AP Midterm Exam 2012
Questions and Answers
- 1.
How many unpaired electrons are in the Lewis- electron dot symbol for an oxygen atom?
- A.
0
- B.
1
- C.
2
- D.
4
Correct Answer
C. 2Explanation
In the Lewis electron dot symbol for an oxygen atom, there are two unpaired electrons. This is because the oxygen atom has six valence electrons, and in the Lewis dot symbol, each electron is represented by a dot. The first four electrons are paired in two sets, and the remaining two electrons are unpaired, represented by two separate dots. Therefore, the correct answer is 2.Rate this question:
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- 2.
Which of the following shows the incorrect number of valence electrons in parentheses?
- A.
Se (4)
- B.
As (5)
- C.
Ca (2)
- D.
Cl (7)
- E.
Li (1)
Correct Answer
A. Se (4)Explanation
The correct answer is Se (4) because Selenium (Se) has 6 valence electrons, not 4. Valence electrons are the electrons in the outermost energy level of an atom and determine its chemical properties. Selenium is in Group 16 of the periodic table, so it has 6 valence electrons.Rate this question:
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- 3.
Which of the following exhibits metallic bonding?
- A.
NH3
- B.
Au-Pd alloy
- C.
MgCl2
- D.
PCl3
- E.
O3
Correct Answer
B. Au-Pd alloyExplanation
An alloy is a mixture of two or more metals, and in the case of the Au-Pd alloy, both gold (Au) and palladium (Pd) are metals. Metallic bonding occurs in metals where the outer electrons of the atoms are delocalized and form a "sea" of electrons that are free to move throughout the material. This type of bonding leads to the characteristic properties of metals, such as high electrical and thermal conductivity, malleability, and ductility. Therefore, the Au-Pd alloy exhibits metallic bonding.Rate this question:
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- 4.
What is the principal quantum number of the electrons that are lost when tungsten forms a cation?
- A.
2
- B.
6
- C.
5
- D.
4
- E.
3
- F.
1
Correct Answer
B. 6Explanation
When tungsten forms a cation, it loses electrons from its outermost energy level. The principal quantum number represents the energy level or shell in which the electron is located. Since tungsten is in the sixth period of the periodic table, its outermost energy level is the sixth energy level, which corresponds to the principal quantum number 6. Therefore, the correct answer is 6.Rate this question:
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- 5.
Which of the following processes would be expected to be exothermic?
- A.
K+(g) + Br-(g) -->KBr(s)
- B.
Br2(l) --> Br2(g)
- C.
K(s) --> K(g)
- D.
K(g) --> K+(g) + e-
- E.
Br2(g) --> 2Br(g)
Correct Answer
A. K+(g) + Br-(g) -->KBr(s)Explanation
The formation of KBr(s) from K+(g) and Br-(g) involves the release of energy, making it an exothermic process.Rate this question:
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- 6.
In which of the following sets are all of the ions or atoms isoelectronic with each other? (i)K+, Na+, Mg2+ (ii)Ag+, Cd2+ (iii)Se2-, Te2-, Kr (iv)Ru2+, Rh3+ (v)As3-, Se2-, Br-
- A.
Ii, iv, and v
- B.
Iv
- C.
Iii
- D.
I
- E.
V
Correct Answer
A. Ii, iv, and vExplanation
In option ii, all the ions (Ag+ and Cd2+) have the same number of electrons, making them isoelectronic. In option iv, both Ru2+ and Rh3+ have the same number of electrons, making them isoelectronic. In option v, all the ions (As3-, Se2-, and Br-) have the same number of electrons, making them isoelectronic. Therefore, the correct answer is ii, iv, and v.Rate this question:
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- 7.
In which of the following sets are all of the ions r atoms isolelectronic with one another? (i)Ba, Lu+, Hf3+ (ii)Nb4+, Y2+, Rb+1 (iii)Te2-, I-, Xe (iv)Br-, Kr, Rb+
- A.
Iii only
- B.
I only
- C.
Iii and iv only
- D.
I and ii only
- E.
Iv only
- F.
Ii only
Correct Answer
C. Iii and iv onlyExplanation
The ions or atoms in set iii (Te2-, I-, Xe) are isoelectronic with each other because they all have the same number of electrons. Similarly, the ions or atoms in set iv (Br-, Kr, Rb+) are isoelectronic with each other because they all have the same number of electrons. Therefore, the correct answer is iii and iv only.Rate this question:
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- 8.
Which of the following has the greatest diameter?
- A.
Na
- B.
Na+
- C.
Na-
Correct Answer
C. Na-Explanation
The correct answer is Na-. This is because Na- has an extra electron compared to Na and Na+. The addition of an extra electron increases the size of the atom, resulting in a larger diameter.Rate this question:
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- 9.
ICl4- has how many total valence electrons?
- A.
35
- B.
28
- C.
8
- D.
36
- E.
34
Correct Answer
D. 36Explanation
ICl4- is a negatively charged ion, which means it has gained one extra electron. To determine the total number of valence electrons, we need to consider the number of valence electrons of each atom in the molecule and add the extra electron gained by the ion. Iodine (I) is in Group 7A, so it has 7 valence electrons. Chlorine (Cl) is in Group 7A as well, so it also has 7 valence electrons. Since there are 4 chlorine atoms in ICl4-, the total number of valence electrons from the chlorine atoms is 4 * 7 = 28. Adding the extra electron gained by the ion, the total number of valence electrons in ICl4- is 28 + 1 = 29. Therefore, the correct answer is 36.Rate this question:
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- 10.
Which of the following bonds is polar?
- A.
O-S
- B.
F-F
- C.
O-O
- D.
S-S
Correct Answer
A. O-SExplanation
The O-S bond is polar because oxygen is more electronegative than sulfur. This means that oxygen has a greater ability to attract and hold onto electrons, creating a partial negative charge on the oxygen atom and a partial positive charge on the sulfur atom. This uneven distribution of charge results in a polar bond.Rate this question:
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- 11.
Which of the following is correctly arranged with respect to the size of the atom/ion? (i) S < S1- < S2- (ii) Mg2+ < Na+ < Ne (iii) Ni < Cu+ < Zn2+
- A.
I and iii only
- B.
Ii only
- C.
I and ii only
- D.
I only
- E.
Iii only
Correct Answer
C. I and ii onlyExplanation
The size of an atom or ion is determined by the number of electrons and the effective nuclear charge. In option i, S has more electrons than S1- and S2-, so it is the largest. S1- has gained an electron, resulting in an increased electron-electron repulsion, making it smaller than S. S2- has gained two electrons, resulting in even more electron-electron repulsion and making it the smallest. In option ii, Mg2+ has lost two electrons, resulting in a higher effective nuclear charge and making it the smallest. Na+ has lost one electron, making it larger than Mg2+. Ne is a noble gas and has a full electron shell, making it the largest. Therefore, options i and ii are correctly arranged with respect to the size of the atom/ion.Rate this question:
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- 12.
Which of the following bonds would be longest?
- A.
P-Br
- B.
P-P
- C.
P-I
- D.
P-Cl
- E.
P-F
Correct Answer
C. P-IExplanation
The bond between phosphorus (P) and iodine (I) would be the longest among the given options. This is because iodine is larger in size compared to the other elements, resulting in a longer bond length. The larger atomic radius of iodine causes the electron cloud to be more spread out, leading to a weaker bond and a longer bond length.Rate this question:
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- 13.
Write a single Lewis structure that obeys the octet rule, and calculate the formal charges on all of the atoms in PO43-.
- A.
P 1+, O 2-
- B.
P 4+, O 2-
- C.
P 2+, O 1-
- D.
P 2+, O 2-
- E.
P 1+, O 1-
Correct Answer
E. P 1+, O 1-Explanation
The Lewis structure provided shows that the central phosphorus (P) atom has a formal charge of +1 and each oxygen (O) atom has a formal charge of -1. This arrangement satisfies the octet rule, which states that atoms tend to gain, lose, or share electrons in order to achieve a full outer electron shell with eight electrons. In this case, the phosphorus atom has 10 valence electrons and each oxygen atom has 6 valence electrons, resulting in the formal charges mentioned.Rate this question:
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- 14.
Using Lewis structures that satisfy the octet rule, determine the number of bonds formed by the central atom in each of the follow: SiO44-, PO43-, SO42-, ClO4-
- A.
2, 3.5, 5, 6.5
- B.
4, 4, 4, 4
- C.
4, 5, 6, 7
- D.
5, 6, 7, 8
- E.
4, 5, 5, 6
Correct Answer
B. 4, 4, 4, 4Explanation
The Lewis structures of SiO44-, PO43-, SO42-, and ClO4- all show that the central atom forms 4 bonds. In SiO44-, the central atom Si forms 4 bonds with 4 oxygen atoms. In PO43-, the central atom P forms 4 bonds with 3 oxygen atoms and 1 double bond with another oxygen atom. In SO42-, the central atom S forms 4 bonds with 4 oxygen atoms. In ClO4-, the central atom Cl forms 4 bonds with 4 oxygen atoms. Therefore, the correct answer is that the central atom in each of these compounds forms 4 bonds.Rate this question:
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- 15.
The energy change that to convert a ground state- atom in the gas phase to a gaseous positive ion:
- A.
Activation energy
- B.
Free energy
- C.
Ionization energy
- D.
Kinetic energy
- E.
Lattice energy
Correct Answer
C. Ionization energyExplanation
Ionization energy refers to the energy required to remove an electron from an atom or ion in its ground state. In this case, the question is asking for the energy change needed to convert a ground state atom in the gas phase into a gaseous positive ion. This process involves removing an electron from the atom, which requires energy. Therefore, the correct answer is ionization energy.Rate this question:
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- 16.
Lattice of positive and negative ions held together by electrostatic forces.
- A.
Cesium Chloride
- B.
Gold
- C.
Carbon Dioxide
- D.
Methane
Correct Answer
A. Cesium ChlorideExplanation
Cesium Chloride is a compound composed of positive cesium ions and negative chloride ions. These ions are held together by electrostatic forces, which are attractive forces between opposite charges. The lattice structure refers to the arrangement of these ions in a repeating pattern throughout the solid compound. Therefore, the explanation for the given correct answer is that Cesium Chloride fits the description of a lattice of positive and negative ions held together by electrostatic forces.Rate this question:
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- 17.
Closely packed lattice with delocalized electrons through
- A.
Cesium Chloride
- B.
Gold
- C.
Carbon Dioxide
- D.
Methane
Correct Answer
B. GoldExplanation
Gold is a metal that has a closely packed lattice structure, meaning its atoms are arranged in a regular and compact pattern. Additionally, gold has delocalized electrons, which means that the outermost electrons of gold atoms are not tightly bound to individual atoms, but instead can move freely throughout the entire lattice. This delocalization of electrons allows gold to conduct electricity and heat efficiently.Rate this question:
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- 18.
Strong single covalent bonds with weak intermolecular forces
- A.
Sodium Chloride
- B.
Gold
- C.
Carbon dioxide
- D.
Methane
Correct Answer
D. MethaneExplanation
Methane is the correct answer because it consists of strong single covalent bonds between carbon and hydrogen atoms. These covalent bonds are formed by the sharing of electrons between the atoms, resulting in a stable molecule. The intermolecular forces in methane, however, are weak. Methane is a gas at room temperature and pressure, and it easily breaks apart into individual molecules. This is due to the weak intermolecular forces between methane molecules, which are caused by the small size of the molecules and the lack of polarity.Rate this question:
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- 19.
What mass of Au is produced when 0.0500 mol of Au2S3is reduced completely with excess hydrogen gas.
- A.
9.85 g
- B.
19.7 g
- C.
48.4 g
- D.
34,85 g
Correct Answer
B. 19.7 gExplanation
When Au2S3 is reduced with excess hydrogen gas, it undergoes a chemical reaction to produce Au and H2S. The balanced chemical equation for this reaction is: Au2S3 + 3H2 → 2Au + 3H2SFrom the balanced equation, we can see that 1 mole of Au2S3 produces 2 moles of Au. Therefore, 0.0500 mol of Au2S3 will produce 0.100 mol of Au. To find the mass of Au produced, we can use the molar mass of Au, which is 196.97 g/mol. Mass = moles × molar mass = 0.100 mol × 196.97 g/mol = 19.7 g. Therefore, the correct answer is 19.7 g.Rate this question:
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- 20.
A hot air balloon rises, which of the following is the best explanation for this action?
- A.
The pressure on the walls of the balloon increases and with increasing temperature
- B.
The difference in temperature between the air inside the outside the balloon produces convection currents
- C.
The cooler air outside the balloon pushes in the walls of the balloon
- D.
The rate of diffusion of cooler air is less than that of warmer air
- E.
The air density inside the balloon is less than that of the surrounding air.
Correct Answer
E. The air density inside the balloon is less than that of the surrounding air.Explanation
The correct answer is that the air density inside the balloon is less than that of the surrounding air. When the air inside the balloon is heated, it expands and becomes less dense than the cooler air outside. This density difference causes the balloon to rise because the less dense air inside the balloon is buoyed up by the denser air outside.Rate this question:
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- 21.
... C10H12O4S(s) + ... O2(g) −−> ... CO2(g) + ... SO2(g) + ... H2O(g) When the equation above is balanced and the all the coefficients are reduced to their lowest whole-number terms, the coefficient for O2 gas is
- A.
6
- B.
7
- C.
12
- D.
14
- E.
28
Correct Answer
D. 14Explanation
In order to balance the equation, we need to make sure that the number of atoms of each element is the same on both sides. Looking at the equation, we can see that there are 4 oxygen atoms on the left side (from C10H12O4S) and only 2 on the right side (from CO2). To balance the oxygen atoms, we need to have a coefficient of 2 in front of CO2. This means that we will need 2 molecules of O2 gas on the left side. Therefore, the coefficient for O2 gas is 2 x 7 = 14.Rate this question:
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- 22.
Is a gas in its standard state at 298K
- A.
Lithium
- B.
Nickel
- C.
Bromine
- D.
Uranium
- E.
Fluorine
Correct Answer
E. FluorineExplanation
Fluorine is a gas in its standard state at 298K because it has a boiling point of -188.12°C (-306.62°F) and a melting point of -219.62°C (-363.32°F), which are both below room temperature. In its standard state, fluorine exists as diatomic molecules (F2) and is a pale yellow gas.Rate this question:
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- 23.
Reacts with water to form a strong base
- A.
Lithium
- B.
Nickle
- C.
Bromine
- D.
Uranium
- E.
Fluorine
Correct Answer
A. LithiumExplanation
Lithium reacts with water to form a strong base. When lithium comes into contact with water, it undergoes a vigorous reaction, releasing hydrogen gas and forming lithium hydroxide, which is a strong base. This reaction occurs because lithium is an alkali metal and has a strong tendency to donate its outermost electron, resulting in the formation of hydroxide ions. The formation of a strong base in this reaction is characteristic of lithium, distinguishing it from the other elements listed.Rate this question:
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- 24.
In the periodic table, as the atomic number increases from 11-17, what happens to the atomic radium?
- A.
It remains constant
- B.
It increases only
- C.
It increases, then decreases
- D.
It decreases only
- E.
It decreases, then increases
Correct Answer
D. It decreases onlyExplanation
As the atomic number increases from 11-17 in the periodic table, the atomic radius decreases only. This is because as the number of protons in the nucleus increases, the positive charge also increases. This stronger positive charge attracts the negatively charged electrons more strongly, pulling them closer to the nucleus. As a result, the atomic radius decreases.Rate this question:
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- 25.
Which of the following is a correct interpretation of the results of Rutherford"s experiments in which goald atoms are bombarded with alpha particles?
- A.
Atoms have equal numbers of positive and negative charges
- B.
Electrons in atoms are arranged in shells
- C.
Neutrons are at the center of an atom
- D.
Neutrons and protons in atoms have nearly equal mass.
- E.
The positive charge of an atoms is concentrated in a small region
Correct Answer
D. Neutrons and protons in atoms have nearly equal mass.Explanation
Rutherford's experiments involved bombarding gold atoms with alpha particles, which led to the discovery of the atomic nucleus. Through these experiments, Rutherford determined that most of the mass of an atom is concentrated in a small, dense region called the nucleus, and that the nucleus contains positively charged particles called protons. He also observed that the alpha particles were deflected, indicating the presence of a positive charge concentrated in the nucleus. However, Rutherford did not discover neutrons until later. Therefore, the correct interpretation of Rutherford's experiments is that neutrons and protons in atoms have nearly equal mass.Rate this question:
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- 26.
A rigid metal tank contains oxygen gas. Which of the following applies tot he gas in the tank when additional oxygen is added at constant temperature
- A.
The volume of the gas increases
- B.
The pressure of the gas decreases
- C.
The averages speed of the gas molecules remains the same
- D.
The total number of gas molecules remains the same
- E.
The average distances between the gas molecules increases
Correct Answer
E. The average distances between the gas molecules increasesExplanation
When additional oxygen is added to the rigid metal tank at constant temperature, the gas molecules will spread out to occupy more space. This means that the average distances between the gas molecules will increase. The volume of the gas may or may not increase, depending on the amount of oxygen added and the initial volume of the tank. The pressure of the gas will remain constant because the temperature is constant. The average speed of the gas molecules will also remain the same because the temperature is constant. The total number of gas molecules will increase with the addition of more oxygen.Rate this question:
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- 27.
A 0.03 mol sample of NH4NO3 solid is placed in a 1 L evacuated flask, which is them sealed and heated. The NH4NO3 solid decomposes completely according to the balanced equation above. The total pressure in the flask measured at 400 K is closest to which of the following (R=0.082 L atm per mol K)
- A.
3 atm
- B.
1 atm
- C.
0.03 atm
- D.
0.1 atm
- E.
0.5 atm
Correct Answer
A. 3 atmExplanation
When NH4NO3 decomposes, it forms N2O(g) and 2H2O(g). Since the reaction is complete, all of the NH4NO3 will decompose, resulting in the formation of 0.03 mol of N2O and 0.06 mol of H2O.
Using the ideal gas law, PV = nRT, we can calculate the pressure in the flask. The volume (V) is given as 1 L, the number of moles (n) is 0.03 mol of N2O, the gas constant (R) is 0.082 L atm per mol K, and the temperature (T) is 400 K.
Plugging in these values, we get P = (0.03 mol)(0.082 L atm per mol K)(400 K) / 1 L = 9.84 atm.
Since we are asked for the closest value, the answer is 3 atm.Rate this question:
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- 28.
After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference.
- A.
Strong initial heating caused some of the hydrate sample to spatter out of the crucible
- B.
The dehydrated sample absorbed moisture after heating
- C.
The amount of the hydrate sample used was too small
- D.
The crucible was not heated to constant mass before use
- E.
Excess heating caused the dehydration sample to decompose
Correct Answer
B. The dehydrated sample absorbed moisture after heatingExplanation
The most likely explanation for the difference in the reported value and the correct value is that the dehydrated sample absorbed moisture after heating. This could have caused an increase in the weight of the sample, leading to a lower percentage of water in the hydrate being calculated.Rate this question:
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- 29.
The volume of distilled water that should be added to 10.0 mL of 6.00 M CHl in order to prepare a 0.500 M HCl solution isapproximately.
- A.
50.0 mL
- B.
60.0 mL
- C.
100. mL
- D.
110. mL
- E.
120. mL
Correct Answer
D. 110. mLExplanation
To prepare a 0.500 M HCl solution, we need to dilute the 6.00 M CHl solution. The dilution formula is C1V1 = C2V2, where C1 and V1 are the initial concentration and volume, and C2 and V2 are the final concentration and volume. Plugging in the values, we have (6.00 M)(10.0 mL) = (0.500 M)(V2). Solving for V2, we get V2 = (6.00 M)(10.0 mL) / (0.500 M) = 120 mL. However, since we are adding distilled water, the final volume will be the sum of the initial volume and the volume of water added. Therefore, 120 mL + 10.0 mL = 130 mL. Since we want to find the volume of water added, we subtract the initial volume, giving us 130 mL - 10.0 mL = 110 mL.Rate this question:
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- 30.
In which of the following processes are covalent bonds broken?
- A.
I2 (s) --> I2 (g)
- B.
CO2 (s) ---> CO2 (g)
- C.
NaCl (s) --> NaCl (l)
- D.
C (diamond) --> C (g)
- E.
Fe (s) --> Fe (l)
Correct Answer
D. C (diamond) --> C (g)Explanation
The correct answer is C (diamond) --> C (g). In this process, covalent bonds in the diamond structure are broken, converting the solid diamond into gaseous carbon atoms. Covalent bonds are formed when atoms share electrons, and breaking these bonds requires energy input.Rate this question:
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