PRACTICAL 1: ROTARY EVAPORATOR AND CENTRIFUGE

Objectives

To understand the principles of rotary evaporator and centrifuge operation.

Introduction

The rotary evaporator is an instrument that is used in the lab for the removal of volatile solvents

from a nonvolatile or less volatile product. Most rotary evaporators have four major components:

heat bath, rotor, condenser, and solvent trap. Additionally an aspirator or vacuum pump needs to

be attached, as well as a bump trap and round bottom flask containing the sample to be

concentrated. The rotovap is designed to be operated under a vacuum (to lower a compound's

boiling point) and to heat the sample at the same time. A cold finger is used to condense the

vapors to a liquid, which are trapped in a separate flask.

Centrifugation is a process that involves the use of the centrifugal force for the sedimentation of

heterogeneous mixtures with a centrifuge, used in industry and in laboratory settings. This

process is used to separate two immiscible liquids. More-dense components of the mixture

migrate away from the axis of the centrifuge, while less-dense components of the mixture

migrate towards the axis. Chemists and biologists may increase the effective gravitational force

on a test tube so as to more rapidly and completely cause the precipitate ("pellet") to gather on

the bottom of the tube. The remaining solution is properly called the "supernate" or "supernatant

liquid". The supernatant liquid is then either quickly decanted from the tube without disturbing

the precipitate. The rate of centrifugation is specified by the angular velocity measured

in revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between

RPM and g depends on the radius of the sample in the centrifuge rotor. The

particles' settling velocity in centrifugation is a function of their size and shape, centrifugal

acceleration, the volume fraction of solids present, the density difference between the particle

and the liquid, and the viscosity.

Procedure

1. The basic operation of the rotary evaporator and centrifuge will be briefed by the scientific

officer.

Questions

1. Label the components of the rotary evaporator as given in the diagram below

2. Indentify the type of aspirator used in the laboratory rotary evaporator. Briefly describe the

function of the aspirator.

3. Explain why does the solvent flask need to be rotated at all times during the evaporation

process?

4. Explain the difference between differential centrifugation and zonal centrifugation based on

their principles and applications. Give examples.