Question

The octane number has zero value for:
(a) iso octane
(b) n octane
(c) n heptane
(d) tetraethyl lead

Answer 1

Hint: Octane number is defined as the presence of isooctane by volume in a mixture of isooctane and n-heptane. It is used as the measurement of the quality or performance of gasoline. The higher is the octane number than more compression from the piston the gasoline can withstand and force the ignition in the engine. The octane number of any compound can be determined by comparing the characteristics of gasoline to isooctane that is 2,2,4 trimethyl pentane and heptanes.

Complete answer:
In this question we need to find the zero octane number compound and that is n heptanes. The reason behind this is that they are available to us with high purity of n heptanes which unmixed with other isomers of heptanes or other alkanes.They distilled from the resin of Jeffrey pine and also from the fruit of Pittosporum resiniferum.
The octane number of isooctane is 100. Due to having octane number 100, it is a compound which burns smoothly and also with little knock. The processes used for increasing the octane scaling is cracking, refining, and isomerization. We can also use anti knock substances to increase octane rating. The substance with octane number is called a bad knock. The substance with octane number 100 is called minimal knock. The higher the octane rating of the substance more is the performance of the engine.

So the correct option for this question is option c which is n heptanes and has zero octane value.

Note: students should learn the definition of octane number. Do understand the concept of octane number. Always describe the minimal knock and bad knock of octane number with examples. Octane number of gasoline is in between 93-97, however there is a cetane number which determines the ignition delay time. It is the cetane number which ranks the fuels. The higher the cetane number, faster is the auto ignition. The only difference between octane number and cetane number is that the former rates the gasoline and the latter rates the diesel.