Chem unit 3 3.8-3.13

A student is trying to separate a mixture of two liquids with similar degree of polarity but very different boiling points. Which of the following would be the BEST technique to separate the two different compounds? a. Filtration b. Chromatography c. Centrifugation d. Distillation

D. Distillation

Suppose there is a solution containing four different liquids that need to be separated using distillation. Based on the vapor pressure of each liquid at 25 oC that is given in the table opposite, which of the following will separate first from the solution? (3.9 #11) a. (C2H5)2O b. Br2 c. C2H5OH d. H2O

a. (C2H5)2O

A student prepared a series of solutions of copper(II) sulfate of known concentration and measured their absorbance at 600 nm using a colorimeter. A graph of the absorbance vs concentration for these solutions is shown at right. The student then measured the absorbance of an unknown solution and found it to be 0.55. Based on the graph, which of the following is the concentration of the unknown solution? (3.13 #1) a. 0.28 M b. 1.45 M c. 3.6 M d. 1.1 M

a. 0.28 M

What is the concentration of a cobalt(II) nitrate solution whose absorbance was measured at 0.55 in a 1.1 cm cuvette with a molar extinction coefficient of 1.5/ M • cm? a. 0.3 M b. 1.5 M c. 0.9 M d. 1.3 M

a. 0.3 M

Which statement correctly compares what occurs when molecules absorb photons in the microwave region with what occurs when molecules absorb photons in the infrared region? a. Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states. b. Microwave photons cause electrons in the molecules to increase their electronic energy states, whereas infrared photons cause the molecules to increase their rotational energy states. c. Microwave photons cause the molecules to increase their vibrational energy states, whereas infrared photons cause electrons in the molecules to increase their electronic energy states. d. Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause electrons in the molecules to increase their electronic energy states.

a. Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons cause the molecules to increase their vibrational energy states.

Based on their Lewis diagrams, which of the following pairs of liquids are most soluble in each other? (3.10 #12) there is a picture a. Shows C2H5OH and H2O b. Shows CCl4 and H2O c. Shows CH3OH and C5H12 d. Shows CH3OH and C6H14

a. Shows C2H5OH and H2O

Which statement concerning visible light is correct? a. The product of wavelength and frequency is a constant for visible light in a vacuum. b. As the wavelength of light increases the energy of a photon increases. c. As the wavelength of light increases its amplitude also increases. d. Green light has a higher frequency than blue light.

a. The product of wavelength and frequency is a constant for visible light in a vacuum.

9. 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 510 nm 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 0.050 M Co2+(aq) ? (3.13 #9) 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 0.100 M Co2+(aq) standard solution in the cuvette when the student put the 0.050 M standard solution in it. c. The student used a cuvette with a longer path length than the cuvette used for the ot

a. There was distilled water in the cuvette when the student put the standard solution in it.

Which of the following types of radiation has the shortest wavelength, the greatest energy, and the highest frequency? a. Ultraviolet radiation b. Infrared radiation c. Visible red light. d. Visible blue light

a. Ultraviolet radiation

Besides concentration, which of the following factors could affect a visible spectrometry or colorimetry absorbance reading of a pure solution? a. Width of cuvette used. b. Temperature of solution. c. Completing filling the cuvette with solution. d. Length of time solution is exposed to light.

a. Width of cuvette used.

For which of the following transitions does the light emitted have the longest wavelength? a. n = 4 to n = 3 b. n = 4 to n = 1 c. n = 3 to n = 2 d. n = 2 to n = 1

a. n = 4 to n = 3

In another paper chromatography experiment, a marker was used to make a dot of green ink on a piece of paper. The bottom edge of the paper was placed in water, and the water travelled vertically up the paper. As a result, the green ink spot separated into two colors: blue and yellow. Which of the following is the BEST explanation for the fact that the blue ink moved farther up the paper than the yellow ink? (3.9 #5) a. The density of the blue ink is greater than the density of the yellow ink b. Blue ink is more soluble in water than yellow ink c. Blue ink has a smaller molar mass than yellow ink d. Molecules of blue ink are smaller in size than molecules of yellow ink

b. Blue ink is more soluble in water than yellow ink

Suppose a student is trying to separate a mixture of different compounds in the liquid state using column chromatography. The column contains the stationary phase made up of long nonpolar chains, while the mobile phase that runs through the column is the polar solvent C2H3N. After the mixture is injected into the column and the solvent starts to run through the column, which of the following compounds should elute first? a. C8H18 b. C2H5OH c. C6H6 d. CCl4

b. C2H5OH

Sodium chloride is LEAST soluble in which of the following liquids? a. H2O b. CCl4 c. HF d. CH3OH

b. CCl4

How would fingerprints on a cuvette during visible spectrometry lab affect the concentration reading? a. Concentration would be lower since more light is being reflected and not detected by the spectrometry light sensor. b. Concentration would be higher since more light is being reflected or absorbed, increasing the absorbance reading. c. Concentration will stay the same since the fingerprints will only deflect the light slightly and not enough to affect the absorbance measurement. d. Concentrations will increase since more light is absorbed by the solution, resulting in a decrease in the absorbance measurement.

b. Concentration would be higher since more light is being reflected or absorbed, increasing the absorbance reading.

A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown below, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs? (3.9 #12) a. Ethyl acetate, because it has fewer C-C bonds to break b. Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces c. Butyl acetate, because it has more C-C bonds to break d. Butyl acetate, because it has a longer carbon chain and weaker dipole-dipole attractions

b. Ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces

Which pairs of substances will dissolve in each other: I. CH3OH II. C6H6 III. CH3CH3 a. I and II only b. II and III only c. I and III only d. I and II, II and III

b. II and III only

Which of the following is true regarding column chromatography? a. The components are separated into different colors. b. It can separate molecules based on affinity, polarity, or size. c. A glass or metal cylinder is used for the mobile phase. d. The slowest components of a sample will reach the end of the column first.

b. It can separate molecules based on affinity, polarity, or size.

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? a. The energies of infrared photons are in the same range as the energies associated with changes between different electronic energy states in atoms and molecules. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the energies of electronic transitions within the molecules. b. The energies of infrared photons are in the same range as the energies associated with different vibrational states of chemical bonds. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the types and strengths of different bonds in the molecules. c. The energies of infrared photons are in the same range as the energies associated with differe

b. The energies of infrared photons are in the same range as the energies associated with different vibrational states of chemical bonds. Molecules can absorb infrared photons of characteristic wavelengths, thus revealing the types and strengths of different bonds in the molecules.

During an experiment, a chemistry student collects absorbance versus concentration data for different concentrations of a salt solution at 750 nm. The experiment is run using a 1.00 cm diameter cuvette and the same spectrophotometer. Which of the following procedural errors BEST accounts for an absorbance reading that is too low? a. The salt solution in the cuvette contains air bubbles. b. The wavelength is set to 480 nm c. The cuvette us rinsed with salt solution prior to being filled with the salt solution. d. The cuvette is ¾ filled with the salt solution.

b. The wavelength is set to 480 nm

When a strontium salt is ignited, it burns with a red flame. The frequency of the light given off by this flame is greater than a. yellow light b. infrared light c. ultraviolet light d. gamma rays

b. infrared light

Green light has a wavelength that is slightly shorter than that of a. gamma rays b. orange light c. violet light d. X-rays

b. orange light

A student prepare a 0.10 M CoCl 2 solution and determines the absorbance of the solution at various wavelengths using a spectrophotometer. A graph the results is shown at right. Which of the following is the optimal wavelength for the absorbance? (3.13 #2) a. 300 nm b. 375 nm c. 410 nm d. 550 nm

c. 410 nm

While testing a sample of CuSO4 at varying wavelengths, you come up with a curve like the one at right. You still need to determine the concentration of the sample. Based on this absorption spectrum, at which of the following wavelengths should you run the standards? (3.13 #3) a. 450 nm b. 550 nm c. 650 nm d. 750 nm

c. 650 nm

A student is trying to separate a solution containing four different liquids using distillation. Which of the following liquids will separate first from the solution? a. C2H5OH b. C3H7OH c. C3H8 d. CH2Cl2

c. C3H8

"Like dissolves like" is a reliable rule of thumb that can be used to predict a solute's solubility in a solvent. Which choice embodies this expression? a. CH3CH2CH2CH2CH2CH3 should dissolve in a polar solvent. b. CH3CH2CH2CH2CH2CH3 should not dissolve in gasoline or kerosene. c. CH3CH2OH should dissolve in water. d. MgSO4(s) should not dissolve in polar solvent.

c. CH3CH2OH should dissolve in water.

Which of the following compounds the LEAST soluble in water a. CH3CH2CH2CH3 b. CH3CH2CH2OH c. CH3COCH3 d. CH3CH2CH2NH2

c. CH3COCH3

An unknown pure substance was analyzed with infrared and ultraviolet light. The sample absorbed infrared but not ultraviolet. Which of the following data can be gathered? a. Molar mass of the substance. b. Electron configuration of the atoms in the substance. c. Strength of bonds in the substance. d. Density of the substance

c. Strength of bonds in the substance.

The diagrams below 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 the measured absorbance? (3.13 #11) 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 280 nm to 300 nm before the student made the measurement.

c. The student forgot to calibrate the spectrophotometer first by using a cuvette containing only acetone.

Beta-carotene is an organic compound with an orange color. The diagram below shows the ultraviolet spectrum of beta-carotene. Which of the following statements is true about the absorption bands in the spectrum? (3.11-12 #13) a. The absorption band between 250 and 320 nm is due to transitions in electronic energy levels, and the absorption band between 380 and 520 nm is due to transitions in molecular vibrational levels. b. The absorption band between 250 and 320 nm is due to transitions in molecular vibrational levels, and the absorption band between 380 and 520 nm is due to transitions in molecular rotational levels. c. 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. d. The two main absorption bands are associated with

c. 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.

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? a. More energy is required to make N2 molecules vibrate than is required to make I2 molecules vibrate. b. More energy is required to remove an electron from an I2 molecule than is required to remove an electron from a N2 molecule. c. Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule. d. The molecular mass of I2 is greater than the molecular mass of N2.

c. Visible light does not produce transitions between electronic energy levels in the N2 molecule but does produce transitions in the I2 molecule.

Which technique determines the mass of a solid substance produced by mixing two liquids or aqueous solutions? a. decantation b. centrifugation c. gravimetric analysis d. crystallization by cooling

c. gravimetric analysis

Which one of the following substances would be the most soluble in CCl4? a. NaCl b. H2O c. NH3 d. C10H22

d. C10H22

All of the following substances will dissolve in water EXCEPT: a. CH3CH2OH b. AlCl3 c. Ca(NO3)2 d. C6H6

d. C6H6

A mixture of four dyes is separated using paper chromatography as seen in the diagram below. If the paper is made up polar cellulose paper, and the solvent is nonpolar, which of the following BEST represents the position where most of the polar dye would be found at the end of the separation. (3.9 #7) a. A b. B c. C d. D

d. D

When polar molecules dissolve in water, the solute solvent interaction is a. hydrogen bonding b. London dispersion forces c. Dipole -dipole forces d. Either A or C e. None of the above

d. Either A or C

Albert Einstein's explanation of the photoelectric effect confirmed which of the following concepts? a. Electrons can absorb energy and change levels in atoms. b. Light energy can be converted into the mass of electrons. c. Electrons have both particle and wave properties. d. Light has both particle and wave properties

d. Light has both particle and wave properties

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 opposite. Which of the following is the most likely explanation for the discrepant data in trial 4? (3.13 #12) 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 0.150 M.

d. The concentration of the solution was actually lower than 0.150 M.

A student created the following Beer's plot by sampling different concentrations of copper(II) sulfate solutions and measuring their absorbance at 600 nm on a spectrophotometer. (3.13 #6) Based on the graph to the right, which of the following does the slope represent? a. The change in absorbance over time (ΔA/time) b. The change in concentration over time (Δc/time) c. The product of the proportionality constant ( e) and the path length ( b). d. The product of the absorbance (A) and the concentration (c).

d. The product of the absorbance (A) and the concentration (c).

Benzene, C6H6, has the structure shown opposite. 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. There are dipole-induced dipole and London dispersion interactions between water and benzene.

During an experiment, a chemistry student collects absorbance versus concentration data for different concentrations of a salt solution at 490 nm. The experiment is run using a 1.00 cm diameter cuvette and the same spectrophotometer. Which of the following procedural errors BEST accounts for an absorbance reading that is too high? a. The wavelength is set to 500 nm. b. The wavelength is set to 480 nm. c. When the salt solution was prepared, not all of the ions dissolved. d. When the salt solution was prepared, an extra 0.400 g of salt was added.

d. When the salt solution was prepared, an extra 0.400 g of salt was added.

In a paper chromatography experiment, a sample of a pigment is separated into two components, X and Y, as shown in the figure below. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results? (3.9 #4) a. X has a larger molar mass than Y does. b. Y has a larger molar mass than X does. c. X is more polar than Y. d. Y is more polar than X.

d. Y is more polar than X

Which of the following is not true regarding solubility? a. the solubility of a gas increases with a decrease in temperature. b. a supersaturated solution will have visible precipitate present. c. CH4 will dissolve easier in BF3 than H2O. d. a decrease in temperature would decrease the solubility of most solids.

d. a decrease in temperature would decrease the solubility of most solids.

In an investigation of the electronic absorption spectrum of a particular element, it is found that a photon having λ = 500 nm provides just enough energy to promote an electron from the second quantum level to the third. From this information, we can deduce the a. energy of the n = 2 level b. energy of the n = 3 level c. sum of the energies of n = 2 and n = 3 d. difference in energies between n = 2 and n=3

d. difference in energies between n = 2 and n=3

The diagram above represents the absorption spectrum for a pure molecular substance. (3.11-12 #11) Which of the following correctly indicates the type of transition observed for the substance in each of the regions of the absorption spectrum Region X Region Y Region Z a. molecular vibration molecular rotation electronic transition b. electronic transition molecular rotation molecular vibration c. molecular rotation molecular vibration electronic transitions d. electronic transition molecular vibration molecular rotation

d. electronic transition molecular vibration molecular rotation

Which of the following statements is (are) true? i. An excited atom can return to its ground state by absorbing electromagnetic radiation. ii. The energy of an atom is increased when electromagnetic radiation is emitted from it. iii. The energy of electromagnetic radiation increases as frequency increases. iv. An electron in the n = 4 state in the H atom can go to the n = 2 state by emitting electromagnetic radiation at the appropriate frequency. v. The frequency and wavelength of electromagnetic radiation are inversely related to each other. a. ii, iii, iv b. iii, v c. i, ii, iii d. iii, iv, v e. i, ii, iv

d. iii, iv, v

When NaCl dissolves in water, aqueous Na+ and Cl- ions result. The force of attraction that exists between Na+ and H2O is called a(n) ______ interaction. a. dipole-dipole b. ion-ion c. hydrogen-bonding d. ion-dipole

d. ion-dipole

The principal reason for the extremely low solubility of NaCl in benzene (C6H6) is the ___. a. strong solvent-solvent interactions b. hydrogen bonding in C6H6 c. strength of the covalent bond in NaCl d. weak solvation of Na+ and Cl- by C6H6

d. weak solvation of Na+ and Cl- by C6H6