Chemistry
Suppose 64 atoms of the radioactive isotope are originally present in a sample. What is the expected amount of time that will pass until only one atom of the isotope remains, given that the half-life for this radioactive isotope is 23 years? Show how you arrived at your answer.
64→32→16→8→4→2→1
6 half-lives required
6x23=138yrs
Note: Method is required
Arteries transport blood away from the heart, but not all arteries transport oxygenated blood. State the name of the artery in the normal human body that transports deoxygenated blood.
Pulmonary artery/Artery that transports blood to the lungs
Duc Do pushes a heavy crate across the floor at constant speed and says “I’m applying a force, so the crate must be accelerating.” Explain the mistake
If it’s moving at constant speed, friction must balance the push. The net force is zero and thus there is no acceleration.
The complete photoelectron spectrum of an element is represented above.
Identify the element.
Nitrogen (N)
Outline two effects that an increase in temperature has on the enzymatic activity
They need to mention both effects
Due to collision theory, increase in enzymatic activity
Once it increases above optimal, the enzyme denatures/denaturation → Decreases enzymatic activity
SeanJangium is an unstable nucleus with too many neutrons compared to protons. What type of radiation is it most likely to emit, and why?
Beta-minus decay, because converting a neutron into a proton plus an electron (and antineutrino) moves the nucleus toward a more stable neutron-to-proton ratio.
At 161 K, SiH4 boils but SiO2 remains as a solid. Using principles of intermolecular forces, explain the difference in boiling points.
SiH4 is composed of molecules, for which the only intermolecular forces are London dispersion forces. SiO2 is a network covalent compound with covalent bonds between silicon and oxygen atoms. LDFs are much weaker than covalent bonds, so SiH4 boils at a much lower temperature than SiO2.
There are three tRNA binding sites on a ribosome. State the name of each site, and outline the function of each site.
Aminoacyl site (Accept A site)
Peptidyl site (Accept P site)
Exit site (Accept E site)
In 2036, Dr. Seo pushes a sealed syringe containing air rapidly and the temperature rises noticeably. However when he compresses the same syringe slowly, the temperature barely changes. Explain why the speed of compression affects the temperature rise.
Rapid compression is nearly adiabatic as there is no time for heat to escape, so work done increases the internal energy raising and thus raises the temperature. Slow compression allows heat to flow out to the surroundings, making the process closer to isothermal with a much smaller temperature change
Calculate the pH of a 0.25 M solution of HCOOH.
I: 0.25 0 0
C: -x +x +x
E: (0.25-x) x x
Let [H3O+] = x
Then 1.8 x 10^-4 = x^2/(0.25-x)
→ x=0.00661881
pH=-log (x) = 2.179… (2.18)
Note:
If assuming x<<0.25, the expression x^2/0.25 can be used. In this case, pH will be 2.17
Duc Do was scuba diving in the Great Barrier Reef, and he noticed that many corals were bleached and some sections of the reef were collapsing. Duc identified a decrease in pH. Suggest a human activity that could have led to coral bleaching and explain.
Combustion of fossil fuels leads to ocean acidification by causing the carbonate in the corals to be consumed to produce carbonic acid.
BJ Park conducts a experiment where two identical strings are stretched with identical tension, except one has a small metal bead attached at its midpoint. When both strings are plucked, the student notices that the string with the bead producess a lower fundamental frequency (ff), even though the total mass added is tiny. Explain why such a small mass has a large effect on the ff
The bead acts as a localized inertia point that disrupts the uniform motion of the standing wave. The midpoint is where the antinode (maximum motion) occurs, so adding mass there dramatically increases the effective inertia of the system and lowers the wave speed and fundamental frequency far more than the small total mass would suggest. The location amplifies this effect.
Benzoic acid can be converted to 3-ethylbenzoic acid when reacted with chloroethane in the presence of an anhydrous aluminium chloride catalyst. Explain the organic reaction occurring in the conversion of these two compounds.
Electrophilic Aromatic Substitution (specifically, Friedel-Crafts Alkylation)
The catalyst, anhydrous aluminium chloride, reacts with chloroethane to generate a highly reactive positively charged species, the ethyl carbocation. This carbocation acts as the electrophile (electron-seeking species). The benzene ring in benzoic acid acts as the electron source. The electrophile substitutes one of the hydrogen atoms on the ring. The existing carboxylic acid group on benzoic acid is a meta-directing and deactivating group. This directs the incoming ethyl group to the meta position (position 3), resulting in 3-ethylbenzoic acid.
A doctor meets a patient named Duc Do, who shows severe fatigue during mild exercise. After investigating the mitochondrial membrane of Duc’s muscle cells, she notices that electrons are flowing normally across the electron transport chain. Suggest a reason why Duc shows fatigue during mild exercise.
Any problems regarding:
Unable to make a proton gradient across the mitochondrial membrane
ATP synthase malfunction
Not enough Oxygen consumption, which could shut down the ETC
Any correct answer about the oxidative phosphorylation defect
Do not accept:
NADH/FADH2 not able to donate electrons
Tony Lee is piloting a spacecraft that accelerates at 1g for several months. One day he notices that the distant galaxies that once filled his view now seem to compressed into a bright, narrow cone directly ahead of him, even though he hasn’t changed his route. Assuming his instruments are functioning normally, explain the physical reason for this effect.
Relativistic aberration occurs because at relativistic speeds the direction of incoming light transforms so that photons from all directions appear shifted toward the direction of motion. This happens because observers moving near light-speed disagree on the angle at which photons arrive. Combined with Lorentz contraction, this compresses the entire visible universe into a bright cone in front of the ship.