Heep Woh College

Form 5 Chemistry Quiz 6

Chapter 24 Part I : Alkanes

Marking Scheme

 

1.   Camping burner uses butane as fuel.

(a) Write the structural formula of butane.                                                              [1]

	H  H  H  H     |  |  |   | H¾C¾C¾C¾C¾H     |  |  |   |     H  H  H  H

 

 

 

 

                                                                                                                                              1

(b)  The butane in the can is compressed to turn it into a liquid.

               What is the advantage of using liquid butane.                                                    [1]

 

Occupies less space than an equal mass of gas.                                           1

 

 

(c)  Give two reasons why many campers use butane burners instead of wood or charcoal?                                                                                                            [2]

 

Cleaner flame / easier to handle / easier to carry.           ANY TWO            1,1

 

 

        (d)  Write the balanced equation for the burning of butane in plenty of air.      [1]

 

2C₄H₁₀(g) + 13O₂(g) ¾® 8CO₂(g) + 10H₂O(g)                                                 1

 

 

        (e)  If the burner is not looked after, the butane may burn with too little oxygen.

        (i)    Why is this dangerous?                                                                                    [1]

       

Highly toxic carbon monoxide is formed.                                                 1

 

        (ii) Write a balanced equation for a reaction that occurs.                              [1]

 

       2C₄H₁₀(g) + 9O₂(g) ¾® 8CO(g) + 10H₂O(g)                                                     1

 

(f)   The boiling point of butane is 0^oC. Explain why it may be difficult to ignite butane on a very cold day.                                                                              [1]

 

Liquids must evaporate before they burn. Difficult to evaporate at low temperatures.                                                                                                               1

 

 

 

 

 

 

2.    A stream of butane gas is bubbled to bromine in 1,1,1-trichloroethane.

        (a)  No reaction occurs. Why?                                                                                      [1]

 

No reaction in dark / reaction takes time.                                                         1

 

        (b)  What would you observe?                                                                                     [1]

 

Bromine turns from brown to colourless                                                              1

 

(c)  Write the structural formulae and IUPAC names of ALL mono-substituted products of the above reaction.                                                                          [4]

 

                CH₃CH₂CH₂CH₂Br                   1-bromobutane                                                    1,1

CH₃CHBrCH₂CH₃                    2-bromobutane                                                    1,1

 

 

3.    (a)  What is “catalytic cracking”?                                                                              [2]

 

Break down the compound                                                                                 1

under heated catalyst in the absence of air.                                                    1

 

(b) Cracking of decane (Alkane contains 10 carbon atoms) produces two organic products, one contain 3 carbon atoms and the other contain 4 carbon atom. Write a chemical reaction of this reaction.                            [1]

 

               C₁₀H₂₂ ¾® 2CH₃CH=CH₂ + CH₃CH₂CH₂CH₃                                                      1

 

(c)  Draw a labelled diagram of this setup.                                                             [3]

 

 

 

 

 

 

 

 

 

 

 

 

Diagram            1

Catalyst              1

Heat                    1

 

 

The End