Chem/Phys Missed Questions Flashcards
Activated fatty acids undergo beta-oxidation, 4 step process in which two carbons at a time are converted to acetyl-CoA.
How many NADH molecules will be produced from palmitoyl-CoA?
1 molecule of NADH is made for every complete cycle of B-oxidation
2 carbons are removed each cycle
palmitoyl-CoA has 16 carbons, 7 cycles, 7 NADH
What is a transferase?
transfers a specific group from one molecule to another (phosphate transfer)
What is a lyase? hydrolase? oxidoreductase?
catalyzes breaking of bonds without using water
catalyzes hydrolysis of a molecule with water
movement of electrons
Molecular geometry in increasing order.
- linear: 2 bonds
- trigonal planar: 3 bonds
- bent: 2 bonds, 1 LP
- tetrahedral: 4 bonds
- trigonal pyramidal: 3 bonds, 1 LP
- trigonal bipyramidal: 5 bonds or 4 B + 1 LP, 3 + 2
- octahedral: 6 bonds, 5/1, 4/2
How do you determine the mole fraction of O2 inhaled?
partial pressure is equivalent to mole fractions
Amount inhaled found by dividing the specific amount by the total pressure
How do you calculate Coulomb’s Law?
electrostatic force
F = kq1q2 / r^2
What is a 30 dB increase do to the magnitude of the sound?
decibels are on a log scale
increases it by 10^3
1000x greater
What is the formula of monosaccharides and disaccharides?
monosaccharides: C6H12O6
disaccharide: C12H22O11
How are peptides formed?
N terminal attacks C
amino acid with free N gets named first: N–>C
What is the potential energy of a spring?
U = (1/2) k x^2
What role does the acid play in Fischer esterification?
protonates the carbonyl oxygen, making the carbon more electrophilic and susceptible to attack
CATALYST
Characteristics of ethanoic anhydride?
highly reactive (in water, forms back into two CA), formed via dehydration, WOULD NOT form in aq solution
List the first 4 alkanes.
methane
ethane
propane
butane
How do you determine priority in R/S configuration?
highest priority groups are highest atomic number. CH3 < CH2X. R clockwise, S counterclockwise
What do salt bridges do in electrochemical cells?
prevent charge build-up in galvanic cells
- maintains the electrical neutrality by releasing spectator ions so that the redox reaction continues
What is the difference between galvanic and electrolytic cells?
galvanic: converts chemical energy into electrical energy through a spontaneous redox reaction
electrolytic: electrical energy to drive a non-spontaneous reaction
What is Gibb’s free energy equation ?
dG = dH - TdS
H: enthalpy; + endothermic
T: temp; 273K
S: entropy; randomness
G: negative is spontaneous
What affects nucleic acid annealing?
spontaneous and driven by formation of H-bonds
electrostatic interactions, histones (structure + protect DNA) negatively affects formation
How do you determine the terminals in a galvanic cell?
anode is terminal where oxidation occurs; higher oxidation potential, lower reduction potential goes here
What happens in beta+ decay?
proton into a neutron, emission of a positron and neutrino from the nucleus
drops atomic number by 1, same atomic mass
What is laminar flow through a closed system?
fluid moves smoothly in parallel layers
v1A1 = v2A2; velocity and cross sectional areas
greatest velocity occurs in region of smallest cross sectional area
What is buoyant force?
upward force exerted by a fluid on an object submerged in it
Fb = pf * V * g
- pf: density of the fluid
- V: volume of the fluid displaced by the object
- g: acceleration due to gravity
An object is submerged in a pool and sinks. Assuming H2O is an ideal fluid, what is true?
the weight (m*g) of the object is greater than the buoyant force because it is accelerating downward (g)
ideal fluids have 0 viscosity (no drag/R), so the object’s acceleration does not decrease as it hits the bottom of the pool
How is focal length related to curvature?
f = r/2
How do you figure out how much energy is liberated from transforming mass in a nuclear fission reaction?
mass defect
mass reactants - mass products = mass turned into energy * conversion factor
Where is pressure the greatest in a static, closed system?
at the lowest point
What is the best approximation of an ideal fluid?
any type of gas because it has lowest viscosity
How does Pascal’s Principle relate to the continuity equation? How does the height of the fluid factor in?
Pascal’s Principle: Pressure is transmitted equally in all directions in a confined fluid in a closed system
Continuity equation: A1v1 = A2v2 –> flow rate is constant for incompressible fluid
greater height increases pressure (P = pgh)
What is the difference between chlorate and hypochlorite?
chlorate: ClO3-
hypochlorite: ClO-
What is required to break an ester?
strong acid or base and water
What cannot be in a rate law?
anything following the rate-determining step
What is an anion exchange column used for? Why would you increase the concentration of NaCl ?
positively charged stationary phase to extract negatively charged molecules
NaCl: Cl- ions compete with the protein for binding, causing it to elute out from the column
What is the average weight of an amino acid?
110 Daltons
How is A and T related in A = log(1/T)
inversely
A tested sample absorbs light at 3 different wavelengths. Overall, the sample has higher maximum wavelengths than expected. What is the identity of the solution?
benzene: has three different sets of pi electrons that absorb at different wavelengths and the conjugation increases the wavelength expected
Rxn of aldehyde with water results in a diol. PCC does not react with aldehydes. what does this imply about PCC?
PCC is anhydrous (does not work in water)
What is a disproportionation reaction?
type of redox reaction in which an element undergoes both oxidation and reduction to form two different products
When you mix a solution of benzoic acid, phenol, and aniline (aromatic amine) in dichloromethane (p=1.33) in a separatory funnel with NaOH, what ends up in the bottom layer?
aniline: only molecule that does not react with NaOH and is not water soluble, so it will stay with dichloromethane (more dense than water and not miscible with it)
How do you determine the position of something in a chair orientation when given the ring structure?
look at the largest group; almost always equitorial
- dashed = above the plane of the ring
preserve all equitorial conformation **
What substrates are needed for the synthesis of a hemiketal?
ketone + alcohol
hemiacetal = aldehyde + alcohol
When do you use fractional vs. simple distillation?
fractional: boiling points are less than 25 degrees apart
simple: boiling points are under 150 degrees and are at least 25 degrees apart
What do solubility curves show?
temperature (x) vs. solubility (y)
-physiologic: 37
- room: 25
above the line is supersaturated, below is unsaturated
solutions with the same solubility do not necessarily have the same molarity
What is necessary for light absorbance on an IR spectrum?
vibration must result in change in the bond dipole moment
- diatomic molecules do not exhibit absorption
What will produce butanoic acid with acetone, CrO3, and aqueous H2SO4?
1-butanol because it is a primary alcohol
in a jones reaction, primary alcohols produce CA, secondary alcohols produce ketones
What solvent would promote a racemization of (R)-2-chloropentane?
heat a solution of it with lithium chloride and DMSO = polar, aprotic solvent that promotes Sn2 reactions
What is gravity filtration used for?
collect liquids from solids in an efficient way
Assuming the continuity equation applies to arteries, what is an explanation for why vascular fluttering (collapses on itself) occurs in atherosclerosis?
the initial narrowing of the blood vessel causes increase in velocity of the blood, decreasing the pressure in the arteries (Bernoulli’s equation). A large enough pressure drop would lead to its collapse
What shape is NH2R?
trigonal pyramidal: 3 bonds, 1 lone pair
linear: 2 bonds
trigonal planar: 3 bonds
tetrahedral: 4 bonds
trigonal bipyramidal: 5 bonds
octahedral: 6 bonds
When placed in an electric field, what would migrate towards the cathode at pH 7?
amino groups are protonated and positive, CA are deprotonated and negative, so need something with more amino groups (NH2)
cathode = negatively charged, amino positively charged
What is efficiency? How does accidentally calibrating weights as 3 pounds heavier than they actually are affect the efficiency in the experiment?
work output / work input
- work output: weight * distance – this would be artificially high
- work input: force needed to move the weights – this would stay the same
produces a high efficiency
percent error is more for smaller weights, skewing it more
What happens if the cross-sectional area of the ductus arteriosus decreases in neonatal lungs?
increases resistance, so blood flow decreases
When a parcel of hot gas rises, it expands adiabatically, doing work on the surrounding air, resulting in decrease temperature. Why does temperature decrease?
as the parcel expands adiabatically, it does work on the surrounding air without taking in any heat
- means the internal energy of the gas decreases (U = Q-W where Q doesn’t change)
- internal energy decreases, so does temp
How does buoyant force change with altitude when looking at two balloons of equal volume?
buoyant = weight of fluid it displaces
the atmosphere is more dense at 2000 m vs. 2600m, so the weight of air displaced by the balloons will be greater at 2000 m than 2600m
What is convection?
heat is transferred by movement of heated fluid (air or water)
What is required for aromaticity?
conjugated, planar ring = 4n + 2 pi electrons
What amino acid would exhibit strongest interaction with the stationary phase of a cation exchange column at pH of 7?
lysine
exchange columns are named for the charge of the ion that binds to the column
cation exchange: negatively charged stationary phase to attract + ions
How do you calculate the voltage of a voltaic cell?
add the reduction potentials without multiplying them by their stoich coefficients; this is an INTRINSIC property (doesn’t depend on the amount of substance involved)
can do this by subtracting the reduction potentials (cat - anode) or by reversing the sign of the thing getting oxidized
must be positive if it is driving a device
What is the specific gravity of water?
1
What is the heat energy of a resistor proportional to ?
power = I V
Describe the characteristics of an ether.
R-O-R’
less polar than alcohols, making it a relatively nonpolar aprotic solvent used for Sn2 reactions
What happens to configuration in an Sn2 reaction?
the stereochemistry is inverted ONLY at the carbon that is attacked by the nucleophile
What is the electrical and molecular geometry of XeCl4?
electrical: octahedral
molecular: square planar
What is the expected m/z peak of the molecular ion peak (M+) in mass spec?
molecular weight of everything in the compound
What is the rule for electrical conductivity?
there is no periodic trend, but
metals > metalloids > nonmetals
What are the strong acids?
HCl, HNO3, H2SO4, HBr, HI, HClO4, HClO3
For converting ring structures into chair conformations, what is important?
you need to move in the same direction as the ring when you count (counterclockwise or clockwise)
dash down, wedge up
What is the N-H stretch on IR?
3600-3200 cm-1
What is ionic bond character?
the difference in electronegativity
- increases with larger difference
further away on the periodic table increases ionic bond character
NaCl > NaBr > MgCl2 > MgBr2
What happens when sound reflects off an interface between two media?
reflection has reduced intensity because some of the sound is transmitted into the new media
- speed, wavelength, and frequency is the same
Where in a system with elastic cords is the potential energy the greatest?
when the user is using maximal effort (tension in the cord is the highest)
U = 1/2 kx^2
What is the loop and junction theorem based on?
conservation of electric charge
- current entering a junction must equal the current leaving a junction
How do you find the equilibrium constant of the reverse reaction?
1/Kc where Kc is the equilibrium constant of the forward reaction
How does the molecular weight of carboxylic acids affect boiling point?
higher molecular weight = higher boiling point
- stronger IMF (LDF)
Explain methyl ethyl propyl naming?
ane to yl when the alkane is a substituent (remove 1 H from each)
methane = methyl (CH3)
ethane = ethyl
propane = propyl
What molecules exhibit the most rigid double bonds?
molecules without resonance structures
- electrons can’t delocalize
ex) ethene
Why can molecular mass (in amu) not be greater than molar mass (in grams)?
amu: mass of single atoms
1 amu = 1.66x10^-24 g
molar mass (g/mol) = weighted average of all possible molecular masses (single molecule, amu)
- some molecular masses will be above or below molar masses
different ways to measure the same thing: one for single molecule, the other for mole
- numerically the same
In adiabatic process, what is the change in internal energy?
U = -W
How do you find nodes and antinodes depending on the type of tube it is?
tube with both ends open
- ends are antinodes
- nodes = n
- antinodes = n + 1
- L = n lambda / 2
tube with one end opened
- closed end is node
- open end is antinode
- only odd harmonics
- 1 (1N, 1AN), 3 (2N, 2 AN), 5 (3N, 3 AN)
- L = n lambda / 4
tube with both ends closed
- both ends nodes
- nodes = n+1
- antinodes = n
- L = n lambda / 2
node = min
antinode = max
Which proton is the most acidic in a dicarboxylic acid?
the ones attached to the oxygen
What does adding salt to water do to the BP?
increase: requires greater average kinetic energy of the liquid to produce a vapor pressure equal to the external pressure
**BP = temp at which vapor pressure of solution = atmospheric pressure
What do boiling chips and vacuum distillation used for in distillations?
boiling chips: site for gas bubbles to form to prevent superheating of the solution
vacuum distillation: lowers the pressure inside the distillation flask, lowering the boiling point of the solution
A book rests on a table. The book experiences a gravitational force of mg due to Earth’s gravity. According to Newton’s third law, what is the corresponding reaction force:
the earth experiences a gravitational force of mg from the book
Fa on b = - Fb on a
What is true about diatomic nitrogen gas?
relatively inert and can be used in the lab to prevent unwanted side reactions
What bond angle between the central carbon of acetone and the other two carbons?
sp2 = 120 trigonal planar
How do the reduction potentials play into the electron transport chain?
electrons are passed from species with less positive reduction potentials to those with more positive reduction potentials
O2 is the final electron acceptor, so it must have the highest reduction potential
When delta G is negative, what is the value of K?
to be spontaneous, G = -RTln(K) has to be negative, so ln(K) must be positive, therefore K > 1 (favors products)
A ray of white light strikes the surface of water in a beaker. The index of refraction of the water is 1.33 and the angle of incidence is 30º. All of the following are true EXCEPT:
I. the angle of reflection is 30°.
II. the angle of refraction is 30°.
III. total internal reflection will result, depending on the critical angle.
II and III
angle of incidence always equals the angle of reflection (I)
light entering a more dense medium will be bent towards the normal (less than 30 degrees)
If delta H is negative, when is the reaction spontaneous?
at low temperatures when delta S is negative (entropy is decreasing)
Researchers have developed a novel enzyme that is able to catalyze the reduction of any partially oxidized nitrogen in the six-atom ring found in the structure of the adenine base pair. Which of the following changes might you expect to see in the base pairs of DNA as a consequence of the action of this enzyme?
Reduction of adenine creates the ability to form 3 or 4 instead of just two, so it would preferentially bond with cytosine (purine + pyrimidine)
What is the primary reason that ammonia is gaseous, but the ammonium ion is not?
NH4+ is charged: net positive charge allows for attraction to polar aqueous solvent, increasing BP
How do you count the number of pi-electrons in a molecule?
double bonds + lone pairs on atoms in hetero ring structures (nitrogen)
What changes the equilibrium constant?
temperature
What does an equilibrium constant close to 1 mean?
reaction does not favor either reactants or products heavily
Is the nitrogen of an amino group a better nucleophile than the oxygen of an alcohol when they are both attached to a benzene ring?
nitrogen is better nucleophile because it doesn’t hold its electron as tightly as oxygen
How does inserting a dielectric between the plates of a capacitor change the energy?
increases the capacitance
the only thing that affects voltage is the battery itself
Why can’t an electric field oriented vertically produce movement horizontally?
the equipotential lines do not have an energy gradient, so no horizontal movement happens
When do electrons in a circuit have the highest electrical potential energy?
when leaving the battery: none of the PE is lost as heat or converted into kinetic energy
In an extraction, what gets eluted first?
the most dense layer
- when specific gravity is greater than 1, that solvent with elute before the aqueous layer does
When a spring is max compressed by 30 cm with a spring constant of 100 N/m, how much kinetic energy does a 113g balloon launched by the spring have when it reaches max velocity?
at max velocity, there is 0 displacement (all PE into KE)
U = 0.5kx^2 = 4.5 J
What bonds have the smallest dipole moment?
- nonpolar covalent bonds (0)
- small difference in electronegativity (atoms close together)
- long bond lengths
What chemical properties do alkaline-earth metals have?
readily oxidized to +2, increasing reactivity with increasing atomic number, group two metals that form hydrogen gas when reacting with water
How are imines and enamines formed?
ketone + primary amine = imine
ketone + secondary amine = enamine
How does number of alkyl substituents affect carbocation and carbanion stability?
carbocation: more = better
- EDG
carbanion: more = worse
- more reactive
Ultrasonic shock wave devices may be used in medical settings to disrupt disease structures located deep in the body. The device user can control the frequency of emitted waveforms. The adjustment of waveform frequency:
enables high-amplitude resonance within diverse target tissues
- shock wave frequency approaches or is equal to the resonance frequency of the target structure
does not eliminate attenuation effects
Why does the tiled part of a floor in a room at room temperature feel colder than the carpeted part?
the thermal conductivity of the tile is higher than the thermal conductivity of the carpet, making heat transfer faster
- objects at the same temp with different thermal conductivity are perceived to be at different temperatures
When dealing with an energy conservation problem, what unit is mass in?
kg
J = kg * m^2 / s^2
Ketose vs. aldose and pyranose vs. furanose?
ketose: monosaccharide with ketone group on second carbon (fructose)
aldose: monosaccharide with an aldehyde group on first carbon (glucose)
furanose: 5 membered ring (4C, 1 O); fructose
pyranose: 6 membered ring (5C, 1O); glucose
Ketoses such as fructose are expected to give a positive Tollens test because:
ketoses tautomerize to aldose
Tollens test: identifies presence of aldehydes and hydroxyl ketones, and uses oxidizing agent [Ag(NH3)2]+ to oxidize to CA
distinguishes aldehydes from ketones
Which amino acids can exist in several diastereomeric forms?
isoleucine and threonine have side chains with a stereocenter
What is the difference between Mg(OH)2 and Ca(CO3)
Mg(OH)2 is a strong base and dissociates completely in water
CaCO3 is a weak base because (CO3)2- reacts with water to produce OH- in a limited extent
Relative to the angle of incidence, how will the angle of refraction change when a monochromatic ray of light enters a medium of greater refractive index?
theta decreases because light travels slower in the new medium
How does naming of alkenes work with E/Z priority rules?
Higher priority groups on opposite sides of double bond, the alkene is E
What does it mean if the displacement of something is less than the distance traveled?
there was a net force acting on the object
- did not travel in a straight line, was not in translational equilibrium, had a net force changing its velocity
Why does nitrogen have a higher first ionization energy than oxygen?
nitrogen has a stable, half-filled p-subshell
second ionization energy is always greater than the first
What types of waves should be used for maximum treatment in ultrasound?
waves that are in phase to get the greatest constructive interference
What describes sound waves?
longitudinal waves: energy propagates in the same direction as the particles move initially
What describes light waves?
transverse waves: energy propagates perpendicular to the direction the wave is traveling
When attached to cyclohexane why do bulky groups such as tert-butyl prefer the equatorial position?
minimizes steric hindrance between other side groups on cyclohexane
What information do you need to calculate percent composition of any compound?
molecular or empirical formula and the atomic mass of each component
What is the only thing that has to be true for a compound to be optically active?
the compound cannot be superimposed on its mirror image
How do you synthesize a lactone?
cyclic ester ring system forms by allowing a hydroxy-carboxylic acid to react intramolecularly
How is power related to kinetic energy?
P = W/t
W = change in kinetic energy
What happens in a base catalyzed aldol condensation?
two carbonyl groups (from ketones or aldehydes)
deprotonation of an alpha-carbon (carbon adjacent to carbonyl), forming enolate nucleophile
carbonyl adjacent to nucleophile remains intact; carbonyl receiving attack is reduced to hydroxyl which is eliminated
same molecule results in cyclization
When does total internal reflection occur?
incident angle of light at the boundary between two materials is greater than the critical angle
- light must travel from more dense to less dense medium (higher to lower refractive index)
What kind of lens should be used when the sensor is 1 cm behind the lens?
convex lens with focal length of 1 cm
- convex = converging lens
What is an acylation reaction?
acyl group R-C=O is added to a molecule
- C-C bond forms
- AlCl3 (Lewis acid catalyst)
What is a lactam?
cyclic amide formed from amine + carboxylic acid, eliminating water
What happens to the stereochemistry of hydrolysis products?
stereochemistry is retained in all carbon atoms
How do you determine the number of soap molecules generated in hydrolysis of a phospholipid?
of ester linkages
How does mass spec work?
1) sample is ionized and can break apart into fragments
2) ions are accelerated toward the magnet
3) ions are deflected according to mass
4) fragmented ions are detected + plot of ion mass abundance vs m/z is recorded
When a sound is transmitted from source to detector, non-conservative forces cause decreases in what properties?
intensity (amplitude decreases as energy is lost to attenuation), loudness/sound level
pitch = frequency; is not affected by non-conservative forces
What remains constant as light passes through media?
frequency
A blood sample undergoes a temperature change such that all of its thermal energy is converted to potential energy. What describes its final state?
absolute zero: all atomic movement ceases (no kinetic energy)
What is the sign of work when a teacher lowers a book from 1.8m to 1 m?
negative: U = mgh, where h is change in height (f-i)
book moved in the direction opposite of the force applied by the teacher, work is done ON the system
What solvent promotes preferential use of I- as a nucleophile vs F- as one?
polar protic solvents: hydrogen bond with anions
- F- is smaller and more highly charged, so binding is stronger
- I- is larger and remains for nucleophilic in polar protic
What wavelength is UV light?
100-400 nm
shorter than visible light
Hot coffee begins to cool while the cup becomes warmer. Each of the following is an accurate description of this process EXCEPT:
net flow of the coffee is reversible: heat flows spontaneously from areas of high kinetic energy to areas of low kinetic energy until equilibrium is reached; once reached, there is no net movement of energy = IRREVERSIBLE
What functional group transformation occurs in the product of the reaction catalyzed by NADH: quinone oxidoreductase?
RC(=O)R –> RCH(OH)R
- two electron reduction of a ketone to an alcohol
The reaction between NADH and ubiquinone is exergonic, but the reaction, when catalyzed, does not generate much heat in vivo. What factor accounts for this difference?
it is coupled to the movement of charged particles against a concentration gradient
- redox reaction and movement of ion against gradient makes the overall process less exothermic
Which of the following substances is polar?
NF3
CCl4
CO2
Li2
NF3
- CO2 and Li2 is linear
- CCl4 is tetrahedral
How do you convert cm^3 to L?
move decimal 3 places to the left (10^-3)
What is necessary to produce fluorescence emission?
the absorbed radiation wavelength has to be shorter than the emitted wavelength because the energy of the radiation has to be greater than the emitted energy to produce an energy difference
E = hc / lambda
A major obstacle to obtaining useful energy from a nuclear fusion reactor is containment of the fuel at the very high temperatures required for fusion. The reason such high temperatures are required is to:
high temperatures provide nuclei with enough kinetic energy to overcome electrostatic repulsion, allowing them to get close enough for the strong nuclear force (proton + neutron) to bind them together
Enantiomers can exhibit a difference in which chemical or physical property?
smell: interact differently with chiral odor receptors
they have the same chemical and physical properties
- differ in 3D arrangement
What is the difference between pyrrole, imidazole, and indole?
pyrrole: 5 membered ring with one nitrogen
imidazole: 5 membered rings with 2 nitrogens
- histidine
indole: 6 membered ring + 5 membered ring with one N
- tryptophan
What is the Ki by definition? How do you find it on a sigmoidal graph of enzyme activity?
Ki = Vmax / 2, so the inflection point (50% activity)
What is bond energy?
amount of energy needed to break a chemical bond between atoms in a molecule
According to the autoionization equation of water, what happens to the pH when temperature increases (+deltaH)?
decreases: increase in H+
- water remains neutral
Positive point charge (4C) is released from rest in uniform electric field of 15 N/C. How much work is done by the electric field moving the point charge 5 cm?
Fe = qE
W = F*d
W = qEd = (4150.05m) = 3 J
When ammonia reacts with H+ to form ammonium, what is the N-H bond that is formed?
coordinate covalent (N contributes both e-) and polar covalent
What reactants promote esterification?
acid: protonates the carbonyl oxygen, making it more electrophilic
What is released during a condensation reaction?
water
What is the intermediate step of the reduction of nonanoic acid by LAH?
LAH reduces CA to aldehydes then to alcohol
nonanal
Saponification of a triglyceride leads to the formation of:
forms glycerol + soap (carboxylate ion/K+)
carboxylic acid salt and water
What is the difference between UV and IR spectroscopy?
UV: movement of electrons; better at determining conjugation of molecules
- unhybridized p-orbitals shift absorption spectrum to higher max wavelength
IR: molecular vibration; better at precise identification of molecules
- vibration of bond must change the bond dipole moment
- bonds have characteristic absorption frequencies, allowing FUNCTIONAL GROUPS to be identified
**BOTH: require absorbance of energy by bonds
Which side of the heart pumps greater volume of blood?
both sides pump equal volumes of blood in healthy individuals
- closed system; equal volume of fluid
What is the intermediate in the reduction of a carboxylic acid to an alcohol by LiAlH4?
aldehyde
What is the difference between traveling, standing, and longitudinal waves?
traveling: propagates through medium; varying levels of displacement along path
- longitudinal or transverse
- ocean waves, sound waves in air
standing: two waves of same frequency and amplitude travel in opposite directions and interfere
- nodes + antinodes; vibrations on guitar string
longitudinal: particle displacement is parallel to direction of wave propagation
- sound waves in air
As the waves from an instrument interact with air, which of the following changes occur?
they transform from standing waves to traveling waves
What is intensity of sound?
I = P/A
- P = power
- A = area
Using IR, which of the following would provide the best evidence that a reaction had successfully converted benzyl alcohol to benzoic acid?
addition of sharp peak at 1680-1710 cm-1
carbonyl group added, retains OH group
One method to concentrate sensitive aqueous suspensions is to place samples in sealed chamber with several vials of saturated brine. In the process, how does the vapor pressure above a sample initially compare to the vapor pressure above the brine?
the vapor pressure above the sample is greater
- when solute is added to solvent, the vapor pressure of the solvent is lower than the vapor pressure above the pure solvent
- water will evaporate from samples and condense in the brine
A patient’s blood pH depends on
1) concentration of bicarbonate in blood
2) concentration of CO2 in blood
3) temperature of blood
all three: equilibrium constants are temperature dependent
A car drives at a constant speed toward the wall of a canyon while sounding its horn at a particular frequency. The sound waves from the horn reflect from the canyon wall and return to the car as it continues to move towards the wall. What happens to the period of the reflected waves observed by the driver of the car?
decreases because the driver moves in the opposite direction from the waves
- source moves closer to the observer, the measured time between emitted wave crests is reduced
What is viscosity?
measure of the internal friction of a fluid
- kinetic energy in fluid flows is dissipated by the viscous shear force acting between different layers of the fluid flow
Why are boiling chips and stir bars necessary in the distillations?
boiling chips: allow bubble formation at nucleation sites, overcoming the surface tension so even heating occurs
no chips + stir bar cause eruption of large bubbles + superheating
Difference between simple, fractional, and vacuum distillation.
simple: <150 and >25 apart
fractional: <150 and <25
vacuum: >150
In gas-liquid chromatography, what elutes first?
most volatile (lowest BP) will vaporize first and move the column quickly = shortest retention time
How does branching affect boiling point?
branching decreases surface area, so BP decreases
- less LDF
What are the assumptions made by the Bohr model of the atom?
1) electrons move around the nucleus in fixed circular orbits
2) electrons farther from the nucleus have higher energy than electrons closer to the nucleus
3) energy is absorbed by an electron moving from lower to higher orbit and energy is emitted by an electron going from higher to lower orbit
A chemist has sodium octanoate in a solution of 50:50 ether and water. After HCl is added, she separates the layers. How do you purify the organic product?
ether layer should be evaporated to collect the organic product
- HCl forms octanoic acid, making it more nonpolar + moving it into the ether layer
- NaCl forms and stays in the aqueous layer, making octanoic acid less soluble
long chain makes it nonpolar
What does the Heisenberg uncertainty principle state?
impossible to simultaneously predict a particle’s position and momentum
Emission vs. absorption spectrum
emission: electrons fall to lower energy levels, releasing light at specific wavelengths = bright lines
absorption: electrons absorb energy and jump to higher energy levels, taking in light at specific wavelengths = dark lines
same wavelengths involved, but one adds light one removes it
Which of the mixtures will not show optical activity?
(I) (2R, 3S)-2,3-dichlorobutane
(II) (2R, 3S)-2,3-dichlorobutane and (2S, 3R)-2,3-dichlorobutane
(III) (2R, 3R)-2,3-dichlorobutane
(IV) (2R, 3R)-2,3-dichlorobutane and (2S, 3S)-2,3-dichlorobutane
I, II, IV
I: (2R, 3S) and (2S, 3R) have an internal plane of symmetry and do not have optical activity
II + IV: cancel out optical activity
III: non-superimposable mirror image
What makes a conjugate base of an alcohol reactive?
nothing to stabilize the negative charge on the oxygen
The transducer which determines the level of air in the tank reads 0 when the tank valve is open and the air is not flowing in or out of the tank at sea level. The air meter acts by measuring:
gauge pressure: air in the tank is in equilibrium with atmospheric air and therefore cannot measure atmospheric or absolute pressure
- measuring the difference between the pressure inside the tank and the atmospheric pressure outside the tank
While lighter noble gases such as helium and neon do not form covalent bonds, heavier noble gases can form covalent bonds with certain elements. Which of the following elements would likely form covalent bonds with Xenon?
O+F: difference in electronegativity between Xe and O/F would likely be the right magnitude to form a covalent bond
What are the best buffers in the body?
buffers with pKa close to physiologic pH of 7.4
Which of the methods would be MOST effective in making methyl ethanoate, a weak electrophile, more electrophilic?
adding strong acid in solvent
- protonates oxygen in ester
Which of the following are true of a reaction between aldehydes and ketones with HCN?
I) enamine can be formed
II) cyanohydrin can be formed
III) nitrogen of HCN attacks the carbonyl carbon
II) cyanohydrins always form
** III) carbon attacks
What is standard pressure in all the different units?
1 atm = 760 mmHg = 101 kPa
Why is the hemoglobin curve sigmoidal?
homotropic regulation by oxygen occurs: affinity for oxygen increases as O2 binds (positive cooperativity)
- homotropic = substrate of an enzyme also acts as allosteric regulator
Fluid pressure changes with depth are assumed to be linear. What best explains why this does not hold true for changes in atmospheric pressure?
the volume of a mass of air is not constant: gases are compressible, so volume is affected by changes in pressure
- air gets less dense as you go higher in the atmosphere
- hydrostatic pressure for liquids is linear because density remains constant as depth changes
What approximates the pKa of phenolpthalein when doing a strong base + acetic acid titration?
9.3: color change near desired pH for weak acid + strong base
When 0.2 moles of hydrofluoric acid are added to 100 mL of water, the resulting solution has a pH equal to 4. What is the percent dissociation of HF?
[H+] = 10 ^ -4
(0.2 moles/0.1 L) = 2 M = [HF]
% dissociation = [H+] / [HF] = 0.5 x 10^-4
An object with a mass of 10 kg is rolled down a frictionless ramp from a height of three meters. If a factory worker at the bottom of the ramp slows the object until it comes to a stop, how much work must the factory worker have done?
conservation of energy + work-energy theorem
PE = KEf
PE = mgh = (10103) = 300 J
W = KEf = PE = 300 J
Given that 93% of 145Pm decays into 145Nd in 100 minutes, if a hospital requires at least 250g of 145Nd to complete a standard cardiac image, how long will it be before it must replace a 2000g sample?
1) 93% of 145Nd decay in 100 minutes –> only 7% remains
2) hospital needs at least 250g from an initial 2000g
- 250/2000 = 1/8 = 12.5%
3) after 100 minutes, only 7% remains (less than 12.5%), less than 100 minutes ~ 75 minutes
pKas of indicators you need to know.
methyl orange: 3-4
bromothymol blue: 6-7.5
phenolphthalein: 8-10
In the electron transport chain, what is reduced but never oxidized? what is oxidized?
reduced: oxygen
oxidized: Ubiquinone, NADH, ADP, FADH2
When a dissolved in an aqueous solution, which of the following metal salts will most likely yield a colorless solution?
Zn(NO3)2
- transition metals are often colored because they have unfilled d-orbitals
- Zn2+ orbitals are filled
Two identical gurneys are placed side-by-side on a ramp. Gurney 1 has a dummy placed on it to give it a total mass of 240 kg, while Gurney 2 is loaded with a dummy that makes its mass 200 kg overall. If the ramp has a coefficient of friction of μs, and its angle of incline is very slowly increased, which gurney will begin to slide down the ramp first?
Both slide down at the same angle of incline
- Fs = uN, Fg = mgsin(theta)
- gurney begins to slide when mgsin(theta) > umgcos(theta) = ma, so mass cancels out
What is the approximate pH of a saturated aqueous solution of hydrochloric acid whose concentration is 10.2 M?
-1
-log(10) = -1
Assuming a 95% yield for each coupling step, what would be the final yield for synthesizing a 10 amino-acid length peptide?
(0.95)^9 = 0.63
or max loss every time is 5% * 9 = 45% max loss, so something a little bigger
How do you convert chair conformation to Haworth?
pretend like you’re looking top down: whatever is coming up at you is up
What is the first peak to be observed in gas-liquid chromatography?
the least polar, most volatile compound elutes first because it spends less time interacting with the stationary phase
Acetic acid and ethanol react to form an ester. To determine which reactant loses the -OH group, which isotopic substitution would be most useful?
replace the hydroxyl oxygen of ethanol with radioactive oxygen – 100% of the oxygen in ethanol will be in the ester
acetic acid supplies OH lost to form water
What does the negative sign of lens strength indicate?
diverging lens
- the eye is a converging lens, so strength is positive
What is the intensity of radiation emitted directly proportional to?
the number of photons emitted
I = E / A * t
What is work and power’s unit of time in?
seconds
Watt : J/s
Describe the formation of disulfide bonds.
two cysteine residues lose hydrogen atoms, becoming oxidized and forming a covalent bond
What amino acids play an important role in cell adhesion?
Aspartic acid (D), arginine (R)
- specifically RGD sequence
What is the difference between kinase and phosphorylase?
kinase transfer phosphate group from ATP to a substrate
- hexokinase, PFK-1
phosphorylase adds inorganic phosphate to a substrate
- glycogenolysis
When a strip of Zn is placed in 0.1 M HCl, H₂(g) evolves. If a strip of Al is placed in 0.1 M HCl, does H₂(g) evolve?
YES
Al is oxidized: Al => 2Al(3+) + 6 e-
H+ is reduced: 6H+ + 6e- => 3H2
Aluminum is more reactive than H
**H gas would not form if the metal is less reactive than H = higher reduction potential > 0 V **
How do you determine what is oxidized and what is reduced in REDOX? When is it spontaneous?
smaller Ered gets oxidized and sign flips
Ecell = Ecat - Ean
+ means it’s spontaneous
In diabetic ketoacidosis, there are excess protons in the blood. In someone with rapid-onset DKA, what happens to the concentration of bicarbonate ions in the blood?
decreases: excess acid is buffered through binding to bicarbonate, decreasing concentration
How do you determine the distance between two adjacent nuclei (NaCl)?
sum of their ionic radii
Why does beta-carotene have orange-red color?
small energy distance between HOMO and LUMO
as the number of conjugated double bonds increases (unhybridized p-orbitals, more e delocalization), allowing smaller energies of light to be absorbed to excite electrons = larger wavelength
What is the difference between glutamic acid and glutamate?
glutamate = anionic form, so the OH of the carboxylic acid is deprotonated
Why would experiment A yield a lower relative retardation factor than experiment B on caffeine?
experiment A was performed at a lower temperature
- molecules have less thermal energy
relative means time spend running the experiment doesn’t matter
In anion-exchange chromatography, what elutes out first?
the most positively charged ion elutes first
the most negatively charged ion elutes last because it is bound to the positively charged stationary phase
A scientist repeats the HPLC experiment in the passage (4 amino acids, glycine/valine/cysteine/aspartic acid), using amino acids whose enantiomers have not been separated. How many peaks would the chromatogram have?
4: there are no chiral reagents in HPLC, so enantiomers are not separated
- plane-polarized light or chiral reagents would separate
How does the waste and the product of recrystallization differ in solubility?
waste product is most soluble so that it is removed when it cools in the solvent
product becomes less soluble as lower temps to recrystallize
What is the difference between aldol formation and retro-aldol reaction?
aldol formation: enolate functions as nucleophile; begins with deprotonation of alpha hydrogen
retro-aldol: enolate is a LG; begins with deprotonation of hydroxyl group
BOTH: reversible (occur simultaneously in solution), strong base and high temperature
If the applied electric field points from anode to cathode, what direction will a negatively charged protein travel in the electric field?
toward the anode: negative charges move against electric field lines
(125) I-glucagon is formed by reacting glucagon with (125) I2. The products are separated with TLC. If a weaker eluent that barely interacts with the stationary phase and thus moves more slowly, how does this affect the movement of each sample?
both (125)-I glucagon and native glucagon would become less mobile
- the eluent carries both
How many electrons have ml in the n = 4 shell?
8 electrons
- n = 4
- l = 3, 2, 1, 0
- ml = -3, 2, 1, 0, 1, 2, 3
go through each l, then determine ml, each has 2 electrons
