Chem Semester Review (Problems I got wrong on AP Classroom) Units 1-7

Which of the following claims about a binary compound in which the bonding is ionic is most likely to be scientifically valid? A Both elements in the compound are metals. B The atomic masses of the elements in the compound are relatively small. C There is equal sharing of electrons between the atoms of the elements in the compound. D The electronegativity difference between the elements in the compound is relatively large.

D

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? A The measured absorbance would be too low, because the distilled water left in the cuvette would slightly dilute the solution. B The measured absorbance would be too low, because the distilled water would change the optimum wavelength of absorbance. C The measured absorbance would be too high, because the water would allow more light to pass through the cuvette. D The measured absorbance would be too high, because the distilled water would also absorb some light.

A

A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture? A The molar mass of each gas B The density of the gases in the vessel C The total pressure of the gases in the vessel D The number of atoms per molecule for each gas

A

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? A About 0.083atm, because the initial volume of the gas mixture was 12 times larger than its final volume. B About 12atm, because the volume of the gas mixture decreased by a factor of 12. C About 120.atm, because the initial volume of the gas mixture was 120 times larger than its final volume. D About 550.atm , because the change in the volume of the gas mixture was 550.mL .

B

A student measures the absorbance of a solution containing FeSCN2+ ions 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? A The measured absorbance of the FeSCN2+ solution will not be affected. B The measured absorbance of the FeSCN2+ solution will be higher than the actual absorbance. C The measured absorbance of the FeSCN2+ solution will be lower than the actual absorbance. D The effect on the measured absorbance of the FeSCN2+ solution depends on the concentration of the FeSCN2+ solution.

B

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment? A What is the density of M? B What is the molar mass of M? C What is the melting point of M? D What is the melting point of MO?

B

A student obtains a mixture of the chlorides of two unknown metals, X and Z. The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XCl(s) and of ZCl(s) in the mixture? A The number of isotopes of Cl B The molar masses of X and Z C The density of either XCl(s) or ZCl(s) D The percent by mass of Cl in the mixture

B

Which of the following claims about a binary compound composed of elements with the same electronegativity is most likely to be true? A The compound has properties similar to those of both elements. B The bonding in the compound is nonpolar covalent. C The boiling point of the compound is above 1000°C. D The compound contains strong ionic bonds.

B