CHEM/PHYS SECTIONED EXAM #7 NS

cos60°

0.5

cos45°

0.7

cos30°

0.87

What can cause TLC streaking?

1. Overloading the spot with sample 2. Using a sample that is too concentrated 3. If a TLC sample is impure, its multiple components will travel different distances along the plate

Refractive myopia is corrected by the use of diverging lens of appropriate optical power. When compared to a healthy eye, a myopic, but otherwise normal, eye's near point is mostly: A: smaller than that of a healthy eye B: larger than that of a healthy eye C: equal to that of a healthy eye D: dependent upon the nature of the light incident on either eye

A: smaller than that of a healthy eye a diverging lens DECREASES the optical power of an instrument by INCREASING its effective focal length. such a lens is corrective for the myopic eye, where its optical power exceeds that required for the axial length of the eye. as a result of this increased optical power, the myopic near point should be SMALLER than that in a healthy eye. this is due to the myopic eye's capacity to focus light of great divergence on the retina

Which is a stronger base, methyl acetate or amines?

Amines methyl acetate is a weaker base

Which of the following has the SMALLEST atomic/ionic radius? A: K+ B: Ca2+ C: Ar D: Cl-

B: Ca2+ -all 4 choices are isoelectronic; they have the exact same configuration & number of electrons. the main difference btwn them is the # of protons in their nuclei. Protons, which are positively charged, attract electrons. Ca has the HIGHEST atomic # (ie, most protons) so its electrons will be pulled closest to the nucleus -anions usually have the largest atomic radius -atomic radius DECREASES from left to right

In order for the image produced by the eyepiece to be ERECT, where must the image focused by the objective lens fall? A: btwn the objective lens and the focal point of the eyepiece B: at a distance from the eyepiece smaller than the eyepiece's focal length C: at a distance from the objective less than the objective's distance from the sample D: at the focal point of the objective lens

B: at a distance from the eyepiece smaller than the eyepiece's focal length this question implies that the image created by the eyepiece is NOT inverted (UPRIGHT). in other words, the image is UPRIGHT & VIRTUAL ( think "MUV" - magnified, upright , virtual for an object distance IN FRONT of the focal point).

After reacting 1-phenylethylamine with (R,R)-(+)-tartaric acid, which of the following best explains what causes the two ionic forms to have different physical properties? A: the ionic forms are enatiomers B the ionic forms are diasteromers C: the ionic forms are meso compounds D: the ionic forms are achiral

B: the ionic forms are diasterormers the two ionic products are diasteromers; this is bc the two ionic forms are NOT mirror images of each other and will have different physical properties, such as solubility

An organic synthesist seeks to identify an efficient stereoselective reagent with which to produce an enatiomer of the biologically active sphingosine molecule pictured in the passage. Which of the following would be the most logical choice to try? A: tert-butoxide B: DMSO C: diethyl tartrate D: propanol

C: Diethyl tartarate The question replies on prior knowledge of stereoselective reagent; A,B,D: all are achiral making C the only possible choice

Which of the following hydrogen bonds has the lowest bond dissociation enthalpy? A: F-H ---F B: F-H---O C:O-H---O D: N-H---O

D:; this is asking for the weakest bond Since N is LESS electronegative than F and O, it will have the weaker bond

What does rate of effusion depend on?

Depends on root-mean square speed -smaller molecular weight means the higher the rate of effusion

In an isolated system, entropy is maximized when: I: the system is at equilibrium II: the system is far from equilibrium III: the system is unable to perform work

I & III only Recall that at equilibrium, deltaG=0. With NO free energy change, the system is unable to perform work. At equilibrium, there are NO energy gradients within the isolated system, so energy is maximally dispersed, resulting in maximal entropy II: a system far from equilibrium contains large gradients which are able to perform work. the formation of large energy gradients requires localization or concentration of enegry, which results in DECREASED entropy

The maximum kinetic energy that corresponds to the energy of the incident photon:

KEmax = E(incident)-E(work function) or KEmax= hf(incident) - hf(work function)

noncompettive inhibition

Km remains unchanged; Vmax DECREASES -an inhibitor binds to an external site on the substrate, altering the enzymes conformation

What are the units for k in the following rate law: rate = k [A]^2[B]? Note that the concentration unit is mol/L

L^2mol^-2s-1 -reaction rates are measured in M/s whereas, concentration is M/l (mol/L) M/s = mol/L x s

Which AA corresponds to K?

Lysine

How to calculate partial pressure (Po2):

Po2= mole fraction of O2 X Ptotal =[(mole O2/total mol)] X Ptotal

How much does the rate of effusion of dichloromethane at 200K change when the temperature is changed to 800k? Assume all other conditions are identical.

Rate of effusion depends on the root-meant square. Since the identity of the gas is CONSTANT, the only factor changing is T. Therefore, for two samples of the same gas with identical pressures but different temps: rate1/rate2= sqrt (T1/T2) =sqrt (800/200) =sqrt (4) = 2 This means that the new rate is TWICE as large or 100% larger than the original rate.

Why do real gases deviate from ideal gases in high pressure?

as the pressure increases, the particles are pushed closer and closer together. as the condensation pressure for a given temp is approached, intermolecular attraction forces become more and more significant, until the gas condenses into a liquid. -at moderately high pressures (few hundred atms) a gas's volume is LESS than would be predicted by the ideal gas law due to intermolecular attraction

[Mo(CO)6] has a bonding hybridization of?

d2sp3 Here the central molybdenum atom is bound to 6 substituents. The number of substituents around the atom is = to the # of orbitals that hybridize; here, there are two 4d, one 5s and three 5p atomic orbitals , giving us 6 atoms bonded

Which AA corresponds to Q?

glutamine

uncompetitive inhibition

inhibitor binds only to enzyme-substrate complex locks substrate in enzyme preventing its release (increasing affinity b/w enzyme and substrate so it lowers Km) Lower Km and vmax

When do gases behave most ideally?

low pressure and high temperature

root mean square velocity

the square root of the average of the squares of the individual velocities of gas particles

What is the molar mass of a compound with a density of 2g/L at STP?

to find MM: density X 22.4 so--> (2g/L)x(22.4L/mol) = 44.8 g/mol

what is the density of neon gas in g/L at STP?

to find density--> density = m/v =molar mass/22.4 so: (20g/mol)/22.4 = 0.9018 g/L