octane number

1. Name: Pujiati
NIM: 06121010018
FKIP Chemistry 2012
Class Indralaya
Octane Number
Octane number is the number of indicators on the gasoline hydrocarbon fuels that show the ease
of perfect fuel to burn when in contact with flame combustion (ignition) during the combustion
process. Octane number is a comparison of the levels of%% iso octane and n-heptane in the fuel
mix. The higher the% Octane fuel in the mixture, the higher the octane number.
The number shows for many knock (knocking) which caused by petrol or gasoline. The higher
the octane number, meaning the less knock generated, the gasoline has a good quality.
Knocking is a bad behavior of the fuel. Which combustion occurs too early before the piston is in
the right position. Knocking reduces fuel efficiency and can damage the engine.
To determine the octane number, there are two types of compounds for a comparison. That are
"isooctane" and “n-heptane "these compounds are two of the many kinds of compounds found in
gasoline. Isooctane produces a knock at least, given a value of 100. And n-heptane produced
most knocking, given the octane number of 0 (zero). A mixture consisting of 80% isooctane and
20% n-heptane has an octane number of (80/100 x 100) + (20/100 x 0) = 80
In general, branched chain alkane has a higher octane number than the chain isomer righteous.
For example, n-hexane has an octane number of 25, while 2,2-dimethyl methyl butane has an
octane number of 92. Pertamax has an octane number of 92. Premium has an octane number 88,
while octane number of pertamax plus is 95. Fraction from the distillation of gasoline has the
lowest octane number. It happened because most of the gasoline from distillation consists of a
straight chain alkane. Octane gasoline should be upgraded before being used as a vehicle fuel.
That is by reforming or addition of an anti-knock. Reforming is a process of converting a straight
chain alkane to be alkane branched.
One of the anti-knock agent which is still used in our country is Tetraethyl lead (TEL, lead =
lead or lead) the chemical formula Pb (C2H5) 4. The addition of 2-3 mL of this substance into 1
gallon of gasoline can increase the octane number of 15 points. Burning the gasoline enriched
with oxide TEL will produce black smoke will come out from vehicle or attached to the
machine. To prevent lead oxide was not attached to the machine, then into the leaded gasoline is

2. mixed with ethylene bromide, C2H4Br2. Bromine atoms of ethylene bromide is forming into lead
bromide, PbBr2, that is volatile. Thus, the leads will come out with car fumes. Unfortunately,
lead is a toxic compound that can damage human’s brain. Thus, the use of leaded gasoline will
pollute the air. As his successor. Now used methyl tertiary buthyl ether (MTBE).