Chem 2L Post Laboratory Discussion

Experiment No. 1-7

Ms. Racquel T. Chua

Laboratory Instructor

Experiment No.1 Organic & Inorganic Compounds

Organic Chemistry- a branch of chemistry concerned with the study of carbon and its compounds. Known as chemistry of organic compounds.

• Tens of thousands inorganic compounds, while millions of organic compounds are known.

Main Sources of Organic Compounds:

Plants Petroleum products

Animals Coal

Who’s the Father of Organic Chemistry?

See video

Friedrich Wohler 1828- F. Wohler, a German chemist prepared urea by heating ammonium cyanate, an inorganic compound

Vitalism/ Vital Force Theory- states that organic compounds could be produced only by living matter. Living matter possess a mysterious or vital force which converts it into organic compounds.

A. Solubility

B. Melting and Boiling Points

C. Stability Towards Heat

D. Combustibility

E. Ionization

F. Acidity and Alkalinity

Other differences..

Experiment No.2 Detection of Common Elements in

Organic Compounds

A. Test for Carbon, Hydrogen & Oxygen

B. Test for Nitrogen

C. Test for Halogens

D. Test for Sulfur and Phosphorus

4

Experiment No.3 Purification of Liquids by Distillation

Definition of Terms Evaporation- escape of molecules from liquid to gas

phase.

Vapor Pressure- is the pressure exerted by the vapor above the liquid. A measure of the tendency of a liquid to pass into the gaseous state. It depends upon the nature of the liquid and the temperature.

Equilibrium Vapor Pressure- pressure exerted by a vapor when in equilibrium with its liquid.

Boiling Point- temperature at which the vapor pressure is equal to the prevailing atmospheric pressure.

Definition of Terms

Residue- liquid that remained in the distilling flask. It contains less of the volatile component as compared to distillate with richer volatile compound.

Azeotropic mixture- mixture of two or more substances that boil at a constant temperature.

Definition of Terms

Distillation- process of heating a liquid to its boiling point, condensing vapors and collecting liquid. Process of purification and separation of mixtures that involves conversion of liquid to vapor state and condensation of the vapor to liquid.

Distillate- vapor that is condensed to a liquid in the condenser and can be collected in a receiving flask (liquid in form).

Types of Distillation

Simple distillation- used if impurities are not volatile and the liquid compounds doesn’t decompose when boiled at normal atmospheric pressure. Used with improvised setup. (See image on the next page)

Simple Distillation Set Up

Types of Distillation

Fractional distillation- a process of separating volatile compounds of a mixture with arbitrary boiling points. Collection of different liquids at its respective boiling temperature. Done in decreasing order of boiling points.

Ex. Crude oil into fractions of gasoline, kerosene, lubricating oil etc.

Fractional Distillation Set Up

Problems Encountered

Importance of Distillation

Answers to Questions

Experiment No.4 Purification by Extraction

Result of Procedure

Description of Residue (after evaporation):

Benzoic Acid- White crystal like

(See set up )

Answers to Questions

1. Definition of Terms:

Extraction- general term for the recovery of a substance from a mixture by bringing it into contact with a solvent which preferentially dissolves the desired material.

Distribution coefficient-ratio of the concentration of the solute in each solvent at a particular temperature that is constant

2. MeOH and EtOH are poor extraction solvents as they are miscible in water, flammable, and have weak solvent action towards organic compounds

Answers to Questions

3. Ether is highly flammable

4. So that pressure is removed/ released for the smooth flow of the liquid

5. See computation on the next page.

Experiment No. 5 Purification by Recrystallization

Result of Procedure

Description of Impure Crystals (1g) :

Dirty white/ grayish

Wt of pure acetanilide crystals:

< 1 gram

% purity= actual yield x 100 e.g. 0.7 g x 100

theoretical yield 1 g

= 70%

(See video)

Answers to Questions

1. Crystals dissolved in warm solvent, however, upon cooling some will remain dissolved in the solvent and may be lost due to transfer from one container to another

2. a. Scratching the inside of the flask below the level of the sol’n. w/ a rod

b. Adding small crystals of pure material (seeding technique)

c. Reheating/boiling the solution to reduce volume of solvent then cooling afterwards to induce crystallization.

Answers to Questions 3. To prevent formation of crust or impure solid

Minimize crystallization of hot sol’n during filtration

4. Charcoal is a good adsorbing agent due to its large surface area that can attract particles to its surface

5. Characteristics of Solvent for Recrystallization

a. Dissolves the solute readily at an elevated temperature and sparingly at a lower temp.

b. Gives no chem’l reaction w/ solute

c. Sufficiently volatile so to easily remove from the purified crystals.

Experiment No.6 Purification by Microscale Sublimation

Result of Procedure

Weight of Benzoic Acid from Act 4 :

1 gram

Wt of pure product:

< 1 gram

% Yield = actual yield (sublimate) e.g. 0.5 g x 100

theoretical yield 1 g

(benzoic acid) = 50%

Answers to Questions 1. Sublimation- transition from solid to gas phase with no

intermediate liquid stage.

2. Sublimation is preferred for small scale purification as compared to crystallization

a)little loss of material during transfer,

b)small amount of material is used/ involved,

c)consumes less time with less transferring operation

d) may yield pure material

3. Applications of Sublimation:

a) when small amount of material is used/ involved

b) solid has high vapor pressure below its melting pt/ decomposition temperature

c) when the impurities have lower vapor pressure than substance purified

Experiment No.7 Paper Chromatography

Paper Chromatography

Answers to Questions

1. Rf- retention factor/rate of flow; ratio between distance travelled by solute and solvent

Importance:

a) Serve as guide and information on the mobility of substance/solute in a solvent system

b) For identification purposes

c) Basis in determining affinity of solute to solvent

Answers to Questions

2. Basis for the separation of components in a mixture by paper chromatography:

Solutes travel at different rates from the starting point (differential migration)

3. Applications of Paper Chromatography: a) Separation and identification of solutes e.g. amino acids b) Determination of pharmaceutical and

biological materials c) Separation of animal and plant products e.g

pigments

Answers to Questions

4. Definition of Terms:

Chromatography- process that involves separation of components in a mixture of compounds.

Development- movement of substance unto the absorbent medium carrying with it the components of a mixture being separated. The component of higher affinity to solvent is carried first.

Solvent front- maximum distance travelled by solvent

Stationary phase- medium having a relatively high surface area that is in fixed position through which the mobile phase is allowed to pass.

Answers to Questions

4. Definition of Terms:

Chromatogram- a series of separate zones on an adsorbent medium in which the different substances are separated by chromatography

Adsorbent- a finely divided solid having a surface area capable of holding other molecules or gases in an extremely thin layer

Mobile phase- usually an organic solvent that is allowed to be absorbed by the stationary phase.

Thank you