Engineering Questions with Answers - Multiple Choice Questions
Applied Chemistry MCQ – Classification of Lubricants – 2
The molecular structure of the organic lubricants consists of ____________
c) trigonal planar
d) long chain
Explanation: The molecular structure of the organic lubricants is in the form of long chains. The molecular chains are parallel. The bonding strength between the molecules is very weak and may slide on each other.
Soaps are metal salts of _________
a) fatty acids
b) carboxylic acids
c) amino acids
d) inorganic acids
Explanation: Soaps are the metal salts of the fatty acids. Lithium, sodium, potassium and calcium are the metal salts. Soap molecules will be attached to substrate surface of the soap lubricant.
Soaps are prepared by chemical treating of _________ by strong alkaline solutions.
a) Oils and salts
b) Oils and fats
c) Salts and fats
d) Fats and proteins
Explanation: Soaps are made up of the chemical treatment of the oils and fats by strong alkaline solution. The soap molecule is the long non-polar tail which is hydrophobic end and the other is salt polar end which is the hydrophilic end.
Mobility of the solid lubricants on the adsorbents promotes ___________
b) Maintain the molecular structure
Explanation: Mobility of solid lubricants on the surface of adsorbates promotes the self healing. It also prolongs the endurance of the films. As long as the film remains intact it can be protected.
Insulators making rubbing contact require _______
a) Low conductivity
b) High conductivity
c) Low pressure
d) High pressure
Explanation: Insulators making rubber contact needed low electrical conductivity. In some other applications of the solid lubricants, the high electrical conductivities. Sliding electric contact requires high electrical conductivity.
Only lamellar structure lubricants provide lubrication.
Explanation: The statement lamellar structure lubricants provide lubrication is wrong because the non-lamellar lubricants also provide good lubrication. The lamellar structure is more likely to produce high lubrication.
If melting point increases, then the atomic bonds will _________
a) Become strong
b) Become weak
c) Be destroyed
d) Be with moderate strength
Explanation: As the melting point increases, the atomic bonds will be destroyed. It makes the lubrication less effective.
The lubricant should have __________ vapor pressure.
Explanation: The ideal lubricant must have low vapour pressure for any application because in most of the applications of the lubricants, the lubricants must have low pressure and high temperature resistant.
What is the range of coefficient of friction for solid lubricants?
Explanation: The range of the coefficient of friction for solid lubricants is very less that of 0.005-0.01. This must be low for effective lubrication because the lubricant is mainly used to control the friction between the machine parts.
What is the thickness of the MoS2 film?
Explanation: The thickness of the MoS2 film is about 15µm. This is the lubricant having lamellar structure with low shear strength and effective in lubrication. It forms a very thin layer on surfaces.