Alkenes and the Bromine Water Test

Lab Brief #3

🎯 Your mission

Predict it first. Then prove yourself right (or wrong).

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

Alkenes contain a carbon-carbon double bond and have formula CₙH₂ₙ. That double bond makes them far more reactive than alkanes. Bromine water is decolourised from orange to colourless by an alkene, but is unchanged by an alkane.

Key words

alkene
An unsaturated hydrocarbon containing a carbon-carbon double bond, CₙH₂ₙ.
unsaturated
Containing at least one carbon-carbon double bond.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

bromine water
hexane
cyclohexene
test tubes with bungs
gloves

Get ready

⚠️ Safety first

Bromine water is toxic and corrosive — fume cupboard, goggles and gloves, and never inhale the vapour.
Hydrocarbons are highly flammable: no flames anywhere in the room.

Step 1 of 4 · Read

Think about what you just learned: say what "alkene" and "unsaturated" mean in your own words before you start.

Step 2 of 4 · Do

Add bromine water to samples of an alkane and an alkene and shake gently. Record the colour of each after mixing and use the result to identify an unknown third sample.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

Bromine water turns from orange to colourless with an:

How sure are you?😐 maybe

Question 2 of 2

Alkenes are more reactive than alkanes because they contain a:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Cracking All lessons

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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Alkenes and the Bromine Water Test

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