MCAT Chem/Phys

Electromotive force (EMF)

The amount of work required to move one unit of charge through an electrochemical cell

Cell potential (E cell)

The voltage difference between the anode and the cathode before current begins to flow

Refraction

The bending of lights, occurs at the boundary between two different mediums with different values of n

Total internal reflection

At a specific critical angle, light is refracted at a 90% angle and continues parallel to the surface. If the incident angle is greater than the critical angle, the light reflects back into the water causing total internal reflection

Diffraction

The bending of light around physical corners to very narrow gaps. Significant diffraction would not occur at the water-air surface

Dispersion

Spreading of light into its different frequencies (colors) dur to differences in the index of refraction for different frequencies of light

Polarization

Aligns transverse electromagnetic radiation along a specific orientation, such as vertical, horizontal,. Light can be polarized during reflection, but polarization does not cause reflection

What is an advantage of x-ray diffraction?

It allows for the determination of a 3d molecular structure. Exposing a sample of purified and crystallized material to x-ray radiation pay produce a diffraction pattern unique to that particular substance.

What is the formula for the occurrence of constructive interference as a function of the incident angle?

2d\*sin(theta) = n(lambda)

Pressure drop across a vessel

The difference between its pressure and the pressure of the next vessel

What is flow resistance dependent on?

It is due to the viscosity of blood and the geometry of the vessel through which it flows. It is independent of the direction of flow

What is viscosity?

A measure of a fluid’s resistance to flow due to internal frictional forces; not a measure of pressure. Acts in the direction opposite to the flow

Combustion

Chemical process through which the chemical energy stored in the molecular bonds of the reactants is released by creating new bonds with less energy. Takes chemical energy and converts it to thermal and kinetic energy

Radiation

Transfers heat through electromagnetic waves

Complex ions (coordination complexes)

Central metal ion surrounded by one or more ions or molecules called ligands that are bound to the metal center by coordinate bonds.

How do coordinate bonds form?

The ligands surrounding the metal center act as Lewis bases and donate a lone pair of electrons to the metal center which acts as a Lewis acid.

Pauli Exclusion Principle

Each orbital subshell can hold a maximum of two electrons, but two electrons in the same orbital must have opposite spins

Principle quantum number n

Describes the main energy level (shell) of the electron and its most probable distance from the nucleus (n = 1, 2, 3..)

Orbital angular momentum quantum number (l)

Corresponds to the subshell type (s, p, d, f) and corresponding shape of the orbital occupied by the electron

Magnetic quantum number (ml)

Determines the number of orbitals of a given type and their orientations within a sublevel

Electron spin quantum number (ms)

Describes the angular momentum of an electron, which is a vector quantity with a magnitude of 1/2 and a direction that is either spin up (positive) or spin down (negative)

Electrochemical cell

a redox reaction converts chemical energy to electrical energy (galvanic cell) or vice versa (electrolytic cell)

Galvanic cell

Spontaneous reaction occurs (E cell is greater than 0)

Electrolytic cell

An external potential source is used to drive a nonspontaneous reaction

Concentration cell

Type of galvanic cell in which electrons flow from a lower concentration half-cell into a higher concentration half-cell, thus generating a potential. E cell is positive

Fuel cell

Type of galvanic cell in which the reactants are continuously supplied at the anode and cathode as the products are continuously removed from the system. E cell is positive

What is electron flow in an electrochemical cell?

Electrons always flow from the anode (electrode where oxidation occurs) to the cathode (electrode where reduction occurs)

Electroplating

The electrolytic deposition of solids onto a metal surface and involves the reduction of a metal ion to a metal solid at the cathode surface

What is the formula for energy density?

(Power \* time) / mass

Overall bond dissociation energy

The total energy required to break the sigma bond and any pi bonds. This energy increases with each additional pi bond

Avogadro’s Law

The volume occupied by a gas is directly proportional to its number of moles (at constant temperature and pressure). V1 / n1 = V2 /n2. Volume is directly proportional to the number of moles

Standard electric potential of a Galvanic cell

E cell = E cathode - E anode

What is a salt bridge?

A conductive electrolytic solution that allows for the migration of ions

Faraday

1 mol of electrons (1 mol e-)

Reducing agent

A substance that gives up electrons (undergoes oxidation) causes reduction in another substance

Cathodic protection

Technique used to protect iron from oxidation (corrosion) by connecting the iron metal to a more easily oxidized metal (a stronger reducing agent)

What is required for cathodic protection?

The sacrificial anode must posses a more negative reduction potential than that of the cathode. Have to be stronger reducing agents

Blue litmus paper

Turns red when dipped in an acidic solution but remains blue when dipped in a basic solution

Red litmus paper

Turns blue when dipped in a basic solution but remains red when dipped in an acidic solution

Atomic mass unit

1/12 the mass contained in a carbon-12 atom (average mass of 6 protons and 6 neutrons)

Conversion for amu

6\.022 E 23 amu = 1 mole of amu = 1.00 g

What liquid is required for gel electrophoresis?

An ionic salt solution is required so the ionic salts dissociate into ions that can freely move and assist the passage of electrons through the solution

Isotopes

Atoms of the same element that have a different number of neutrons in the nucleus, and isotopes are identified by their mass number (sum of protons and neutrons)

What value of delta H does an endothermic reaction have?

Endothermic reactions have a positive delta H because heat is being added to the system

What value of delta H does an exothermic reaction have?

Exothermic reactions have a negative delta H because heat is produced by and lost from the system

What is the formula for delta G

delta H - temp ( delta S)

What is the equation for delta G relating to K eq?

delta G = -RTlnKeq

Catalysts affect the reaction rate but do NOT change

Equilibrium, enthalpy, entropy, and temperature

Why are dissociation reactions typically endothermic?

Because energy must be added to the system (as heat) to dissociate (break) bonds in the reactants

What is the buffering range?

Typically it is 1 pH unit away from the buffer’s pKa moving in either direction along the pH scale

What is the equation for enthalpy from q?

q reaction / # of moles

Hess’ law

if a reaction can be performed in more than one step, the heat of the overall reaction (its overall enthalpy) is equal to the sum of the enthalpy charges from each step

Condensation

Process of a gas moving back into its liquid phase. “Liquefication”

Sublimation

Conversion of a solid to a gas. Increases entropy

Which values in the heating curve are the same but have opposite signs?

Solidification = - Fusion and Condensation = - vaporization

What bonds are broken during melting?

Noncovalent intermolecular forces (London dispersion, dipole-dipole, hydrogen…)

Latent heat of vaporization

The amount of heat a substance must absorb to transition from a liquid to a gas

What does a catalyst do to a reaction?

It decreases the activation energy and increases the amount of reactant that is consumed per unit of time. Rate of reactant consumption increases

How do you qualitatively measure the change in entropy when looking at a reaction?

Compare the moles of gas/liquid in both the reactants and products. Solids have the least amount of entropy and if there are more gas/liquids in the reactants than entropy has decreased. if there are more gas/liquids in the products then entropy has increased

Why is water a good solvent?

Because it is polar which is helped by oxygen being more electronegative than hydrogen, it is small, and it has a bent orientation

Raoult’s Law

The addition of any solute to a pure liquid lowers the freezing point temperature and the vapor pressure

What is the freezing point of a solution dependent on?

Only dependent on the strength of the intermolecular forces. Not dependent on the melting point of the solute.

When does a liquid boil?

When the ambient pressure equals the vapor pressure. If the vapor pressure is lower, then the boiling point is higher because a higher temperature is required for the vapor pressure to equal the ambient pressure

Complex ion/coordination compound

A molecule in which a cation is bonded to at least one electron pair donor that are held together with coordinate covalent bonds

Normality

the number of equivalent s of interest per liter of solution. Molarity of the stuff of interest in the reaction

Saturation point

Where the solute concentration is at its maximum value for the given temperature and pressure

Solubility product constant

the equilibrium constant for its solubility in aqueous solution,

How does temperature affect the solubility product constant?

the solubility product constant increases with temperatures for non-gas and decreases with temperature for gas solutes

how does pressure affect the solubility product constant?

higher pressure favors dissolution of gas solutes

Ion product

Analogous to the reaction quotient but has the concentrations at a given point in time

Unsaturated solution

If a salt’s IP is less than the Ksp. At this point, dissolution is thermodynamically favored over precipitation

Supersaturated solution

If the IP is greater than the Ksp. Thermodynamically unstable

Colligative properties

Physical properties of solutions that are dependent on the concentration of dissolved particles, but not on the chemical identity of the dissolved particles

Raoult’s Law

As solute is added to a solvent, the vapor pressure of the solvent decreases proportionately. This is because the presence of the solute molecules can block the evaporation of solvent molecules but not their condensation which reduces the vapor pressure of the solution compared to the pure solvent

Osmotic pressure

a “sucking” pressure generated by solutions in which water is drawn into a solution. Amount of pressure that must be applied to counteract this attraction of water molecules for the solution

Arrhenius acid

Dissociate to form an excess of H+ in solution (usually contains an H in the front)

Arrhenius base

Dissociate to form an excess of OH- (usually contains OH at the end)

Bronsted Lowry acid

Donates a hydrogen ion Bro

Bronsted Lowry base

Accepts a hydrogen

Lewis acid

An electron pair acceptor

Lewis base

An electron pair donor

Autoionization

When water reacts with itself to produce hydronium and hydroxide

Common strong acids

HCl (hydrochloric acid), HBr (hydrobromic acid), HI (hydroiodic acid), H2SO4 (sulfuric acid), HNO3 (nitric acid), HCLO4 (perchloric acid)

Common strong bases

NaOH (sodium hydroxide), KOH (potassium hydroxide),

How to choose an indicator for a titration reaction?

Find the pH of the equivalence point and then find the indicator with the closest pKa

What is the equivalence point of a strong acid and a weak base?

The pH will be less than 7

What is the equivalence point of a strong acid and a strong base

The pH will be exactly 7

What is the equivalence point of a weak acid and a strong base

The pH will be greater than 7

AN OX RED CAT Mnemonic

anode is the site for oxidation and cathode is the site for reduction

Electromotive force

the voltage or electrical potential difference of the cell

How does emf dictate the spontaneity of the cell?

If the emf is positive then the cell is able to release energy (delta G is neg) so it is spontaneous. If the emf is negative, then the cell must absorb energy (delta G is pos) which means it is non spontaneous

What is the direction of electron movement in an electrochemical cell?

Move from anode to cathode. This is opposite of the direction of current which moves from cathode to anode.

What type of cells are batteries?

Galvanic/voltaic cells. These cells must be spontaneous

What is the difference between galvanic cells and electrolytic cells?

Electrolytic cells house non spontaneous reactions that require the input of energy to proceed. Galvanic cells on the other end are completely spontaneous and generate energy

Electrolysis

Oxidation-reduction reaction that is driven by an external voltage source

Faraday’s constant

The amount of charge contained in one mole of electrons. 10^5 C/ mol e-

What is the charge designation in a galvanic cell?

In a galvanic cell, the anode is negative and the cathode is positive

What is the charge designation in an electrolytic cell?

In an electrolytic cell, the anode is positive and the cathode is negative

Isoelectric focusing

A technique used to separate amino acids or polypeptides based on their pH. Anions will gravitate towards anodes and cations will gravitate towards cations

How many acidic protons would H3PO4 have?

It has 3 acidic protons and therefore it has 3 equivalence points on a titration graph