ORGANIC CHEMISTRY 1 LAB

EXPERIMENT NO. 1 to 6 DISCUSSION

EXPERIMENT NO. 1: Mel=ng Points And Boil ing Points Of Organic Compounds Mel=ng Point

- temperature at which the liquid and solid are in equilibrium at a pressure of 1 atm

Mel=ng Point Range

- determines the purity of a solid sample - temp at which the solids start to liquefy - temp at which the solid is completely liquid.

Importance of Mel/ng Point Determina/on: 1. Calibra=on of Thermometer 2. Determina=on of the purity of the substance

MP range Factors Aec=ng the Mel=ng Point: 1. Intermolecular forces of ASrac=on 2. Geometric isomers 3. Purity

Intermolecular Forces of ASrac=on

A. Hydrogen Bonding - strongest of all intermolecular forces of aSrac=on -Only when a hydrogen shares electrons with a highly electronega=ve atom (O, N, F, or Cl) will it carry a large par=al posi=ve charge.

B. Dipole-dipole Forces - result when polar molecules line up their

OPPOSITE charges.

C. London Dispersion Forces - weakest of all intermolecular forces of aSrac=on - uneven electron distribu=on due to constant random mo=on of the electrons in the molecule that produces a temporary dipole, which can induce a temporary dipole in a neighboring molecule.

Consider the compounds used in the experiment:

Explain the observed trend in the mel=ng points.

OOH

OH

Salicyclic Acid

O

O

Benzoin

NH2

O

NH2

Urea

OOH

Benzoic Acid Naphthalene

decreasing melting point

Geometric Isomers A chemical compound having the same molecular formula as another but a dierent geometric congura=on, as when atoms or groups of atoms are aSached in dierent spa=al arrangements on either side of a bond or a ring.

With rings and C=C double bonds, cis and trans nota=on is used to d is=nguish between stereoisomers. Cisiden=cal groups are posi=oned on the SAME side of a ring.

Transiden=cal groups are posi=oned on OPPOSITE sides of a ring.

OH

O

OH

O

Maleic Acid

OH

O

OH

O

Fumaric Acid

Which one has the higher mel=ng point? Why?

Boiling Point

- temperature at which the vapor pressure of a substance is already equal to the atmospheric pressure.

Factors Aec=ng the Boiling Point: 1. Intermolecular forces of ASrac=on 2. Molecular Weight 3. Branching

Intermolecular Forces of ASrac=on

Explain the boiling point trend observed.

O

OH

propanoic acid

OH

butan-1-ol

O

butan-2-oneheptane hexane

Decreasing Boiling Point

Molecular Weight

Explain the boiling point trend observed.

Branching

Explain why more highly branched molecules generally have lower boiling points.

Eutec=c Point -lowest possible temperature of solidica=on for any mixture of specied cons=tuents. Used especially of an alloy whose mel=ng point is lower than that of any other alloy composed of the same cons=tuents in dierent propor=ons.

EXPERIMENT NO. 2: Recrystalliza=on

- method of purifying a solid substance based on solubility

Solubility - maximum amount of solute that a solvent can dissolved at a given temperature

Solubility We use the principle that like dissolves like. Polar compounds GENERALLY mix well with other polar compounds: If the compounds mixing are all capable of H-bonding and/or strong dipoledipole interac=ons, then there is no reason why they shouldnt mix.

Nonpolar compounds GENERALLY mix well with other nonpolar compounds: If none of the compounds are capable of forming strong aSrac=ons, then no strong aSrac=ons would have to be broken to allow them to mix.

Property of Solvent for Recrystalliza/on: 1.Dissolve all of the compound at high temperature. 2.Dissolve very liSle or none of the compound at low temperature.

3.Have a dierent solubility for the compound and the impuri=es.

4.Have a boiling point below the mel=ng point of the compound (60 100 deg. C)

5.Inert 6.Inexpensive

Steps in Recrystalliza=on

Filtration Proper way of folding the filter paper

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Precipitation Gravimetry Proper way of filtering

The trap is used to prevent water from a water aspirator from backwashing into the suction flask.

Sample Problem: Sucrose is the chemical name for the sugar that we consume. Its solubility at 20oC is 204 g / 100 g water, and at 100oC is 487 g / 100 g water. A solu=on is prepared by mixing 139 g of sugar in 33.0 g of water at 100oC . (a) What is the minimum amount of water required to dissolve the sugar at 100oC ? (b) What is the maximum amount of sugar that can be dissolved in the water at 100oC ? (c) The solu=on is cooled to 20oC . How much sugar (if any) will crystallize out? (d) How much water is required to dissolve all the sugar at 20oC?

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EXPERIMENT NO. 3: Simple And Steam Dis=lla=on Dis/lla/on -a physical method of assor=ng mixtures depending upon the dierence in the boiling point of the component substances.

Dis/lland - mixture being dis=lled and usually placed in a dis=lling ask

Dis/llate - liquid separated from dis=lla=on process

Types of Dis=lla=on

A. Simple Dis=lla=on - for a mixture in which the boiling point of the components dier by at least 70C. It is also followed for the mixtures contaminated with nonvola=le par=cles (solid or oil) and those that are nearly pure with less than 10 percent contamina=on.

B. Frac=onal Dis=lla=on

- Those mixtures, in which the vola=lity of the components is nearly similar or diers by 25C (at 1 atmosphere pressure), cannot be separated by simple dis=lla=on. - the cons=tuents are separated by a frac=ona=ng column. - used for the alcohol purica=on and gasoline purica=on in petroleum rening industries.

C. Steam Dis=lla=on - used for the purica=on of mixtures, in which the components are temperature or heat sensi=ve; for example, organic compounds. - prac=ced for the large-scale separa=on of essen=al oils and perfumes.

D. Vacuum Dis=lla=on -a special method of separa=ng compounds at pressure lower than the standard atmospheric pressure. Under this condi=on, the compounds boil below their normal boiling temperature. Hence, vacuum dis=lla=on is best suited for separa=on of compounds with higher boiling points (more than 200C), which tend to decompose at their boiling temperature.

Type of Dis=lla=on Set-up 1. Open type 2. Close type

Type of Condenser: 1. Water condenser 2. Air condenser

In Steam Dis=lla=on: PT = Pwater + PA

For two compounds, steam and compound A: nsteam Psteam _______________ = ________ nA PA

EXPER IMENT NO. 4 :F rac=ona l Dis=lla=on used when the component parts boil at less than 25 C from each other under a pressure of one atmosphere (atm).

Frac=ona=ng Column - heart of the dis=lla=on process

Principle involved: Raoults Law

PA = Po Xvola=le component Where: PA = par=al pressure of substance Po = vapor pressure of pure component X = mole frac=on

Sample Problem

At 40oC , the vapor pressure of pure heptane is 92.0 torr and the vapor pressure of pure octane is 31.0 torr. Consider the solu=on that contains 1.00 mole of heptane and 4.00 mole of octane. Calculate the vapor pressures of each component and the total vapor pressure above the solu=on

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E x p e r i m e n t N o . 5 : Chromatography -a physical method of separa=on in which the components to be separated are distributed between two phases, one of which is sta=onary (sta=onary phase) while the other (the mobile phase) moves in a denite direc=on.

Components in Chromatography: 1. Immobilized/Sta/onary phase

- a sta=onary phase which is immobilized on the support par=cles, or on the inner wall of the column tubing.

2. Mobile phase - the phase which moves in a denite direc=on. It m a y b e a l i q u i d ( L C a n d C a p i l l a r y Electrochromatography (CEC)), a gas (GC), or a supercri=cal uid (supercri=cal-uid chromatography, SFC). - consists of the sample being separated/analyzed and the solvent that moves the sample through the column.

Types of Chromatography: 1.Column Chromatography 2.Planar Chromatography - a separa=on technique in which the sta=onary phase is present as or on a plane.

Types of Planar Chromatography 1. Paper chromatography 2. Thin layer chromatography

Reten/on Time , Rate of Flow, Rf -the characteris=c =me it takes for a par=cular analyte to pass through the system (from the column inlet to the detector) under set condi=ons.

distance travelled by solute Rf = -------------------------------------- distance travelled by solvent

EXPERIMENT NO. 6: Extrac=on

Liquid-Liquid Extrac/on - a method to separate compounds based on their rela=ve solubili=es in two dierent immiscible liquids, usually water and an organic solvent.

Sal/ng-out Eect - addi=on of salt causes the solubility of organic solute in a given solvent to decrease. - enhances extrac=on process for compounds not eciently transferred to organic layer during extrac=on

The organic solvent used for extrac=on must meet a few criteria:

1. Should readily dissolve substance to be extracted. 2. Should not react with the substance to be extracted. 3. Should not react with or be miscible with water (the usual second solvent).

4. Should have a low boiling point so it can be easily removed from the product.

Distribu=on Coecient, KD

[solute]organic layer KD = ----------------------- [solute]aqueous layer

Mul=ple Extrac=on

Where: (caq)n = conc. of solute in the aqueous layer aser nth extrac=ons

n = number of extrac=on D = distribu=on coecient, KD Vaq = volume of aqueous solu=on Vorg = volume of organic solvent (caq)o = conc. of solute in the aqueous layer ini=ally

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Sample Problem

The distribu=on coecient for iodine between CCl4 and water is 85. Calculate the concentra=on of I2 remaining in the aqueous layer aser extrac=on of 50.0 ml of 1.00 x 10-3 M I2 with the following quan==es of of CCl4 : (a) 50.0 ml, (b) two 25.0 ml por=ons, and (c) ve 10.0 ml por=ons.

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Preliminary Examina=ons of Mixture

Physical state is noted Solubility / miscibility in water Presence or absence of residue is determined by evapora=on to dryness.

For liq-liq mixtures, presence or absence of water is detected by: Anhydrous Copper sulfate test Dis=lla=on test (using anhydrous toluene)