chemical-page3

16.What is a solvent?

Ans:

According to the US Solvent Council, "A solvent is a liquid which has the ability to dissolve, suspend, or extract other materials without chemical change to the material or solvent. Solvents make it possible to process, apply, clean, or separate materials.

17.What is happening when paint dries?

Ans:

During the manufacture of paint, solvents are added to make the paint thinner so that it can be applied to various surfaces. Once the paint is applied, the solvents evaporate and the resins and pigments that make up the paint for a thin, solid layer on the surface.

18.What is quicklime and what are the uses?

Ans:

Quicklime (Calcium Oxide) is an efficient scavenger of moisture in its dehydrated state. It is also cheap, compared to orthe scavengers such as silica gel, drierite, oxazolidines, etc. It is commonly found in water sensitive paint formulations (such as polyurethanes and polyureas).

19.In case of welded vessels why is stress relieving in the form of post-weld treatment necessary?

Ans:

When a metal is welded together the point at which the two surfaces are joined are subjected to very high temperatures. During this time period the metals can go through a lot of random metallurgical processes. This causes the metal to be harder and brittle. This depends on the amount of carbon content. In order to relieve the metal of these properties heat treatment is done on the affected areas. By doing so the affected areas ductility increases. In this process the heat is maintained in the affected metal according to the thickness of the metal. The temperature of the heat is calculated from the P number which is unique for a particular composition.

20.What significance the angle of repose holds in the chemical industry, Explain?

Ans:

The angle of repose is a property of particulate solids. A conical pile is formed when a bulk solid is poured onto a flat surface. The angle formed between the flat surface and the pile edge is called the angle of repose. The angle of repose depends on the following factors:

> Density of the material

> Surface area

> Coefficient of friction of the material

A material having a low angle of repose would always create float piles as compared to materials with a high angle of repose. This is used in the designing of equipments which are used for particulate solids. In addition to that this angle can be used to calculate the size of the conveyor belt that is used to transfer the materials.

21.What is the difference between vapor and gas?

Ans:

A vapor is formed by heating any liquid and it can be condensed at atmospheric conditions either by reducing temperature or be increasing pressure. But a gas has already above the critical temperature and can’t be condensed by application of above methods. First it has to be brought below critical temperature. Then only it can be condensed.

22.What is the difference between evaporation and boiling?

Ans:

Evaporation happens at any temperature whereas boiling occurs only at a single temperature for a single component like water. For example the water at sea surface evaporates everyday. It may happen either at 300C or 350C, whereas water boils only at 1000C when the vapor pressure becomes equal to atmospheric pressure.

23.Differentiate compressors, fans and blowers?

Ans:

Fans, blowers and compressors are differentiated based on the method used to move the air and specific ratio (specific ratio= discharge pressure/suction pressure). As per the American Society of Mechanical Engineers (ASME) the compression ration for fans is up to 1.11, blowers- 1.11 to 1.2 and for compressors above 1.2

24.Why earthing done in reactors?

Ans:

To ground the static electricity that may be produced in the reactor due to reaction. 
      

25.Why SS are not corrosive?

Ans:

The SS (stainless steel) contains some percentage of chromium. The chromium reacts with oxygen (which is present in air) to form Cr2O which prevents further oxygen to react with Iron (Fe) of SS to form rust.



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