Unit 3 + Unit 4-MCQ ?'s

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

1.0 M

Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When the reaction represented above proceeds, heat is produced. Which of the following best describes the reaction?

It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced.

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is evidence that ionic bonds formed during the precipitation?

The precipitate has a high melting point.

Assume that 50.0mL of 1.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined. According to the balanced equation, if 50.0mL of 2.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined, the amount of precipitate formed would

not change, because the amount of AgNO3(aq) did not change

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

1.5 g

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 313283.

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^−19J

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?

5.6×10^14s^−1

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^−19J

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

62.5mL

When students added 2.0g of NaI crystals to 100.mL of Pb(NO3)2(aq), a yellow precipitate formed. After the solution was filtered, the yellow solid was dried and weighed. Data from the experiment are shown in the table above. Which of the following claims is best supported by the observations?

A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed.

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.

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is the balanced net ionic equation for the formation of the precipitate?

Ag+(aq)+Cl−(aq)→AgCl(s)

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.

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 CH4molecules 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 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.

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.

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.

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.

A beaker was half filled with freshly distilled H2O and placed on a hot plate. As the temperature of the water reached 100°C, vigorous bubbling was observed in the beaker. The gaseous contents of the bubbles were analyzed. The presence of which of the following substances would support the claim that the observed phenomenon was a physical change?

H2O(g)

Which of the following is the correct net ionic equation of the neutralization reaction between hydrofluoric acid and sodium hydroxide in aqueous solution?

HF(aq)+OH−(aq)→H2O(l)+F−(aq)

2Mg(s)+SiCl4(l)→2MgCl2(s)+Si(s) Which of the following statements about the reaction represented above is correct?

It is an oxidation-reduction reaction, and Mg is oxidized.

A student carried out a titration using HC2H3O2(aq) and NaOH(aq). The net ionic equation for the neutralization reaction that occurs during the titration is represented above. The NaOH(aq) was added from a buret to the HC2H3O2(aq) in a flask. The equivalence point was reached when a total of 20.0mL of NaOH(aq) had been added to the flask. How does the amount of HC2H3O2(aq) in the flask after the addition of 5.0mL of NaOH(aq) compare to the amount of HC2H3O2(aq) in the flask after the addition of 1.0mL of NaOH(aq), and what is the reason for this result?

It is less because more HC2H3O2(aq) reacted with the base.

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 of the following is the correct net ionic equation of the reaction that occurs when aqueous solutions of ammonia and hydrochloric acid are combined?

NH3(aq)+H+(aq)→NH4+(aq)

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

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.

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 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.

A student was given two clear liquids; a colorless liquid and a dark-blue liquid. The student was asked to combine the liquids in a beaker and record observations. Which of the following results, if true, would provide the best evidence that a chemical change took place when the liquids were combined?

The resulting mixture was cloudy.

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.

According to the balanced chemical equation above, when 100.0mL of 0.100MK2SO3(aq) is mixed with 100.0mL of 0.200MHNO3(aq) at 30°C and 1 atm, the volume of SO2 gas produced is 0.24 L. If it is assumed that the reaction goes to completion, which of the the following changes would double the volume of SO2 produced at the same temperature and pressure? (For each change, assume that the other solutions and volumes remain the same.)

Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because these are the required stoichiometric amounts

which of the following would be the best procedure for separating a mixture of methanol and water?

distillation

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