How is carbon black obtained ?
- A.By heating wood at high temperature in absence of air
- B.By heating coal at high temperature in absence of air
- C.By burning hydrocarbons in a limited supply of air
- D.By heating coal at high temperature in presence of air
Correct answer
Explanation
The correct answer is C, By burning hydrocarbons in a limited supply of air. When natural gas or heavy oil burns with too little air, the carbon cannot all turn into carbon dioxide and separates as a very fine black soot, which is collected as carbon black.
Carbon black is an almost pure, finely divided form of amorphous carbon. Its biggest use is as a filler in rubber: it makes vehicle tyres stronger, longer-lasting and black. It is also used in printing ink, black paint, toner and shoe polish. The same incomplete combustion is why a kerosene lamp with a poor air supply gives a sooty flame.
A is wrong because heating wood without air (destructive distillation) gives charcoal.
B is wrong because heating coal without air gives coke, along with coal tar and coal gas.
D is wrong because heating coal in air simply burns it to carbon dioxide and ash.
Exam tip: wood without air → charcoal; coal without air → coke; hydrocarbons in limited air → carbon black (lamp black).
Practice Questions
View allThe potential difference between the terminals of an electrical heating device is 40 V, when it draws a current of 2 A from the source. Which one of the following is the correct value of current drawn by the heating device if the potential is increased to 140 V?
- A.7 A
- B.5 A
- C.4 A
- D.2 A
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By Ohm's law the heater's resistance is 40 V divided by 2 A, which is 20 ohms, so at 140 V it draws 140 divided by 20, or 7 A. Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across…
Read the full explanation →Consider the following statements in the light of octane number and cetane number of fuels: 1. Cetane number is used for gasoline and octane number is used for diesel. 2. Octane number of n-hexadecane is 100 and cetane number of isooctane is 100. Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Both statements swap the two scales: octane number rates petrol, cetane number rates diesel, and their reference fuels are the other way round.
Read the full explanation →Which one among the following statements related to human eye is correct?
- A.For a person suffering from short-sight defect, the image of a distant object is focused behind the retina.
- B.Short-sight defect can be corrected by a converging spectacle lens.
- C.For a person suffering from long-sight defect, the image of a near object is focused behind the retina.
- D.Long-sight defect can be corrected by a diverging spectacle lens.
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In long-sightedness (hypermetropia) the eye cannot see nearby objects clearly because their image is formed behind the retina.
Read the full explanation →When sunlight (white light) falls on a triangular glass prism, a band of colours called a spectrum is obtained. Which one among the following represents this effect appropriately?
- A.Reflection
- B.Diffraction
- C.Refraction
- D.Dispersion
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The splitting of white light into its seven component colours by a prism is called dispersion. White light is a mixture of colours, and glass bends each colour by a different amount because its refractive index depends on wavelength.
Read the full explanation →Which one of the following statements is correct?
- A.The number of electrons in alpha particle is 2.
- B.The coordination number of EDTA is 6.
- C.The charge of beta (β) particle is +2.
- D.Both carbon and silicon form ionic compounds.
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EDTA is a hexadentate ligand: one EDTA ion binds a metal ion through six donor atoms, so it forms complexes with coordination number 6.
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