- No.16. What is the difference between crude oil and residual oil?
Answer. Crude oil is the dark brownish viscous liquid formed by decomposition of remains of dead plants and animals in the absence of air because of high pressure, temperature and bacterial effects. When it is heated in a furnace up to 400°C under high pressure it gives important fraction of petroleum.
While, residual oil is the left behind residue of crude oil that does not vaporize when crude oil is seated in a furnace up to 400°C under high pressure. Residual oil is collected from the fractionating volume and is heated above 400°C to obtain four fractions; lubricants, paraffin wax, asphalt and petroleum coke.
- No.17. Which petroleum fraction is used in dry cleaning?
Answer. The fraction of petroleum used in dry cleaning is gasoline or petrol.
ANSWERS TO THE LONG QUESTIONS
- No.1. Describe in detail the various processes involved in the concentration of ore. Explain your answer with the help of diagrams.
Answer. The process of removal of gangue from the ore is technically known as concentration and the purified ore is called the concentrate. Concentration of the crushed ore is carried out by the following methods:
(a) Gravity separation
Gravity separation is based on the differences in densities of the metallic ore and the gangue particles.
In the process, the powdered heavy met
al bearing ore settles down on agitation in a stream of water, while the lighter gangue particles are carried away by the water as shown in figure below:
(b) Froth flotation process
Froth flotation process is based on the wetting characteristic of the ore and the gangue particles with oil and water, respectively.
The ore particles are preferentially wetted by the oil and the gangue particles by the water. Hence ore particles come to the surface in the form of a froth that can be skimmed as shown in figure below:
Fig.16.2. Froth floatation process
(c) Electromagnetic separation
Electromagnetic separation is based on the separation of magnetic ores from the non-magnetic impurities by means of electromagnets or magnetic separators. The powdered ore is dropped over a leather belt moving over two rollers, one of which is magnetic. The ore gets attracted and is collected nearer to the magnet while the nonmagnetic impurities fall further away as shown in figure below:
- No.2. Explain the process of roasting with reference to copper.
Answer. Roasting: It is a process of heating the concentrated ore to a high temperature in excess of air. For example; copper pyrite (CuFeS2) is strongly heated in excess of air to convert it into a mixture of cuprous sulphide and ferrous sulphide (Cu2S + FeS). While impurities sulphur, phosphorus arsenic etc. react with oxygen to form volatile oxides. Such as
2 CuFeS2(8) + O2(g) ———> Cu2S(s) + 2FeS(s) + SO2(g)
- No.3. Write a detailed note on Ammonia Solvay process.
Answer. Principle of Solvay process lies in the low solubility of sodium bicarbonate at low temperature i.e. at 15°C. When CO2 is passed through an ammonical solution of NaCl called ammonical brine, only NaHCO3 precipitates.
Na+(aq) + HCO3–(aq) NaHCO3(s)