume
or M = D x V
Substitute: 0.63 g for mass and multiply by 22.4 L to find the answer.
0.63 g x 22.4 L = 14.1 g
18. The heat of fusion of a compound is 30 joules per gram. What is the
total number of joules of heat that must be absorbed by a 15.0 gram
sample to change the compound from a solid to a liquid at its melting
point?
a) 15 J
b) 45 J
c) 150 J
d) 450 J
d- Multiply the heat of fusion (30 J/g) times the number of grams (15
g). Heat of fusion is the amount of heat needed to change a solid to
liquid at the melting point.
30 J/g x 15 g = 450 J/g
19. How many joules of heat are absorbed when 70.0 grams of water is
completely vaporized at its boiling point? The heat of vaporization for
water is 2259 J/g.
a) 23, 352
b) 7, 000
c) 15, 813
d) 158, 130
d- Multiply heat of vaporization by the grams to find the calories
absorbed in vaporizing water.
70 g x 2259 J/g = 158, 130 J.
20. Under which conditions are gases most soluble in water?
a) high pressure and high temperature
b) high pressure and low temperature
c) low pressure and high temperature
d) low pressure and low temperature
b- Think of a can of soda. The contents are under pressure and if you
shake the can before opening, the soda fizzes out all over as you open it.
So the higher the pressure, the more gas or more CO2 can be dissolved in
the sugar water. Eliminate choices C and D. Now focus on the
temperature. Soda goes flat (loses carbonation or gas) as it warms up.
Soda is usually served cold because more of the carbonation or CO2
stays in the sugar water when the soda is cold (low temp.)
21. Given: (52.6 cm) (1.214 cm)
What is the product expressed to the correct number of significant
figures?
a) 64 cm2
b) 63.9 cm2
c) 63.86 cm2
d) 63.8564 cm2
b- Rule: the answer has as many significant figures as the least
precise measurement. 52.6 has 3 significant figures; 1.214 has 4
significant figures. The answer can not have more than 3 significant
figures. Significant figures informs the reader how precise a
measurement is. For example, 80 cm tells the reader, "This measurement
is correct to within one cm. It might be a bit less than 80 (79) or a bit
more than 80 (81) but it is very close to 80 cm." This is okay if you are
installing carpet or sewing a dress but what if you are performing heart
surgery or connecting fiber optic cables for a computer? Greater
precision is required for this.
80.002 informs the reader that the measurement is within a
thousandth of a cm. Could be 80.001 or 80.003. When multiplying and
dividing significant figures the answer can only be as precise as the least
precise measurement: if 52.6 cm is multiplied by 1.214 cm, the answer
cannot be correct to .004 (Remember only 1 measurement was this
precise). It is only accurate to tenths of a cm (.1).
22. Which measurement contains three significant figures?
a) 0.08 cm
b) 0.080 cm
c) 800 cm
d) 8.08 cm
d- Rule 1: all non zero digits are significant.
Rule 2: zero digits are significant if they are part of the measurement,
not place holders. In choices 1 and 2 the zeros are place holders. The
answers could be written as 8 x 10-2 and 8.0 x 10-2. Choice four states
that a measurement is 8 cm and 8/100 cm long or accurate to hundredths
of a cm.
Another way to thinks of this: choice C suggests the measurement is
about 800 cm: a little more or a little less but not as accurate as choice D
and not accurate to hundredths of a cm.
23. A student determined the heat of fusion of water to be 366.9 J/g. If
the accepted value is 333.3J/g, what is the student's percent error?
a) 8.0%
b) 10.0%
c) 15%
d) 30.0%
b- Per cent of error is found by subtracting the accepted value from the
calculated value, dividing by the accepted value and then multiplying by
100. (Calculated value - accepted value )/ accepted value x 100 =
366.9 - 333.6 / 333.6 x 100 = 33.3 / 333.6 x 100 = 10%
24. What is the sum of
6.6412 g + 12.85 + 0.046 g + 3.48 g
Expressed to the correct number of significant figures?
a) 23 g
b) 23.0 g
c) 23.017 g
d) 23.02 g
d- Rule: when adding measurements, the number of decimal places
in the sum (answer) is the same as the number of decimal places in
the least precise measurement. The least precise measurement was
measured to hundredths of a g (12.85 and 3.38). Therefore the sum of
the numbers cannot be more precise than this. Even though other
measurements were taken to 0.001 or 0.0001 of a gram, in addition and
subtraction the least accurate measurement rules.
25. What occurs as potassium nitrate is dissolved in a beaker of water,
indicating that the process is endothermic?
a) The temperature of the solution decreases.
b) The temperature of the solution increases.
c) The solution changes color.
d) The solution gives off a gas.
a- Endothermic reactions cause heat to be absorbed. The potassium
nitrate needs heat to dissolve. It takes this heat energy from the water. As
the water loses heat energy, the temperature of the water decreases.
Note: an exothermic reaction would do the opposite: the temperature
would rise as heat was given off.
26. Salt A and salt B were dissolved separately in 100 mL beakers of
water. The water temperatures were measured and recorded as shown in
the table below:
Salt A: initial water temp. 25.1°C final water temp. 30.2°C
Salt B: initial water temp. 25.1°C final water temp. 20.0°C
Which statement is a correct interpretation of these data?
a) The dissolving of only salt A was endothermic.
b) The dissolving of only salt B was exothermic
c) The dissolving of both salt A and salt B was endothermic.
d) The dissolving of salt A was exothermic and the dissolving of
salt B was endothermic.
d- First eliminate answer c: temp. of salt A increased and temp. of salt
B decreased. Both salts did not react the same way.
Exothermic reactions give off heat--this causes temperatures to rise.
Endothermic reactions absorb heat--this causes temperatures to fall.
The temperature of salt A increased (exothermic reaction) while the
temperature of salt B decreased (endothermic reaction).
27. A solid is dissolved in a beaker of water. Which observation suggests
that the process is endothermic?
a) The solution gives off a gas.
b) The solution changes color.
c) The temperature of the solution decreases.
d) The temperature of the solution increases.
3- Endothermic reactions absorb heat. As the solid dissolves, the heat
energy needed to keep the reaction going will be taken from the water.
As a result, the water temperature will decrease. Hint: temperature is a
measure of the average kinetic energy of the molecules. As the
molecules lose energy, the temperature will drop.
Kinetics/Equilibrium: 13 Questions
1. When a catalyst is added to a system at equilibrium, a decrease occurs
in the
a) activation energy
b) heat of reaction
c) potential energy of the reactants
d) potential energy of the products
a- A catalyst speeds up a chemical reaction by lowering (decreasing) the
activation energy.
2. Which statement describes characteristics of an endothermic reaction?
a) The sign of H is positive, and the products have less potential
energy than the reactants.
b) The sign of H is positive, and the products have more potential
energy than the reactants.
c) The sign of H is negative, and the products have less potential
energy than the reactants.
d) The sign of H is negative, and the products have more
potential energy than the reactants.
b- Endothermic reactions absorb energy so there is more potential
energy in the reactants than in the products. (Gain in Heat energy =
increase in potential energy of reactants.) Endothermic reactions are
positive. Eliminating choices C and D, only choice B has a positive H
and a gain in potential energy.
3. Which statement explains why the speed of some chemical reactions
is increased when the surface area of the reactant is increased?
a) This change increases the density of the reactant particles.
b) This change increases the concentration of the reactant.
c) This change exposes more reactant particles to a possible
collision.
d) This change alters the electrical conductivity of the reactant
particles.
c- Reaction rate is affected by nature and concentration of reactants,
temperature, surface area and a catalyst.
Increasing surface area exposes more particles to contact with reactants,
increasing the number of particle collisions. Imagine a cube of chocolate
3 feet by 4 feet and 2 inches thick. Take the same block and make it into
a 24 candy bars. A class of chemistry students could eat the bars faster
than the single chocolate block.
4. Which conditions will increase the rate of chemical reaction?
a) decreased temperature and decreased concentration of
reactants?
b) decreased temperature and increased concentration of
reactants?
c) increased temperature and decreased concentration of
reactants?
d) increased temperature and increased concentration of
reactants?
d- Rate or speed of reaction is influenced by temperature, concentration,
surface area, nature of reactants, and presence of a catalyst. To speed up
a reaction, increase the number of effective collisions between
molecules. Temperature is a measure of the average kinetic energy, so
increasing temperature speeds up a reaction. Increasing the
concentration of the reactants adds more particles and this also increases
the number of effective collisions.
5. In a chemical reaction, a catalyst changes the
a) potential energy of the products
b) potential energy of the reactants
c) heat of reaction
d) activation energy
d- Activation energy is the minimum amount of energy needed to start a
chemical reaction. (Sort of like the minimum amount you can pay on a
credit card balance each month). The total $ due has not changed but you
can get by paying the smaller amount. Activation energy does not
change the potential energy of the reactants or products and it has no
effect on the heat of reaction. A catalyst speeds up the reaction because it
decreases the amount of energy needed to start the reaction (minimum
balance payment).
6. Which is a property of a reaction that has reached equilibrium?
a) The amount of products is greater than the amount of
reactants.
b) The amount of products is equal to the amount of reactants.
c) The rate of the forward reaction is greater than the rate of the
reverse reaction.
d) The rate of the forward reaction is equal to than the rate of the
reverse reaction.
d- Equilibrium means equal reaction rates. Choices A and C are "greater
than", not "equal to" and choice B does not mention reaction rates. Only
choice D states" equal reaction rates." A system in equilibrium can have
unequal amounts of product and reactants; or it could have equal
amounts of product and reactants. Equal reaction rates, however, are
necessary for dynamic equilibrium to result.
7. Which procedure will increase the solubility of KCl in water?
a) stirring the solute and solvent mixture
b) increasing the surface area of the solute
c) raising the temperature of the solvent
d) increasing the pressure on the surface of the solvent
c- This is an easy but tricky question. Choices A and B make KCl
dissolve faster (rate of reaction) but do not increase the solubility of
KCl. A glass of soda pop goes flat as it warms up on the counter; hot
chocolate can dissolves more marshmallows than a cup of cold
chocolate milk can. Temperature affects solubility. In the case of HCl,
increasing the temperature, increases the solubility.
8. Given the equilibrium system at 25°C:
NH4Cl(s) ↔ NH4+(aq) + Cl-(aq) (ΔH = +3.5 kcal/mol)
What change will shift the equilibrium to the right?
a) decreasing the temperature to 15°C?
b) increasing the temperature to 35°C?
c) dissolving NaCl crystals in the equilibrium mixture?
d) dissolving NH4NONH3 crystals in the equilibrium mixture?
b- Part 1: in the equation ΔH = + 3.5 kcal/mol: the reaction is
endothermic. If you forget that a positive H indicates an endothermic
reaction. Part 2: supplying heat (by increasing the temp.), favors the
reaction that absorbs or uses up the extra heat (favors the endothermic
reaction). Which one is that? The forward reaction or right side because
ΔH was +. This illustrates the Le Chatelier's principle: if a stress (like a
change in temperature or concentration) is added to a system at
equilibrium, the reaction is shifted in a way that uses up the stress.
Increasing temperature of a system at equilibrium, favors the
endothermic reaction.
9. Given the reaction at equilibrium: N2(g) + O2(g) ↔ 2NO(g) as the
concentration of N2(g) increases, the concentration of O2(g) will
a) decrease
b) increase
c) remains the same
a- LeChatelier's principle: if a stress (like a change in temp. or
concentration) is added to a system at equilibrium, the reaction is shifted
in a way that uses up the stress. Increase the left side, the right side tries
to use up the extra N2(g). But to make more NO(g), you need to use
some of the O2(g) from the left side--remember you did not add any
extra O2(g)--so the amount of O2(g) has to decrease.
10. Given the reaction at equilibrium: 2CO(g) + O2(g) ↔ 2CO2(g) When
the reaction is subjected to stress, a change will occur in the
concentration of
a) reactants, only
b) products, only
b) both reactants and products
c) neither reactants nor products
c- This question can be solved several different ways. First by logic:
pretend you become a new cable subscriber (a change or stress is added
to your life). This will also affect the number of hours you watch TV
(reaction). The reverse is also true: stop the cable and you probably will
watch less TV. Only choice C makes sense. Remember the math rule?
Whatever you do to one side of the equation, effects the other side.
Second way: Le Chatelier's principle applies here (if a stress like a
change in temperature or concentration is added to a system at
equilibrium, the reaction is shifted in a way that uses up the stress). If
more CO(g) and O2(g) were added, more CO2(g) would result.
If more product, CO2(g), was added, the concentration of the reactants
would increase by using up the excess product and changing it back to
CO(g) + O2(g.
11. Given the change of phase: CO2(g) changes to CO2(s), the entropy of
the system
a) decreases
b) increases
c) remains the same
a- Entropy is a measure of the disorder or randomness (lack of order) of
a system. Molecules in gases have no definite volume and are more free
to move than molecules in solids. As molecules change phase from a gas
to a solid, the molecules are becoming more orderly and therefore have
less disorder, less entropy. Compare the room of a teenage to the room of
a parent. The teen has a more disorderly room (higher entropy). As the
teen gets older and becomes a parent, the disorder in the room decreases.
12. In which reaction will the point of equilibrium shift to the left when
the pressure on the system is increased?
a) C(s) + O2(g) ↔ CO2(g)
b) CaCO3(s) ↔ CaO(s) + CO2(g)
c) 2Mg(s) + O2(g) ↔ 2MgO(s)
d) 2H2(g) + O2(g) ↔ 2H2O(g)
b- A change in pressure affects equilibrium when gases are involved.
An increase in pressure favors the formation of the smaller number of
moles of gas (shifts to the side with the smaller number of moles of gas).
If there is no change in the number of moles of gas, pressure has no
effect on equilibrium.
There is no effect on Choice A because each side has only 1 mole of gas.
Choice C has 1 mole of gas on the left, none on the right so increased
pressure shifts it to the right.
Choice D has 3 moles of gas (2H and 1 O) on the left, 2 moles on the
right, so increased pressure shifts it to the right. Choice B has no gas
moles on the left and 1 mole of gas on the right, so increased pressure
shifts equilibrium to the left. Voila: Choice B.
13. Given the reaction at equilibrium:
2 SO2(g) + O2(g) ↔ 2 SO3(g) + heat
Which change will shift the equilibrium to the right?
a) adding a catalyst
b) adding more O2(g)
c) decreasing the pressure
d) increasing the temperature
b- To get more product [right side, SO3(g )], add more reactants (left
side). As the reaction reaches equilibrium, the extra reactants are being
converted into product [SO3(g) +heat] and the reaction shifts to the right.
Organic Chemistry: 8 Questions
1. Which element is present in all organic compounds?
a) carbon
b) nitrogen
c) oxygen
d) phosphorous
a- In general, organic molecules contain carbon and organic chemistry
is the study of carbon compounds.
2. Which property is generally characteristic of an organic compound?
a) low melting point
b) high melting point
c) soluble in polar solvents
d) insoluble in nonpolar solvents
a- High melting points (450 degrees and higher) are characteristic of
ionic compounds but organic compounds generally have low melting
points. Wax and street tar melt in the summer heat; sugar melts and can
burn on the kitchen stove. Wax, tar, and sugar are examples of organic
compounds.
3. Which statement explains why the element carbon forms so many
compounds?
a) Carbon atoms combine readily with oxygen.
b) Carbon atoms have very high electronegativity.
c) Carbon readily forms ionic bonds with other carbon atoms.
d) Carbon readily forms covalent bonds with other carbon atoms.
d- Carbon forms four covalent or shared bonds with other carbon atoms
as well as many other kinds of atoms. It has an almost limitless ability to
bond with other carbon atoms making possible a very large number of
compounds.
4. In a molecule of CH4, the hydrogen atoms are spatially oriented
toward the centers of a regular
a) pyramid
b) tetrahedron
c) square
d) rectangle
b- Organic compounds are three dimensional and CH4 has 4 equivalent
single bonds. Tetra means 4.
5. The reaction CH2CH2 + H2  CH3CH3 is an example of
a) substitution
b) addition (combination)
c) esterification
d) fermentation
b- Addition usually involves adding one or more atoms at a double or
triple bond. Here H2 combines with CH2CH2 changing ethene (double
bond) into ethane (single bond).
6. What type of reaction is CH3CH3 + Cl2  CH3CH2Cl + HCl?
a) an addition reaction
b) a substitution reaction (single replacement)
c) a saponification reaction
d) an esterification reaction
b- In the above reaction, notice how a Cl atom has been substituted for
one H atom. This is similar to a baseball or basketball player taking the
place or substituting for another player.
7. What is the maximum number of covalent bonds than an atom of
carbon can form?
a) 1
b) 2
c) 3
d) 4
d- Because carbon has 4 valence electrons, it can form 4 shared
(covalent) bonds. Refer to the Periodic Table for the number of valence
electrons in the element carbon.
8. What substance is made up of monomers joined together in long
chains?
1. ketone
2. protein
3. ester
4. acid
b- Proteins are composed of amino acids (monomers) joined into long
chains.
Oxidation-Reduction: 13 Questions
1. A battery consists of which type of cells?
a) electrolytic
b) electrochemical
c) electroplating
d) electromagnetic
b- Electrochemical cells do what their names suggests: they make
electricity from chemicals stored in the cell by redox reactions. A battery
is a great example of this. The chemicals are stored in the cell until you
complete the connection (turn on the flashlight, boom box, or car).
Choices A and C use electricity for electrolysis and plating metal on
objects (gold and silver plating). Electromagnetic usually refers to
electric and magnetic fields oscillating at right angles to each other.
2. Given the reaction for the nickel-cadmium battery:
2NiOH + Cd +2H2O 2Ni(OH)2 + Cd(OH)2
What species is oxidized during the discharge of the battery?
a) Ni3+
b) Ni2+
c) Cd
d) Cd2+
c- The NiCd battery is a rechargeable battery used in cordless
appliances and tools. During discharge the Cd0 is oxidized to form Cd2+.
Cd loses 2 electrons to become positively charged. Remember in
oxidation atoms lose (or seem to lose) electrons.
3. Given the redox reaction:
2I-(aq) + Br2(l)  2Br-(aq) + I2(s)
What occurs during this reaction?
1. The I- ion is oxidized, and its oxidation number increases.
2. The I- ion is oxidized, and its oxidation number decreases.
3. The I- ion is reduced, and its oxidation number increases.
4. The I- ion is reduced, and its oxidation number decreases.
a- First, determine what happens to the I- ion. On the left side of the
equation, the I ion is negatively charged. On the right side of the
equation, the I ion is neutral. The I ion lost its negative charge by losing
an electron. By definition oxidation occurs when electrons are lost .The
ion becomes more positive (has a higher oxidation state). Pretend
electrons are dollars. If you lose a dollar, you have less money. If you
find a dollar or are given one, you no longer have a negative cash flow.
You can also look at the half reaction of the I- ion: 2I-(aq)  I2(s) + 2 eeach I- ion loses an electron, increasing its oxidation # from -1 to 0.
4. Which half-reaction correctly represents reduction?
a) Cr3+ + 3e-  Cr(s)
b) Cr3++  Cr(s) + 3ec) Cr(s)  Cr3+ + 3ed) Cr(s) + 3e-  Cr3+
a- In reduction half reactions, the oxidation number is lowered because
electrons are added. When Cr3+ gains electrons, the negative charge of
the electron cancels out the positive charge and an uncharged Cr (Cr0)
atom results.
5. What is the oxidation number of carbon in NaHCO3?
a) +6
b) +2
c) -4
d) +4
d- In a compound, the sum of the oxidation numbers equals zero. The
oxidation number of oxygen is always -2 unless it is a peroxide
(oxidation number of -1) or when oxygen combines with fluorine. In O3,
O (-2) x 3 oxygen atoms = a charge of -6. Na is always +1. When H acts
as a metal, the charge is +1.
+2 plus -6 results in a charge of -4. Therefore each carbon atom must
have a charge of +4 to result in 0 charge.
(+1) plus (+1) plus (+4) = +6 and (-2)(3) = -6
or +6 plus -6 = 0
6. Which statement correctly describes a redox reaction?
a) The oxidation half-reaction and the reduction-half reaction
occur simultaneously.
b) The oxidation half-reaction occurs before the reduction half
reaction
c) The oxidation half-reaction occurs after the reduction halfreaction
d) The oxidation half-reaction occurs spontaneously but the
reduction half-reaction does not
a- Both reactions occur at the same time in a reduction reaction: as one
atom losses the electron(s), another atom gains the electron(s).
7. Which quantities are conserved in all oxidation-reduction reactions?
a) charge, only
b) mass only
c) both charge and mass
d) neither charge and mass
c- Matter can never be created or destroyed but it can change its form.
Mass is always conserved in chemical reactions. Because the loss of
electrons (by oxidation) must equal the gain of electrons (by reduction),
charge must also be conserved. Only choice C includes conservation of
charge and mass.
8. Given the reaction: 2Li(s) + Cl2(g) 2LiCl(s)
As the reaction takes place, the Cl2(g) will
a) gain electrons
b) lose electrons
c) gain protons
d) lose protons.
a- Eliminate choices C and D because only electrons are lost or gained
in oxidation-reduction reactions. Write the half reaction for Cl2(g):
Cl2(g) + 2e-  2Cl-(s) (In 2LiCl(s), Li has an oxidation number of +1.
Therefore Cl must have an oxidation number of -1). Cl on the left side of
the equation had an oxidation number of 0. It has to gain electrons to
have an oxidation of -1.
9. Given the balanced equation:
2Al(s) + 6H+(aq)  2Al3+(aq) + 3H2
When 2 moles of Al(s) completely reacts, what is the total number of
moles of electrons transferred from Al(s) to H+(aq)?
a) 5
b) 6
c) 3
d) 4
b- The left side of the equation shows 6H+(aq) combines with 2 Al(s).
Another way to view this is to look at the half reactions:
2 Al(s)  2Al3+(aq) + 6 e6H2 + 6 e-  3H2
Or 6 moles of e- are transferred from Al(s) to H+(aq).
10. Which statement best describes how a salt bridge maintains electrical
neutrality in the half cells of an electrochemical cell?
a) It prevents the migration of electrons.
b) It permits the migration of ions.
c) It permits the two solutions to mix completely.
d) It prevents the reaction from occurring spontaneously.
b- In oxidation-reduction reactions, ions need to migrate. A salt bridge
is a U-shaped tube that acts as a porous barrier between two half cells. It
prevents the solutions from mixing but allows the ions to move (migrate)
from one half cell to the other. This keeps the half cells neutral. If the
solutions mixed, neutrality would not be maintained in the half cells and
the reaction would stop.
11. Which atom forms an ion that would migrate toward the cathode in a
electrolytic cell?
a) F
b) I
c) Na
d) C
c- Reduction occurs at the negative electrode (cathode) in an electrolytic
cell. Only positive ions will migrate toward the cathode in this type of
cell. Only Na always forms positive ions; F always forms negative ions;
C and I can form positive or negative ions depending on the reaction.
12. Given the reaction:
__Mg + __Cr3+  __Mg2+ + __Cr
When the equation is correctly balanced using smallest whole numbers,
the sum of the coefficients will be
a) 10
b) 7
c) 5
d) 4
a- Correctly balancing the equation requires several steps.
First write the half reactions:
Cr3+ + 3e-  Cr and Mg  Mg2+ + 2 eRemember electrons lost must equal electrons gained.
2 ( Cr3+ + 3e-  Cr ) equals 6 e- gained; 3( Mg  Mg2+ + 2 e- ) equals
6 e- lost.
Last step: add the half reactions and ignore the electrons:
3Mg + 2 Cr3+  3Mg2+ + 2Cr
3 plus 2 plus 3 plus 2 = 10
13. When a substance is oxidized, it
a) loses protons
b) gains protons
c) acts as an oxidizing agent
d) acts as a reducing agent
d- Eliminate choice A and B because electrons not protons are lost or
gained in oxidation-reduction reactions. Oxidation is a loss of electrons
and these electrons are gained by a second substance (reduction). The
oxidized substance causes reduction to occur. In other words, it is the
reducing agent. Hint: Reducing agents cause oxidation (loss of e-);
oxidizing agents cause reduction. Reducing diets cause weight to be lost.
Acids, Bases, & Salts: 9 Questions
1. Which formula represents a salt?
a) KOH
b) KCl
c) CH3OH
d) CH3COOH
b- CH3COOH is an organic acid, acetic acid also called ethanoic acid.
Choice 1 will yield the OH- ion in solution (this compound is therefore a
base, See Table L). Choice C is an alcohol, Salts are ionic compounds
that do not form OH- or H+ ions. KCl forms K+ and Cl- ions. Therefore it
is a salt.
2. Which substance can be classified as an Arrhenius acid?
a) HCl
b) NaCl
c) LiOH
d) KOH
a- By definition an Arrhenius acid yields hydrogen ions as the only
positive ions in aqueous solution. Choice B is a salt. Choice C forms Li+
and OH- ions; choice D also forms OH- ions: these compounds are
Arrhenius bases. Choice A forms H+ ions and is therefore an Arrhenius
acid.
3. Which solution will change red litmus to blue?
a) HCl(aq)
b) NaCl(aq)
c) CH3OH(aq)
d) NaOH(aq)
d- Red litmus turns blue when a base is present. Hint: blue for base.
Choice A is an acid; choice B is a salt and salts neutralize acids and
bases. The litmus does not change color with salts. Choice C is an
alcohol. NaOH is a strong base and will change litmus to blue.
4. An acidic solution could have a pH of
a) 7
b) 10
c) 3
d) 14
c- On the pH scale, a pH of less than 7 is acidic; a pH of more than 7 is
basic. A neutral solution such as pure water has a pH of 7.
5. What is the pH of a 0.00001 molar HCl solution?
a) 1
b) 9
c) 5
d) 4
c- By definition pH is the negative log (logarithm) of the hydronium ion
concentration. A 0.00001 molar solution has a H+ concentration of 10-5
M (move the decimal point 5 places to the right). The value of the
negative exponent (-5) gives a pH of 5.
6. What is the pH of a solution with a hydronium ion concentration of
0.01 mole per liter?
a) 1
b) 2
c) 10
d) 14
b- By definition pH is the negative log (logarithm) of the hydronium ion
concentration. A 0.01 molar solution has a H+ concentration of 10-2
(move the decimal point 2 places to the right). The value of the negative
exponent (-2) gives a pH of 2.
7. There are alternate acid base theories that define an acid as any
species that can
a) donate a proton
b) donate an electron
c) accept a proton
d) accept an electron
a- According to Bronsted-Lowry theory, an acid is any species that can
donate a proton to another species.
8. When HCl(aq) is exactly neutralized by NaOH(aq), the hydrogen ion
concentration in the resulting mixture is
a) always less than the concentration of the hydroxide ions
b) always greater than the concentration of the hydroxide ions
c) always equal than the concentration of the hydroxide ions
d) sometimes greater and sometimes less than the concentration
of the hydroxide ions
c- Answer D is impossible. Neutralization means equivalent amounts of
hydronium and hydroxide ions react in solution to produce water. Water
has a pH of 7. By definition, only answer C is correct.
9. As the hydrogen ion concentration of an aqueous solution increases,
the hydroxide ion concentration of this solution will
1. decrease
2. increase
3. remain the same
a- (OH-) multiplied by (H3O+) is a constant number equal to 1 x 10-14
for aqueous solutions. In other words, (A) (B) = -14. Substituting
numbers, (-7) (2) = -14.
But if 7 is increased to 14, 2 must decrease to -1 to keep the answer -14.
(14) (-1) =-14.
If (H3O+) increases, (OH-) must decrease.
Nuclear Chemistry: 9 Questions
1. Which radioactive emanations have a charge of -1?
a) neutrons
b) gamma rays
c) alpha particles
d) beta particles
d- gamma rays have no mass or charge, alpha particles have a mass of 4
amu and a charge of +2, beta particles are negative with relatively no
mass.
.
2. As the temperature of a sample of a radioactive element decreases, the
half-life will
a) decrease
b) increase
c) remain the same
c- Half-life depends on time. Factors like temperature, pressure, and
volume have no effect.
3. What kind of radiation will travel through an electric field on a
pathway that remains unaffected by the field?
1. a proton
2. a gamma ray
3. an electron
4. an alpha particle
b- Particles with charges will be deflected. The only kind of radiation
given that has no charge is a gamma ray. It is pure energy and therefore
without charge.
4. In a fusion reaction, reacting nuclei must collide. Collisions between
two nuclei are difficult to achieve because the nuclei are
a) both negatively charged and repel each other
b) both positively charged and repel each other
c) oppositely charged and attract each other
d) oppositely charged and repel each other
b- In fusion light nuclei like hydrogen (deuterium) join to form heavier
nuclei like helium. Because these nuclei are positively charged, they
repel each other. Hint: Like charges repel and unlike charges attract
5. To make nuclear fission more efficient, which device is used in a
nuclear reactor to slow the speed of neutrons?
a) internal shield
b) external shield
c) control rod
d) moderator
d- Neutrons can be quickly slowed down by colliding with particles
such as graphite, heavy water (deuterium oxide), and water. These
substances keep the reaction from getting out of control much like a
moderator keeps both sides from getting into an argument or fight.
12
1
6. In the reaction 4Be + X  6C+ 0n, the X represents
a) an alpha particle
b) a beta particle
c) an electron
d) a proton
a- Answer B and C are the same so eliminate these. The sum of the
protons (sum of the atomic numbers) must be the same on the right side
as on the left side. Likewise the sum of atomic masses must be the same
on each side of the equation.
There are 6 protons on the right side; there must be 6 protons on the left
side. Be has 4 so X must have 2 protons (2X). The masses on the right
(12 + 1) equal 13 so the masses on the left must equal 13. Be has a mass
of 9 so X must have a mass of 4. An alpha particle or 2He, is the only
correct answer.
7. Control rods in nuclear reactors are commonly made of boron and
cadmium because these two elements have the ability to
a) absorb neutrons
b) emit neutrons
c) decrease the speed of neutrons
d) increase the speed of neutrons
a- Moderators control the speed of a reaction (answers C and D) so
control rods must absorb neutrons. Emitting more neutrons into a
nuclear reaction would make the reaction out of control.
8. Heavy water and graphite are two examples of materials that are can
be used in a nuclear reactor to slow down neutrons. These materials are
called
a) fuels
b) shields
c) coolants
9
d) moderators
d- Do not be tricked into picking water as a coolant. The question did
not ask for a coolant: it asked for "traffic cops" that slow down or
moderate or keep "the lid on" a reaction.
9. Which reaction illustrates fusion?
4
2
2
a) 1H + 1H  2He
27
24
1
4
b) 0n + 13Al  11Na + 2He
27
30
4
1
c) 13Al + 2He  15P + 0n
14
1
4
17
d) 7N + 2He  1H + 8O
a- Fusion is the process of joining two light nuclei to form a
heavier one. High pressure and high temperatures4 are used to
make this happen. Tremendous energy is released when the
fusion takes place. Answers B, C, and D are all examples of
artificial transmutation or bombardment of an element by a
neutron or alpha particle. Only answer A shows two light
elements combining.