IGCSE Chemistry
section 3
Investigating alkanes and
alkenes
Part A: Comparing combustion of
an alkane and an alkene - demonstration
1.
Put
a few drops of hexane (an alkane) on a watch glass or in an evaporating basin.
2.
Make
sure the bottle is well away, then, ignite the liquid (preferably in a fume
cupboard).
3.
Repeat
this using hexene (an alkene).
Questions
1.
Describe
the colour of the flame when hexane was burning
2.
Was
there any difference between the alkane and alkene?
3.
Write
a word equation for the complete combustion of hexane
4.
What
is the black substance visible at the top of each flame and why is it formed?
5.
Write
a word equation for the reaction in question 5
6.
What is the environmental impact of burning alkanes?
Part B: Using bromine water
1. Place two small clean dry test tubes into your test
tube rack.
2. Place approximately 2 ml of the hexane into the
first test tube and one ml of hexene into the second.
3. Add 5 drops of the bromine water into each of the
two samples, taking care to not breath the bromine vapor or spill the bromine
on your skin.
4. Cover each test tube with a bung and, with your
finger on the bung, shake each test tube.
5. Record any colour changes i.e. colour before and after
the addition of the bromine water in a table.
Questions
1. In which test tube did an immediate reaction take
place? Give a reason for your answer.
2. What reaction took place in the test
tube you answered in (1)?
3. Write a word equation and balanced
symbol equation for the reaction.
4. Could we use bromine water to find out
if a hydrocarbon is an alkane (saturated) or an alkane (unsaturated). Explain
your answer.
Part C: Using potassium manganate
Repeat
steps 2 to 5 with both hexane ands hexane but using potassium manganate. Record
your observations in a table
Questions
1. In which test tube did an immediate reaction take
place? Give a reason for your answer.
2. Could we use potassium manganate to
find out if a hydrocarbon is an alkane (saturated) or an alkane (unsaturated).
Explain your answer.
