What is the colour change when aqueous bromine?
David Craig
Updated on March 20, 2026
What is the colour change when aqueous bromine?
Teaching notes
| Colour after shaking with hydrocarbon solvent | Reaction with potassium chloride solution | |
|---|---|---|
| Bromine water | Aqueous layer: yellow-orange to colourless Hydrocarbon layer: colourless to pale yellow-orange | No reaction |
| Iodine solution | Aqueous layer: brown to colourless Hydrocarbon layer: colourless to purple | No reaction |
What changes in color when bromine reacts with an alkene?
Alkene is an unsaturated compound. Bromine is dark red in color. When bromine is treated with alkene, it loses its dark red color and becomes colorl…
Does alkene react with aqueous bromine?
Alkenes react in the cold with pure liquid bromine, or with a solution of bromine in an organic solvent like tetrachloromethane. The double bond breaks, and a bromine atom becomes attached to each carbon. If an aqueous solution of bromine is used (“bromine water”), you get a mixture of products.
What color is a positive bromine test?
orange
Bromine Test. Bromine, Br2, adds rapidly to carbon-carbon double bonds to form the dibromide. Bromine is a dark orange and the dibromide is colorless so the rapid discharge of the bromine color is used as a positive test. Anilines and phenols also react rapidly with bromine with the formation of HBr.
What colour is bromine liquid?
reddish brown
Physical and chemical properties Free bromine is a reddish brown liquid with an appreciable vapour pressure at room temperature. Bromine vapour is amber in colour.
Why do alkenes turn bromine water Colourless?
An alkene will turn brown bromine water colourless as the bromine reacts with the carbon-carbon double bond. The bromine atoms break the carbon–carbon double bond and from C–Br bonds. This type of reaction is called an addition reaction and the addition of bromine to an alkene is called bromination.
What is the color of bromine before it will react with alkene?
Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene.
What happens when alkene reacts with KMnO4?
When a purple solution of the oxidizing agent KMnO4 is added to an alkene, the alkene is oxidized to a diol and the KMnO4 is converted to brown MnO2. Thus, if the purple color changes to brown in this reaction, it is a positive reaction. Alkanes and aromatic compounds do not react with potassium permanganate.
What type of reaction is bromine water and alkene?
The bromine water turns colourless confirming the presence of an alkene. The bromine atoms break the carbon–carbon double bond and from C–Br bonds. This type of reaction is called an addition reaction and the addition of bromine to an alkene is called bromination.
How do alkenes react with bromine water?
Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. This has the effect of ‘saturating’ the molecule, and will turn an alkene into an alkane. For example: C 2H 4 + H 2 → C 2H.
Do alkenes Decolourise bromine?
Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. Alkenes can decolourise bromine water, but alkanes cannot. This has the effect of ‘saturating’ the molecule, and will turn an alkene into an alkane.
What does a positive bromine test look like?
A positive test is indicated by: It turns red/brown if only saturated compounds are present. The degree of unsaturation of a compound can be determined by slowly adding bromine solution until the first red/brown color is observed. The more bromine solution required, the greater the unsaturation.
