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CHEMICAL ACID BATH

An acid bath is a container containing acid in which the labware is placed and kept for some time until clean. The container should be made of moulded plastic or pyrex glass with a loose fitting lid. The size and shape may vary according to wash load and need.

Making 1m nitric acid Use Fume Hood to carry out this dilution.
Concenrated nitric acid is 16.4 M according to product label of the acid used here. 1M dilution is 61 mls/lier. Measure 62 mis of conc nitric acid and add it slowwly with stirring into a 2 liter container with 1 liter distilled in it. Allow to stand and cool.

Making 1:1 nitric acid Use Fume Hood to carry out this dilution.
1:1 acid is an equal mix of conc acid and distilled water. For a 2 liter solution, measure 1 liter of conc acid and add it slowly with stirring into a container Bucket or polythene trough, containing 1 liter of distilled water. Allow to stand and cool.

Cleaning glass,plastics,ceramic items.

Immerse apparatus into a 1M nitric acid and allow to soak overnight for low contamination. For heavy contamination use a 1 : 1 nitric acid mixture and keep in bath for about one week.
The cleaned labware is then taken out off the bath and rinsed with distilled water and put to dry. A rinse with acetone or placement in a glassware dryer at low temperature can be used.
Items made out of metal such as tongs, spatulas, and stirring bars should not be placed in the bath becuuse the strong acid will carode them out of shape.
Acid baths are in the range of ph 4 - 6 and a temperature range of 60 - 90 degrees centigrade. Plastics tend to float when put into the cleaning solution and can be sunk to the bottom using a pair of tongs.

OIL and CHEMICAL TEMPERATURE BATHS

bath mixture media

Media	m.p. °C	b.p. °C	Working range °C	Flash point °C	REMARKS
Water	0	100	0 to 80	none	Ideal within the stated range
Ethylene glycol	-12	198	-10 to 180	111	Flammable, difficult to remove from equipment
Silicone oil	-60	>250	20 to 250	300	becomes viscid at lower temp; non-corrosive
Triethylene glycol	-7	287	0 to 250	156	water-soluble, stable
Glycerol	18	290	20 - 260	160	water-soluble, non-toxic, viscid
Paraffin liquid		300-500	20 to 200	230	Flammable
Heating bath fluid	-40		0 to 170	280	miscible with water, non-toxic
Potassium nitrate (51.3%)	219		230 to 500		stable in air,strong oxidizing agent, non flammable
Sodium hydroxide (40%)	167		200 to 800		corrosive and harmful

FREEZING MIXTURES

Media	Temperature that can be reached °C	REMARKS
Ice water and salt (sodium chloride)	can reach up to -20 °C with this mixture	This is the standard laboratory freezing mixture
Ice water and hydrous calcium chloride	temperatures can be obtained as low as -55 °C with this mixture	This temperature could not be achieved in this lab
Dry ice and acetone	One can go as low as -78 °C with this combination	It takes patience, effort and dedication to achieve such low temperatures
Dry ice and Diethyl ether	may be possible to reach down to -100 °C with this mixture	This temperature could not be obtained. It seems most likely that the temperatures are highly dependent upon the relative proportion of the reactants in the combination mixtures.

Delloyd's lab resources

Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
Last Update: February 2004.