Unit 3 Test Review AP Chemistry

The frequency and energy ranges of photons in some parts of the electromagnetic spectrum are given in the table above. Which of the following could be the energy of a photon in the visible range?

4×10^−19 J

Electromagnetic radiation with a maximum wavelength of 540nm (5.4×10−7 m ) is needed for the study of the photoelectric effect in potassium atoms. What is the approximate frequency that corresponds to this wavelength?

5.6×10^14 s−1

What volume of a 0.100M HCl stock solution should be used to prepare 250.00mL of 0.0250M HCl?

62.5mL

A gaseous air‑fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air‑fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air‑fuel mixture?

About 12atm , because the volume of the gas mixture decreased by a factor of 12.

The diagrams above represent two allotropes of solid phosphorus. Which of the following correctly identifies the allotrope with the higher melting point and explains why?

Allotrope II , because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P4 molecules in allotrope I .

KEEP 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.

The structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite?

Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces.

Which of the following best explains what happens as photons of visible light are absorbed by dye molecules?

Certain electrons in the dye molecule move to a higher energy level, with the difference in energy between the lower and higher energy levels being the same as the energy of the absorbed photons.

Which of the diagrams above best represents the interactions that are responsible for the relatively large solubility of KCl crystals in water, and why?

Diagram 1, because strong ion-dipole interactions between KCl and water help to dissociate the solute.

The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why?

Diagram 2, because the particles have a variety of different speeds.

One type of organic molecule can be converted to another type of organic molecule through an oxidation-reduction process, as represented in the diagram above. Which of the following best explains why infrared spectroscopy is an appropriate method to confirm that the product contains a carbonyl?

The absorption of infrared radiation leads to an increase in molecular vibrational level associated with the stretching of the carbonyl.

The original solution used to make the solutions for the standard curve was prepared by dissolving 2.60g of CoCl2 (molar mass 130.g/mol) in enough water to make 100.mL of solution. What is the molar concentration of the solution?

0.200M

A 500.mL aqueous solution of Na3PO4 (molarmass=164g/mol) was prepared using 82 gof the solute. What is the molarity of Na3PO4 in the resulting solution?

1.0M

How many grams of NaCl (molarmass=58g/mol) are needed to prepare 100.mL of a 0.25M NaCl solution?

1.5g

KEEP 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.

At 10.°C, 20.g of oxygen gas exerts a pressure of 2.1atm in a rigid, 7.0L cylinder. Assuming ideal behavior, if the temperature of the gas was raised to 40.°C, which statement indicates the new pressure and explains why?

2.3atm , because the pressure P increases by the proportion 313/283 .

In an experiment on the photoelectric effect, a photon with a frequency of 7×1014s−1 was absorbed by a sample. What is the approximate energy of this photon?

5×10^−19 J

KEEP A gas mixture at 0°C and 1.0atm contains 0.010mol of H2H2, 0.015mol of O2, and 0.025mol of 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.

Equimolar samples of CH4(g) and C2H6(g) are in identical containers at the same temperature. The C2H6(g) deviates much more from ideal behavior than the CH4(g) does. Which of the following best helps explain this deviation?

C2H6 molecules have a larger, more polarizable electron cloud than CH4 molecules do.

The gases CO2(g) and NH3(g) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(g) can be liquefied at a lower pressure than CO2(g) can be liquefied. Which of the following is the best justification for this claim?

CO2 is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH3 molecules.

The crystal structure of NaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(s) to molten NaBr(l) in terms of electrical conductivity?

Crystalline NaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.

KEEP 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+Na+ ions and the Cl− ions are weaker than those between the ions in MgS.

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C2H6O, molecules?

Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule.

Methanol, CH3OH, dissolves completely in water to form a solution that does not conduct electricity. Which of the following diagrams best shows the major type of attractive force that exists between the particles in the solution?

Diagram C

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

When methanol and water are mixed together, they form a homogeneous mixture. Based on the information in the table above, which of the following would be the best procedure for separating a mixture of methanol and water?

Distillation

The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct?

Gas Z has a smaller molar mass than gas X .

KEEP 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.

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.

The diagram above represents four cations, all shown to the same scale. Which cation would be predicted by Coulomb's law to have the strongest ion-dipole attraction to water, and why?

Mg2+ , because it has the largest charge-to-size ratio

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

Which of the following methods is most appropriate to use to determine the number of different-colored components in a sample of black ink?

Paper chromatography using different solvents with a range of polarities as the mobile phase

The graph above shows how a particular real gas deviates from ideal behavior at very high pressures. Based on this information, which of the following is most likely the gas and gives the reason based on kinetic molecular theory?

SO2 , because it has the largest molecular volume.

The diagram above shows thin-layer chromatograms of the same mixture of two compounds. Based on the chromatograms, which solvent would be most effective at separating the two compounds if the same stationary phase is used for column chromatography?

Solvent C

The infrared spectrum above represents the absorption of certain wavelengths of radiation by molecules of CO2. Which of the following best explains what occurs at the molecular level as the CO2 molecules absorb photons of the infrared radiation?

The atoms in the CO2 molecules increase their vibration as the bonds between the atoms bend and stretch.

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 student adds a 1g sample of an unknown, brittle solid to distilled water, stirs the mixture, and then measures its conductivity. The student repeats this procedure with more samples of the unknown solid and then produces the graph above. Which of the following statements about the graph and the properties of the solid is correct?

The increase in conductivity indicates that the unknown is an ionic solid that dissociates into ions when it dissolves in water.

A student measures the absorbance of a solution containing FeSCN2+ ion using a spectrophotometer. The cuvette used by the student has two frosted walls and two transparent walls. The student properly orients the cuvette so that the path of the light goes through the transparent sides of the cuvette when calibrating the spectrophotometer. How will the measured absorbance of the FeSCN2+ be affected if the student incorrectly orients the cuvette so that the path of the light is through the frosted sides of the cuvette?

The measured absorbance of the FeSCN2+ solution will be higher than the actual absorbance.

A student uses a spectrophotometer to analyze a solution of blue food dye. The student first rinses a cuvette with distilled water. Then the student adds the blue dye solution to the cuvette, forgetting to rinse the cuvette with the blue dye solution first. The student places the cuvette in the spectrophotometer and measures the absorbance of the solution. Assuming that some distilled water droplets were still in the cuvette when the blue dye solution was added, how would the measured absorbance be affected?

The measured absorbance would be too low, because the distilled water left in the cuvette would slightly dilute the solution.

KEEP 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.

A solid compound of a group 1 (alkali) metal and a group 17 (halogen) element dissolves in water. The diagram above represents one type of solute particle present in the solution. Which of the following identifies the solute particle and best helps explain how the solute particle interacts with water molecules?

The particle is a positive ion, and the interactions are ion-dipole attractions.

The absorption spectrum of a certain red dye is shown above. If a student analyzing the same concentration of this dye neglected to wipe fingerprints off the cuvette before placing it in the spectrophotometer, how would the absorption curve be affected?

The peak of the curve would be higher because more light would be absorbed.

Two sealed, rigid 5.0L containers each contain a gas at the same temperature but at a different pressure, as shown above. Also shown are the results of transferring the entire contents of container 1 to container 2. No gases escape during the transfer. Assuming ideal behavior, which statement is correct regarding the total pressure of the gases after they are combined?

The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant.