Heep Woh College

Form 5 Chemistry Quiz 4

Chapter 22 : Fossil Fuels

Marking Scheme

 

1.     Crude oil is often considered as a fossil fuel. The following experimental set-up is used to separate a sample of crude oil into different fractions.

(a)  Why is crude oil considered as a fossil fuel?                                                        [1]

 

Crude oil originates from dead remains of marine plants and animals that lived millions of years ago.                                                                                       1

 

(b)  (i)    Name the process shown in the above diagram.                                   [1]

 

Fractional distillation                                                                                         1

 

(ii)    Why can crude oil be separated into different fractions by this process?                                                                                                                                       [1]

It is because the components in the crude oil have different boiling points / boiling point range.                                                                         1

 

(c)   (i)    What is the function of cold water in the experimental set-up?                [1]

 

To condense the vapour given off into liquid.                                           1

 

(ii)    Why should the thermometer be placed exactly next to the opening of the delivery tube?                                                                                    [1]

 

To ensure the temperature measured is exactly the boiling point of the

vapour leaving the boiling tube.                                                                  1

 

(d)  Two fractions, A and B, are collected at 100^oC and 250^oC respectively. State how these two fractions are different in

(i)    sootiness of flame;                                                                                            [1]

 

Fraction A burns with a less sooty flame than fraction B.                 1

 

                (ii)    viscosity; and                                                                                                      [1]

 

Fraction A is less viscous than fraction B.                                                     1

 

        (iii)   molecular size.                                                                                                    [1]  

 

Molecules in fraction A are smaller than molecules in fraction B.       1

 

2.     Petroleum is a complex mixture, mainly of hydrocarbons, with molecular sizes ranging from C₁ to about C₇₀. During the refining process it is possible to produce the following fractions: (Some of the fractions can be used directly; others require further treatment.)

 

       

(a)     Which fraction has the lowest boiling point?    E                                      1      [1]

What name is given to this fraction, and what is the molecular formula of the simplest compound present?                                                                                [2]

 

                Liquified petroleum gas / refinery gas, CH₄                                                        1,1

 

(b)     Which fraction would be most suitable for the followings:

 

(i)    making detergent                            B                                                      1      [1]

 

(ii)    cover the surface of roads             A                                                     1      [1]

 

(iii)   fuel for aeroplane                              B                                                      1      [1]

 

(iv)  fuel for motor cars                             D                                                     1      [1]

 

 

 

The End