C125 Final- Simple & Correct

The lines observed in H-lamp are parts of Balmer Series. All these lines are due to a transition from various higher n value to a common n. What is this common lower n value for all these lines? - Answer- 2 The bright violet line of Hg lamp has a wavelength of 435.8 nm. What is the energy of the photon associated with this emission line? - Answer- 4.56*10^-19 J Given: In Atomic Spectra lab, a student obtained his best-fit line equation to be y = 0.29 x + 46.8 when he plotted his Vernier reading on the y-axis and wavelength in nm on the x-axis. Question: If the Vernier reading for a line is 188.4, what is the predicted wavelength of this line in nm? (Keep 4 sig figs with one decimal place.) - Answer- 488.3000 The only electron in a hydrogen atom moved from n=3 to n=5. What is the wavelength of photon (in nm) being associated with this transition? Use whole numbers of nm without any decimal places, such as "415", "1125". - Answer- 1283.0 Which of the following transitions in H will absorb the longest wavelength photon? n=1 to n=2 n=3 to n=100 n=2 to n=4 n=10 to n=3 - Answer- n=3 n=100 A student obtained the Rydberg constant to be 1.96*10-18 J. What is the % error of the measurement? Answer as percentage and keep one decimal place. For example, if your answer is 12.5%, please either use 12.5% or 12.5. The fraction 0.125 will NOT be counted as correct answer. You Answered - Answer- 10.1 Which of the following orbitals of oxygen has the highest energy? 4s 3d 3p 2s - Answer- 3d A 100-mL sample of Pb initially has a concentration of 19.7 ppm. If this sample was diluted to 300 mL, what is the new concentration in ppm? Keep one decimal place for your answer. - Answer- 6.6 Which of the following is directly proportional to the concentration of a solution sample? absorbance of light intensity of light passing through extinct coefficient transmittance of light - Answer- absorbance of light When measuring the transmittance of digested cereal sample, what is used as blank? - Answer- Cereal sample without complexing agents When intensity of light changes due to sample absorption, which of the following change accordingly? wavelength frenqency energy of each photon transmittance - Answer- transmittance The green line of Hg lamp has a wavelength of 546.1 nm. What is the energy of photon associated with this emission line? - Answer- 3.64*10^-19 J Given: In Atomic Spectra lab, a student obtained his best-fit line equation to be y = 0.29 x + 46.8 when he plotted his Vernier reading on the y-axis and wavelength in nm on the x-axis. Question: If the Vernier reading for a line is 196.8, what is the predicted wavelength of this line in nm? (Keep 4 sig figs with one decimal place.) - Answer- 517.2 The only electron in a hydrogen atom moved from n=2 to n=6. What is the wavelength of photon (in nm) being associated with this transition? Use whole numbers of nm without any decimal places, such as "415", "1125". - Answer- 411.0 Which of the following transitions in a hydrogen atom will end up with the most energetic emission of photon? n = 1 to n = 2 n = 10 to n = 3 n = 2 to n = 100 n = 4 to n = 2 - Answer- n=4 to n=2 A student obtained the Rydberg constant to be 2.17*10-18 J. What is the % error of the measurement? Answer as percentage and keep one decimal place. For example, if your answer is 12.5%, please either use 12.5% or 12.5. The fraction 0.125 will NOT be counted as correct answer. - Answer- 0.5 Which of the following orbitals of H has the highest energy? 3d 4s 2p 1s - Answer- 4s A 100-mL sample of Pb initially has a concentration of 14.7 ppm. If this sample was diluted to 300 mL, what is the new concentration in ppm? Keep one decimal place for your answer. - Answer- 4.9 When measuring the transmittance of the Fe standard solution, what is used as blank? - Answer- DI water If a Fe stock solution has a concentration of 1.7 mg/mL, what is the concentration when 2 mL of this stock solution is diluted to 50. mL? Keep 2 sig figs for the answer. - Answer- 0.068 What is the absorbance if the % transmittance is 43%? Keep 2 sig figs for the answer. - Answer- 0.37 The Total Cereal has a Fe concentration of 0.6 g Fe per g of Cereal. However, it is very common for students to get less than 0.6. Which of the following can be contributors to this lower experimental result than the manufacturer listed value? There are three correct answers and find all of them. Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe Under-digestion of cereal sample Other materials from Cereal sample absorbs too much light Some Fe was lost during a few transfers between glassware The Fe was oxidized from 2+ ion to 3+ ion - Answer- Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe Under-digestion of cereal sample Some Fe was lost during a few transfers between glassware A=ebc, where A is absorbance, which is unit-less, b is path length that is 1 cm for the cuvette used. If the concentration c uses mol/L, what unit should the extinction coefficient e have? - Answer- L/(mol*cm) Keep in mind that the absorbance was plotted on the y-axis and concentration of Fe in mg/mL was plotted on x-axis to get best-fit line equation from the standard solutions. If the best fit line equation is y = 100x +0.01 What is the Fe concentration in mg/mL if the absorbance is 0.78 based on the best-fit line equation? Keep two sig figs for your answer. - Answer- 0.0077 According to VSEPR theory, molecules generally adopt a structure that - Answer- separate electron pairs as far away from others as possible around the central atom of the molecule Based on Lewis structures and Valence Bond Theory, which of the following is true? Both CH4 and H2O have sp hybridization. CH4 has sp3 hybridization and H2O has sp hybridization. CH4 has sp4 hybridization and H2O has sp2 hybridization. Both CH4 and H2O have sp3 hybridization on their central atom. - Answer- Both CH4 and H2O have sp3 hybridization on their central atom. NO3- has ______ resonance structures. - Answer- 3 Based on VSEPR theory, SF4 molecule should have ________ electron domain geometry. - Answer- trigonal bipyramidal Based on VSEPR theory, SF4 molecule should have ________ molecular geometry. - Answer- seesaw In the picture of HOMO orbitals generated by Spartan software, the bigger the lobe on an atom in the CN- ion, the _____ available the electrons are of that atom, the ________ the H+ ion will form bond with that atom. - Answer- more, more likley Which of the following is/are the possible methods of deciding which atom in the CN- ion has more negative charge? - Answer- determine which atom is more electronegative determine the formal charges What is the absorbance if the % transmittance is 48%? Keep 2 sig figs for the answer. - Answer- 0.32 Keep in mind that the absorbance was plotted on the y-axis and concentration of Fe in mg/mL was plotted on x-axis to get best-fit line equation from the standard solutions. If the best fit line equation is y = 100x +0.01 What is the Fe concentration in mg/mL if the absorbance is 0.37 based on the best-fit line equation? Keep two sig figs for your answer. - Answer- 0.0036 Draw the best Lewis structure of N2O. What is the formal charge of the terminal N - Answer- 0 What is the electron geometry of N2O - Answer- linear Which of the following molecules has the smallest bond angle? - Answer- H20 What is the bond angle in SF6 molecule - Answer- 90 Resonance structures lower the energy through - Answer- electron delocalization N2O has a few resonance structures as shown below (all lone pair electrons are purposeful left out): N=N-O N=N=O N-N=O True or False: all these three resonance structures are equally important contributors to the overall properties of N2O. - Answer- false What is the hybridization of the central atom in H2O? - Answer- Sp3 Which of the following are correct about nodal planes in molecular orbitals? There may have more than one correct answers. Pictures of sigma and pi bonding and antibonding molecular orbitals for 2nd period elements may help you solve this problem. Pictures are available from C105 textbook or lecture slides or you may use "" to do some internet searching. In sigma 2p bonding molecular orbital, there are no nodal planes. Regardless it is sigma or pi, the antibonding molecular orbitals always have a nodal plane that is perpendicular to the internuclear axis Since 1s orbitals do not have any node, the sigma 1s antibonding orbitals cannot have any node Both bonding and antibonding molecular orbitals may have nodal planes. - Answer- Regardless it is sigma or pi, the antibonding molecular orbitals always have a nodal plane that is perpendicular to the internuclear axis Both bonding and antibonding molecular orbitals may have nodal planes.