ANALYTICAL CHEMISTRY(Storage and handling of

Chemicals)

Dr.S.SURESHAssistant Professor

Email:avitsureshindia@gmail.com

Storage and handling of chemicals

The following rules should be strictly observed in storing and handling of chemicals.

• After using a chemical, the container should be tightly closed and returned to its original place.

• Care should be taken to see if all the containers have the appropriate labels stuck to them. No bottle should be left unlabelled.

• Corrosive chemicals should be stored in corrosion-resistant chambers.

• Some chemicals especially concentrated acids, produce lot of fumes on exposing to the atmosphere and therefore it is advisable to handle these inside a fume-hood.

Storage and handling of chemicals

• Flammable solvents like benzene, alcohol, ether and carbon disulphide should never be handled without turning off burners, heaters, etc.

• Some of the organic solvents like ether, because of their high volatility, build-up a pressure in the containers. Such containers should be cooled in ice and then opened.

• Flammable liquids should not be heated in an open vessel over a free flame. They should be heated in a flask fitted with a reflux condenser

Handling of acids• Store strong acids separately and away from

volatile organic chemicals.• Wear acid resistant chemical gloves and aprons,

when working with acids. Emergency flood showers or eye wash foundation must be available.

• Dilute acids by stirring the concentrated acid slowly into the water. Do not pour water in to acid.

• When using acids, make available suitable neutralizing agents for use in the event of spills.

• Acids should be neutralized with weak bases such as sodium carbonate or bicarbonate.

Handling of Ethers

• When ethers are exposed to air for long periods, peroxides are formed. Accidentally detonation of peroxides will lead to explosions. This danger is more, when ether is distilled. When there is a doubt about the presence of peroxides in ethers, these should not be handled without check.

Toxic chemicalsThe various chemical classes of toxic compounds

S.No Class Examples

1 Aromatic hydrocarbons Benzene, toluene, xylene, naphthalene, Anthracene

2 Amines Aliphatic amines, anilines, Napthyl amine

3 Chlorinated aliphatic hydrocarbons CHCl3, CCl4, CHCl2, CH2Cl

4 Inorganic CompoundsCompounds of the elements Be, Cd, Co, Cr, Ni, Pb, Ti, V etc.

Safe limits of vapour concentrations

• The safe limits of concentrations of chemical vapours in the air we breathe are much smaller than what we normally assume. For example, the threshold concentration limit for mercury vapour is 0.1µg/cubic metre, which can be easily attained from mercury spills on warm laboratory floors. Therefore stringent safety rules and careful handling of chemicals are essential for keeping the laboratory atmospheric concentrations of chemicals below the threshold limits.

Threshold limit values for some toxic vapours

S.No Substance Threshold limit(µg/cubic metre )

1 Acetone 2400

2 Ammonia 70

3 Carbon monoxide 110

4 Ethyl amine 45

5 Hydrogen sulphide 30

6 Mercury 0.1

7 Nitric acid 25

8 Formaldehyde 6

Antidotes

• An antidote is a substance which can counteract a form of poisoning. It is prudent to assume that every chemical used in the laboratory is a poison and hence handle it with care.

Treatment of specific poisons

• If a chemical is swallowed, immediate treatment should be given to the patient.

• Acetone: Induce vomiting and administer universal antidote. Keep the patient awake.

• Universal antidote: This is prepared by mixing 2 parts of pulverised charcoal, 1 parts of magnesium oxide and 1 part of tannic acid. A few grams of this can be added to a cup of warm water and then administered. This universal antidote is administered when a specific antidote is not known.

• Acids: Do not induce vomiting, administer magnesium oxide, or lime water immediately. Repeat the dose every fifteen or twenty minutes. Administer milk or white egg in cold water. Carbonates should not be given to the patient. Administer a few millilitres of mineral oil four or five times every fifteen minutes.

• Alkalis:Do not induce vomiting, administer 5% acetic acid or vinegar. Then administer, milk or white of egg.

• Methyl alcohol:Induce vomiting and then administer milk or white of egg

First aid Technique

Organic substances on the skin:• Wash liberally with rectified spirit, then with soap

and warm water.Acid on clothing:

• Apply dilute ammonium hydroxide to the affected area of the dress and then wash thoroughly with water.Alkali on clothing:

• Apply dilute acetic acid on the affected portion and then wash with plenty of water

Heating methods• A variety of methods for heating chemicals can be used in the

laboratory. Some of the method includes, the use of Bunsen burner, hot plate, and heating mantle. Heating with a Bunsen burner:

• The Bunsen burner is used routinely in the general chemistry laboratory. Many organic chemicals are flammable, and an open flame is an invitation to starting a laboratory fire or an explosion of combustible vapours. Never use a Bunsen burner in the presence of highly flammable solvents. In the organic chemistry laboratory, the Bunsen burner provides a high-temperature heat source (1000°C) for heating.

Heating with a Hot Plate • The variable-temperature hot plate is a very versatile

heating unit. The main advantage of using a hot plate is that it provides a flameless variable-temperature heat from a flat surface, so no additional support is normally required when using a flat- bottomed flask.

Heating with a Heating Mantle • A heating mantle is a specialized kind of heating

device designed to be used only with round-bottomed flasks when liquids are being heated under reflux or are being distilled. There are different heating mantles for each size of flask.

Stirring • A mixture can be agitated with a magnetic stirrer and with a

mechanical stirrer. Magnetic Stirrers:

• Magnetic stirring is the method of choice if an extended period of continuous agitation is required, since it is easy to set up the apparatus; particularly for small scale set-ups or closed systems.

Mechanical Stirrers • Larger scale reactions or viscous mixtures require

the greater power of an external motor unit turning a stirrer blade. It is highly advantageous for the motor to possess a variable speed control and a typical model is shown in the diagram

Filtration • There are few experiments in organic

chemistry that do not involve atleast one filtration step. Filtration is done by allowing the liquid to pass through a porous barrier, such as filter paper or sintered glass, whereby the solid remains on the barrier.

Gravity Filtration • Gravity filtration is a simple technique only

requiring a filter funnel, a piece of filter paper and a vessel, called the filter flask, usually an Erlenmeyer flask, for collecting the filtrate. Glass funnels are available in several sizes

Vacuum Filtration

• Carrying out a filtration using vacuum is faster than using gravity alone, but requires some additional equipment.

• Since the technique relies on producing a partial vacuum in the receiving flask, a thick-walled filter flask with a side arm, often called a Buchner flask, must be used.

Pipette

Calibration of Pipette

Calibration of Pipette

• The pipette is first rinsed with distilled water and the pipette is filled with distilled water.

• The water in the pipette is then drained into a clean, weighed stoppered weighing bottle.

• The draining should be done slowly by keeping the tip of the pipette in contact with the side of the bottle.

• The draining from the pipette is completed when the meniscus comes to rest slightly above the end of the pipette tip.

• The weighing bottle is reweighed. The temperature of the water is noted.

• The exact volume of the pipette is obtained from the weight of the water drained using Table1

Calibration of pipette

• The volume and weight of water contained in the pipette depends upon the temperature.

Volume occupied by 1.0g of water weighed

S.No Temperature (°C) Volume (ml)

1 10 1.0013

2 11 1.0014

3 12 1.0015

4 13 1.0016

5 14 1.0018

Burette

Calibration of Burette

Calibration of Burette

• The burette is filled with distilled water.• The water level in the burette is adjusted to the zero

mark. • The water is then drained fully into clean dry

stoppered weighed 100cm3 flask. • Any drop adhering to the tip must be removed by

touching the neck of the flask against the tip. • Restopper and reweigh the flask. Find out the weight

of water drained and note it carefully. • Repeat this procedure for for every cm3 or every 5

cm3 in a 50cm3 burette.

Calibration of Burette

• Note the temperature of the water and find out the volume delivered at each point from the weight using Table 1

• Volume occupied by 1.0g of water weighed

S.No Temperature (°C) Volume (ml)

1 10 1.0013

2 11 1.0014

3 12 1.0015

4 13 1.0016

5 14 1.0018

Calibration of standard measuring flask

Calibration of standard measuring flask

• The standard flask is first thoroughly cleaned and dried.

• Deionised water is then added slowly in to the flask through a small funnel until the mark is reached.

• When water is near the graduation mark, using a dropping tube, water is added drop wise until the meniscus stands on the graduation mark.

• The stopper is replaced and the flask is reweighed.• The actual volume of the water filling the flask up to

the mark can be calculated with the help of Table 1.

Chemical Balance

Weighing process in a chemical balance

In using analytical balance usually the following sequence is followed.• Sit opposite the balance, so that you face the centre of the

balance.• Remove any dust on the pans gently using a brush.• Release the beam carefully without jerk and check that the

pointer swings equally on either side of the zero reading on the scale. Otherwise adjust carefully to obtain this condition.

• Arrest the beam and then gently place the objects on the centre of the left side pan and close the balance case.

• Place suitable weights on the right side pan and check for equal oscillation. The pointer should swing through four or five divisions beyond the mid-point of the scale. At the final stage, rider must be used

Weighing process in a chemical balance

• When it is necessary to add more of solid or liquid, this must be done outside the balance case.

• Adding and removing the weights is done with minimum disturbance on the pan and always on the arrested position of the beam.

• The pans must on no account be touched while the beam is swinging.

• When the oscillation is equal, note carefully the weight of the object correct to 0.1mg.

• Arrest the beam, return the weights to the weight box, remove the object from the pan and clean the pans and the floor of the balance gently with the brush. Remember to close the balance case before you leave the balance room.

Single pan balance

Weighing in a single pan balance

• Rotate the arrest knob to the full release position and adjust the zero adjusting control until the illuminated scale indicates a reading of zero.

• Arrest the balance and place the object to be weighed on the pan. After turning the arrest knob to its partial release position, rotate the dial controlling the heaviest likely weight for the object until the illuminated scale changes position.

• The removal of the correct range of weight is indicated by the gentle movement of the illuminated scale being in view. Inadequate or excessive removal will make the illuminated scale disappear from the illuminated window

Weighing in a single pan balance

• When weights equivalent to the weight of the object have been removed, turn the arrest knob to its full release position and allow the balance to achieve equilibrium.

• The weight of the object is found by taking the sum of the weights indicated on the dials and that which appears on the illuminated scale.

• A vernier is use in reading the scale to the nearest tenth of a milligram.