4. Why is it important to a. avoid inhaling vapors of organic solvents? b. know

Question

4. Why is it important to
a. avoid inhaling vapors of organic solvents?
b. know the location and operating instructions of the nearest fire extinguisher when using 95% ethanol or petroleum ether for testing solubilities?
NAME: ____________________________ DATE: ___________ TA: ______________________
5. The flash points of 95% ethanol and petroleum ether (bp 60–80 oC) are __________ and ___________, respectively.
6. By marking gravity (G) or vacuum (V) in the space provided, indicate which of the two different filtering
techniques is more suitable for each of the following operations.
______ a. Hot filtration.
______ b. Removing decolorizing carbon.
______ c. Isolating recrystallized solute from solution.
7. Why is flameless heating used for heating a solution in hexane or diethyl ether during a recrystallization?
8. What is the process of seeding, as it applies to recrystallization? What purpose does it serve?
9. What is meant by the term, “oiling out,” as it applies to crystallizations?
6. How is the purity of a recrystallized solid assessed?

Explanation / Answer

A)organic solvent are hazardous to human body ,they effect diffrant parts of the body

1)Respiratory tract

Vapours may be irritating to the lining of the respiratory tract, affecting the nose, throat and lungs. Asthmalike reactions have been reported with some organic solvents.

2)Skin

Solvent contact with the skin often causes drying, cracking, reddening and blistering of the affected area, leading to both irritant or allergic dermatitis. Absorption of solvents through the skin may also produce systemic health effects.

3)Eyes- Direct contact with vapour or liquid may cause eye irritation.

4)Liver - Many organic solvents are potentially toxic to the liver, either alone or in combination with other solvents. Kidneys Both short term and long term exposure to certain organic solvents has been found to be harmful to the kidneys. Carbon tetrachloride, trichloroethane and petroleum distillates are amongst the most toxic.

5)Cardiovascular system- Chlorinated hydrocarbon solvents (methylene chloride, chloroform and trichloroethane) may cause harmful effects on the heart, including abnormal heart rhythms and contribute to coronary heart disease.

6)Nervous system- Exposure to organic solvents can result in a variety of serious effects in both the central and peripheral nervous systems. The acute effects range from alcohol-like intoxication, stupor and insensibility, to unconsciousness and eventually lead to death from respiratory failure. Other symptoms may include drowsiness, headache, dizziness, gastric discomfort and nausea. Long term exposure to both n-hexane and methyl n-butyl ketone is associated with degeneration of nerve cells in the peripheral nervous system, resulting in symptoms such as restless legs, muscle cramps, pains , weakness and loss of sensation in the limbs.

5)The flash point of a volatile material is the lowest temperature at which vapors of the material will ignite, given an ignition source.

The flash points of 95% ethanol and petroleum ether (bp 60–80 oC) are ____12.8______ and _____-43______, respectively.

7)flameless heating used for heating a solution in hexane or diethyl ether becouse both solvent have low boiling point if they heat directly they catch fire

8)The principle behind recrystallization is that the amount of solute that can be dissolved by a solvent increases with temperature.

After cooling for some time, crystals should form on the bottom of the flask, You can often aid crystallization in stubborn cases by scratching the inside of the flask with a glass rod at the air-solvent junction. This scratching flecks off small shards of glass that form a surface upon which the solid can crystallize.

so Sometimes, the solution can be "seeded" by adding a small seed crystal of pure sample to the cold solution. This seed crystal also forms a surface for the solid to crystallize upon.

9)Oiling out has initially been observed during cooling crystallization of complex molecules like pharmaceuticals, proteins or polymers from solution

10)purity of a recrystalized solid is assessed by melting or boiling point of that solid they are charectristics of diffrent compounds

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