AAMC Chem/Physics

Question 1

What are the units for each order of rate constants?

Answer 1

For zero order reactions the units for k are M*s^-1 and the units for rate are the same. For first order reactions the units for k are 1/s and the units for rate are M/s. IN second order reactions the units for k are 1/Ms and the units for rate are M/s. So the units for rate are always M/s while the units for k will chnage

Question 2

What are the characteristics for polar vs nonpolar substance? How does polarity contribute to solubility?

Answer 2

Nonpolar bonds form between two atoms that share their electrons equally. Polar bonds form when two bonded atoms share electrons unequally. (ionic bonds are different eg NaCl) non polar = hydrophobic, water fearing eg lipids and cholesterol or steroids. Hydrophilic are water loving they will be water soluble. hydrophobic effect is the observed tendency of nonpolar substances to aggregate in an aqueous solution and exclude water molecules. Non polar hydrophobic have a lot of carbons and hydrogens. The rule for solubility is like dissolves like so a nonpolar thing is good in a non polar thing and polar molecules can normally H bond with water making them soluble in water and hydrophilic

Question 3

Describe what happens in alpha decay

Answer 3

During alpha decay, alpha particles (He nuclei) are emitted by the heavy-atom nuclei.

Question 4

Describe alpha absorption

Answer 4

During alpha absorption, alpha particles (He nuclei) are absorbed by the target atoms.

Question 5

Describe gamma absorption

Answer 5

Absorption of gamma rays consists of the process in which high energy photons (also called gamma ray photons) are absorbed by target atoms.

Question 6

Describe gamma decay

Answer 6

Gamma decay, type of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process. In the most common form of gamma decay, known as gamma emission, gamma rays (photons, or packets of electromagnetic energy, of extremely short wavelength) are radiated.

Question 7

Describe beta decay

Answer 7

Beta decay is the decay in which a beta particle (electron or positron) is emitted from a heavy-atom nucleus. In beta minus (β−) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; while in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. β+ decay is also known as positron emission.

Question 8

List diverging vs converging for all lens’ and mirrors

Answer 8

concave mirror = converging mirror, concave lens = diverging lens, convex mirror = divergent, convex lens = convergent

Question 9

What do the variables i, f, o, and m mean and how do they relate to each other

Answer 9

f = focal length, i =image distance, m = magnification,, o = object distance m=-i/o 1/f = 1/i +1/0

Question 10

What does it mean for the focal length f to be positive?

Answer 10

If focal length is positive this means the focal point is on the same side as the observer, converging optics (concave mirror and convex lens) have a positive focal length

Question 11

What does it mean for the focal length f to be negative?

Answer 11

If f is negative that signifies a diverging optics so convex mirror and concave lens have a negative focal length

Question 12

How does a positive or negative sign affect the image distance, i?

Answer 12

If image distance, i is positive is on the same side of the observer and negative if on the opposite side of the observer. (with mirrors the object is always on the same side as the observer, with lenses the object is always on the opposite side of the observer) Images with a negative i are virtual and upright and images with a positive image distance are real and inverted

Question 13

How does a positive or negative sign affect the object distance, o?

Answer 13

Object distance, o is always positive

Question 14

How does a positive or negative sign affect the magnification, m?

Answer 14

Since o is always positive the sign of m is determined solely by the sign of i. A positive m means a negative i and there fore (virtual upright image) a negative m means a positive i and therefore (real inverted image)

Question 15

How do o and f relate to convergence and divergence?

Answer 15

If converging and of then real, inverted. Diverging is always virtual upright, mathematically it is impossible to have anything other than virtual, upright, and real, inverted. If o=f no image formed. If o=infinity then the image will show up exactly where the focal length would be

Question 16

Where does the focal point fall for different mirrors?

Answer 16

The focal point falls behind the mirror for convex mirrors, and focal point falls in front of a concave mirror. f = 1/2(radius of curvature)

Question 17

Describe nucleophiles/ nucleophilicity?

Answer 17

A nucleophile is a chemical species that donates an electron pair to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Good examples are anions, electron dense molecules, good bases are normally good nucleophiles, but not every good nucleophile is a good base. Examples of nucleophiles Br- OH- CN

Question 18

What factors affect nuclephilicity?

Answer 18

As negative charge increases nucleophilicity increases, as electronegativity increases nucleophilicity decreases, as steric hindrance increases nucleophilicity decreases, as a solvent becomes protic nucleophilicity decreases, nucleophilicity increases down the periodic table in polar protic solvents, in polar aprotic solvents it increases up the periodic table

Question 19

Describe electrophiles

Answer 19

electrophile molecule attracted to electron dense species, more positive = better electrophile

Question 20

What makes a good leaving group?

Answer 20

A good leaving group takes electrons when the bond is broken and is stable after leaving, increases as moving down the periodic tabel because more room to localize charge, e.g. Tosylate (OTs), halides, water, alcohols, ethers

Question 21

How is the boiling point of a substance determined? What factors would effect the boiling point of a liquid?

Answer 21

The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the surface pressure. The normal boiling point is measured at 1 atm pressure. The vapor pressure of a liquid increases with increasing temperature. Hence, the boiling point of a liquid decreases as the pressure on the surface of the liquid is decreased. If a leak develops in the apparatus, the surface pressure will increase, as will the boiling points of both liquids. Thus, answer choice A is the best answer.

Question 22

What can the volume of a gas be approximated at in STP conditions?

Answer 22

It is an important fact that one mole of an ideal gas, at STP, will occupy a volume of 22.4 L. Therefore, 11.2 L of CO2 gas, at STP, must represent 0.5 mole of CO2. (Virtually all gases can be approximated as ideal gases at common temperatures and pressures.)

Question 23

How do you determine the conjugate acid/base of a substance?

Answer 23

An acid differs from its conjugate base only by the presence of an additional H+. A base differs from its conjugate acid only in the lack of a single H+. Since HPO4–2 has one fewer hydrogen atom, and one more negative charge, than H2PO4–, then HPO4–2 must be the conjugate base of H2PO4–.

Question 24

What does the Ksp value say about a molecules solubility in water?

Answer 24

The lower the value of Ksp is, the lower the concentrations of the cation and anion in an aqueous solution and the lower the solubility of the compound in water.v

Question 25

How does electric field relate to voltage? How does it relate to force?

Answer 25

E = V/d, V=Ed. An electric field can be given in volts per meter. Because 1 V ≡ 1 J/C, the electric field value V/m = N/C. F=qE, which makes sense because columbs law F = k(q1)(q2)/r^2, while electric field, E = k(q)/r^2

Question 26

Describe the change in frequencies seen with the Doppler effect. What is the relationship between wavelength and relative speed as a consequence of the doppler equation.

Answer 26

Approaching (either the person approaching the source or the source is approaching the person) corresponds to higher perceived frequency. Receding ( source receding from person or person receding from source) corresponds to lower perceived frequency.
f(perceived)= f(actual)/(1+/-v(source)/v(sound)). + for receding and - for approaching. The linear relation between relative speed v and change in detected wavelength is a consequence of the Doppler equation, Δλ/λ = v/c

Question 27

What is capacitance related to?

Answer 27

C=Q/V (charge over voltage). Capacitance is also equal to C=eA/d. Where e is the permitivitty dielectric, A is the area of the plate, and d is the distance between the plates.

Question 28

What is the equation for potential energy of oscillatory motion?

Answer 28

The potential energy of an oscillatory motion is ½kx^2 where x is the displacement.

Question 29

What does archimedes principle tell us about what would float and what would remain submerged based on density?

Answer 29

If you rank the densities D1, D2, and D3, three balls with identical volumes at rest at different locations in the stationary water. Ball 3 rests on the bottom of the tank, Ball 2 is suspended half-way between the surface the water and the bottom, and Ball 1 floats partially submerged. Objects denser than water sink to the bottom of the tank, objects with density equal to that of the water remain suspended (or float) wherever they are placed, provided that they are completely submerged, and objects less dense than water float at the surface partially submerged. Ball 3 sinks and touches the bottom of the tank, so it must be denser than water because the bottom of the tank also supports it. Ball 2 is suspended in the water without touching the bottom, so its density equals that of the water. Ball 1 floats at the surface, so its density is smaller than that of the water. Using Archimedes’ formula of the buoyant force that depends on density and volume, the densities are ranked D1 < D2 < D3

Question 30

Describe the direction of the magnetic force on a charge? Direction of electric field on a charge?

Answer 30

A magnetic force acts on a moving charge in a direction that is perpendicular to both the velocity of the charge and the direction of the magnetic field.
The direction of the electric field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.

Question 31

Why is water often omitted from equilibrium constant

Answer 31

Aqueous acid-base equilibria very often feature water acting as either an acid or a base. It is also the solvent for aqueous systems. In the equilibrium constant expression for such reactions, water is usually omitted. The simplest explanation is that, because it is the solvent, the concentration of water stays essentially constant throughout the reaction. In such a case, that constant could be included in the value of Keq, the equilibrium constant for the reaction. Also because in general pure solids and liquids are not included in Keq calculations only gases and aqueous solutions

Question 32

What are the different strong acids? What is the primary property

Answer 32

Strong acids completely dissociate in water, (HCl, HBr, HI, H2SO4, HNO3, HClO4, HClO3), everything else is a weak acid if it donates protons or accepts electron pair.

Question 33

What is the difference between EEG CAT scan, PET scan, MRI and fMRI?

Answer 33

MRI looks at structural anatomy using highly specialized magnets. So you can visualize brain structures on a 3d level with a lot of detail, such as bone, fluids, cartilage, etc.

fMRI, also known as functional MRI, measures blood flow to certain areas of the body. It provides information as to which areas are most activated by showing which receive the most blood.

CT/CAT scan is similar to MRI that gives structural information, yet it is less detail and uses radiation. It’s very similar to an X-ray. Used to measure brain structure. Uses x-rays to create an image of the brain

PET is positron emission topography where a radioactive dose, usually glucose, is ingested by the patient and the substance will release positrons via beta decay. As a result, the gamma rays biproduct can be visualized. Usually this procedure is used to detect for tumors, since they will have the highest consumption of radioactive glucose.

EEG Measures electrical activity generated by neurons in the brain using electrodes placed on someone’s scalp. Used to determine brain function. Looks at the sum total electric field that is generated from the brain. Tells us what awareness state we are in (sleep vs awake), what difficulty of cognitive task we are doing, etc.

Question 34

Describe the difference between simple distillation, vacuum distillation, fractional distillation?

Answer 34

Simple distillation: can be used to separate two liquids with boiling points below 150 C and at least 25 C apart
Vacuum distillation should be used when a liquid to be distilled has a boiling point above 150 C. To prevent degradation of the product the incident pressure is lowered thereby lowering the boiling point.
Fractional distillation should be used when two liquids have boiling points less than 25 C apart By introducing a fractionation column the sample boils and refluxes back down over a larger surface area improving the purity of the distillate

Question 35

What are the irregular electron configurations?

Answer 35

The most common are chromium and copper. Intuitively, we would think chromium would have an electronic configuation of [Ar]4s^2 3d^4, but what we actually observe is that its electron configuration is [Ar]4s^1 3d^5 because it is very favorable to have the 3d orbital half-filled, so an electron from 4s goes to fill it. We see the same idea with copper. I’m sure you’d see the same thing with any of the transition metals in those groups. copper, Cu should be [Ar] 3d9 4s2 but is [Ar] 3d10 4s1.
Silver (Ag), Gold (Au), Palladium (pd), and are other irregulars, (and Mo)

Question 36

What should you know about electric fields and electric field lines?

Answer 36

Electric field is denoted by the vector E.
Lines that are closer together denote stronger fields than lines that are farther apart.
Electric fields come out of positive charges, and goes into negative charges.
The unit for electric field is N/C, or Newtons per Coulomb.
Electric field in between a capacitor is uniform until it reaches the ends of the capacitor.
Electric field lines never intersect. In an uniform electric field, the field lines are straight, parallel and uniformly spaced.

Question 37

What is n and how does it relate to energy?

Answer 37

The principal quantum number n represents the relative overall energy of each orbital. Thus the Principal quantum number is directly related to the potential energy of an electron as well and through this it is proportional to coloumbs law and the radial “size” of the electron cloud.
l = n-1, and l must be 0 and above. The value of n and l help identify the orbital type of the molecule

Question 38

What are the effects of a branched vs a straight chained molecule on melting point and boiling point?

Answer 38

effect of chain branching on physical properties: going from straight chain to branched alkane (with same # carbons) = higher freezing/melting point, lower boiling point.
Branched alkanes normally exhibit lower boiling points than unbranched alkanes of the same carbon content. This occurs because of the greater van der Waals forces that exist between molecules of the unbranched alkanes.
linear versus branched —> higher melting/boiling points due to better stacking and surface area contact.
highly branched vs. branched —> more sphere-like –> better stacking –> higher melting point
highly branched vs. branched —>more sphere-like – -> lower surface area —> lower boiling point.

Question 39

Discuss the energy differences when you make a bond versus breaking one?

Answer 39

Breaking a bond is endothermic, you add energy energy must be added to the system as heat in order to dissociate/break the bond. Making bonds is the exothermic reaction.

Question 40

Discuss the types and the strength of intermolecular forces

Answer 40

The rule of thumb is that the stronger the intermolecular forces of attraction, the more energy is required to break those forces. This translates into ionic and polar covalent compounds having higher boiling and melting points, higher enthalpy of fusion, and higher enthalpy of vaporization than covalent compounds.
Ion-dipole>hydrogen bonds>dipole-dipole>van Der Waals forces
Ion-dipole forces are the strongest of the intermolecular forces.
Hydrogen bonding is a specific term for a particularly strong dipole-dipole interaction between a hydrogen atom and a very electronegative atom (oxygen, fluorine, or nitrogen). However, hydrogen bonds are still not as strong as ion-dipole interactions.
In order from strongest to weakest, the intermolecular forces given in the answer choices are: ion-dipole, hydrogen bonding, dipole-dipole, and Van der Waals forces.
Ionic bonding is stronger than any of the given intermolecular forces, but is itself NOT an intermolecular force. Ionic bonds are a permanent chemical connection between two atoms, whereas intermolecular forces as a more transient and temporary attraction between independent molecules.

Question 41

Discuss types and strength of intramolecular forces.

Answer 41

Metallic bond, Metal cations to delocalized electrons 1, strongest.
Ionic bond Cations to anions 2
Polar covalent bond, Partially charged cation to partially charged anion 3
Nonpolar covalent bond, Nuclei to shared electrons 4, weakest
Intermolecular forces are much weaker than the intramolecular forces of attraction but are important because they determine the physical properties of molecules like their boiling point, melting point, density, and enthalpies of fusion and vaporization.

Question 42

What fills first and leaves first between the 4s and 3d orbital? What has the higher energy?

Answer 42

4s fills first and electrons are also taken from there first. First to fill first to leave.
The energy level is based on the principal quantum number + the azimuthal number (n + l) the lower the value, the lower the energy
So 4s, n=4, l=0, 4 + 0 = 4
3d n =3 l=2, 3+2 = 5
you remove from the highest n bc those electrons are the furthest away, and the easiest to remove! Because they experience the least Zeff from the nucleus.
4s orbitals are lower in energy than 3d orbitals when the 3d orbitals are EMPTY, therefore, 4s orbitals fill first. Once 3d orbitals begin to fill, the filled 4s orbitals are higher in energy than the partially-filled 3d orbitals. Because of this, 4s orbitals are removed before 3d orbitals.

Question 43

Describe the relationship between Km level and affinity.

Answer 43

Km is the concentration of substrate at 0.5Vmax, it is an inverse measure of its substrate affinity, because a lower Km indicates that less substrate is needed to reach a certain reaction speed. Hence, a low Km means a high substrate affinity.