Chem125 Final Review
Draw the best Lewis structure of N2O. What is the formal charge of O?
-1
If in one trial of titration, a student used 20 mL of 0.020 mol/L KMnO4 to titrate all the oxalate ion, how many moles of oxalate ions are there in the sample, assuming that all the oxalate ions are completed titrated by KMnO4?
.001
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 0.51 based on the best-fit line equation? Keep two sig figs for your answer.
.005
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.
.0077
If a Fe stock solution has a concentration of 1 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.
.04
If a Fe stock solution has a concentration of 1.6 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.
.064
What is the absorbance if the % transmittance is 55%? Keep 2 sig figs for the answer.
.26
What is the absorbance if the % transmittance is 50%? Keep 2 sig figs for the answer.
.3
Draw the best Lewis structure of cyanide ion (CN-). What is the formal charge on N?
0
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?
1283
How many valence electrons are there in a CO2 molecule?
16
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?
2
A solution has a temperature change of 20 K. What is the temperature change in degrees Celsius?
20
Which of the following orbitals of O has the lowest energy? 3d 2p 2s 4s
2s
NO3- has ______ resonance structures.
3
A 100-mL sample of Pb initially has a concentration of 15.5 ppm. If this sample was diluted to 400 mL, what is the new concentration in ppm?
3.9
The molar mass and molar heat capacity of aluminum is 27.0 g/mol and 24.3 J/(mol K), respectively. If a 27.0-g Al sample, at 300. K, absorbed 195 J of heat, what is its final temperature?
308
Which of the following orbitals of oxygen has the highest energy? 3p 4s 2s 3d
3d
If we apply the HOMO and LUMO concepts in atomic orbitals, we will have HOAO (Highest Occupied Atomic Orbitals) and LUAO (Lowest Unoccupied Atomic Orbitals). What is the LUAO of Na atom?
3p
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?
4.56*10^-19 J
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".
411
The lines on Absorption Atomic Spectra correspond to energies needed for electrons to be excited from a lower energy level to a higher energy level. Assume that the energy needed for an electron in 2p orbital in an O atom to jump to 3s orbital is 4.09*10-19 J, what is its wavelength of the line atomic spectra in nanometer (nm)?
486
A 100-mL sample of Pb initially has a concentration of 15.7 ppm. If this sample was diluted to 300 mL, what is the new concentration in ppm?
5.2
A student obtained the Rydberg constant to be 2.06*10-18 J. What is the % error of the measurement? Answer as percentage and keep one decimal place.
5.5
In a coffee-cup calorimeter, 50.0 g hot water at 60.0 C was mixed with 50.0 g cold water at 20.0 C. If the final temperature is 37.7, what is the heat capacity of the calorimeter in J/C? Specific heat of water is 4.184 J/(g C)
54
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 203.5, what is the predicted wavelength of this line in nm? (Keep 4 sig figs with one decimal place.)
540.3
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 205.6, what is the predicted wavelength of this line in nm? (Keep 4 sig figs with one decimal place.)
547.6
Oxalate ion is used as a ligand in this lab. It is a bidentate ligand. What is the coordination number of Fe in the green compound you synthesized?
6
A student obtained the Rydberg constant to be 2.04*10-18 J. What is the % error of the measurement? Answer as percentage and keep one decimal place.
6.4
Sample % yield question: For the following reaction with the amount of reactants and molar masses given, if 15 g of C is produced, what is the % yield of this reaction? Answer to 2 sig figs. Sample input: if 20% is the correct answer, use 20 instead of 20%; do NOT use fraction such as 0.20. A + B --> C Molar masses: A = 100 g/mol; C = 200 g/mol Starting materials: A = 10. g; B = In excess
75
How many valence electrons are there in a hydronium ion, H3O+?
8
What is the bond angle in SF6 molecule?
90.0 (with margin: 1.0)
Which one is correct about the bond lengths in PCl5? Axial bonds are longer because they experience higher repulsion Equitorial bonds are longer because they experience smaller repulsion All P-Cl bonds have the same bond length. The axial bonds are shorter because they are far away from other bonds
Axial bonds are longer because they experience higher repulsion
Which of the following has the lowest bond order? Be2 O2 N2 B2 C2
Be2
Which of the following statements are correct regarding bonding and antibonding molecular orbitals? Choose all correct statements. Bonding molecular orbitals are due to in-phase constructive overlap of two atomic orbitals Both bonding and antibonding molecular orbitals will contribute the same toward bonding in the molecule Bonding molecular orbitals have lower energy than their parent atomic orbitals Antibonding molecular orbitals are due to out-of-phase destructive overlap of two atomic orbitals Antibonding molecular orbitals have higher energy than their parent atomic orbitals
Bonding molecular orbitals are due to in-phase constructive overlap of two atomic orbitals. Bonding molecular orbitals have lower energy than their parent atomic orbitals Antibonding molecular orbitals are due to out-of-phase destructive overlap of two atomic orbitals Antibonding molecular orbitals have higher energy than their parent atomic orbitals
Based on Lewis structures and Valence Bond Theory, which of the following is true? CH4 has sp4 hybridization and H2O has sp2 hybridization. Both CH4 and H2O have sp3 hybridization on their central atom. Both CH4 and H2O have sp hybridization. CH4 has sp3 hybridization and H2O has sp hybridization.
Both CH4 and H2O have sp3 hybridization on their central atom.
When measuring the transmittance of the Fe standard solution, what is used as blank?
Di water
A sample of solid X was dissolved in 200. g of water at 20. C. If the final temperature of the solution was 15. C, which of the following is true about the dissolution of X in water? Exothermic with negative heat of solution Endothermic with positive heat of solution Exothermic with positive heat of solution Endothermic with negative heat of solution
Endothermic with positive heat of solution
Which of the following might be a contributing factor to low experimental purity of green crystals? Forming the crystals too quickly by cooling it down in an ice-water bath Some green crystals are lost during filtration last week All of them will contribute to a low experimental %purity Over-titration
Forming the crystals too quickly by cooling it down in an ice-water bath
Which of the following molecules has the smallest bond angle? H2O BF3 CH4 NH3
H2O
According to Bohr's Model, which one is correct about a transition from n=2 to n=1 in a hydrogen atom? The photon associated with this transition will be in visible range. It is a transition from an excited state to a ground state It is the most energetic transition in a hydrogen atom. It has to absorb a photon for this transition to happen
It is a transition from an excited state to a ground state
The purity of green crystal will be determined by a titration. This titration does not need an indicator because: This is not an acid-base reaction. KMnO4 is dark purple and any excessive KMnO4 will show its unique color in the titration. KMnO4 is a very strong oxidizing agent and it might react with indicators. A pH meter will be used instead to monitor the reaction process.
KMnO4 is dark purple and any excessive KMnO4 will show its unique color in the titration.
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?
L/(mol*cm)
How many unpaired electrons are there in O2?
O2
All of the following molecules have all bonds being equivalent except: NH3 PCl5 CH4 SF6
PCl5
Red and purple are two lines of hydrogen lamp. Which one is correct when comparing these two lines? Choose all correct answers. Red line has higher frequency than the purple one. The light of red line travels faster than the purple one. Red line has smaller energy than the purple one. Red line has longer wavelengthh than the purple one.
Red line has smaller energy than the purple one. Red line has longer wavelengthh than the purple one.
Which of the following are correct about nodal planes in molecular orbitals? There may have more than one correct answers. Since 1s orbitals do not have any node, the sigma 1s antibonding orbitals cannot have any node 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 Both bonding and antibonding molecular orbitals may have nodal planes.
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.
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. Other materials from Cereal sample absorbs too much light Some Fe was lost during a few transfers between glassware Under-digestion of cereal sample The Fe was oxidized from 2+ ion to 3+ ion Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe
Some Fe was lost during a few transfers between glassware Under-digestion of cereal sample Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe
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. The Fe was oxidized from 2+ ion to 3+ ion Under-digestion of cereal sample Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe Other materials from Cereal sample absorbs too much light Some Fe was lost during a few transfers between glassware
Under-digestion of cereal sample Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe Some Fe was lost during a few transfers between glassware
In the Lewis structure of NH3, there is one lone pair on N atom. What orbital will this lone pair on N reside?
a sp3 hybrid orbital
Which of the following is directly proportional to the concentration of a solution sample? absorbance of light extinct coefficient intensity of light passing through transmittance of light
absorbance of light
Which of the following is directly proportional to the concentration of a solution sample? transmittance of light intensity of light passing through extinct coefficient absorbance of light
absorbance of light
Which one is correct about the reaction yield of K3[Fe(C2O4)3]*3H2O? Percent yield is the fraction of theoretical yield that was actually obtained, or %Y = (actual Y) / (theoretical Y) * 100% The theoretical yield must be calculated through stoichiometry. The mass of green crystal collected is the actual yield. all of them are correct.
all of them are correct
The LUMO of cyanide ion is: (multiple answers) bonding MO sigma MO antibonding MO Pi MO
antibonding MO pi MO
In the calibration step (part I) of the thermochemistry experiment, a student recorded all temperatures for 3 min after the two water samples were combined in calorimeter. The temperature first increased, then slowly leveled off and then start to decrease by 2 min. If the student used the temperature at 3-min mark as his final temperature, his calculated heat capacity of calorimeter will be: Artificially lower Artificially higher accurate
artificially higher
Predict the molecular shape of SF2. trigonal planar bent linear tetrahedral
bent
Which of the following is/are the possible methods of deciding which atom in the CN- ion has more negative charge? Neither method mentioned is valid. Determine which atom is more electronegative. Determine the formal charge of each atom in the ion. Both methods mentioned.
both methods mentioned
Resonance structures lower the energy through
electron delocalization
Since we can only see visible lines from a hydrogen lamp, hydrogen lamp does not produce any UV light. true or false
false
N=N-O and N=O=N are resonance structures to each other. true or false
false To be called resonance structures, all Lewis structures must have the same general atomic arrangement.
Evaporation of water __________. (Choose all correct answers.) has negative enthalpy change has positive enthalpy change is endothermic is exothermic
has positive enthalpy change is endothermic
Draw the best Lewis structure of N2O and consider resonance structures if there are any. What is the bond order between the two N atoms in N2O?
more than 2 but less than 3
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.
more, more likely
Which of the following transitions in a hydrogen atom will absorb the highest amount of energy? n = 2 to n = 100 n = 10 to n = 10000 n = 5 to n = 1 n = 1 to n = 2
n = 1 to n = 2
Which of the following transitions in H will absorb the longest wavelength photon? n=3 to n=100 n=10 to n=3 n=1 to n=2 n=2 to n=4
n=3 to n=100
Draw the best Lewis structure of nitrate ion first and consider resonance structures if there are any. Which one is correct about the bonds in nitrate ion? There is two single bonds and one double bond None of the statements are correct One bond is stronger than the other two One bond will be shorter than the other two All the statements are correct
none of the statements are correct
VSEPR Theory also applies to coordination complex. The only difference is that the central metal, as cation and electron deficient, never have lone pairs. So using VSEPR Theory, what is the molecular geometry of the complex of the green compound synthesized?
octahedral
Based on VSEPR theory, SF4 molecule should have ________ molecular geometry.
seesaw
According to VSEPR theory, molecules generally adopt a structure that has the smallest number of resonance structures. has the smallest number of valence electrons. separate electron pairs as far away from others as possible around the central atom of the molecule. has the smallest number of lone pairs around the central atom.
separate electron pairs as far away from others as possible around the central atom of the molecule.
According to VSEPR theory, molecules generally adopt a structure that has the smallest number of resonance structures. separate electron pairs as far away from others as possible around the central atom of the molecule. has the smallest number of lone pairs around the central atom. has the smallest number of valence electrons.
separate electron pairs as far away from others as possible around the central atom of the molecule.
The HOMO of cyanide is: (multiple answers) a sigma MO a pi MO a bonding MO an antibonding MO
sigma MO bonding MO
What is the hybridization of C atom in CO32-?
sp^2
When intensity of light changes due to sample absorption, which of the following change accordingly? frenqency transmittance energy of each photon wavelength
transmittance
Based on VSEPR theory, SF4 molecule should have ________ electron domain geometry.
trigonal bipyramidal
What is the electron geometry of SF4?
trigonal bipyramidal
What is the molecular geometry of carbonate ion, CO32-?
trigonal planar
what is the electron geometry of CO32- ion?
trigonal planar
What is the molecular geometry of NH3?
trigonal pyramidal
