MCAT Error Log Takeaways

boiling points

what to look at to determine

1. polarity (more polar, higher bp) —> if they have the same polarity then look at branching

2. branching if the molecules have similar structures (less branching, higher boiling points bc more surface area)

*if pressure dec, bp dec

determining where enantiomers differ

enantiomers differ at their chiral centers—> this leads to different spatial arrangements so look for sp3 hybridized carbon atomsand substituents that vary

avogadro’s number

6.022 × 10²³ molecules per mole

thin layer chromatography

used to separate non-volatile mixtures based on differences in their polarity and adsorption to stationary and mobile phases, more polar travels less distance/ slower (smaller Rf) and vice versa

hydrogen bonding

is an intermolecular force that occurs when a hydrogen atom, covalently bonded to a highly electronegative atom like oxygen or nitrogen, is attracted to another electronegative atom

to participate, a molecule must have a hydrogen atom attached directly to nitrogen, oxygen, or fluorine (acting as a donor), or if it contains an N, O, or F atom with lone pairs (acting as an acceptor)

pH

pH +pOH = 14

pH = -log[H+]

strong acids

are acids that completely dissociate in water

HI, HCl, HBr, HClO₃, HClO₄, HNO₃, H₂SO₄ (hi cool bro clo clo no so, 3434)

strong bases

are bases that completely dissociate in water

metal cation (Group 1 and 2) and a hydroxide group (OH)

thin line chromatogrpahy

movement along paper, migration of components is based on h-bonding, size of spots is based on solute concentration

converging vs diverging lens

Converging lenses focus light rays to a point, while diverging lenses spread light rays apart.

Converging lenses are typically convex, and diverging lenses are concave.

Nearsightedness = converging eye lens, must have a positive sign of lens strength

catalyst

is a substance that increases the rate of a chemical reaction without being consumed in the process

lowers the activation energy

stabilization of transition state is done by an enzyme to lower the Ea of a reaction. (Stabilizing the SUBSTRATE would inc Ea and slow the reaction)

le chatelier's principle

states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium will shift to counteract that change

atmospheric pressure

1 atm, 760 mmHg, 101.3 kPa

gas-liquid chromotography

Least polar, most volatile, first peak to emerge in gas-liquid chomatography

boiling chip

small, porous piece of material added to a liquid to promote smooth boiling and prevent bumping, prevents superheating by providing nucleation sites for bubble formation.

VESPR

remember.

similar properties

elements in the same group with have similar properties

ion responsible for color of solution

the ion responsible for color in a solution is typically a transition metal ion, which can absorb certain wavelengths of visible light, giving the solution a characteristic color

most vs least soluble in water

solubility differences are based on intermolecular forces; substances with stronger hydrogen bonding are generally more soluble —> more polar (less C-H bonds)

inc yield of product or byproduct

increase the reagents

pKa

is a measure of the acidity of a solution, higher pKa means more basic

to determine the highest vs lowest pKa, consider the strength of the acid: less EN atoms and smaller atoms hold electrons more tightly and thus a higher pKa

K_eq

is the equilibrium constant for a reaction, representing the ratio of the concentrations of products to reactants at equilibrium

henderson-hasselbalch equation

equation is used to calculate the pH of a buffer solution

pH = pKa + log [A-]/[HA]

leaving groups

weaker bases make the best leaving groups, while strong bases make bad leaving groups

you can make a bad leaving group a good one by protonating it to increase its stability (or reduce its basicity or turn the LG into a neutral molecule)

aliphatic

compounds that consist of carbon and hydrogen arranged in open-chain or branched structures, not including aromatic rings

how can you know if something would be a good nucleophile

a good nucleophile is typically characterized by a strong base, high electron density, and less steric hindrance, allowing it to effectively attack electrophiles

aromatic compounds can be good nucleophile if they possess a negatively charged or electron-rich substituent and are not sterically hindered

number of possible peptides that contain one each of n amino acids

The formula for the number of possible peptides that contain one each of n amino acids is n! (n factorial). For n = 3 (a tripeptide), n! = 3! = 3 × 2 × 1 = 6 = Answer C. Alternatively, for a tripeptide ABC, the following combinations are possible: ABC, ACB, BAC, BCA, CAB, and CBA, or six = Answer C.

ionic character in the periodic table

difference in EN means greater ionic character

periodic trends

describe the predictable patterns in properties

entropy

entropy = randomness in a system

delta(S) is the change in entropy; if it is positive, the system becomes more disordered and entropy inc BUT if it is negative, less disordered and entropy decreases

one factor that affects entropy is if bonds are made, entropy dec