psyc 3 exam

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) ? A There was distilled water in the cuvette when the student put the standard solution in it. B There were a few drops of the 0.100MCo2+(aq)0.100MCo2+(aq) standard solution in the cuvette when the student put the 0.050 M0.050 ⁢M standard solution in it. C The student used a cuvette with a longer path length than the cuvette used for the other standard solutions. D The student did not run a blank between the 0.050MCo2+(aq)0.050MCo2+(aq) solution and the one before it.

A

Each set of lettered choices below refers to the numbered statements immediately following it. Select the one lettered choice that best fits each statement. A choice may be used once, more than once, or not at all in each set. Refer to the following compounds. (A) CH3CH2CH2CH3 (B) CH3CH2CH2OH (C) CH3COCH3 (D) CH3COOH (E) CH3CH2CH2NH2 Is the LEAST soluble in water A CH3CH2CH2CH3 B CH3CH2CH2OH C CH3COCH3 D CH3COOH E CH3CH2CH2NH2

A

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

A

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 ofC6H14(l), and shakes the mixtures. The results are shown above. What do the results indicate about the intermolecular interactions of the substances? A I2 and H2OH2O have similar intermolecular interactions, and I2I2 and C6H14C6H14 do not. B I2 and C6H14C6H14 have similar intermolecular interactions, and I2 and H2OH2O do not. C I2, H2OH2O, and C6H14C6H14 all have similar intermolecular interactions. D I2, H2OH2O, and C6H14C6H14 have three completely different types of intermolecular interactions.

B

Sodium chloride is LEAST soluble in which of the following liquids? A H2O B CCl4 C HF D CH3OH E CH3COOH

B

Which of the following molecules is least soluble in water? A C(h3c)2O B CCl4 C H3COH D H3COCH3

B

Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO3(aq) into their beakers. The reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. To determine the number of moles of Cu in the sample of the mixture, the students measured the absorbance of known concentrations of Cu(NO3)2(aq) using a spectrophotometer. A cuvette filled with some of the solution produced from the sample of the mixture was also tested. The data recorded by one student are shown in the table above. On the basis of the data provided, which of the following is a possible error that the student made? A The Cu(NO3)2(aq) from the sample of the mixture was not diluted properly. B The spectrophotometer was calibrated with tap water instead of distilled water. C The student labeled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentration. D The spectrophotometer was originally set to an inappropriate wavelength, causing the absorbance to vary unpredictably.

C

Fe3+(aq) + KSCN(s) → FeSCN2+(aq) + K+(aq) To determine the moles of Fe3+(aq) in a 100. mL sample of an unknown solution, excess KSCN(s) is added to convert all the Fe3+(aq) into the dark red species FeSCN2+(aq), as represented by the equation above. The absorbance of FeSCN2+(aq) 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+(aq) were present in the 100. mL sample? (Assume that any volume change due to adding the KSCN(s) is negligible.) A 4 × 10−4 mol B 3 × 10−4 mol C 4 × 10−6 mol D 3 × 10−6 mol

C

Of the following organic compounds, which is LEAST soluble in water at 298 K? A CH3OH, methanol B CH3CH2CH2OH, l-propanol C C6H14, hexane D C6H12O6, glucose E CH3COOH, ethanoic (acetic) acid

C

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water? A CH4 B CCl4 C NH3 D PH3

C

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 280nm, the result is too high. Which of the following is most likely responsible for the error in the measured absorbance? A The student added too little solute to the acetone before measuring its absorbance. B The student rinsed the cuvette with the solution before filling the cuvette with the solution. C The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone. D The wavelength setting was accidentally changed from 280nm280nm to 300nm300nm before the student made the measurement.

C

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 ofO2 in H2O, and why? A Diagram 1, because O2O2 molecules can form hydrogen bonds with the H2OH2O molecules. B Diagram 1, because O2O2 and H2OH2O are polar molecules that can interact through dipole-dipole forces. C Diagram 2, because the polar H2OH2O molecules can induce temporary dipoles on the electron clouds of O2O2 molecules. D Diagram 2, because the nonpolar O2O2 molecules can induce temporary dipoles on the electron clouds of H2OH2O molecules.

C

A student prepared five solutions of CuSO4 with different concentrations, and then filled five cuvettes, each containing one of the solutions. The cuvettes were placed in a spectrophotometer set to the appropriate wavelength for maximum absorbance. The absorbance of each solution was measured and recorded. The student plotted absorbance versus concentration, as shown in the figure above. Which of the following is the most likely explanation for the variance of the data point for the 0.600 M CuSO4 solution? A The cuvette into which the 0.600 M solution was placed had some water droplets inside. B The cuvette into which the 0.600 M solution was placed was filled slightly more than the other cuvettes. C The wavelength setting was accidentally moved away from that of maximum absorbance. D The cuvette used for the 0.600 M solution had not been wiped clean before being put in the spectrophotometer.

D

Benzene, C6H6 , has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best describes the intermolecular forces of attraction between water and benzene? A Benzene is nonpolar, therefore there are no forces between water and benzene. B The H atoms in benzene form hydrogen bonds with the O atoms in water. C Benzene is hydrophobic, therefore there is a net repulsion between water and benzene. D There are dipole-induced dipole and London dispersion interactions between water and benzene.

D

Using a spectrophotometer, a student measures the absorbance of four solutions of CuSO4 at a given wavelength. The collected data is given in the table above. Which of the following is the most likely explanation for the discrepant data in trial 4 ? A The solution was at a lower temperature than the solutions in the other trials. B The measurement was made using a different spectrophotometer that uses a cell with a longer path length. C The solution was saturated and the flow of light through the solution was restricted. D The concentration of the solution was actually lower than 0.150M0.150M.

D

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? A Z < Y < X B Y < Z < X C Y < X < Z D X < Z < Y E X < Y < Z

E

Based on their Lewis diagrams, which of the following pairs of liquids are most soluble in each other?

h20 and c2h6o

Beer-Lambert Law

law stating that intensity of color change is directly proportional to the concentration of an analyte in a solution