3.4 Recall the products of the complete and incomplete combustion of alkanes

1.    Saturated hydrocarbons are called alkanes

2.    Small chain alkanes are used as fuels

3.    The reaction is called combustion

4.    The word equation for this chemical reaction is :

5.    Fuel (alkanes) + Oxygen → Carbon Dioxide+ Water + ENERGY (heat, light, sound)

6.    If there is insufficient oxygen then the word equation is:

7.    Fuel (alkanes) + Oxygen → Carbon monoxide + Water+ ENERGY (heat, light, sound)

8.    The problem with this reaction is that carbon monoxide is produced this gas is poisonous to the human body (see objective 5.11):  The substance haemoglobin in the blood has a bigger liking of carbon monoxide than oxygen, therefore less oxygen can be transported while carbon monoxide attaches itself to the red blood cell and does not come off the red blood cell, so there would be less room for oxygen to be diffused around the body. When it gets serious, its fatal

9.    Where can you find incomplete combustion?

 In cars

10.  What is used to reduce the harmful products from incomplete combustion? 

Catalytic Converter ( converts carbon monoxide -->carbon dioxide)

11.   During incomplete combustion a smoky flame is often seen, explain this observation

Soot is formed from the unburnt carbon coming from incomplete combustion

12.   Describe the two chemical tests for water

a.     Cobalt chloride paper is paper soaked in cobalt(II) chloride (CoCl2) solution. When there is water, the paper turns from blue to pink.

b.    If we add white crystals of (anhydrous) copper sulphate to a substance and a blue solution is obtained, water is present

13.   Describe the chemical test for carbon dioxide gas:

 Lime water turns milky

14.  Describe a physical test for water:

Boiling point (boils at 100 degrees C)

15.  Extn: write a balanced equation (with state symbols) for the combustion of propane gas:

C₃H₈ + 5 O₂ ---> 3 CO₂ + 4 H₂O