Answer
Part II: Alkane and Alkene Tests
Part A: Bromine in Nonaqueous Solution
- In this test, bromine (Br2) in dichloromethane acts as a reagent to detect unsaturation.
- Cyclohexene, an alkene, reacts with bromine via an electrophilic addition mechanism, breaking the double bond and resulting in the loss of the red-orange bromine color.
- Hexane, an alkane, lacks a double bond and thus does not react under normal conditions. The bromine color remains.
- If the reaction is slow, exposure to light can accelerate the process by promoting homolytic cleavage of bromine.
Observation: Disappearance of bromine color in the cyclohexene test tube confirms the presence of a C=C double bond.
Part B: Acid Permanganate Test
- This test uses a purple solution of potassium permanganate (KMnO4) in acidic medium as an oxidizing agent.
- Alkenes such as cyclohexene are oxidized to diols, reducing KMnO4 and causing the solution to lose its purple color.
- Hexane does not undergo oxidation, so the solution retains its color.
- Additional reagent may be added to confirm sustained decolorization.
Observation: If the purple color fades, the compound contains unsaturation (a double bond).
Part C: Test for Unsaturation
- By applying either the bromine or permanganate test to the two unknowns (1 and 2), you can determine which one is unsaturated.
- Pinene is a bicyclic compound with a double bond — it will react and decolorize bromine or permanganate.
- Cyclohexane, a saturated compound, will not cause color change in either test.
Conclusion: The sample that causes decolorization contains an alkene (likely pinene), while the other (which retains color) is the alkane (cyclohexane).