CHEM 102L QUIZ QUESTIONS
Location for these wastes: 1. a paper towel that was used to wipe up a spilled solution 2. a small amount of sodium bicarbonate solution was not used in the experiment 3. a kim wipe that was used to polish the sides of a cuvet 4. Green or silver lab gloves
1. into the chemical solid waste container 2. into the liquid waste container 3. into the regular trash 4. in a small bin just above the TA bench
Match the following species used in the standardization of NaOH with their correct function: 1. Secondary Standard 2. Primary Standard
1. sodium hydroxide (NaOH) 2. potassium hydrogen phthalate (KHP)
Order the following steps you would take if you find broken glassware in your lab drawer, or if a piece of glassware breaks during the lab. 1. Clean up large pieces and dispose of in the designated glass only waste container 2. use the dustpan and brush found in the lab room to sweep up small shards and chips in the area where the glassware was broken and dipose of these in the designated glass waste 3. notify your TA so that he or she can help you 4. use a pair of leather gloves found in the lab room to prevent nicks or cuts
3, 4, 1, 2
The correct process for disposing of liquid waste containing hazardous material would be: 1. Read the label on the waste bottle to be sure it is meant for the correct experiment and correct waste material 2. Close the funnel lid until the latch snaps into place 3. check the liquid level in the waste bottle- if the level is within 2" of the neck of the bottle, notify your TA so that the bottle won't be overfilled 4. Bring the waste to the liquid waste bottle in the fume hood 5. Open the latch, lift the funnel cover out of the way, and pour the waste material into the funnel
4, 3, 1, 5, 2
Order the following steps in the correct procedure for lighting and working with a Bunsen burner: 1. shut off the burner and gas valve as soon as experimental work is completed- or anytime you have to leave it unatteneded 2. inspect the burner to be sure that the air intake and fuel valves move properly and can be adjusted 3. monitor the flame and all nearby materials closely until the experiment is complete. Never leave an open flame unattended. 4. make sure all loose clothing and hair have been properly restrained and will not contact the flame accidentally 5. inspect the tubing to the gas valve to be sure it does not have any cracks or holes that would allow gas to leak 6. with the sparker in hand, turn on the gas and light the flame as soon as possible to minimized unburned gas in the air 7. prepare the work space to be sure no flammable materials are in the vicinity of the open flame 8. adjust the fuel valve to set the height of the flame and adjust the air intake to adjust the temperature (color) of the flame, according to the instructions in the lab manual
4, 7, 5, 2, 6, 8, 3, 1
A titration curve of an unknown diprotic acid has a first end point corresponding to 15.23 mL of 0.1094 M NaOH. The molar mass calculated from this end point is 154.32 g/mol. The curve shows two additional endpoints, giving pKa values of 3.80, 8.04, and 11.33. When compared with a chart of unknowns, the experimenter finds a triprotic acid with a mass of 155.16 g/mol but the pKas are very different. There is a second triprotic acid with pKa values of 3.96, 7.54, and 11.14. Which statement expresses the most likely identity of the unknown? A. The unknown that matches closest in molar mass is most likely the correct one, because the rapid change in pH identifies the end point, and the volume of standardized base is the most accurate measurement in the experiment. B. The unknown that matches closest in pKa is most likely the correct one, because it is possible that the pH meters were poorly calibrated, but they are still probably the most accurate and precise measurement in the experiment. C. There is no way to tell which unknown is a better fit because a poor calibration of the pH meter would throw off both the molar mass and the pKa values determined in the experiment. D. There is no way to tell which unknown is a better fit because the standardized base and the pH sensor calibration are equally accurate and precise.
A
Consider the uncertainties in your kinetics experiment. Which of the following statements is true? A. If the colorimeter has an error that causes the absorbance reading to be consistently 0.05 higher than when the calibration curve was prepared, the error will cause the value of the rate coefficient to be calculated incorrectly, but the determination of reaction order should be okay. B. If the colorimeter has an error that causes the absorbance reading to be consistently 0.05 higher than when the calibration curve was prepared, the error will cause the order of reaction to be calculated incorrectly, but the rate coefficient should be okay. C. If the colorimeter has an error that causes the absorbance reading to be consistently 0.05 units higher than when the calibration curve was prepared, the error will not cause any inaccuracy in either the order of reaction or the value of the rate coefficient. D. If the colorimeter has an error that causes the absorbance reading to be consistently 0.05 units higher than when the calibration curve was prepared, the error will cause both the order and value of the rate coefficient to be calculated incorrectly. E. None of these statements is correct.
A
During a titration between KHP (204.221 g/mol) and sodium hydroxide (40.01 g/mol), the end point was determined to be at a volume of 13.17 mL of NaOH titrant for a 0.1111-g sample of solid KHP dissolved in 50.00 mL of water. What is the concentration of the NaOH titrant? HINT: The equation for the titration reaction is: KHP (aq) + NaOH (aq) Na+(aq) + K+(aq) + P2-(aq) + H2O(l) A. 0.04131 M B. The concentration cannot be determined from the information provided. C. 0.007165 M D. 0.2108 M E. 0.3375 M
A
If you need to work with a flammable or volatile solvent, which piece of lab equipment should you be sure NOT to use? a. Bunsen or Meker burner, or anything with an open flame. b. Fume Hood with good ventilation. c. Volumetric flask. d. Hot plate. e. Heating mantle.
A
In an experiment, a container with a volume of 269 mL was filled with air and sealed. Pressure was allowed to vary with temperature in the container. Based on the best fit line, the number of moles of air in the container would be: A. 0.019 moles B. 0.13 moles C. 0.0017 moles D. 19 moles
A
To determine the order of a reaction with respect to one reactant, A, experimentally, a useful experiment would be: A. Two of these would work. B. None of these would work. C. Run a reaction for three trials in which [B] has a concentration of 0.800 M and [A] has a concentration of 0.05 M, 0.04M, and 0.025 M, respectively. D. Run a reaction until both [A] and [B] are much less than their initial values. E. All of these would work. F. Hold [B] at 0.25 M and vary [A] between 0.30, 0.25, and 0.20 M. G. Run a reaction with a concentration of [A] = 0.800 M and a concentration of [B] = 0.001 M. Continue the run until [A] is <0.001 M and [B] ~ 0.001 M.
A
Which of the following must be completed before taking the quiz? Select one or more: a. Tie back long hair. b. Put on your goggles. c. Put on your lab coat. d. Store your backpack, cell phone, jacket, and all other nonessential items in designated storage areas. e. Put on gloves
A, B, C, D
Which of the following precautions is important when using a Bunsen burner or Meker burner? (Check all that apply.) a. Always tie back hair, even long bangs, that might accidentally come in contact with the flame. b. Set up your work space so that wires and cables cannot accidentally make contact with the flame or hot glassware and melt. c. Only the TA should ever operate an open flame. d. Set up your work space with the burner in a secure location away from the edge of the bench so that you won't accidentally bump it and spill hot liquids. e. Remember that any glassware heated by the burner will look the same when hot as cold, and will not cool down until well after the burner has been shut off. f. Set up the work space so that flammable materials - notebooks, paper towels, other reagents, etc. - are far away from the burner to prevent them coming in contact with the hot surface. g. Never leave an open flame unattended, even for a brief time.
A, B, D, E, F, G
For which of the following situations should you be sure to notify your TA and fill out an incident report form? a. During check-in you discover a broken funnel in your drawer, and the broken end of the stem causes a small nick through your glove. Correct b. You begin to feel faint and dizzy in lab because you had to skip lunch. Correct c. You arrive in lab, but realize that your cold medicine is making you feel groggy. Correct d. You accidentally pick up a beaker from the hot plate, not realizing that it was already hot, and the edge of the beaker leaves a small red mark on your thumb. Correct e. During lab check-out at the end of the semester, your lab partner accidentally drops a beaker, and a small chip of glass causes a scratch on your ankle because you weren't wearing socks.
ALL of them
When should you be sure to wear full PPE (proper attire, lab coat, goggles) in the laboratory? a. During the lab quiz. b. While cleaning up after experimental work is done. c. As soon as you enter the lab, and until you are ready to walk out the door. d. While waiting in the lab room for a friend to finish. e. Once the experimental work has begun.
ALL of them
Which of the following is a behavior that can pose a safety risk in the laboratory environment? a. Looking away from your work to answer a question from your TA or lab partner b. Leaving your lab drawer open while you set up your apparatus and obtain your reagents c. Sitting on lab benches, lab floors, or hallway floors, while waiting for lab to begin or for another student to finish d. Staying focused on your own experiment and not being distracted by what nearby groups are doing e. Moving rapidly around the lab to be sure to finish the experiment in time
ALL of them
A solution of 0.613 g erucic acid in 8.115 g stearic acid is measured to have a freezing point of 68.60 ºC. What is the molar mass of erucic acid? HINT: MW stearic acid is 284.48 g/mol. Tf (stearic acid) = 69.60 ºC. Kf (stearic acid) = 4.50 ºC/m. Density (stearic acid) = 847 kg/m^3 A. 315 g/mol B. 339 g/mol C. None of these answers is correct. D. 0.340 g/mol E. 96.8 g/mol
B
An unknown diprotic acid reached its second equivalence point at a volume of 21.39 mL of 0.1013 M NaOH, with a general chemical equation in the form: H2A + 2 NaOH → 2 H2O + Na2A. If the mass of the unknown acid sample was 0.180 g, the molecular weight of the unknown acid would be: A. 41.5 g/mol B. 166 g/mol C. 12.0 g/mol D. 83.1 g/mol
B
Beer's law is useful for the [Fe(SCN)]2+ equilibrium experiment because: A. The absorbance of the iron thiocyanate in the red region of the spectrum is proportional to its concentration. B. The absorbance of the iron thiocyanate in the blue region of the spectrum is proportional to its concentration. C. The colored iron thiocyanate will change the reflectivity of the solution. D. The red color of the iron thiocyanate can be used to determine the energy of the electron transitions in the product.
B
Before the unknown concentration of the iron thiocyanate can be determined for the equilibrium experiment, a calibration curve was constructed using solutions with known concentration. If done correctly, a line fit of calibration curve data should provide: A. A straight line with a negative slope, in which the slope represents the rate at which the purple product is decreasing in solution and the intercept represents the initial concentration. B. A straight line with a positive slope, in which the slope represents the product of the molar absorptivity and the path length of the cuvette and the intercept represents absorbance or interferences that are not due to the red product species C. A straight line whose slope represents the change in energy of the electron as it emits red light. D. A polynomial curve in which the terms represent the molar absorptivity, the path length of the cuvette, and the wavelength of the absorbance.
B
During a titration of KHP with 0.1 M NaOH, what is the pH of the solution before any NaOH is added? Molecular equation: KHP(aq) + NaOH (aq) →NaKP (aq) + H2O (aq) Select one: A. pH = 7 B. pH < 7 C. pH >7 D. The answer cannot be determined without knowing the Ka value for KHP.
B
During lab, a beaker containing a solid reagent cracks. To be safe you should ____________ a. immediately place the beaker and contents into the solid waste container in the hood, then begin the experiment again. b. immediately dispose of the solid reagent into a solid waste container in the hood, then dispose of the beaker in the glass waste container, and begin the experiment again. c. notify your TA and, as long as the beaker doesn't need to be heated, continue the experiment normally. d. immediately place the beaker and contents into the glass waste container, then begin the experiment again
B
If lnP is known to 4 significant figures, and 1/T is known to 3 significant figures, what are the correct significant figures for the intercept of the regression line? A. 4 B. 3 C. Cannot be determined from the information given. D. 2
B
In a Clausius-Clapeyron plot of lnP vs. 1/T, the regression line for one sample has an equation of y = -3750x + 23.89. If the value of R = 8.3145 J mol-1 K-1, the value of ΔHvap for the molecule would be: A. 451 J/mol B. 31.2 kJ/mol C. -31.2 kJ/mol Incorrect D. 23.89 kJ/mol E. -451 J/mol F. -23.89 kJ.mol
B
In some circumstances, using the fire extinguisher found in the laboratory may be necessary. Which of the following scenarios represents an appropriate use of a fire extinguisher? a. Fumes from a solution contained in a beaker have caught fire, and the fire seems to be contained to the beaker. b. A handful of paper towels in the garbage can has caught fire. The fire is small and relatively contained within the trash can. c. Several bottles of reagents in the fume hood have caught fire and are in danger of creating an explosion. d. A handful of paper towels was left too close to a Bunsen burner and caught fire on the lab bench. The flames are contained for the moment, but might spread to other lab notebooks and flammable materials on the bench.
B
What is your BEST resource for understanding the nature of the chemical hazards of materials you work with in lab? a. Your TA, or other TAs you visit during office hours. b. Safety Data Sheets (SDS) that should be consulted before coming to lab each week. c. The label on the reagent bottles found in the fume hood. d. Your friend who took the lab last semester and saved his notes.
B
When should you be sure NEVER to use a sealed container and/or secondary containment in the laboratory? a. When disposing of liquid waste. b. When heating a solution over a hot plate, burner, or heating mantle. c. When transporting materials from one lab room to another. d. When transporting materials from the hood to the bench.
B
When the procedure calls for making a more dilute solution of an acid, or mixing an acid with other solutions, what is the correct order of steps? a. Always Add Acid - the acid should be added first and then the other materials to prevent a dangerous reaction. b. Always Add Acid - Either add all of the water or non-acid component first, or add a significant portion, before adding the acid to the mixture. This helps to minimize the heat generated, which could otherwise create dangerous fumes or reactions. c. Neither of these methods is safe.
B
Which of the following is the reason backpacks must be stored during lab? a. Backpacks on the floor of the lab or on the benches may be exposed to hazardous materials, which might then lead to student exposure outside the lab. b. Both of these are good reasons to keep nonessential items stored properly c. Backpacks on the floor present a tripping hazard to students in lab, which may lead to spills and other incidents.
B
While weighing out a reagent for use in an experiment, a student finds he has leftover reagent. The student should: a. Leave the dispensed material out on the bench so that another group can use it, which will minimize the waste generated. b. Place the excess reagent in the appropriate solid or liquid waste container to prevent contamination of the stock reagent. c. Return the excess reagent to the stock bottle to minimize the amount of waste generated. d. Notify the TA immediately.
B
Your lab partner accidentally trips and douses the front of your lab coat and shirt with a hazardous material. The TA immediately takes you to the safety shower, since the spill has soaked into your clothing. What do you need to do at this point? (Check all that apply.) a. Stay under the shower until the shirt has been completely rinsed. b. Stay under the shower for at least 15 minutes. c. Remove your shirt and any other clothing that were in contact with the chemical.
B, C
A cooling curve to determine freezing point is shown in the figure. The behavior in the graph can be explained in the following way: A. None of these explanations is correct. B. The process of freezing is an endothermic process; therefore, the substance cools until the freezing process is complete. Once all of the material is in the solid phase, the temperature stops decreasing. C. When the heat source is removed, the molten substance cools. However, when the substance begins to freeze, the change to solid phase releases energy that allows it to maintain a stable temperature until the freezing is complete. D. When the heat source is removed, the molten substance cools. However, when the substance begins to freeze, the change to solid phase absorbs energy that allows it to maintain a stable temperature until the freezing is complete.
C
How many times should you read the label on a reagent container and compare it with the lab manual? a. At least twice. b. At least once. c. At least twice each time you remove material from the container.
C
In Experiment 15, two sets of cuvets were prepared in which the same equilibrium reaction occurred. One set was used to define the Beer's Law relationship between Absorbance and the Concentration of the product ion. In the other set, the concentration of the product ion at equlibrium was treated as an unknown, and was used to solve for the value of Keq. What is the principal difference between these two sets of solutions that allow them to be used in different ways? Select one: a. In one set of cuvets there was a limiting reagent that allowed the concentration of the product ion to be known. b. Because the value of Keq is so small, the value of the change in concentration could be neglected when calculating the equilibrium concentrations of the reactants. c. In one set of cuvets, LeChatelier's principle was used to drive the equilibrium so nearly to completion that the equilibrium concentration could be assumed. d. Only one reagent was used in the cuvets used for the Beer's Law curve, while both reagents were used to determined Keq. e. None of these is true.
C
In an experiment to determine the Keq associated with a particular reaction, two different solutions are measured 3 times each on a colorimeter with the following results: Cuvet E1, %T Cuvet E2, %T 48.0 23.4 46.1 22.5 46.0 22.4 sigma 1.12 0.544 mean 46.7 22.8 Which of the following statements correctly assesses the data? a. Cuvet E1 gave better data because the %T was higher. b. Cuvet E2 was more precise because the value of sigma was smaller. c. The two cuvets gave data of the same precision, because the value of the CV is the same for each. d. No assessment of accuracy or precision can be made until the value of Keq is determined from the data. e. Cuvet E2 was more accurate because the value of sigma was smaller.
C
In some circumstances, materials that are being heated in the lab could catch fire. If a flammable substance in a beaker should catch fire while you are working but the flames are relatively contained, what is a simple method for extinguishing the flame? a. Use water from the sink nearest the bench to douse the flames. b. Use the chemical fire extinguisher located in the lab. Pull the pin, aim the nozzle into the beaker, and pull the lever. c. Turn off the heat source immediately, and use a watch glass to cover the beaker and minimize the oxygen around the flame.
C
In the event the fire alarm for Morehead Laboratory sounds, you must evacuate the building. Assuming the emergency does not interfere with your best route, you should__________ . a. exit the lab and proceed to the stairs nearest the Venable parking lot and Columbia Street. After exiting on the ground floor you should meet your TA in the driveway to the Venable parking lot just off of South Road so that you can be included in a head count of those safely evacuated. b. exit the lab and proceed to the stairs nearest the elevator. After exiting on the ground floor you should meet your TA in front of the sign for Kenan Laboratories just off of South Road so that you can be included in a head count of those safely evacuated. c. exit the lab and proceed to the stairs nearest the Venable parking lot and Columbia Street. After exiting on the ground floor you should meet your TA on the far side of the driveway to the parking lot so that you can be included in a head count of those safely evacuated, keeping the drive clear for emergency vehicles. d. exit the lab and proceed to the stairs nearest the elevator. After exiting on the ground floor you should meet your TA on the loading dock between Kenan Laboratories and Morehead Laboratory so that you can be included in a head count of those safely evacuated.
C
The equation of the best fit line for a Beer's law plot for [FeSCN]2+ is determined to be A=(4328)C + 0.115, where A is the absorbance of the solution and C is its concentration. If the transmittance of a solution is measured at 54.4%, what is the concentration of the unknown solution? A. The answer cannot be calculated from the information given. B. 7.06 x 102 M [FeSCN]2+ C. 3.45 x 10-5 M [FeSCN]2+ D. 8.76 x 10-5 M [FeSCN]2+ E. 1.11 x 10-5 M [FeSCN]2+
C
The equilibrium concentrations of Fe3+, SCN-, and [FeSCN]2+ are determined experimentally to be 1.43 x 10-3 M, 2.86 x 10-4 M, and 5.96 x 10-5 M, respectively, for the reaction Fe3+ + SCN- —► [FeSCN]2+. What is the experimental value of the equlibrium constant? A. The equilibrium constant cannot be determined experimentally. B. 6.86 x 10-3 C. 146 D. Initial concentrations of Fe3+ and SCN- must be known to calculate the equilibrium constant.
C
The results of an experiment with a solution of an unknown fatty acid in stearic acid are shown in the table. Unfortunately, the value of the molar mass of the unknown is significantly different in each calculation. What is a reasonable explanation for this result? A. The experiment should have been carried out for the same mass of unknown in each trial. The differences in the mass of unknown leads to the different molar masses calculated. B. The experiment wasn't carried out correctly. The dramatic increase in the temperature change indicates that the steps needed to prevent supercooling were not followed. C. The calculation of molar mass was done using the mass of each portion of the unknown acid added, but it should have been calculated for the total mass of unknown acid. When this calculation error is corrected, the calculated molar mass should be consistent for each trial. D. There is not enough information provided to determine the nature of the problem.
C
Why should you inspect glassware for chips, cracks, or chemical residues before using it? a. If the glassware breaks during use, experimental results may be lost and it may take extra time to repeat the work and complete the experiment. This can lead to rushing, which can also lead to accidents and injuries. b. Weak spots in a glass beaker or flask can cause it to burst suddenly while heating, cooling, or clamping in place, creating a significant safety hazard. c. All of these are potentially hazardous outcomes of using compromised glassware. d. Chemical residues from previous experiments can cause unwanted and potentially dangerous side reactions.
C
Your lab partner accidentally gets a mist of your solution in her eye. You immediately help her to the eye wash to rinse it. After about a minute, she feels better and is ready to get back to work. You should: a. Let the TA inspect her eye to see if it is okay. b. Keep her in the eye wash for at least 5 minutes and then let the TA decide if she can continue working. c. Keep her in the eye wash for at least 15 minutes, and then make sure she goes to student health, just to be sure. d. Check to see if her eye is still red. If not, hurry so that you can finish the experiment
C
When reading the label on a reagent container, what are the three most important pieces of information? a. Color b. Chemical formula c. Name d. Concentration e. Hazard warning(s) f. CAS Number
C, D, E
For which of the following should gloves be used in the laboratory? a. When using a calculator during an experiment when reagents are in use. b. When leaving the lab to get a drink or use the rest room, since you will be coming right back to the lab. c. Handling glassware, even without any reagents present. d. When cleaning up the bench, after the experiment is over. e. When typing notes into the spreadsheet while the experiment is still in progress. f. When wiping flog from the inside of your goggles. g. When using reagents, even nonhazardous materials.
C, D, G
After performing this experiment, a pair of students discover that their thermometer was miscalibrated and was reading consistently 2.62°C lower than the actual temperature. How will this impact their results? A. They should redo the entire experiment with a correctly calibrated thermometer, because the relative strength of intermolecular forces in the various liquids will be impossible to determine for certain. B. The relative strengths of the intermolecular forces will be the opposite of their true order if the measurements had been made correctly. C. If the temperature reading is lower than the actual temperature, the vapor pressure will appear to be lower than the true vapor pressure at that temperature. This will cause all of the intermolecular forces to appear stronger than they actually are, but the relative strengths of intermolecular forces will be correct. D. If the temperature reading is lower than the actual temperature, the vapor pressure will appear to be higher than the true vapor pressure at that temperature. This will cause all of the intermolecular forces to appear to be weaker than they actually are, but the relative strengths of intermolecular forces will be correct.
D
In the attached titration curve, two unknown acids are titrated by the same standardized base. Based on the information in the plot, which of the following statements is true? I. Both unknowns have an end point at a volume of ~14.5 mL, which means it is likely that Unknown 1 and 2 are the same acid, but Unknown 1 wasn't titrated far enough to see the second end point. II. Both unknowns have an end point at a volume of ~14.5 mL, which means they must have very similar pKas. III. Both unknowns have an end point at a volume of ~14.5 mL, which means they must have similar molar mass. IV. Unknown 1 appears to be a monoprotic acid, while Unknown 2 is a diprotic acid. V. Unknown 1 has a larger peak at the end point, so it must have twice as much acid in solution. VI. Unknown 2 shows the peak for the end point at ~28 mL, and a peak for the pKa at ~14.5 mL. Unknown 1 was titrated improperly. Either the pKa should have appeared at ~7.25 mL and was missed due to the large volume of base added, or there is a second peak that should appear ~28 mL as with Unknown 2. A. Both unknowns have an end point at a volume of ~14.5 mL, which means it is likely that Unknown 1 and 2 are the same acid, but Unknown 1 I. B. II. C. III. D. IV. E. V. F. VI. G. I and VI are correct. H. II and IV are both correct
D
What is the most important consideration to preserve safety when it is necessary to feed glass tubing, thermometers, or other apparatus through a rubber stopper? a. Using sufficient vacuum grease that the apparatus slides smoothly. b. Letting your TA handle the procedure for you. c. Using sufficient force that the apparatus will slide through the stopper. d. Using the correct hand position so that if something goes wrong you can avoid coming into contact with broken or sharp ends
D
You arrive to Morehead Laboratories two minutes after your lab has officially started and you do not want to miss the quiz. As you enter the building you notice that the fire alarm is sounding. The best way to be sure you will be able to take the lab quiz is to _________________________ a. wait just inside the door to the building to see if anyone else enters or leaves the building, so that you can catch your TA and take the quiz. b. cross the bridge into Kenan Laboratories and find a place to open your laptop and take the quiz. c. wait at the door of your laboratory room so that you are present when the TA returns. d. meet at the correct designated rally point for your lab section and look for your TA and classmates there, where you will receive additional instructions.
D
A solution was prepared using 3000 microliters of distilled water, 325 microliters of 2.00 x 10-3 M NaSCN, and 175 microliters of 0.201 M Fe(NO3)3•9 H2O. What is the initial concentration of Fe3+ in solution before the reaction begins? (NOTE: NaSCN molar mass is 81.07 g/mol. Fe(NO3)3•9 H2O is 403.9 g/mol. Molarity is measured in moles of solute per liter of solution.) A. The concentration cannot be determined if the equilibrium constant is not known. B. 0.0117 M C. 2.17 x 10-4 M D. 1.86 x 10-4 M E. 0.0101 M
E
A student uses experimental data to create a Beer's Law plot for a set of standard solutions; the resulting graph is shown below. Based on a careful study of the results shown, what assessment of the success of the experiment can be made? A. The solution concentrations fell outside the range that can be successfully measured by the colorimeter. B. The distribution of standards around the line indicate that the solutions were not prepared properly with the micropipettes. C. The R2 value indicates that the experimenter mixed up the stock solution and the solution used to dilute it. D. Apparent curvature in the response of standard solutions indicates that Fe3+ was not in sufficient excess in the standards. E. The experimenter has not plotted the correct information for Beer's law. No assessment of the quality of results can be made until the correct information is given on the plot. F. The slope of the line is negative, not positive; therefore the solution concentrations must have been calculated incorrectly.
E
An experiment is run that demonstrates that the rate law of a reaction has the form R =k [A]2[B]1, where k=0.25. If the reaction was run with initial concentrations of [A] = 0.25 M and [B] = 0.005 M, which graph would you expect to best fit a straight line that would confirm reaction order? A. [A] vs time B. 1/R vs time C. R vs time D. 1/[B] vs time E. ln [B] vs time F. [B] vs time
E
In a gas law experiment, an experimenter uses the volume of a syringe, 5.00 mL and the density of dry air, 0.001185 g/mL, to calculate the mass of air in the syringe. A value of 28.96 g/mol is then used as the molar mass of air to calculated the number of moles of air in the syringe. This value, in turn, is used to calculate the value of the ideal gas constant, R. One valid criticism of this approach would be: I. The calculation was done incorrectly. The value of the density is not needed to correctly calculate R. II. The calculation was done correctly, however the value 28.96 g/mol is not a true molar mass because air is a mixture of gases. III. The experiment would be more accurate if pure nitrogen was used, because its molar mass and density are more accurately known. IV. The experiment would be more accurate if the humidity of the air was included in the calculation, because this would tend to reduce the effective molar mass when it was included in the weighted average. A. I. B. II. C. III. D. IV. E. All but I. are valid assessments. F. All but III. are valid assessments.
E
In the Clausius-Clapeyron plot shown, methanol, CH3OH, is represented by the red points. If the other two molecules shown are n-nonane and 3,3-diethylpentane, both with the formula C9H20, the molecules represented by Sample A and Sample B can best be identified by which statement: A. Sample A cannot be either n-nonane or 3,3-diethylpentane, because neither has H-bonding and therefore must have weaker intermolecular forces than methanol. B. Sample A could be either n-nonane or 3,3-diethylpentane, because both have a much larger molecular weight than methanol and therefore must have stronger intermolecular forces. C. Sample B cannot be either n-nonane or 3,3-diethylpentane, because both have a much larger molecular weight than methanol and therefore must have stronger intermolecular forces. D. Sample B is most likely n-nonane, because it is a straight chain and has the weakest dispersion forces. Sample A is most likely 3,3-diethyl pentane, which has stronger dispersion forces due to its branched structure and high molecular weight, giving it slightly stronger IMF than methanol. E. Sample B is most likely 3,3-diethyl pentane, because it is branched and has the weakest dispersion forces. Sample A is most likely n-nonane, which has stronger dispersion forces due to its straight chain and high molecular weight, giving it slightly stronger IMF than methanol.
E
In the plot of pressure vs. temperature shown, the data appear somewhat scattered around the regression line. Which of the following statements offers a well-reasoned assessment of the data? I. The regression line likely offers the best value for the relationship between pressure and temperature, because individual points are more likely to have a higher error or uncertainty. II. Some of the data shown in the plot should be eliminated if they don't fall on the regression line to improve the accuracy and precision of the results. III. If the container was imperfectly sealed, "burping" of the stopper could cause some results to be inconsistent because the number of moles of air were allowed to change during the experiment. IV. If the stopper was inserted too far into the flask, some results could have been affected by the changing volume. A. I. B. II. C. III. D. IV. E. Both I and III are sound assessments. F. Both I and IV are sound assessments. G. All of these statements are sound assessments. H. None of these statements is a sound assessment of the data.
E
Which of the following explains why the lab safety policy specifically addresses loose clothing, contact lenses, and large, loose, or dangling jewelry? a. In the event of a spill or spray of reagent, all of these items are likely to hold the chemical close to the skin, making it harder to remove and therefore increasing the risk of injury. b. Loose clothing and jewelry is more likely to impede movement, or accidentally knock materials over, causing a spill or other accident. c. Loose clothing or jewelry is more likely to present a fire hazard if open flames are used in the lab for any reason, or if a fire begins accidentally. d. Contact with chemicals in the lab might damage these items. e. All of these answers are true.
E
In an experiment studying colligative properties, a solid reagent was heated until it was fully molten, then allowed to cool to determine the freezing point. For this experiment to work, which of the following precautions must be taken to prevent supercooling? A. I. Temperature must be monitored to the nearest hundredth decimal place. B. II. The thermometer must be kept as still as possible near the middle of the material to avoid temperature fluctuations. C. III. The test tube holding the reagent must be insulated to minimize temperature gradients within the material. D. IV. The material must be stirred to encourage crystallization, so that freezing occurs uniformly throughout the material. E. I and II are correct. F. III and IV are correct.
F
In the titration curve shown, the value of the pKa(s) are best indicated by: A. Region 4 B. Region 2 and Region 4. C. None of these. D. Region 3 E. Region 1 and Region 3. F. Region 2 G. Region 1
F
Is this shoe appropriate for lab: a pair of flats
False, the shoe covers the toes and heel completely, but lacks coverage for the top of the foot
This shoe is appropriate for lab: mesh topped slide ons
False; coverage but not protective
This shoe is appropriate for lab: a black slide on shoe- full toe and top of foot coverage
False; no coverage on the heel
This shirt is appropriate for lab: white, tank top (covers complete shoulder), mesh shoulders and a mesh V in the front
False; shoulders must be covered, no protection of the mesh spots
Two trials in a kinetics experiment give relative initial rate values of 0.997, and 0.487. The general rate law for the reaction is R=k[A]x[B]y, where [A] = 0.250 M for both trials and [B] = 0.0100 in the first trial and 0.0050 M in the second trial. Assuming the value of x = 1, round the value of y determined in the experiment above to calculate the value of the rate coefficient, k, in the first trial. A. 1.60 x 103 M-2 s-1 B. The answer cannot be determined from the information given. C. 466 M-1s-1 D. k =2.51 x 10-3 M-1s-1 E. k =3.99 x 104 M-2s-1 F. k = 2.51 x 10-5 M-2s-1 G. k = 399 M-1s-1 H. 390 M-1s-1
G
For which of the following graphs will a linear fit provide the value of R, the ideal gas constant, in standard units? A. All of these. B. Graph II C. None of these. D. Graphs III and IV. E. Graph III F. Graph I G. Graphs I and II. H. Graph IV
H
The end point in the titration of potassium hydrogen phthalate (KHP) with sodium hydroxide (NaOH) is determined to be the point when the color of a phenolphthalein indicator added to the solution turns very pale pink, but fades to colorless a few minutes later. True False
True
This clothing is appropriate for lab: A t-shirt
True; good coverage, durable material
Is this clothing appropriate for lab: long maxi skirt with black shoes
True; the coverage is good, including the ankle
The air intake determines...
how much oxygen is supplied and therefore the temperature of the flame
The fuel valve of a bunsen or meker burner determines...
how quickly fuel is delivered, which affects the height of the flame