Investigating alkanes and alkenes

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.