Q.Suggest a simple chemical test to distinguish propane and propene.

Step 1. Propene (CH3-CH=CH2) has a reactive C=C double bond; propane (CH3-CH2-CH3) has only single bonds and is comparatively inert.

Step 2. Shake or bubble each gas through bromine water (reddish-brown): propene reacts by rapid electrophilic addition, forming colourless 1,2-dibromopropane and instantly decolourising the bromine water; propane does not react with bromine water under these mild, uncatalysed, dark conditions, so the reddish-brown colour persists.

Step 3. (An equally valid alternative test) Shake or bubble each gas through cold, dilute, alkaline KMnO4 (Baeyer's reagent, purple): propene is oxidised to propane-1,2-diol, discharging the purple colour (via a brown MnO2 precipitate); propane does not react, and the purple colour persists. …

Recall that both bromine water and Baeyer's reagent are standard qualitative TESTS FOR UNSATURATION -- a colour change specifically signals a C=C or C-C triple bond, …

• Reaching for combustion or a flame test to distinguish them -- both propane and propene burn similarly, so a simple burning test does not reliably distinguish a saturated …