CHem 43a

What is melting point determination

when a melting apparatus is used to determine the melting point range for a compound

When is melting point determination used

After synthesizing a derivative or other compound

After carrying out a purification technique

Why is melting point determination used

It is used to determine a compounds and purity

What is the definition of melting point

The temperature at which melting and solidifying are at equilibrium

What is recrystallization

is a purification technique based upon the difference is solubilities of the compounds and the thermodynamically favorable process of crystal formation

when is recrystallization used

Used when we have an impure solid that can be dissolved in a solvent that is hot but is insoluble in that same solvent when cooled

Why is recrystallization done

to purify an impure solid

What are the properties of an ideal solvent is recrystallization

insoluble at low temp and soluble at higher temp

Why are boiling chips used

to provide nucleation sites to avoid bumping

Why is the compound dissolved in a minimal amount of solvent

so that crystallization can occur and so the solution isn’t too dilute

What can you do if there is to much solvent

If you have too much volume you can evaporate some of it off

Why is charcoal used

it adsorbs the colored impurities

What is hot filtration used for

to remove insoluble impurities

Why is the filter paper prewarmed with hot water

to prevent early crystallization

Why is slow cooling ideal

so that no impurities get trapped in the crystal lattice

What can you do if no crystals form

 can use seeding or scratching

when crystals form slowly _____ process is favored

thermodynamic

when crystals form quickly _____ process is favored

kinetic

When crystals form slowly ______ is favorable and _____ is unfavorable

enthalpy and entropy

What is vacuum filtration

A process that removes soluble impurities

Why are the crytsals washed with cold solvent during vacuum filtration

To prevent dissolving the crystals.

What is liquid- liquid extraction

a separation method based on differing solubility of components of a mixture in two immiscible solvents

When is liquid-liquid extraction used

Often used after synthesizing a compound to separate certain compounds in a mixture from each other, remove a natural product of interest

Compounds with less than equal to 4-5 carbons and have a polar functional group are _______

water miscible

Why is it important to vent the sep funnel

because the volatile compounds cause pressure build up

The more dense solvent is usually on the ____

bottom

What factor can effect how the layers are separated

the concentration of solutes

What test can be used to check which layer is which

water drop test

what is sublimation

when a material goes from a solid to a gas

Why is sublimation considered a purification technique

impurities don't sublime in the same conditions as caffeine

what non water soluble is removed during solid-liquid extraction (tea brewing in the water)

cellulose

What is left in water when caffeine is extracted into DCM

protein and pigments

What are tannins

soluble in water and DCM)- hydrolyze using sodium carbonate to make them more soluble in water

Why are organic acids and bases used in E3

used to convert hydrophobic compounds to hydrophilic salt forms

Why do the acids and bases need to be organic in E3

to increase solubility and extract it from other organic compounds

What is column chromatography

a separation technique based on polarity

Mobile phase

is less polar and usually solvent(s)

Stationary phase

is more polar

what is the common stationary phase used in this lab

silica

polar compounds react with a _____ stationary phase

polar

nonpolar compounds react with a _____ mobile phase

nonpolar

What kind of compounds have lower Rf values in TLC and elute slower in in column chromatography

polar compounds

What kind of compounds have higher Rf values in TLC and elute faster in in column chromatography

nonpolar

what kind of method is TLC

a component identification method

In UV visualization which type of compounds fluoresce more

organic compounds

is more nonpolar and higher Rf because of intermolecular bonding

Ortho

polar, higher Rf more intramolecular bonding

Para

Does para have a higher or lower mp compared to ortho

higher

During TLC which compound is the most nonpolar and comes out first

Ferrocene

During TLC which compound is the most polar and comes out last

acetylferrocene

During TLC which compound comes out second

9-fluorenone

What is distillation

A method used to separate compounds via boiling point

What is the purpose of the fractional column

it causes repeated condensation and vaporization allowing for separation based on volatility (bp)

higher vapor pressure = more volatile = ____ boiling point

lower

How does branching affect bp

it lowers it

why does n-heptane have a higher bp than n-hexane

because it has more surface area

In gas chromatography what is the mobile phase

gas

In gas chromatography what is the stationary phase

liquid

True or False: lower boing points mean lower RT

true

what principle pushes the esterification in E6 to the right

Le Chatelier's

How is the equilibrium in E6 pushed to the right

with excess reagents(carb acid), very dry glass ware+ drying tube to prevent H20, and application of heat

How is the excess carboxylic acid removed

with excess Na2CO3

How is boiling point determination done

A bell is placed into a capillary tube containing the sample

How does boiling point determination work

As heat is applied the air inside the bell expands and pushes out until it is replaced with the compound vapors

What is IR

the absorbance/transmittance of infared light

How is IR helpful

It helps identify specific functional groups

Where does the O-H bond show on the IR spectrum

3200

Where does the C-O bond show on the IR spectrum

1100-1300

Where does the C=O bond show on the IR spectrum

1600-1800

What does the OH bond look like on the IR spectrum

broad

what do the C-O and C=O bonds look like on the IR spectrum

sharp defined peaks

What is the Jones test positive for

aldehydes and primary and secondary alcohols

What is the Lucas test positive for

secondary and tertiary alcohols

What is the 2,4-DNP test positive for

aldehydes and ketones

What is the Tollens test positive for

aldehydes

What does a positive Jones test look like

a color change from red-orange to blue-green

What does a positive Lucas test look like

homogeneous solution become cloudy or 2 layers form

What does a positive 2,4 DNP test look like

formation of yellow-red precipitate

What does a positive Tollens test look like

formation of silver “mirror”

What type of solvents aren’t good for liquid-liquid extraction

water miscible (ethanol)