Lab Techniques

solubility is directly related to ?

intermolecular forces (LDF, DD, HB)

precipitation

formation of a solid-liquid mixture from a homogenous solution

trituration

using mortar and pestle and solvent to get pure solid from impure mixture

extraction

desired solute is transferred to the organic solvent layer

wash

desired solute remains in the original solvent and impurities are extracted

In SEP funnel, the bottom layer has ?

higher density

neutral molecules are soluble in ?

organic solvents

ionized molecules are soluble in ?

aqueous solutions

distillation

separated based on differences in boiling point

simple distillation

one vaporization-condensation cycle

separate substances with larger boiling point difference

often one major volatile component

(boiling point gaps greater than 25)

vacuum distillation

the interior of a distillation setup is placed under partial pressure, so boiling points of distillate components are decreased

use magnetic stir bar instead of boiling chips

ideal for substances with high atmospheric boiling points

fractional distillation

more successive cycles = more separation = greater enrichment of lower-boiling point liquid

increased separation efficiency from more than 1 vaporization-condensation cycle

ideal for separations of liquids with boiling points <25

chromatography

stationary and mobile phase; separation based on how molecules interact with the phases

gas chromatography

mobile phase is a stream of an inert gas

stationary phase is a solid or liquid

mixtures separated based on their vapor pressure and polarity

liquid chromatography

liquid mobile phase and solid stationary phase, separates based on affinity for the stationary phase

normal phase

polar stationary phase and nonpolar mobile phase

reversed phase

nonpolar stationary phase and polar mobile phase

paper chromatography

paper stationary phase, composed of polar cellulose

highly polar organic mobile phase

normal phase separation method

thin layer chromatography

stationary phase can be silica gel or alumina (both polar) or alkylated silica gel (nonpolar)

can be analytical (thinner) or preparative (thicker)

column chromatography

preparative separation in the lab to isolate relatively large samples of a compound for further study (use TLC logic and flip upside down for down the column)

substances with larger Rf will elute first

high performance liquid chromatography

good for separating small sample sizes, separation based on polarity

litmus paper

color changing dyes to determine acidity

limitations: qualitative, pH ranges for color changes (blue only changes to red below 4.5 and red only changes to blue above 8.3

wide-range pH paper

several organic dyes for more specificity

initially colorless and changes based on pH

pH meter

quantitative, probe calibrated to determine pH

polarimetry

optical activity of chiral molecules

enantiomers

same melting point, boiling point, and density but different signs for optical activity (same magnitude, different directions)

meso compounds are ?

optically inactive

long to short wavelength

radio, micro, infrared, visible light, UV, x-rays, gamma rays

absorption spectroscopy

absorbed photons promote specific molecular changes for study

x-rays can ?

emit the full electron (mass spec)

UV-Vis light can ?

move the electron from a lower energy ground state to a higher energy excited station (electron transition; UV-Vis Spec)

infrared light can ?

cause molecular vibrations, makes bonds wiggle (IR)

microwave region can ?

promote the rotation of whole molecules

radio waves can ?

cause atoms to transition from a lower energy spin state alpha to a higher energy nuclear spin state beta (NMR)

Mass spec

analyzes the population of ions following nonspecific ionization

white object

absorbs no visible light and reflects all visible light

black object

absorbs all visible light, reflects no visible light

red object

absorbs most visible light, reflects red light

NMR Spec

nuclear spin: nucleus acts as bar magnet and interacts with stuff in surroundings

H NMR

higher resonance frequencies on the left, which are a result of more deshielding, low electron density

spin-spin splitting

nearby nonequivalent protons act as miniature bar magnets themselves and increase or decrease the chemical shift of a resonating proton