Chem 101 Lab

According to the stoichiometry of the exothermic reaction equation 2 HCl (aq) + Mg (s) → H2 (g) +MgCl2 (aq), the maximum energy that can be released by this reaction would occur at a HCl:Mg ratio of...

2:1

In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by 12.11 mL of a H2SO4 solution. Given the end point volume of titrant, what is the concentration of the H2SO4 solution? (Hint: No calculator necessary.)

4.15 x 10-3 M

In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are combined and produce an extrapolated ΔT = -22.4˚C. If the density of each solution is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn would be:

A. 9.36 kJ

To carry out a calorimetry experiment quantitatively, which of the following would be necessary (select all correct answers): Select one or more: A. All solutions must be equilibrated to room temperature before beginning the experiment. B. The calorimeter must be calibrated to account for heat loss from the system. C. Calculations must be made in moles rather than in grams. D. None of these is true. E. The thermometer must be calibrated to give accurate temperature readings in °C.

A. All solutions must be equilibrated to room temperature before beginning the experiment. B. The calorimeter must be calibrated to account for heat loss from the system. C. Calculations must be made in moles rather than in grams. E. The thermometer must be calibrated to give accurate temperature readings in °C.

A 2.00-mL sample of a soft drink is diluted with distilled water to 3.50 mL in a cuvet. The concentration of the diluted solution is determined to be 4.58 x 10-6 M in Allura Red AC. Based on this result, what is the mass of Allura Red AC in a 946-mL sample of the drink? (NOTE: The molar mass of Allura Red AC is 496.43 g/mol.) A. None of these. B. 1.23 mg C. 123 mg D. 15.1 g E. 0.615 mg F. 15.1 mg

A. NONE OF THESE

When should you be sure to wear full PPE (proper attire, lab coat, goggles) in the laboratory? (Check all that apply.) a. As soon as you enter the lab, and until you are ready to walk out the door. If you are in the laboratory, you should be wearing PPE (or be in the process of putting it on.) b. While cleaning up after experimental work is done. c. Once the experimental work has begun. d. While waiting in the lab room for a friend to finish. e. During the lab quiz.

ALL OF THEM a. As soon as you enter the lab, and until you are ready to walk out the door. If you are in the laboratory, you should be wearing PPE (or be in the process of putting it on.) b. While cleaning up after experimental work is done. c. Once the experimental work has begun. d. While waiting in the lab room for a friend to finish. e. During the lab quiz.

A student creates the following graph after an experiment measuring the density of water. Suppose the thermometer the student used was improperly calibrated and always read a value 1.5 degrees above the true temperature. Which of the following statements would be true?

B. The slope of the regression line would be correct, but the intercept would read a value that was greater than the true value.

In Experiment 7, the purpose of creating the Beer's Law plot of absorbance vs. concentration of Allura Red AC is best described as:

B. to determine the mg/serving of Allura Red AC in a solution prepared from a soft drink sample.

The molecular equation for the reaction previously used reaction in Experiment 4 is: Ba(OH)2 (aq) + H2SO4 (aq) →BaSO4 (s) + 2 H2O (l) Based on the conductivity properties of these reactants and products that you observed in the lab, which is the correct net ionic equation?

Ba2+(aq) + 2 OH-(aq) + 2 H+(aq) + SO42-(aq) →BaSO4(s) + 2 H2O(l)

A Beer's law calibration curve for a particular analyte has a best-fit equation of A=(11765 M-1)C + 0.197, with an R2 value of 0.9373. If a sample solution has an absorbance reading of 0.624, the concentration of the unknown sample would be:

C. 0.0363 mM

When calculating the displacement volume of the thermometer, the volume reading on the buret is 29.37 mL without the thermometer, and 28.72 mL with the thermometer in place. How many significant figures should be recorded for the displacement volume of the thermometer?

C. 2

The volume marking at the sealed bottom of a buret segment is 38.60 mL, and has markings for every 0.1 mL. When water is added, the bottom of the meniscus sits about halfway between the line for 18.3 mL and the next mark up. What volume of water is contained in the buret segment?

C. 20.35 mL

When viewed through a spectroscope, calcium ions produce three distinct lines in the visible region of the spectrum, at spectroscope positions of 7.30, 7.85, and 8.45. Assuming the linear fit for the calibration of the spectroscope has a positive slope, the line corresponding to the lowest energy would have a spectroscope position of:

C. 8.45

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. Never leave an open flame unattended, even for a brief time. c. Set up your work space so that wires and cables cannot accidentally make contact with the flame or hot glassware and melt. 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. Only the TA should ever operate an open flame.

CORRECT FROM A-F a. Always tie back hair, even long bangs, that might accidentally come in contact with the flame. b. Never leave an open flame unattended, even for a brief time. c. Set up your work space so that wires and cables cannot accidentally make contact with the flame or hot glassware and melt. 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.

Using the graph shown from an experiment measuring the density of water, what would be the correct value, units, and significance of the slope of the trendline?

D. -8.92 x 10-4 g mL-1 oC-1 represents the change in density as temperature increases.

The temperature at the start of a reaction was 22.8°C and the final temperature was 32.9°C. Based on these observations, the reaction of sodium bicarbonate with hydrochloric acid would be:

D. exothermic, because energy is transferred from the reaction to the surroundings.

Given the Rydberg equation: ΔE = RH (1/(nf2)- 1/(ni2)) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 434.1 nm? REMEMBER: h = 6.626 x 10-34 J⋅s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J

E. 5

In the reaction NaOH(s) + HCl (aq) → NaCl(aq) + H2O(l), the spectator ion(s) would be: (select all that apply.)

E. Cl-

In a determination of the mass of Allura Red AC in one serving of a food sample, the result is found to be ~10% too low when compared with another determination. The most likely experimental error to explain this result would be:

E. When the 1 x 10-5 M stock standard was prepared, instead of transferring 500 microliters of the 2 x 10-3M stock to the 10.00-mL volumetric flask, the experimenter transferred 450 microliters. This decreased the slope of the calibration line by 10%, causing the sample solution concentration to be calculated 10% too low.

3.5 g of white crystalline solid is added to a calorimeter containing 30 mL of water at 22 °C. During the reaction, the solid crystals disappear and the temperature of the solution decreases. Based on these observations the reaction would be classified as:

Endothermic

The molecular equation of a reaction is NaHCO3 (aq) + HCl (aq) →NaCl (aq) + H2O (l) + CO2 (g). Both the initial solutions and the final solution were transparent and colorless, but bubbles were seen during the reaction. Based on this equation and the observations of the reaction, the spectator ions in the ionic equation would be: Select one: A. Na+ B. Cl- C. H+ D. CO2 E. H2O F. Two of the above G. Three of the above H. None of the above

F. TWO OF THE ABOVE

All of the following three actions could produce a significant source of error in the results for Experiment 5: -Losing H2 gas because it is much less dense than air. -Losing O2 gas because it is much denser than air. -Collecting gases while the reaction is still hot, resulting in mostly H2O vapor in the bulb.

FALSE

This clothing would be appropriate for lab.--- Leggings with holes or mesh? Select one: True False

False

The following equations represent reactions used in Experiment 5. Of these reactions, choose the correctly balanced catalytic reaction.

G. 2 H2O2 (aq) →catalase→ 2 H2O (l) + O2 (g)

A conductivity plot for the titration of silver nitrate with lithium chloride is shown below. Assuming lithium chloride is the titrant, which ion species would you expect to be present in solution when 12.62 mL of titrant had been added? Select one: A. Ag+ B. NO3- C. Li+ D. Cl- E. A, B, and D. F. B and C only. G. B,C, and D. H. None of these

G. B,C, AND D

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select all that apply.) A. -(qsoln + qcal) B. qcal -qsoln C. qsoln -qcal D. ΔH / nreagent E. the heat gained or lost by the reaction in units of joules. F. the heat gained or lost by the reaction in units of joules/mol. G. the difference between the extrapolated maxiumum temperature and the initial temperature in a reaction. H. qsoln + qcal I. Both A and E are true. J. Both D and F are true.

I. Both A and E are true.

Using the graph provided, for the reaction of 1.25 g of sodium bicarbonate with 150 mL of 0.5 M citric acid, the value of ΔT/mol (°C/mol) would be: (NOTE: molar mass of sodium bicarbonate is 84.007.) Select one: A. 945 °C/mol B. 7.20 °C/mol C. None of these D. 11.7 °C/mol E. 605 °C/mol

NONE OF THESE

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it: Select one: A. Grows cold. B. Dissolves a solid reactant. C. Forms a precipitate. D. Causes water condensation farther downstream E. Two of these answers are correct. F. Three of these answers are correct. G. Causes a loud popping noise. H. Produces bubbles.

TWO OF THESE ANSWERS ARE CORRECT

During a conductivity titration, 15.0 mL of AgNO3 is placed in a beaker with 35 mL of H2O. At the start of the titration, the initial conductivity reading is nearly double that of a previous trial and decreases to a minimum at twice the expected volume of lithium chloride added. One possible explanation for these observations would be:

The experimenter mistakenly added twice as much silver nitrate to the beaker.

Is this clothing appropriate for lab.--Black short sleeve shirt Select one: True False

True

Which of the following is the reason backpacks must be stored during lab? Select one: a. Both of these are good reasons to keep nonessential items stored properly b. 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. c. Backpacks on the floor present a tripping hazard to students in lab, which may lead to spills and other incidents.

a. Both of these are good reasons to keep nonessential items stored properly

When should you immediately turn off the gas valve for a Bunsen or Meker burner? (Check all that apply.) a. If you smell gas in the room. b. If you must leave the open flame unattended and there is no one else to monitor it. c. Only at the end of lab when everyone has completed the experiment. d. If the flame suddenly goes out.

a. If you smell gas in the room. b. If you must leave the open flame unattended and there is no one else to monitor it. d. If the flame suddenly goes out.

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. Keep her in the eye wash for at least 15 minutes, and then make sure she goes to student health, just to be sure. b. Check to see if her eye is still red. If not, hurry so that you can finish the experiment c. Let the TA inspect her eye to see if it is okay. d. Keep her in the eye wash for at least 5 minutes and then let the TA decide if she can continue working.

a. Keep her in the eye wash for at least 15 minutes, and then make sure she goes to student health, just to be sure

While weighing out a reagent for use in an experiment, a student finds he has leftover reagent. The student should: a. Place the excess reagent in the appropriate solid or liquid waste container to prevent contamination of the stock reagent. b. Return the excess reagent to the stock bottle to minimize the amount of waste generated. c. Notify the TA immediately. d. Leave the dispensed material out on the bench so that another group can use it, which will minimize the waste generated.

a. Place the excess reagent in the appropriate solid or liquid waste container to prevent contamination of the stock reagent.

For which of the following situations should you be sure to notify your TA and fill out an incident report form? (Check all that apply.) a. You arrive in lab, but realize that your cold medicine is making you feel groggy. Even though the cause of this issue did not originate in lab, it is important that your TA knows and that an incident report is filed. In this case, your TA would recommend an excused absence. You should never attend lab if you have medication or other substances in your system that impair your awareness or ability to function in lab. If you shouldn't drive, you shouldn't come to lab. b. 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. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential contamination. c. 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. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential contamination. d. You begin to feel faint and dizzy in lab because you had to skip lunch. Even though the cause of this issue did not originate in lab, it is important that your TA knows and that an incident report is filed. In this case, your TA would recommend that you take a breat to get water and/or a snack. The lab is a terrible place to faint. You should never attend lab if you have an illness or medical condition that would impair your awareness or ability to function in lab. If you shouldn't drive, you shouldn't come to lab. e. 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. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential contamination.

a. You arrive in lan, but realize that your cold medicine is making you feel groggy. Even though the cause of this issue did not originate in lab, it is important that your TA knows and that an incident report is filed. In this case, your Ta would recommend an unexcused absence. You should never attend lab if you have medication or other substances in your system that impair your awareness or ability to function in lab. If you shouldn't drive, you shouldn't come to lab. b. During check-in you discover a broken funnel in your drawer, and the broken end of the stem causes nock through your glove. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential l contamination. c. 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. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential contamination d. You begin to feel faint and dizzy in lab because you had to skip lunch. Even though the cause of this issue did not originate in lab, it is important that your TA knows and that an incident report is filed. In this case, your TA would recommend that you take a break to get water and/or a snack. The lab is terrible place to faint. You should never attend lab if you have an illness or medical condition that would impair your awareness or ability to function in lab. If you should not drive, you should not come to lab. e. 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. No matter how small the injury, you should report it to your TA and be sure to wash the area thoroughly to be sure you have washed away any potential contamination.

What shoes are appropriate for lab? a. closed all around toes, ankle, front b. flip flops c. open toed shoes d. crocs

a. closed all around toes, ankle, front

The graph shows the calibration of a spectroscope against a series of emission lines of known wavelength. Based on this calibration, which is the wavelength of a line that appears at 4.71 mm on the spectroscope scale?

b. 479 nm

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. Neither of these methods is safe. 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. 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.

Consider the following scenario: A student has prepared a series of analytical solutions to be run on an instrument in another room. The student has worn gloves throughout the preparation of the solutions, and has wiped up all drips and spills that occurred during that process. The student removes her gloves before leaving the lab room and carries her solutions in scintillation vials in a large clean beaker to the room where the instrument is located. Once in the new room, the student obtains a new pair of gloves before dispensing the solutions for analysis. Which of the following changes could improve the student's procedure? (Check all that apply.) a. No changes, the student handled the process correctly. b. The student could have worked with her lab partner so that one of them could carry the materials with gloved hands, while the other opened doors and pressed elevator buttons with non-gloved hands. c. The student could have chosen a plastic bin, or other less breakable container to carry her solutions to the instrument so that she wasn't carrying glassware with her bare hands. d. The student could have worn a single glove on the hand she used for transporting the solutions to the instrument room, and used her non-gloved hand for opening doors and pushing elevator buttons. e. The student should have kept her gloves on the entire time, as she was handling glassware and reagents. Therefore, that takes priority over any contact with doorknobs or elevator buttons, and gloves should be worn. Also, this would conserve one pair of gloves and keep them from being wasted.

b. The student could have worked with her lab partner so that one of them could carry the materials with gloved hands, while the other opened doors and pressed elevator buttons with non-gloved hands. c. The student could have chosen a plastic bin, or other less breakable container to carry her solutions to the instrument so that she wasn't carrying glassware with her bare hands. d. The student could have worn a single glove on the hand she used for transporting the solutions to the instrument room, and used her non-gloved hand for opening doors and pushing elevator buttons.

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. Letting your TA handle the procedure for you. b. Using the correct hand position so that if something goes wrong you can avoid coming into contact with broken or sharp ends. c. Using sufficient vacuum grease that the apparatus slides smoothly. d. Using sufficient force that the apparatus will slide through the stopper.

b. Using the correct hand position so that if something goes wrong you can avoid coming into contact with broken or sharp ends.

How many times should you read the label on a reagent container and compare it with the lab manual? a. At least once. b. At least twice. c. At least twice each time you remove material from the container.

c. At least twice each time you remove material from the container.

Why should you inspect glassware for chips, cracks, or chemical residues before using it? Select one: a. 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. b. Chemical residues from previous experiments can cause unwanted and potentially dangerous side reactions. c. 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. d. All of these are potentially hazardous outcomes of using compromised glassware.

d. All of these are potentially hazardous outcomes of using compromised glassware.

Which of the following is a true statement about the bright yellow flame seen during a flame test of a 1 M solution of NaCl in a Meker burner flame?

d. The yellow color is characteristic of the changes in energy of an electron in the Na+ metal ion.