AP Chemistry Unit 3
Based on concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water?
(E) X < Y < Z
A 360. mg sample of aspirin, C9H8O4, (molar mass 180. g), is dissolved in enough water to produce 200. mL of solution. What is the molarity of aspirin in a 50. mL sample of this solution?
0.0100 M
If 50. mL of 1.0 M NaOH is diluted with distilled water to a volume of 2.0 L, the concentration of the resulting solution is
0.025 M
How many moles of Na+ ions are in 100 mL of 0.100 M Na3PO4?
0.0300 mol
Solid Al(NO3)3 is added to distilled water to produce a solution in which the concentration of nitrate, [NO3-], is 0.10 M. What is the concentration of aluminum ion, [Al3+], in this solution?
0.033 M
If 200. mL of 0.60 M MgCl2(aq) is added to 400. mL of distilled water, what is the concentration of Mg2+(aq) in the resulting solution? (Assume volumes are additive.)
0.20 M
A 0.20 mol sample of MgCl2 and a 0.10 mol sample of KCl are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution?
1.0
Given that the density of Hg(l) at 0°C is about 14 g mL-1, which of the following is closest to the volume of one mole of Hg(l) at this temperature?
1.4 mL
A sealed vessel contains 0.200 mol of oxygen gas, 0.100 mol of nitrogen gas, and 0.200 mol of argon gas. The total pressure of the gas mixture is 5.00 atm. The partial pressure of the argon is
2 atm
An equimolar mixture of N2(g) and Ar(g) is kept inside a rigid container at a constant temperature of 300 K. The initial partial pressure of Ar in the mixture is 0.75atm. An additional amount of Ar was added to the container, enough to double the number of moles of Ar gas in the mixture. Assuming ideal behavior, what is the final pressure of the gas mixture after the addition of the Ar gas?
2.25atm , because doubling the number of moles of Ar doubles its partial pressure.
When the 4.0L of He(g), 6.0 L of N₂(g) and 10 L of Ar(g), all at 0C and 1 atm, are pumped into an evacuated 8.0L rigid container, the final pressure in the container is 0C.
2.5 atm
The volume of water that must be added in order to dilute 40 mL of 9.0 M HCl to a concentration of 6.0 M is closest to
20 mL
A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. A wavelenth of 510nm corresponds to an approximate frequency of...
4×10−19J
Equal masses of He and Ne are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 6 atm?
5 atm
Under which of the following conditions of temperature and pressure would 1.0 mol of the real gas CO2 behave most like an ideal gas?
800 K and 0.1 atm
A gas mixture at 0°C and 1.0atm contains 0.010mol of H2, 0.015mol of O2, and 0.025molof N2. Assuming ideal behavior, what is the partial pressure of hydrogen gas (H2) in the mixture?
About 0.20atm, because H2 comprises 20% of the total number of moles of gas.
At standard temperature and pressure, a 0.5 mol sample of H2 gas and a separate 1.0 mol sample of 02 gas have the same
Average molecular kinetic energy
The following questions refer to the 1 L flasks shown below. In which flask do the molecules have the greatest average speed?
B 50 degrees .5 atm
The structure of one form of boron nitride is represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?
Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.
Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas?
C: 500K and 0.10 atm
Sodium chloride is LEAST soluble in which of the following liquids?
CCl4
In which of the following liquids do the most intermolecular forces include dipole-dipole forces?
CH2F2
The table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4. On the basis of the data provided above, the gas in container 3 could be
CH4
In the diagram below, which of the labeled arrows identifies hydrogen bonding in water?
D
The diagram above represents the absorption spectrum for a pure molecular substance. Which of the following correctly indicates the type of transition observed for the substance in each of the regions of the absorption spectrum?
D
The graph above shows the speed distribution of molecules in a sample of a gas at a certain temperature. Which of the following graphs shows the speed distribution of the same molecules at a lower temperature (as a dashed curve)?
D: [graph w speed on x axis and number of molecules on y axis, dashed line peaks before solid line]
The ionic compounds NaCl and MgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why?
Diagram 1 represents NaCl; it has a lower melting point than MgS because the coulombic attractions between its singly charged Na+ ions and the Cl− ions are weaker than those between the ions in MgS.
The survival of aquatic organisms depends on the small amount of O2 that dissolves in H2O. The diagrams above represent possible models to explain this phenomenon. Which diagram provides the better particle representation for the solubility of O2 in H2O, and why?
Diagram 2 bc polar H20 molecules...
The diagram above shows the distribution of speeds for a sample of O2(g). Which of the following graphs shows the distribution of speeds for the same sample at a higher temperature (dashed line) ?
Diagram C
A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs?
Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces
Which flask contains the sample with the greatest density?
Flask C
This question refers to three gases in identical rigid containers under the conditions given in the table below. The density of the gas, in g/L, is
Greatest in container B
A student places a piece of I2(s) in 50.0 mL of H2O(l), another piece of I2(s) of the same mass in 50.0 mL of C6H14(l), and shakes the mixtures. The results are shown above. What do the results indicate about the intermolecular interactions of the substances?
I2 and C6H14 have similar intermolecular interactions, and I2 and H2O do not.
The diagram above is a molecular model of a gaseous diatomic element that is just above its boiling point. Intermolecular forces between the gas molecules will cause them to condense into the liquid phase if the temperature is lowered. Which of the following best describes how the model is limited in its depiction of the phenomenon?
It does not show how the temporary fluctuating dipoles of the molecular electron clouds result in a net force of attraction between the molecules.
At room temperature I2(s) is a molecular solid. Which of the following provides a characteristic of I2(s) with a correct explanation?
It is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs
The ideal gas law describes the properties of which of the following gases at 0C and 1 atm?
N2
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
Which of the following best helps explain why the pressure of a sample of CH4 is closer to the pressure predicted by the ideal gas law than a sample of NH3?
NH3 molecules are polar while CH4 molecules are not, and the greater attractions between NH3 molecules cause the molecules to collide with the walls of the container with less force.
Which of the following could be the identity of a white crystalline solid that exhibits the following properties?
NaOH
Equal numbers of moles of He(g), Ar(g), and Ne(g) are placed in a glass vessel at room temperature. If the vessel has a pinhole-sized leak, which of the following will be true regarding the relative values of the partial pressures of the gases remaining in the vessel after some of the gas mixture has effused?
PHe < PNe < PAr
Which of the following gases deviates most from ideal behavior?
SO2
At constant temperature, the behavior of a sample of a real gas more closely approximates that of an ideal gas at its volume is increased because the
The average distance between molecules becomes greater
A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. The temperature is kept constant. Which of the following statements about combining the gases is correct?
The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.
A vessel contains Ar(g) at a high pressure. Which of the following statements best helps to explain why the measured pressure is significantly greater than the pressure calculated using the ideal gas law.?
The combined volume of the Ar atoms is too large to be negligible compared with the total colume of the container.
Ar deviates more from ideal behavior at extremely high pressures than Ne does. Which of the following is one reason for this difference?
The particle volume of Ar is greater than that of Ne
The diagrams above show the ultraviolet absorption spectra for two compounds. Diagram 1 is the absorption spectrum of pure acetone, a solvent used when preparing solutions for an experiment. Diagram 2 is the absorption spectrum of the solute for which the absorbance needs to be measured to determine its concentration. When the student reads the absorbance of the solution at 280 nm, the result is too high. Which of the following is most likely responsible for the error in measured absorbance?
The student forgot to calibrate the spectrophotometer first by using a curvette containing acetone.
A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration. The student made the standard curve above. Which of the following most likely caused the error in the point the student plotted at 0.050MCo2+(aq) ?
There was distilled water in the cuvette when the student put the standard solution in it.
N2 molecules absorb ultraviolet light but not visible light. I2 molecules absorb both visible and ultraviolet light. Which of the following statements explains the observations?
Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule.
In a paper chromatography experiment, a sample of a pigment is separated into two components, X and Y, as shown in the figure above. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results?
Y is more polar than x
The pressure, in atm, exerted by 1.85 mol of an ideal gas placed in a 3.00 L container at 35.0ºC is given by which of the following expressions?
[(1.85)(0.0821)(308)]/3.00 atm
A student prepared five solutions of CuSO4
d) the curvet used for the 0.6 M solution had not been wiped clean before being put in the spectrophotometer-oils could absorb light which cause abs to be higher than expected
A certain crystalline substance that has a low melting point does not conduct electricity in solution or when melted. This substance is likely to be
molecular solid
When the actual gas volume is greater than the volume predicted by the ideal gas law, the explanation lies in the fact that the ideal gas law does NOT include a factor for molecular.
volume
Which of the following is the best piece of laboratory glassware for preparing 500.0 mL of an aqueous solution of a solid?
volumetric flask
A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration.
0.200M
A 40.0 mL sample of 0.25 M KOH is added to 60.0 mL of 0.15 M Ba(OH)2. What is the molar concentration of OH-(aq) in the resulting solution? (Assume that the volumes are additive.)
0.28 M
How many grams of CaCl2 are needed to prepare 100 mL of 0.100MCl- ions?
0.555 g
A student prepares a solution by dissolving 60.00 g of glucose (molar mass 180.2 mol-1) in enough distilled water to make 250.0 mL of solution. The molarity of the solution should be reported as
1.332
How many mL of 10.0 M HCl are needed to prepare 500. mL of 2.00 M HCl?
100 mL
A flask contains 0.25 mole of SO2(g), 0.50 mole of CH4(g), and 0.50 mole of O2(g). The total pressure of the gases in the flask is 800 mm Hg. What is the partial pressure of the SO2(g) in the flask?
160 mm Hg
A 2 L sample of N2(g) and a 1 L sample of Ar(g), each originally at 1 atm and 0°C, are combined in a 1 L tank. If the temperature is held constant, what is the total pressure of the gases in the tank?
3 atm
When 6.0 L of He(g) and 10. L of N2(g), both at 0oC and 1.0 atm, are pumped into an evacuated 4.0 L rigid container, the final pressure in the container at 0oC is
4.0 atm
Based on their Lewis diagrams, which of the following pairs of liquids are most soluble in each other?
A
A sample of an ideal gas is cooled from 50.0 C to 25.0 C in a sealed container of constant volume. Which of the following values for the gas will decrease? 1. the average molecular mass of the gas 2. the average distance between the molecules 3. the average speed of the molecules
Average speed of the molecules
Infrared spectroscopy is a useful tool for scientists who want to investigate the structure of certain molecules. Which of the following best explains what can occur as the result of a molecule absorbing a photon of infrared radiation?
B
Which flask contains the smallest number of moles of gas?
B
A student performed a fractional distillation of a mixture of two straight-chain hydrocarbons, C7H16 and C8H18. Using four clean, dry flasks, the student collected the distillate over the volume ranges (A, B, C, and D) shown in the graph above. Over what volume range should the student collect the distillate of the compound with the stronger intermolecular forces?
D
Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds. Which of the following diagrams shows the correct representation of the hydrogen bonding (denoted by dashed lines) between thymine and adenine base pairs? (In each diagram, thymine is shown at the left and adenine is shown at the right. The bases are attached to the backbone portion of the DNA strands.)
D
The table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4. Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is
Greatest in container 1
Gases generated in a chemical reaction are sometimes collected by the displacement of water, as shown above. Which of the following gases can be quantitatively collected by this method? A H2 B CO2 C HCl D SO2 E NH3
H2
The London (dispersion) forces are weakest for which of the following gases under the same conditions of temperature and pressure?
H2
Which of the following behaves most like an ideal gas at the conditions indicated?
H2(g) molecules at 10-3 atm and 200oC
The experimental apparatus represented above is used to demonstrate the rates at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time ,the gases diffuse From each end and meet somewhere in between, where they react to form a white solid. Whivh of the following combinations will produce a solid closest to the center of the tube?
HCl and CH3NH2
A 0.5 mol sample of He(g) and a 0.5 mol sample of Ne(g) are placed separately in two 10.0 L rigid containers at 25°C. Each container has a pinhole opening. Which of the gases, He(g) or Ne(g), will escape faster through the pinhole and why?
He(g) will escape faster because the He(g) atoms are moving at a higher average speed than the Ne(g) atoms.
Equal masses of three different ideal gases, X, Y, and Z, are mixed in a sealed rigid container. If the temperature of the system remains constant, which of the following statements about the partial pressure of gas X is correct?
It depends on the relative molecular masses of X, Y, and Z.
In solid methane, the forces between neighboring CH4 molecules are best characterized as
London dispersion forces
Two flexible containers for gases are at the same temperature and pressure. One holds 0.50 gram of hydrogen and the other holds 8.0 grams of oxygen. Which of the following statements regarding these gas samples is FALSE?
The average speed of the hydrogen molecules is the same as the average speed of the oxygen molecules.
The diagrams opposite represent two samples of Xe gas in containers of equal volume at 280 K. Which of the following correctly compares the two samples in terms of their deviation from ideal gas behavior and explains why?
The gas in sample 2 would deviate more from ideal behavior because the Xe atoms are closer together, leading to an increase in intermolecular attractions.
The graph above shows the distribution of molecular speeds for four different gases at the same temperature. What property of the different gases can be correctly ranked using information from the graph and why?
The molecular masses of the gases, because the gas molecules have the same average kinetic energy and mass can be calculated using the equation KEavg=12mv2.
Diagram 1 above shows equimolar samples of two gases inside a container fitted with a removable barrier placed so that each gas occupies the same volume. The barrier is carefully removed as the temperature is held constant. Diagram 2 above shows the gases soon after the barrier is removed. Which statement describes the changes to the initial pressure of each gas and the final partial pressure of each gas in the mixture and also indicates the final total pressure?
The partial pressure of each gas in the mixture is half its initial pressure; the final total pressure is half the sum of the initial pressures of the two gases.
The reaction between NO(g) and O2(g) to produce NO2(g) in a rigid reaction vessel is represented in the diagram above. The pressure inside the container is recorded using a pressure gauge. Which of the following statements correctly predicts the change in pressure as the reaction goes to completion at constant temperature, and provided the correct explanation?
The pressure will decrease because there are fewer molecules of product than of reactants.
The average kinetic energy of the gas molecules is
The same in all three containers
Four different liquid compounds in flasks at 20°C are represented above. The table below identifies the compounds. Flask C shows the most particles in the vapor phase. Which of the following is not shown in the model but best helps to explain why flask C must contain pentane?
The strength of the intermolecular forces between the particles in the liquids
The best explanation for the fact that diamond is extremely hard is that diamond crystals
are giant molecules in which each atom forms strong covalent bonds with all of its neighboring atoms
Of the following, the best explanation for the fact that most gases are easily compressed is that the molecules in a gas
are relatively far apart
Benzene, C6H6, has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best described the intermolecular forces of attraction between water and benzene?
dipole-induced-dipole, London dispersion interactions
Using the wavelength information provided above, what is the color of the light?
orange
What is the molarity of I- in a solution that contains 34 g of SrI2 in 1.0 L of the solution?
0.20 M
For an experiment, a student needs 100.0 mL of 0.4220 M NaCl. If the student starts with NaCl and distilled water, which of the following pieces of laboratory glassware should the student use to prepare the solution with the greatest accuracy?
100 mL volumetric flask
The volume of distilled water that should be added to 10.0 mL of 6.00 M HCl(aq) in order to prepare a 0.500 M HCl(aq) solution is approximately
110 mL
The figure above represents three sealed 1.0 L vessels, each containing a different inert gas at 298 K. The pressure of Ar in the first vessel is 2.0 atm. The ratio of the numbers of Ar, Ne, and He atoms in the vessels is 2:1:6, respectively. After all the gases are combined in a previously evacuated 2.0 L vessel, what is the total pressure of the gases at 298 K?
4.5 atm
When 70. milliliter of 3.0-molar Na2CO3 is added to 30. milliliters of 1.0-molar NaHCO3 the resulting concentration of Na+ is
4.5 m
A student wishes to prepare 2.00 liters of 0.100 molar KIO3. The proper procedure is to weigh out
42.8 grams of KIO3 and add H2O until the final homogeneous solution has a volume of 2.00 liters
Which of the following is closest to the frequency of the light with photon energy of 3.3x10^-19J?
5.0 x 10^14 s^-1
Approximately what mass of CuSO4...
6.2 g
At 27°C, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO (s), NaBr(s), Cu( ), or I ( ) s s s s 3 2 , as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mm Hg. All four vessels are heated to 127°C and allowed to reach a constant pressure. The gas particles in vessel 3 at 27°C are represented in the diagram above. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles when vessel 3 is heated to 127°C?
A
The electron cloud of HF is smaller than that of F2 , however, HF has a much higher boiling point than F2 has. Which of the following explains how the dispersion-force model of intermolecular attraction does not account for the unusually high boiling point of HF?
Liquid F2 has weak dispersion force attractions between its molecules, whereas liquid HF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules.
A sample of an unknown gas from a cylinder is collected over water in the apparatus shown opposite. After all the gas sample has been collected, the water levels inside and outside the gas collection tube are made the same. Measurements that must be made to calculate the molar mass of the gas include all of the following except
Mass of the water in the apparatus
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 of electricity?
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.
Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C?
NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3
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
The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure P1, as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?
The average kinetic energy stays the same.
A rigid metal tank contains oxygen gas. Which of the following applies to the gas in the tank when additional oxygen is added at constant temperature?
The average speed of the gas molecules remains the same.
Beta-carotene is an organic compound with an orange color...
The two main absorption bands are associated with transitions in electronic energy levels. The band in the region corresponding to shorter wavelengths shows a lower absorbance than the band in the region corresponding to longer wavelengths.
The diagram above shows a thin-layer chromatogram of a mixture of products from a chemical reaction. The separation was performed using 50% ethyl acetate in hexane as the solvent (mobile phase) and silica gel as the polar stationary phase. On the basis of the chromatogram and the information about solvents in the table above, which of the following would be the best way to decrease the distance that the products travel up the plate?
decrease the percentage of ethyl acetate in the solvent
Which of the following techniques is most appropriate for the recovery of solid KNO3 from an aqueous solution of KNO3?
evaporation to dryness
The table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4. The best explanation for the lower pressure in container 4 is that SO2 molecules
have stronger intermolecular attractions than the other three gases
A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance?
ionic bonds
When a sample of oxygen gas in a closed container of constant volume is heated until its absolute temperature is doubled, which of the following is also doubled?
pressure of gas
The distribution of speeds of H2 molecules at 273 K and 1 atm is shown in the diagram above. Which of the following best shows the speed distribution of He atoms under the same conditions of temperature and pressure?
smaller solid curve, taller dotted line with curve on left
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
Using a spectrophotometer, a student measures the absorbance of four solutions...
the concentration of the solution was actually lower than 0.150 M