Download UNIT 8 STEAM AND OIL BATHS

UNIT 8
STEAM AND OIL BATHS
I PRE-READING TASK (ANTICIPATION)
l. Look at the picture and try to explain the use of the steam bath.
2. How often do you use it in the laboratory?
For reactions which do not require heating above about 90°C, the steam bath is the heating
source of choice as it is inexpensive to purchase and operate and very safe. A steam baths
important limitation is that its maximum temperature is dictated by the boiling point of water.
A steam bath is much more useful than a free flame for heating low-boiling liquids. Any
vapors which escape from the distilling apparatus simply mingle harmlessly with water vapor
rather than igniting. Since the maximum temperature of steam at atmospheric pressure is
lOO0C, boiling is often less vigorous than with a free flame. A real advantage to using a
steam bath is that a reaction mixture which is somehow forgotten cannot heat above 100oC
and usually does not char.
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A reflux apparatus on top of a steam bath is a convenient way to reflux low-boiling organic
solvents. Boiling chips in the reaction mixture usually provide enough agitation to make
additional stirring unnecessary. The distance between the bottom of the flask and the bottom
of the steam bath makes magnetic stirring difficult. Overhead stirring is common in research
laboratories but too expensive for most teaching laboratories.
The several concentric rings supplied with a steam bath facilitate proper placement of the
flask. Remove as many rings as necessary for the reaction flask to rest on the ring which is
only slightly smaller than the flask. Do not completely immerse the flask in the steam bath.
Adjust steam pressure so that the flask heats but very little steam escapes. Turning up the
steam very high has little effect on the reaction vessel.
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Control the rate of reflux by varying steam pressure or by using a towel to keep in the heat.
Oil baths are particularly useful for heating reaction mixtures. The contact is intimate because
hot oil completely surrounds the bottom and sides of a flask. This results in even heating and
effective control. Oil baths are relatively inexpensive and are usually safe since:
1) lack of a flame makes ignition of solvent vapors unlikely; and
2) the temperature of a bath is proportional to the amount of heat put in and usually cannot
rise above some maximum value. Charring is thus less likely with oil bath than with either an
electric mantle or a bunsen burner.
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Problems associated with use of oil baths are:
1) they are often slow to heat;
2) when very hot, they fume and can catch fire; and
3) they cool slowly after use. In addition, the flask retains an oily residue, which not only is
sloppy but can cause burns when hot. Despite these difficulties, oil baths are very useful for
heating reaction mixtures.
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Adapted from " Experimental Organic Chemistry" by H.Dupont Durst & C. W'.Coekel
Figure 8 Oil bath
http://www-users.york.ac.uk/~dks3/facilities_frame_middle_files/oilbath.JPG
(2012-09-19)
Figure 9 Steam bath
http://www.chem.wisc.edu/areas/organic/orglab/images/tech/Steambath.jpg
(2012-09-19)
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II TEXT ORGANIZATION
Skim the text and find the main topic sentences and their supporting details.
Topic sentence
Supporting details
___________________________________________________________________________
III TEXT COMPREHENSION
Decide whether the following statements are true or false.
1. A steam bath is less useful than a free flame for heating low-boiling liquids.
2. The maximum temperature of steam at atmospheric pressure is 90°C.
3. Overhead stirring is usual in research laboratories.
4. Oil baths are useless for heating reaction mixtures.
5. Oil baths heat and cool quickly.
6. Charring is very likely to happen with oil baths.
TF
TF
TF
TF
TF
TF
IV FUNCTION WORDS
Scan the text to find the function words which show the relationship of:
CONTRAST
ADDITION
CAUSE-EFFECT
_________
_______
_________
V VOCABULARY
Match the words in the left-hand column with their explanations the right-hand column.
Immerse
Purchase
Ignition
Vigorous
Agitate
Reflux
- to heat so that the vapours condense and return
- the act of buying something
- to put into liquid so that it is covered
- to stir or shake strongly
- energetic
- the process by which an engine is started
VI WORD FORMATION
Common prefixes and suffixes that give negative meaning to adjectives are:
-un, -less, -in, e.g. undesired, helpless, ineffective. Scan the text to find the opposites for these
adjectives :
Expensive
Harmful
Useful
Necessary
Likely
__________________________
___________________________
___________________________
___________________________
___________________________
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VII WORD FAMILIES
Complete the following table.
Noun
Verb
ignite
Adjective
additional
immerse
reflux
vapor
placement
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