CHEM 101L UNC FiNaL ExaM witH aNswErs
100% CorrECt GradEd a+
What experimental components hindered the launch of the rocket in Experiment 5? ✔✔ Capped the
bulb with a gloved finger only, excess water on the bulb prevented full combustion
Why were you asked to full the pipet bulb up with water before adding the gases? ✔✔ The displacement
of water allowed us to determine how much gas was being collected.
Reactions in Experiment 5: Rockets ✔✔ Redox: Zinc and HCl
Decomposition: Hydrogen peroxide
Conclusion for Experiment 5: Rockets ✔✔ Based on the experimental data, the order of gas addition did
not have a strong effect on the distance traveled by the pipette bulb.
Purpose for experiment 6: Thermochemistry ✔✔ The purpose of this lab is to determine the enthalpy
change of the dissolution of sodium hydroxide, the neutralization of hydrochloric acid by sodium
hydroxide, and the dissolution and neutralization of sodium hydroxide by hydrochloric acid. A
calorimeter will be used to monitor the temperature changes of each of the reactions. In order to
accurately and precisely measure the temperature of the reactions, a temperature probe with be used
that connects to the computer and consistently records the temperature and the calorimeter provides
precise results.
Procedures for Experiment 6: Thermochemistry ✔✔ Set up the calorimeter.
Perform Reaction 1 in the calorimeter and record temperature values.
Perform Reaction 2 in the calorimeter and record temperature values.
Perform Reaction 3 in the calorimeter and record temperature values.
Reactions for Experiment 6: Thermochemistry ✔✔ Reaction 1: Dissolution of solid sodium hydroxide
Reaction 2: Neutralization of liquid sodium hydroxide and hydrochloric acid
Reaction 3: Dissolution and neutralization of solid sodium hydroxide and hydrochloric acid
,Hess's Law ✔✔ Delta H of reaction = (Sum of delta h for products) - (sum of delta h for reactants)
Equations for Experiment 6: Thermochemistry ✔✔ qcal = | qcold + qhot |
q = mcDT
ccal = (Dqcal) / (DTcold)
Tmax = y intercept for equation when temperature begins to decrease
qsoln = (msoln) * (DT) * (cH2O)
qrxn = - | qsoln + qcal |
DH = (qrxn) / (moles of reagent)
Calculations for Experiment 6: Thermochemistry ✔✔ (mliq) + (msolid) = (msoln)
qcal = (ccal) * DT
Conclusion from Experiment 6: Thermochemistry ✔✔ The enthalpy changes of the three reactions with
sodium hydroxide were calculated by using change in temperature through calorimetry. This calculation
of enthalpy change through change in temperature in exothermic reactions demonstrates Hess's Law by
showing, with minimal variance from theoretical values, that the sum of the change in enthalpy of two
reactions is equal to the change in enthalpy for that combined reaction.
Purpose of Experiment 7: Beer's Law ✔✔ The purpose of this experiment is to design an experiment to
determine the concentration of Allura Red AC dye in Gatorade and Powerade by utilizing Beer's Law.
Data will be used with Beer's Law in order to compare the amount of dye in Gatorade and Powerade by
measuring the absorbance values of dilutions of red Gatorade and Powerade and plugging those
absorbance values into the calibration curve regression line. This experiment also allows the researchers
to compare diluted concentrations and neat concentrations in order to determine the amount of Allura
Red AC in both red Gatorade and Powerade.
Procedures for Experiment 7: Beer's Law ✔✔ Prepare the stock standard solution.
Calibrate the spectrometer with different concentrations of Allura Red AC dye.
Use the spectrometer to determine the absorbance of the varying concentrations of the dye.
Prepare standard concentrations of Gatorade and Powerade.
, Use the spectrometer to determine the absorbance of the Gatorade and Powerade.
Equations for Experiment 7: Beer's Law ✔✔ Absorbance = (Molar absorptivity e) * (the path of light l) *
(Concentration of analyte C)
For the most accurate determination, the absorbance of the samples should fall in the middle of your
calibrated range (~0.5-0.7 absorbance units). What will you do if the absorbance for your sample is
greater than 1.2? Explain the process in detail, including the instruments used. Remember that you must
preserve the precision to 4 significant figures. ✔✔ If the absorbance for your sample is greater than 1.2,
we must consult our TA to determine whether calibration standards should be prepared again or if any
standard concentrations should be adjusted. Because of the relationships seen in the equation for
absorbance (A=ειC), a higher absorbance would result from a higher concentration (considering ε and ι
are constant). To lower the absorbance, a decrease in concentration would be required and the solution
providing the higher absorbance value should be diluted. For this experiment, 501 nm wavelength gave
the highest absorbance value. If it was necessary to decrease this maximum wavelength, lower
concentrations should be used.
Conclusion for Experiment 7: Beer's Law ✔✔ In this experiment, we put Beer's Law into practice while
understanding measurements regarding concentrations and how they relate to wavelength and
absorbance ranges. While comparing different concentrations of solutions, the higher concentrations
had a higher absorbance value, thus proving that absorbance and concentration are directly
proportional.
Purpose of Experiment 8: Spectroscopy ✔✔ The purpose of this experiment is utilize spectroscopy
through observing the continuous and line spectra of different mixtures to determine the wavelengths,
frequencies, and energies of the different mixtures and to identify unknown mixtures. Comparative
observations and measurements will allow the researchers to make connections between observed line
and emission spectra and energy levels.
Procedures for Experiment 8: Spectroscopy ✔✔ Calibrate the spectroscope.
Use the spectroscope to record the spectral characteristics of three sources of light.
Use the spectroscope and spectrometer to determine the line and emission spectra of hydrogen gas.
Use the spectroscope to observe the spectral characteristics of different metals.
Identify an unknown metal from the previously observed spectral characteristics of different metals.
100% CorrECt GradEd a+
What experimental components hindered the launch of the rocket in Experiment 5? ✔✔ Capped the
bulb with a gloved finger only, excess water on the bulb prevented full combustion
Why were you asked to full the pipet bulb up with water before adding the gases? ✔✔ The displacement
of water allowed us to determine how much gas was being collected.
Reactions in Experiment 5: Rockets ✔✔ Redox: Zinc and HCl
Decomposition: Hydrogen peroxide
Conclusion for Experiment 5: Rockets ✔✔ Based on the experimental data, the order of gas addition did
not have a strong effect on the distance traveled by the pipette bulb.
Purpose for experiment 6: Thermochemistry ✔✔ The purpose of this lab is to determine the enthalpy
change of the dissolution of sodium hydroxide, the neutralization of hydrochloric acid by sodium
hydroxide, and the dissolution and neutralization of sodium hydroxide by hydrochloric acid. A
calorimeter will be used to monitor the temperature changes of each of the reactions. In order to
accurately and precisely measure the temperature of the reactions, a temperature probe with be used
that connects to the computer and consistently records the temperature and the calorimeter provides
precise results.
Procedures for Experiment 6: Thermochemistry ✔✔ Set up the calorimeter.
Perform Reaction 1 in the calorimeter and record temperature values.
Perform Reaction 2 in the calorimeter and record temperature values.
Perform Reaction 3 in the calorimeter and record temperature values.
Reactions for Experiment 6: Thermochemistry ✔✔ Reaction 1: Dissolution of solid sodium hydroxide
Reaction 2: Neutralization of liquid sodium hydroxide and hydrochloric acid
Reaction 3: Dissolution and neutralization of solid sodium hydroxide and hydrochloric acid
,Hess's Law ✔✔ Delta H of reaction = (Sum of delta h for products) - (sum of delta h for reactants)
Equations for Experiment 6: Thermochemistry ✔✔ qcal = | qcold + qhot |
q = mcDT
ccal = (Dqcal) / (DTcold)
Tmax = y intercept for equation when temperature begins to decrease
qsoln = (msoln) * (DT) * (cH2O)
qrxn = - | qsoln + qcal |
DH = (qrxn) / (moles of reagent)
Calculations for Experiment 6: Thermochemistry ✔✔ (mliq) + (msolid) = (msoln)
qcal = (ccal) * DT
Conclusion from Experiment 6: Thermochemistry ✔✔ The enthalpy changes of the three reactions with
sodium hydroxide were calculated by using change in temperature through calorimetry. This calculation
of enthalpy change through change in temperature in exothermic reactions demonstrates Hess's Law by
showing, with minimal variance from theoretical values, that the sum of the change in enthalpy of two
reactions is equal to the change in enthalpy for that combined reaction.
Purpose of Experiment 7: Beer's Law ✔✔ The purpose of this experiment is to design an experiment to
determine the concentration of Allura Red AC dye in Gatorade and Powerade by utilizing Beer's Law.
Data will be used with Beer's Law in order to compare the amount of dye in Gatorade and Powerade by
measuring the absorbance values of dilutions of red Gatorade and Powerade and plugging those
absorbance values into the calibration curve regression line. This experiment also allows the researchers
to compare diluted concentrations and neat concentrations in order to determine the amount of Allura
Red AC in both red Gatorade and Powerade.
Procedures for Experiment 7: Beer's Law ✔✔ Prepare the stock standard solution.
Calibrate the spectrometer with different concentrations of Allura Red AC dye.
Use the spectrometer to determine the absorbance of the varying concentrations of the dye.
Prepare standard concentrations of Gatorade and Powerade.
, Use the spectrometer to determine the absorbance of the Gatorade and Powerade.
Equations for Experiment 7: Beer's Law ✔✔ Absorbance = (Molar absorptivity e) * (the path of light l) *
(Concentration of analyte C)
For the most accurate determination, the absorbance of the samples should fall in the middle of your
calibrated range (~0.5-0.7 absorbance units). What will you do if the absorbance for your sample is
greater than 1.2? Explain the process in detail, including the instruments used. Remember that you must
preserve the precision to 4 significant figures. ✔✔ If the absorbance for your sample is greater than 1.2,
we must consult our TA to determine whether calibration standards should be prepared again or if any
standard concentrations should be adjusted. Because of the relationships seen in the equation for
absorbance (A=ειC), a higher absorbance would result from a higher concentration (considering ε and ι
are constant). To lower the absorbance, a decrease in concentration would be required and the solution
providing the higher absorbance value should be diluted. For this experiment, 501 nm wavelength gave
the highest absorbance value. If it was necessary to decrease this maximum wavelength, lower
concentrations should be used.
Conclusion for Experiment 7: Beer's Law ✔✔ In this experiment, we put Beer's Law into practice while
understanding measurements regarding concentrations and how they relate to wavelength and
absorbance ranges. While comparing different concentrations of solutions, the higher concentrations
had a higher absorbance value, thus proving that absorbance and concentration are directly
proportional.
Purpose of Experiment 8: Spectroscopy ✔✔ The purpose of this experiment is utilize spectroscopy
through observing the continuous and line spectra of different mixtures to determine the wavelengths,
frequencies, and energies of the different mixtures and to identify unknown mixtures. Comparative
observations and measurements will allow the researchers to make connections between observed line
and emission spectra and energy levels.
Procedures for Experiment 8: Spectroscopy ✔✔ Calibrate the spectroscope.
Use the spectroscope to record the spectral characteristics of three sources of light.
Use the spectroscope and spectrometer to determine the line and emission spectra of hydrogen gas.
Use the spectroscope to observe the spectral characteristics of different metals.
Identify an unknown metal from the previously observed spectral characteristics of different metals.
