SUBLIMATION- lab report

          ORGANIC CHEMISTRY

                 LAB REPORT 04

EXPERIMENT TITLE: SUBLIMATION


ABSTRACT

Sublimation is the transition of solid into a gas phase without passing the liquid phase. Small samples of unclean solids can be purified by sublimation, or evaporation consolidation. The imperfect solid is heated on a hot surface, evaporation and condensation (solidifying) on ​​a cold surface. Once on the cold surface, the purified compound can be carefully extracted collected, leaving the impurities behind the hot surface. Sublimation is useful a purification technique if the impurities are essentially non-volatile and a desirable substance its melting point has a vapor pressure of at least a few Torre. Sublimation is best used on small sample sizes since the product loss in transfer and collection is small.

INTRODUCTION

Sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase. This endothermic phase transition occurs at temperatures and pressures below the triple point. The term "sublimation" only applies to physical changes of state and not to the transformation of a solid into a gas during a chemical reaction. The opposite process of sublimation where a gas undergoes a phase change into solid form is called deposition or DE sublimation.

Sublimation is widely used to separate volatile components from non-volatile components. As such, it is a useful preparation technique for the recovery of compounds that can be emptied at reasonable temperatures, atmospheric pressure or reduced pressure. The temperature at which a sublimate is observed in a particular system is often called the sublimation temperature, but it is useless for comparative purposes unless the variables such as pressure, size, and geometry of the sublimation apparatus are standardized. The list of substances that can be sublimation includes aromatic hydrocarbon hydrocarbons, benzoic acid, salicylic acid, camphor, saccharin, quinine, cholesterol, pallet and stearic acids, acetylsalicylic acid and atropine. Despite its success, sublimation has limited application and extraction dependence on the vapor pressure of the analyses at a given temperature and pressure, and the nature of the matrix, make it difficult to optimize trace analysis.

OBJECTIVES

1)    Purifying small amount of solid organic substances

MATERIALS AND METHOD

MATERIALS

·       Naphthalene

·       Small dry beaker

·       Round bottom flask

·       Watch glass

·       Ice

 METHODS

 

1.     1g of dry crude material (naphthalene) was placed in a small beaker.

2.     A round bottom flask which is smaller than the largest diameter of the beaker containing ice, was put on the top of the beaker

3.     Beaker was heated gently.

4.     Heating was stop after the material vaporized and the vapor reached the cold surface of the round bottom flask where it cools and condenses as fine crystal.

5.     The system was led to cool for a while and collect the pure crystals formed on dry clean watch glass.

6.     Product was weighted and percentage yield of the pure compound was calculated.

RESULTS

Mass of the impure sample = 1g

Mass of the weighing paper = 1.03 g

Mass of the naphthalene crystals + weighing paper = 1.95

1st time:

Mass of the pure sample = 1.95 g- 1.03 g= 0.92 g

Percentage yield of the pure compound = 0.92/1.0 X100 % = 92 %

2nd time:

Mass of paper + naphthalene extract = 1.79

Mass of pure sample = 1.79 – 1.03 = 0.76

Percentage yield of pure sample= 0.76/1.0 x 100% = 76%

DISCUSSION

This experiment conducted to study the sublimation of naphthalene. Naphthalene is a compound which has formula of C10H8. The aim of this experiment was to observe the phase changes of naphthalene and also the ability of naphthalene to sublime and so deposit. Naphthalene crystals disappear with time because they undergo the method of sublimation within which solids directly change to gas without probing liquid state. Sublimation is a purification method of organic compounds was a way or methods to clean the useful substances from impurities so as to get the required pure substances.

The impure naphthalene was heated in a beaker covered with round bottom flask filled with ice cubes. Once the material vaporizes and the vapor passes up into the cold surface of the round bottom flask where it cools and condenses as fine crystals which called as sublimate. The sublimate was collected afterwards for computing percentage recovery. If we want to collect maximum amount of crystals the system was fixed and the processes are repeated .This percentage recovery was affected thanks to some possible errors. Sources of errors would come with excess heat and another error would be the innate difficulty of extracting all of the crystals, which might affect the percent recovery.

QUESTIONS

 

1.     Define the following terms

a.     Evaporation

Evaporation is the process of which, element or compound transition from its liquid state to its gaseous state below the temperature at that it boils

b.     Sublimation

Sublimation is the process of which, element or compound transition from solid phase to gaseous phase without passing through the liquid phase

2.     Naphthalene, C10H8 is insoluble in water but sublimes easily when heated. How could you separate a mixture of naphthalene and NaCl?

Naphthalene will sublime easily but common salt won't sublime. Heat the mixture of Naphthalene and NaCl. Naphthalene will sublime into a gas. Place a cooled surface above the fumes. The cooled surface cause the Naphthalene vapors to return to the solid phase. But the NaCl will remain within the original container due to it'll be unaffected by the heating.



APENDIX








Figure 1; heat water bath with naphthalene beaker with ice.



   



Figure 2; crystals made from naphthalene




REFERENCES

1.     Joaquín Isac-García, ... Henar Martínez-García, in Experimental Organic Chemistry, 2016

2.     Donald M. Mattox, in Handbook of Physical Vapor Deposition (PVD) Processing (Second Edition), 2010

3.     Wilfred L.F. Armarego, in Purification of Laboratory Chemicals (Eighth Edition), 2017











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