20-21 FallSem ap chem final exam
based on the structures shown above, which of the following statements identifies the compound with the higher boiling point and provides the best explanation for the higher boiling point? (figure 1 is more of a branch-shaped bond, and figure 2 looks more linear)
compound 2, because it forms hydrogen bonds, whereas compound 1 does not. (more linear, two h connected at the end)
at 298k and 1 atm, br2 is a liquid with a high vapor pressure, and cl2 is a gas. those observations provide evidence that under the given conditions, the
forces among br2 molecules are stronger than those among cl2 molecules
which of the following has the bonds arranged in order of decreasing polarity?
h-f > n-f > f-f
solid carbon tetrachloride, ccl4, is represented by the diagram above. the attractions between the ccl4 molecules that hold the molecules together in the solid state are best identified as
intermolecular attractions resulting from temporary dipoles
which of the following most likely describes the solid represented in the diagram above> (big negative circles and small positive circles)
it is a brittle, water-soluble electrolyte that is a poor thermal and electrical conductor as a solid
equimolar samples of ch3oh and c2h5oh are placed in separate, previously evacuated, rigid 2.0l vessels. each vessel is attached to a pressure gauge, and the temperature are kept at 300k. in both vessels, liquid is observed to remain present at the bottom of the container at all times. the change in pressure inside the vessel containing ch3oh is shown below. compared to the equilibrium vapor pressure of ch3oh at 300k, the equilibrium vapor pressure of c2h5oh at 300k is
lower, because London dispersion forces among c2h5oh molecules are greater than those among ch3oh molecules
on the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water?
nh3
based on the information in the table above, which of the compounds has the highest boiling point, and why? (the table that has butane pentane and propanoic acid)
propanoic acid, because it can form intermolecular hydrogen bonds
based on the structural formulas, which of the following identifies the compound that is more soluble in water and best helps to explain why?
propanol, because molecules can form hydrogen bonds with water molecules but those of ethane cannot.
three substances were studied in the laboratory, and the data in the table above were collected. based on the data, which of the following shows the type of bonding in each substances? (x, y, z / 1600, 650, 1418 / none, high, none / none, high, high)
substance x: network covalent substance y: metallic substance z: ionic
a student is given a sample of a pure, white, crystalline substance. which of the following would be most useful in providing data to determine if the substance is an ionic compound?
testing the electrical conductivity of an aqueous solution of the substance
which of the following can be inferred from the diagram above that shows the dependence of potential energy on the internuclear distance between two atoms? (the curve threshold graph)
the atoms form a bond with a bond length of 75 pm
a sealed 10.0l flask at 400k contains equimolar amounts of ethane and propanol in gaseous form. which of the following statements concerning the average molecular speed of ethane and propanol is true?
the average molecular speed of ethane is greater than the average molecular speed of propanol
which of the following best helps to explain why na is more reactive with water than mg is?
the first ionization energy of na is less than that of mg
the diagram above represents a particle in aqueous solution. which of the following statements about the particle is correct?
the particle must be an anion because the positive end of each water molecule is pointed toward it
(picture of a gas pump) a mixture of two gases, 0.01 mol of C4H10 and 0.065 moll of O2, is pumped into a cylinder with a movable piston, as shown above. the mixture, originally at 200*c and 1.0 atm, is sparked and the reaction represented below occurs [2c4h10 + 13o2 = 8CO2 + 10H2O] which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (assume all gases behave ideally)
the piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules
a mixture of two gases, 0.01 mol of C4H10 and 0.065 mol of O2 is pumped into a cylinder with a movable piston, as shown above. the mixture, originally at 200*c and 1.0 atm, is sparked and the reaction represented below occurs 2C4H10 + 13O2 = 8CO2 + 10H2O which of the following is true after the product gases return to the original temperature and pressure, and why will the change occur? (assume all gases behave ideally)
the piston will be higher than its original position, because the cylinder will contain a greater number of gas molecules
a mixture of CO and O2 is placed in a container, as shown above. A reaction overs, forming CO2. which of the following best represents the contents of the box after the reaction has proceeded as completely as possible? (key: black circle=C, white circle=O) (four black circles, 10 white circles)
B 4 black circles with 2 white circles on each side, one pair of only white circles (4 candies and 1 snowman)
a mixture of H2 and O2 is placed in a container as represented above.The H2 and O2 react to form H2O. Which of the following best represents the container after the reaction has gone to completion? (4 black snowman, 4 white snowman)
B 4 white circles with black circle on each side, 2 pairs of only white circles (4 candies, 2 snowman)
Equal volumes of solutions in two different vessels are represented above. if the solution represented in vessel 1 is KCl, than the solution represented in vessel 2 could be
CaCl2 with twice the molarity of the solution in vessel 1
based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(l) is a good conductor or electricity? (solid and liquid versions of MgO)
MgO(s) consists of separate Mg2+ ions and O2- ions held in a fixed lattice, but in MgO (l), the ions are free to move and conduct electricity
the ideal gas law best describes the properties of which of the following gases at 0*c and 1atm?
N2
[Fe3+ + KSCN = FeSCN2+ + K+] to determine the moles of Fe3+ in a 100.ml sample of an unknown solution, excess KSCN is added to convert all the Fe3+ into the dark red species FeSCN2+, as represented by the equation above. the absorbance of FeSCN2+ at different concentrations is shown in the graph below. if the absorbance of the mixture is 0.20 at 453 nm, how many moles of Fe3+ were present in the 100.ml sample? (assume that any volume change due to adding the KSCN is negligible)
4x10^(-6) mol
CO2 + 2LiOH = Li2CO3 + H2O in a one-person spacecraft, an astronaut exhales 880g of CO2 (molar mass 44g/mol) per day. To prevent the buildup of CO2 in the spacecraft, a device containing LiOH is used to remove the CO2, as represented by the equation above. What mass of LiOH (molar mass 24g/mol) is needed to react with all of the CO2 produced by an astronaut in one day?
960g
which of the following particle diagrams best represents the products when four molecules of H2O2 decompose into water and oxygen gas at room temperature? (key: black circle=Hydrogen, white circle= Oxygen)
D 4 white circles with black circle on each side, 2 pairs of white circles only (4 candies, 2 snowman)
the Maxwell-boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. which gas has the greater molar mass?
Gas A (the higher curve)
NH3 reacts with BF3 to form a single species. which of the following structural diagrams is the most likely representation of the product of the reaction?
H F | | H - N - B - F | | H F D
Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?
HF, because its molecules form hydrogen bonds
in the reaction represented above, what is the hybridization of the c atoms before and after the reaction occurs?
before- sp2 after- sp3
which of the following best helps to explain why ccl4 is a liquid whereas cl4 is a solid when both are at 25*c?
the London dispersion forces are stronger in cl4 than in ccl4 because cl4 has a more polarizable electron cloud than ccl4
the table above provides some information about two types of steel, both of which are alloys of iron and carbon. which of the following best helps to explain why high-carbon steel is more rigid than low-carbon steel?
the additional carbon atoms within the alloy make it more difficult for the iron atoms to slide past one another
which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?
the atomic radius of Cl is smaller than that of S because Cl has a larger nucleus charge than S does
of the following diagrams, which best represents the structure of solid kf?
+-+-+-+-+- +-+-+-+-+- +-+-+-+-+- B
of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why?
0.1 m ki because ki completely dissociates in water to produce ions
a group of students was asked to recover Cu from a blue-green aqueous solution containing an unknown concentration of Cu2+. the students took a 100.0ml sample of the solution and added an excess of 1.0M Na3PO4, causing the Cu2+ to precipitate as Cu3(PO4)2, as shown in step 1 below if 3.8g of Cu3(po4)2 was recovered from step 1, what was the approximate Cu2+ in the original solution? (the molar mass of Cu3(PO4)2 is 381g/mol)
0.30M
what is the approximate h - o - c bond angle in the glycinium cation?
105
when 4.0l of he, 6.0l of n2, and 10.l of ar, all at 0*c and 1.0 atm, are pumped into an evacuated 8.0l rigid container, the final pressure in the container at 0*c is
2.5 atm
Li3N + 2h2 = LiNH2 + 2LiH when 70.g of Li3N (molar mass 35g/mol) reacts with excess H2, 8.0g of LiH is produced. The percent yield is closest to
25%
which of the following lewis electron-dot diagrams represents the molecule that is the most polar?
B :::Br-F:::
which of the following is the molecular formula of the unknown compound? (table of 30g, 60g, ?)
C4H8O2
(CH3OH and C2H5OH table) equimolar samples of CH3OH and C2H5OH are placed in separate, previously evacuated, rigid, 2.0l vessels. each vessel is attached to a pressure gauge, and the temperatures are kept at 300k. in both vessels, liquid is observed to remain present at the bottom of the container at all times. the change in pressure inside the vessel containing CH3OH is shown below. which of the following best describes the change that takes place immediately after the CH3OH is introduced into the previously evacuated vessel? (curve of pressure and time)
a physical change takes place because intermolecular attractions are overcome
the first five ionization energies of an unknown element are listed in the table above. which of the following statements correctly identifies the element and cites the evidence supporting the identification?
al, because of the large difference between the third and fourth ionization energies
A 1.0l sample of a pure gas is found to have a lower pressure than that predicted by the ideal gas law. the best explanation for the observation is that the molecules of the gas
are attracted to each other and do not exert as much force on the container walls as they would if they had no mutual attractions
a 1.0 mol sample of he at 25*c is mixed with a 1.0 mol sample of Xe at 50*c. which of the following correctly predicts the changes in average kinetic energy and the average speed of the Xe atoms that will occur as the mixture approaches thermal equilibrium?
average kinetic energy of xe atoms: will decrease average speed of Xe atoms: will decrease
the structural formula of the glycinium cation is shown above. arrows indicate the pka values for the labile protons in the molecule. which of the following is true about the geometry of the glycinium cation?
both c atoms and both o atoms lie in the same plane
the compound ccl4 is nonflammable and was once commonly used in fire extinguishers. on the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistant chemical?
cbr4
the structure of the haloacetic acids, xch2cooh (where x is either f, cl, br, of I), is shown above. the dissociation constants and molar masses of four haloacetic acids are listed in the table below. which compound, chloroacetic acid or iodoacetic acid, most likely has the lower boiling point, and why?
chloroacetic acid, because the London dispersion forces among its molecular are weaker
based on Coulomb's law and the information in the table above, which of the following anions is most likely to have the strongest interactions with nearby water molecules in an aqueous solution?
s2- (184)
the masses of carbon and hydrogen in samples of four pure hydrocarbons are given above. the hydrocarbon in which sample has the same empirical formula as propene, c3h6?
sample b (72g carbon, 12g hydrogen)
if a pure sample of an oxide of sulfur contains 40. percent sulfur and 60. percent oxygen by mass, then the empirical formula of the oxide is
so3
a group of students was asked to recover Cu from a blue-green aqueous solution containing an unknown concentration of cu2+. the students took a 100.0ml sample of the solution and added an excess of 1.0mna3po4, causing the cu2+ to precipitate as cu3(po4)2, as shown in step 1 below. The cu3(po4)2 was filtered, dried, and weighed. then the cu3(po4)2 was dissolved in a 3.0 mhcl solution, as shown in step 2 below. the students added a strip of zn to the solution to recover the cu, as shown in step 3 below. finally, the cu was filtered, dried, and weighed. the mass of the cu produced in step 3 was slightly more than the mass predicted from the 3.8g of cu3(po4)2 recovered from step1. which of the following could account for the discrepancy in the yield of cu from step 3?
some unreacted zn was mixed in with the cu
A sample of a solid labeled as NaCl may be impure. a student analyzes the sample and determines that it contains 75 percent chlorine by mass. Pure NaCl contains 61 percent chlorine by mass
the sample contains nacl and licl
the structural formulas for two isomers of 1, 2-dichloroethene are shown above. which of the two liquids has the higher equilibrium vapor pressure at 20*c, and why? (cis and trans)
the trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions
a balloon filled with 0.25 mol of He at 273 and 1 atm is allowed to rise through the atmosphere. which of the following explains what happens to the volume of the balloon as it rises from ground level to an altitude where the air temperature is 220k and the air pressure is 0.1 atm?
the volume will increase because the decrease in air pressure will have a greater effect than the decrease in temperature
the ionization energies of an unknown element, x, are listed in the table above. which of the following is the most likely empirical formula of a compound formed from element x and phosphorous, p?
x3p2
