CHEM 1411- LAB PRACTICAL 2 EXAM
QUESTIONS WITH 100% CORRECT
ANSWERS L LATEST VERSION 2025/2026.
Why does the Neon discharge lamp produce more distinct spectral lines tan the hydrogen lamp?
- ANS Neon is transferring more electrons than Hydrogen, producing more spectral lines of
color, which means more energy is being transferred.
Why do KCL and CaCl2 produce different flame colors even though K+ and Ca2+ are
isoelectronic? - ANS The number of protons are not the same for K+ and Ca2+. Each has
different energy levels causing different flame colors.
A mercury discharge tube produces numerous strong spectral bands, however the spectrum of
the mercury-filled fluorescent lights in the lab shows only three strong bands of color. Why? -
ANS Lamps contain mercury that is coated with a fluorescent substance. High energy UV rays
are produced when an electric current passes through. The UV rays react with coating, which
produces the visible light. The electrons emitted from the coating is what makes the red, blue,
green light.
Calculate the energy of the 285 nm photon that is associated with skin cancer and the energy of
the 290 nm photons associated with essential vitamin D3 production. - ANS E= hv
E=hc/v
E285= (6.626x10^-34)(2.998x10^8)/(285x10^-9) = 6.97x10^-19J
E290= (6.626x10^-34)(2.998x10^8)/(290x10^-9) = 6.85x10^-19J
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, frequency - ANS V=C/Y
(2.998x10^8m/s)/(700x10^-9) = 4.28x10^14s^-1
Experimental Errors for Lab 9 - ANS Adding too much KMnO4 would cause it to become dark
purple and would cause the molarity to be low
If you had not rinsed your buret with the stock KMnO4 solution before beginning the titration? -
ANS Low molarity since the solution is slightly diluted
If you thought you reached the end point, but the color faded within 15 seconds and you did
not add more KMnO4? - ANS High molarity of KMnO4 since the end point is not reached and
less volume of KMnO4 solution was used
If you had been unable to complete the titration in a single period, but had stored the KMnO4
solution for several days before returning and picking up where you left off on the experiment
without additional standardization? - ANS The KMnO4 would oxidize if you stored it. This
causes MnO4 to form in the solution. The MnO2 causes the apparent concentration of the
solution to change as it is used. This would require more KMnO4 to titrate the oxalic acid and it
would lead to a lower calculated molarity
If you had added the KMnO4 too rapidly and your end point was an opaque purpleish-brown
rather than a clear solution with a hint of purple? - ANS More volume of KMnO4 would be
used causing the molarity of KMnO4 to be low
If you had added twice as much sulfuric acid and water as was called for in the procedure? -
ANS There would be no impact. KMnO4 only reacts with the oxalic acid. The molarity would
remain the same
Theoretical yield - ANS (474.38 g/mol)(weight of Al foil used) / molar mass of Al = 14.16g
Percent Yield - ANS actual/ theoretical
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
QUESTIONS WITH 100% CORRECT
ANSWERS L LATEST VERSION 2025/2026.
Why does the Neon discharge lamp produce more distinct spectral lines tan the hydrogen lamp?
- ANS Neon is transferring more electrons than Hydrogen, producing more spectral lines of
color, which means more energy is being transferred.
Why do KCL and CaCl2 produce different flame colors even though K+ and Ca2+ are
isoelectronic? - ANS The number of protons are not the same for K+ and Ca2+. Each has
different energy levels causing different flame colors.
A mercury discharge tube produces numerous strong spectral bands, however the spectrum of
the mercury-filled fluorescent lights in the lab shows only three strong bands of color. Why? -
ANS Lamps contain mercury that is coated with a fluorescent substance. High energy UV rays
are produced when an electric current passes through. The UV rays react with coating, which
produces the visible light. The electrons emitted from the coating is what makes the red, blue,
green light.
Calculate the energy of the 285 nm photon that is associated with skin cancer and the energy of
the 290 nm photons associated with essential vitamin D3 production. - ANS E= hv
E=hc/v
E285= (6.626x10^-34)(2.998x10^8)/(285x10^-9) = 6.97x10^-19J
E290= (6.626x10^-34)(2.998x10^8)/(290x10^-9) = 6.85x10^-19J
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, frequency - ANS V=C/Y
(2.998x10^8m/s)/(700x10^-9) = 4.28x10^14s^-1
Experimental Errors for Lab 9 - ANS Adding too much KMnO4 would cause it to become dark
purple and would cause the molarity to be low
If you had not rinsed your buret with the stock KMnO4 solution before beginning the titration? -
ANS Low molarity since the solution is slightly diluted
If you thought you reached the end point, but the color faded within 15 seconds and you did
not add more KMnO4? - ANS High molarity of KMnO4 since the end point is not reached and
less volume of KMnO4 solution was used
If you had been unable to complete the titration in a single period, but had stored the KMnO4
solution for several days before returning and picking up where you left off on the experiment
without additional standardization? - ANS The KMnO4 would oxidize if you stored it. This
causes MnO4 to form in the solution. The MnO2 causes the apparent concentration of the
solution to change as it is used. This would require more KMnO4 to titrate the oxalic acid and it
would lead to a lower calculated molarity
If you had added the KMnO4 too rapidly and your end point was an opaque purpleish-brown
rather than a clear solution with a hint of purple? - ANS More volume of KMnO4 would be
used causing the molarity of KMnO4 to be low
If you had added twice as much sulfuric acid and water as was called for in the procedure? -
ANS There would be no impact. KMnO4 only reacts with the oxalic acid. The molarity would
remain the same
Theoretical yield - ANS (474.38 g/mol)(weight of Al foil used) / molar mass of Al = 14.16g
Percent Yield - ANS actual/ theoretical
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
