In which of the following are crude oil
fractions arranged in order of increasing viscosity? A) Kerosene, diesel oil, gasoline. B) Diesel oil, gasoline, kerosene. C) Gasoline, kerosene, diesel oil. D) Kerosene, gasoline, diesel oil. Or E) gasoline, diesel oil, kerosene.
Crude oil fractions come from fractional
distillation. The chemicals in crude oil, which is a
huge mixture of different chemicals, are separated broadly by boiling point. Crude oil fractions are actually mixtures
of many different chemicals, but the fraction as a whole will have a pretty reliable boiling
point. You can easily remember the fractions of
crude oil in order through the mnemonic playful naughty gray kittens dance like ferocious
tigers. This puts the fractions in order from the
lowest boiling point to the highest boiling point. The full names of the fractions are
petroleum gas, naphtha, gasoline, kerosene, diesel, lubricating oil, fuel oil, and tar.
The three we’ll need for this question
are gasoline, kerosene and diesel. Our job is to put these three fractions
in order of their viscosity. We already know that moving down the
list, the boiling point of the fraction increases. This is because, as we go down the list,
the average size of hydrocarbon in each fraction tends to increase. Another key property of a bigger
hydrocarbon is that it will have a higher viscosity. This is because as the hydrocarbons get
bigger, they tend to entangle around one another and stick to each other more. This makes them thicker, more like syrup,
less like water.
So, gasoline is less viscous than
kerosene. And kerosene is less viscous than
diesel. This means our answer is C. Gasoline, kerosene, diesel oil is the
correct order of increasing viscosity for these three crude oil fractions.