MIDTERM: ORG. CHEM LAB

Sodium Sulfate

Amorphous, polar powder created in sublimation

Distillation

Limited to selected organic compounds because some decompose when distilled at normal atmospheric pressure.

*Cooling

Responsible for changing the hot gas into a liquid.

Induces the creation of crystals

Addition of benzoic acid, agitation, and scratching

Contaminant in recrystallization

Sodium Chloride & Methylene Blue

Solute (Exercise 5)

NaCl was dissolved in a beaker with hot water. Therefore, NaCl is a solute.

Appropriate Solvent

Most critical step in recrystallization

Activated Charcoal

One of the components of the universal antidote.

Silver Nitrate Test

A test for completeness of recrystallization.

White precipitate in AgNO3

Indicates the presence of sodium chloride impurity.

Crystal forms during recrystallization

• Needle-like

• Feather-like

• Scaly-like

• Blocks

Benzoic Acid

• Antifungal

• Preservative

Lower Boiling Point

A liquid with a _____ boiling point evaporates/vaporizes first during distillation.

Solvent

Too much _____ will not yield crystals.

Not react

The solvent should ______ chemically with the substance being purified.

Amorphous Powder

Appearance of residue in experiment 5

Acetone

A compound that was collected at 57 degrees Celsius.

Dissolves

Water in reaction with Na nitroprusside.

Form a homogeneous solution

Acetone in reaction with acetic acid.

0.57

Theoretical retention factor value (RF) of Glycine.

Good Solvent

The best solvent will dissolve the solute in hot solution but not in the cold solution.

Fractional Crystallization

Recrystallization’s other term

Recrystallization

The dissolution of the solid in an appropriate solvent at an elevated temperature and the re-formation of the crystals upon cooling.

Hot Solvent

Where solids are more soluble and solution crystallization takes advantage of this fact.

Desired Compound

Soluble in the hot solvent and insoluble in the cold solvent.

Removed from the crystals

The boiling point of the solvent should be low enough so that it can be _____

Poor Solvent

The solvent will dissolve the solute in cold solution but not hot solution.

Organic Compounds

Most dissolve in hot solvents rather than in cold ones.

Too much solvent is used

May decrease recovery

Supersaturated Solution

Too less solvent will not yield crystals

Decolorization with Activated Charcoal

Removes high molecular weight impurities which are often colored and relatively less soluble.

Decolorization with Activated Charcoal

High degree of microporosity; has a large surface area.

Short-stemmed or Stemless Glass Funnel

Used to minimize crystallization in the funnel.

Oiling Out

Solute separates from the solution as an oil instead of a solid and contains impurities.

Vacuum Filtration

Solid product is isolated by _____

Buchner or Hirsch Funnel

Solid product is isolated by vacuum filtration using a _____

Gravitational Filtration

Solid product is isolated by vacuum filtration using a Buchner funnel or a ______.

Air or Oven Drying

Removes the last traces of solvent from the crystalline product.

Melting Point Determination

How purity of the crystals is usually assessed as the presence of impurities decreases the melting point of the product.

Silver Nitrate Test

To detect any sodium chloride (NaCl) impurity left on the purified crystals (white precipitate).

Sublimination

The direct conversion of a substance from its solid phase to its gas phase without passing the liquid phase.

Sublimination Process

Relies on the equilibrium between the solid and gas phases rather than solid and liquid phases.

Sublimation Mechanism

Enough energy builds up in the molecules during heating and then escapes into gas phase.

Sublimation Set-Up

• Outer or lower vessel: Impure sample location

• Inner or upper vessel: Pure solid

Upper Vessel

Must be cold for the pure solids to form on it.

Sublimate

The crystals obtained when a substance is heated.

Sublimate

• High vapor pressure

• Low melting point

• More volatile

Residue

The solid particle that remains on the dish.

Residue

• Low vapor pressure

• High melting point

• Less/Non-volatile

Purification

Depends on volatility

Sublimation Limitation

It cannot be used for separating compounds that have similar vapor pressures.

Barium Chloride Test

Employed to differentiate the organic substance from the inorganic residue.

White Precipitate

Produced when barium chloride reacts with sodium carbonate, therefore identifying the residue from the sublimate.

Benzoic Acid

• Colorless crystalline

• 122.12 g/mol

• Melting: 122-123° C

• Boiling: 249°

• Toxic to the lungs & nervous system

Impurities

Sodium Chloride & Methylene Blue

Methylene Blue

• Separated upon filtration after the addition of activated charcoal.

• Crystals will remain if methylene blue is incompletely separated.

Sodium Chloride

Should not yield white precipitate to complete separation.

Salicylic Acid

• Colorless, needle-like crystals

• 138.12 g/mol

• Melting: 158°

• Boiling: 211°

• Toxic through ingestion (Salicylism)

Salicylic Acid

Keratolytic (for acne, seborrhea, corn, calluses and warts)

Sublimate

• Salicylic Acid

• Needle-like crystal

• Non-polar

• Organic

• 8.2 × 10^-5 mmHg at 25°

Residue

• Sodium Sulfate

• Amorphous Powder

• Polar

• Inorganic

• 3.4 × 10^-5 mmHg at 25°

FALSE - Non-polar

All hydrocarbons are polar.

Catenation

Ability of hydrocarbons to bond with themselves.

Criteria for aromaticity

• Cyclic structure

• Planar

• Follow Huckle’s rule

• With conjugated bonds

Benzene

The most common example of an aromatic compound.

Hydroxyl

Functional group present in alcohols

Methanol

Alcohol that undergoes oxidation to form formaldehyde.

Baeyer’s Test

This test is used as a qualitative test for compounds that has a presence of a double and triple bond.

Unsaturated Hydrocarbons

More reactive than saturated ones.

Double Bonds

• 1 sigma bond

• 1 pi bond

Single Bonds

• 1 sigma bond

Triple Bonds

• 1 sigma bonds

• 2 pi bonds

Paraffins

Synonym of alkanes

Carbon Monoxide

Produced during incomplete combustion.

R2CHOH

General formula for secondary alcohol

Alcohols

Have a higher boiling point than hydrocarbons.

Jones Test

A test used to distinguish primary and secondary alcohols from tertiary alcohols.

Non-luminous Flame (Ignition Test)

• Gasoline

• Kerosene

Luminous Flame (Ignition Test)

• Benzene

• Cyclohexane

• N-Hexane

Incomplete Combustion

Combustion of luminous flame.

Complete Combustion

Combustion of non-luminous fame.

Presence of Soot: Absent

• Gasoline

• Kerosene

presence of soot: Present

• Benzene

• Cyclohexane

• N-Hexane

Jones Test for Tert-butyl Alcohol

Orange Solution

Lucas Test for Sec-butyl Alcohol

Two-layer solution

Positive test result of methanol test/test for methanol

Red violet ring at the junction

Baeyer’s Test: Purple colored solution

• Benzene

• Cyclohexane

• N-Hexane

Baeyer’s Test: Reddish-brown precipitate

• Gasoline

• Kerosene

Test for Aromaticity: N-Hexane

Clear colorless solution

Nitronium Ion

Very powerful; linear electrophile

Nitration Test

Predicts the presence of aromatic ring through the formation of a yellow colored layer.

Bromine Test: Alkene product

Dibromo

Bromine Test: Alkyne product

Tetrabromo

Weak pi bond

A bond in alkenes and alkynes that are susceptible to addition reaction.

Baeyer’s Test: Alkene product

Diol

Baeyer’s Test: Alkyne product

4 hydroxy