Practice Exam 1: Chem
Terms in this set (77)
Thin Layer Chromatography
- used to identify compounds, determining purity, etc.
- measure distance spots traveled from the distance between start to solvent front
- solid, or liquid on a solid
- usually silica gel (silica attached to OH)
- very polar because OH groups can form H bonds and van der Waals and dipole-duple attractions
- can also use Aluminum Oxide
- liquid or gas
- flows through stationary phase and carries components of mixture with it
- what does a high Rf value mean? a low Rf value?
- distance travelled by component/distant travelled by solvent
- high Rf: non polar (interacts less with stationary phase)
- low Rf: polar (interacts more with stationary phase via H bonding or Van Der Waals)
In the chromatography of the reaction mixture, water absorbed on cellulose functions as the stationary phase. What's the principle factor determining the migration of individual components in the sample?
a. Hydrogen bonding
b. Solute concentration
c. Stationary phase concentration
d. Thickness of paper
A: amount of hydrogen bonding to stationary phase determines rate of migration
What type of functional group is formed when an aspartic acid reacts with another amino group to form a peptide bond?
a. amine group
b. aldehyde group
c. amide group
d. carboxyl group
D: amide group
Gas Liquid Chromatography
- mobile phase is a gas (helium)
- stationary phase is high boiling point liquid adsorbed onto a solid
- how fast the compound travels will depend on how much of its time is spent moving with the gas as opposed to being attached to the liquid
- compound might condense on the stationary phase, dissolve in liquid on surface of stationary phase, or remain in gas phase
In gas layer chromatography, what does the area under the peaks represent?
- measures relative quantity of compounds present (usually only for mixtures of similar compounds)
- proportional to the amount of each compound that's passed the detector
What type of compounds will migrate the fastest in gas chromatography?
- low molecular weight and weak intermolecular forces will migrate the fastest and represent the first peak in the gas chromatograph
What does the position of a peak from gas chromatography represent?
- measures retention time and is a function of the structure of the compound
- converts individual molecules to ions so they can be manipulated by electric and magnetic field
- small sample is ionized to cations by loss of electrons
- ions are sorted and separated according to mass and charge
- separated ions are measured
What do the bars from mass spectrometry represent? What do the lengths mean?
- bars: an ion with a specific mass-t-charge ratio (m/z)
- length: relative abundance of the ion
- most intense ion
- two steps: leaving group leaves first, then nucleophile attacks carbocation
- unimolecular (subraye only)
- depends on carbocation stability: tertiary compounds are more reactive because they form more stable carbocations
- make weak nucleophiles
- mix of retention and inversion stereochemistry
- occurs in one step: nucleophile and substrate are both involved in the rate determining step
- bimolecular (substrate and nucleophile)
- steric hindrance: primary compounds more likely to be deprotonated because less hindrance
- strong nucleophiles
- polar parotid (DMSO)
- inverted stereochemistry
Acetic acid (CH3COOH) and ethanol (CH3CH2OH) react to form an ester product (CH3COOCH2CH3) and water. In determining which reacting loses the OH group, which of the following isotopic substitutions would be most useful?
a. replace the acidic H of acetic acid with D
b. replace the alcoholic H with ethanol with D
c. replace the carbonyl oxygen of acetic acid with O18
d. replace the hydroxyl oxygen of ethanol with O18
D: labeling a group that doesn't exchange with other groups present prior to reaction
- will give information about true identity of the group
A person whose eye has a lens-to-retina distance of 2 cm can only clearly see objects that's closer than 1 m away. what's the strength S of the person's eye lens? (1/0 + 1/I = S)?
D = 1/f = (1/1m) + (1/0.02)
D = 51D
Which statement correctly describes how enzymes affect chemical reactions? Stabilization of:
a. substrate changes free energy of the reaction
b. transition state changes free energy of reaction
c. substrate changes activation energy of reaction
d. transition state changes activation energy of the reaction
- stabilization of transition state, not substrate, provides binding energy that's used to lower the activation energy
Which will DECREASE the percentage ionization of 1.0M acetic acid, CH3CO2H(aq)?
a. chlorinating the CH3 group
b. diluting the solution
c. adding concentrated HCl(aq)
d. adding drop of basic indicator
- HCl is a strong acid that'll increase the amount of H+ in a solution, which will decrease the percentage of CH3CO2H that ionizes
- use Le Chatlier's principle: adding a strong acid to a solution of weak acid will decrease the amount of ionization of the weak acid
- amount of weak acid that exists as ions at a particular concentration
- [H+]/[HA] X 100%
- acid dissociation constant
Index of Refraction
n = c/v
c = 3X10^8
- ratio of speed of light in vacuum to speed of light in the medium
Intensity of the radiation emitted by the oxygen sensor is directly proportional to
a. propagation speed of radiation
b. wavelength of the radiation
c. polarization of photons emitted
d. number of photons emitted
- energy of electromagnetic radiation is directly proportional the number of photons
- intensity of electromagnetic radiation is energy emitted per unit time
- intensity is directly proportional to number of photons emitted
n1/n2 = sin2/sin1 OR
n1sin1 = n2sin2
Intensity of Electromagnetic Radiation
- energy emitted per unit time
- directly proportional to number of photons emitted
- more photons emitted = more intense radiation
How to calculate speed of a wave
velocity (v) = f/lamda
- higher wavelength= slower speed
What is the energy of photons emitted by the LED at a frequency of 610 THz? h = 6.6 X 10^-34
use Planck's equation: E = hv
- h = 6.6X10^-34
- v = frequency
- E = (6.6X10^-34)(610X10^12)
- E = 4 X 10^-19
The half life of 15O is T1/2 = 2min. What fraction of 15O decays in 10 min?
- 10 minutes = 5 half lives
- (1/2)^5 = 1/32 (the amount of sample left after 10 minutes)
- 31/32 of original sample decayed
Force (N) X Distance (m) = Work (in Joules)
- hold atoms together WITHIN a molecule
- metallic bonds (strongest)
- ionic bonds
- polar covalent bond
- non polar covalent bond (weakest)
- forces that exist BETWEEN molecules
- hydrogen bonding
- van Der Waals
A compound was designed to exhibit pH-dependent self-assembly. What features of the molecule are responsible for pH dependence of aggregation?
a. thiol side chains that can hydrogen bond
b. long alkyl tail that exhibits predominantly London forces
c. side chains whose net charge responds to pH
d. covalent linkages that reversibly hydrolyze
C: molecule must contain acidic side chains that were deprotonated and negatively charged at high pH
- inhibited aggregation to to electrostatics
- at low pH, these groups are neutral and allowed to aggregate
Why is the velocity of blood flow slower in capillaries than in arteries?
a. capillary walls are more elastic than arterial walls
b. capillaries have less resistance to blood flow than arteries
c. total cross sectional area of capillaries exceeds that of arteries
d. blood pressure is higher in capillaries than in arteries
- high number of capillaries in body means that total cross-sectional area of these vessels is larger than any other vessel type in circulatory system
- large cross-sectional area causes velocity of blood to decrease
Which of the following types of orbitals of the central atom are involved in bonding in octahedral compounds?
- octahedral: six atoms are symmetrically arranged around central atom; has eight faces
- no lone pairs
- central atom requires hybridization of six atomic orbitals, d2sp3
- Ex: (Mo(CO)6); [Co(NH3)5]3+
How many electron pairs and hybrid orbitals for linear geometry?
- 2 electron pairs
How many electron pairs and hybrid orbitals for trigonal planar geometry?
- 3 electron pairs
How many electron pairs and hybrid orbitals for tetrahedral geometry?
- 4 electron pairs
How many electron pairs and hybrid orbitals for trigonal bipyramidal geometry?
- 5 electron pairs
How many electron pairs and hybrid orbitals for octahedral geometry?
- 6 electron pairs
The term "ideal gas" refers to a gas for which certain assumptions have been made. Which is an assumption?
a. PV = nRT2 is strictly obeyed
b. Intermolecular molecular forces are infinitely large
c. Individual molecular volume and intermolecular forces are negligible
d. one gram occupies a volume of 22.4L at 25C and one atmosphere pressure
C: ideal gas is composed of particles that have negligible volume and don't exert intermolecular forces
Ideal Gas Law
- don't attract or repel each other
- take up no volume
- PV = nRT
- P (atm), V (L), T (K), R = 8.31, n (mol)
Proportions of Ideal Gas Law
P1V1/T1 = P2V2/T2
The production of a variety of opsins functions to...
a. increase sensitivity to low light
b. enable detection of different colors
c. ensure fast recovery of 11-cis-retinal after exposure
d. increase refractive index of the eye lens
B: wavelength of light absorbed by a molecule depends on its structure
- production of variety of structurally related opsin funcions to enable detection of different colors
- light-sensitive proteins found in photoreceptor cells of retina
- enables detection of different colors
- closely packed cones in the eye
- located center of the macula of the retina
- sensitivity to fine details
- no rods so not sensitive to dim lighting
How do your eyes function to observe dim light?
- look to the periphery of the eyes where density of rods is greater so dim objects are more visible
Rods vs. Cones
Rods: vision at low light; contain light sensitive purple rhodopsin; more numerous than cone cells; located in periphery; don't give color vision
Cones: cone-shaped; required for bright, day light vision; contain violet iodopsin; located in center of retina (red, blue, green)
What does lipase do?
- cleave fatty acids
What type of bond is formed by glycogen synthase upon release of UDP?
a. a-1, 4-glycosidic bond
b. a-1, 6-glycosidic bond
c. b-1, 4-glycosidic bond
d. b-1, 6-glycosidic bond
A: a-1, 4-glycosidic bond formed by glycogen synthase
In addition to glucose, what other monosaccharide is part of the UDP-glucose structure?
- UDP contains UDP contains uridine, ribose, and glucose
- electrophoreses used to separate proteins based on molecular weight, based on differential rates of migration through a gel
- SDS coats protein with uniform negative charge and SDS-treated proteins will move toward positive anode at different rates depending on molecular weight
- neutron converted to proton so process creates an electron and an electron anti-neutrino
- 40/19K -> 40/20Ca + -e
- electron is ejected from nucleus so charge on nucleus increases by 1
- proton converted to neutron and process creates positron and electron neutron
- aka positron emission
- 40/19K -> 40/18Ar + (+e)
- electrons or positrons (electrons with positive charge)
- pair of protons bound to pair of neutrons
What type of decay is this?
Ra -> Rn + He2+
- alpha decay
- radium (88) breaks up into Helium nucleus and daughter nucleus, Radon (86)
- nucleus emits radiation without changing its composition
- 60/27Co -> 60/27Co + gamma
Lafora bodies are sparsely branched, insoluble glycogen-like polymers. Compared to normal glycogen, the amount of what type of bond is decreased in Lafora bodies?
c. a-1, 4-glycosidic bonds
d. a-1, 6-glycosidic bonds
- Lafora bodies don't have branching bodies so you woudn't see as much alpha-1, 6-glycosidic bonds, which is where branching occurs in glycogen
Each shows the dissociation of acid in water. Which occurs to the LEAST extent?
a. HCl + H20 -> H3O+ + Cl-
b. HPO42- + H2O -> H3O+ + PO43-
c. H2SO4 + H2O -> H3O+ + HSO4-
d. H3PO4 + H2O -> H3O+ =
HPO42- is highly negative so dissociation will occur to the least extent
- strong acids will dissociate the most (Hal, H3PO4)
Magnification for lenses
hi/h0 = -di/do = M
Gamma decay occurs when a nucleus emits...
A: gamma decay means the emission of photons by the nucleus, but nucleus doesn't change
When 0.1M H2SO4 solution is added to pulverized blackboard chalk, the following takes place: CaCO3 + H2SO4 -> CaSO4 + CO2 + H2O.
At 25C, the reaction is spontaneous and has...
a. negative G and positive S
- negative G and negative S
c. positive G and negative S
d. positive G and positive S
A: negative G and positive S
- spontaneous reactions must have -G and positive S
CO2 + H2O -> H2CO3 -< HCO3- + H+
Which of the following most likely will occur if a homogenous catalyst CANNOT be separated from products at the end of a reaction?
a. catalyst will become heterogenous
b. products will be contaminated
c. the reaction will not occur
d. reaction rate will speed up
B: products will be contaminated
- if a homogenous catalyst can't be separated from the products at the end of a reaction, then the products will be contaminated with the catalyst
How will the rate of a catalyzed reaction be affected if the solid catalyst is finely ground before it's added to the reaction mixture?
a. rate will be faster because greater mass of catalyst will be present
b. rate will be faster because greater surface area of catalyst will be exposed
c. rate will be slower because fine catalyst particles will interfere with product formation
d. rate will remain the same because the mass of catalyst will be the same
B: grinding a heterogenous catalyst increases the amount of catalyst available to the reaction and increases its rate
How would you increase current when voltage is fixed?
V = IR
- if I needs to be increased, must decrease resistance
When a strip of Zn is placed in a beaker containing 0.1M HCl, H2 evolves. If a strip of Al is placed in a beaker containing 0.1M HCl, does H2 evolve?
a. Yes, Al is reduced and H+ is oxidized
b. Yes, Al is oxidized and H+ reduced
c. No, Al is reduced and Cl- is oxidized
d. No, Al is oxidized and H2O is produced
- When Al is mixed with Zn2+, it's assumed that Al(s) is more susceptible to oxidation than Zn(s)
For a reaction to be spontaneous, what must E be?
- E must be positive and G must be negative
BaCrO4(s) -> Ba2+ + CrO42- exists in a saturated aqueous solution of BaCrO4. Dissolution of Na2CrO4 in a saturated aqueous BaCrO4 solution would:
a. have no effect on position of this equilibrium
b. shift equilibrium left
c. shift equilibrium right
d. shift equilibrium first right than left
B: dissolution of Na2CrO4 would introduce CrO42-, which would reduce the solubility of BaCrO4 due to common ion effect
Common Ion Effect
- - reduction in solubility of an ionic precipitate when a soluble compound containing one of the ions of the precipitate is added to the solu
When NaCl and KCl are dissolved in the same solution, which is the common ion?
Cl- ions are common to both salts
Which CANNOT be used to express power?
- Power is measured in Watts (J/s = ftXlb/s = kgXm2/s3
- unified atomic mass
- standard unit of mass that quantifies mass or an atomic or molecular scale
- equal to 1 g/mol
Standard Reduction Potential
- E must be positive for a spontaneous reaction
- subtract "E" values from each half reaction to find total E
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