Lab Activity: Unsaturation Test using Bromine
🧪 English: Today in the lab, I conducted an unsaturation test. I started with 10 ml of ethyl alcohol and added a few drops of concentrated sulfuric acid. This mixture helped me generate ethene gas via a dehydration reaction. Thos time the solution was transparent in color. I means it was colorless. To verify the presence of unsaturation, I added carbon tetrachloride, which led to the formation of an oily layer, typical of hydrocarbon presence.
I then carefully broke a sealed glass ampoule of bromine (orange liquid). The vapor spread rapidly due to bromine's volatile nature. I immediately covered my face with a handkerchief due to the pungent and irritating odor. Thankfully, the lab window was open, which provided ventilation. Upon adding a few drops of bromine to the solution, a red gel-like layer appeared with an orange layer floating on top.
Since the standard tripod stand could not support my tall candle, I placed the candle above the inverted beakers and filter paper above the tripod stand and thereafter I began slow heating.
After about an hour, the orange and red colors completely disappeared. This confirmed the presence of unsaturation, as bromine reacts with double bonds in alkenes, causing decolorization.
Chemistry Behind the Reaction
Ethene is an alkene, containing a carbon-carbon double bond (C=C). When bromine is added, it reacts with this double bond to form a dibromo compound. The disappearance of bromine's orange color is a qualitative indicator of unsaturation:
CH2=CH2 + Br2 → CH2Br-CH2Br
Why Bromine is Used
- Bromine is highly reactive with alkenes and alkynes.
- Its orange color makes it easy to observe changes.
- It doesn’t react with saturated hydrocarbons, so it's selective.
Safety Measures
- Always wear gloves and goggles when handling bromine.
- Work in a well-ventilated area or fume hood.
- Never inhale bromine vapors — they are toxic and corrosive.
- Use a handkerchief or mask in emergency exposure.
Applications of Unsaturation Test
This test is commonly used in organic chemistry labs and industries for:
- Detecting unsaturated fats and oils
- Verifying the presence of alkenes in synthetic reactions
- Educational demonstrations in chemistry classes
MCQs for Practice
Q1. What color change occurs when bromine reacts with an unsaturated compound?
- A) Red to blue
- B) Orange to colorless ✅
- C) Yellow to green
- D) No change
Q2. Which gas is evolved by dehydrating ethyl alcohol with sulfuric acid?
- A) Ethene ✅
- B) Methane
- C) Acetylene
- D) Propane
Bromine Properties
Bromine Properties
- Symbol: Br
- Atomic Number: 35
- Appearance: Reddish-orange liquid
- Boiling Point: 58.8°C
- Highly volatile, toxic, and corrosive
