Question

How many gm of bromine will react with 21 gm C₃H₆
A. 80
B. 160
C. 240
D. 320

Answer 1

Hint: In this question we have to use the reaction between bromine and propene to find out the amount of bromine that will react with 21 gm of propene. Unsaturated molecule C₃H₆ (propene) reacts with bromine to produce a decoloured product.

Complete Step by Step Answer:
Alkenes with pure liquid bromine or a bromine solution in an organic solvent, such as tetrachloromethane, react in the cold. Each carbon now has a bromine atom connected to it when the double bond dissolves. The bromine turns into a colourless liquid after losing its original reddish-brown hue. 1,2-dibromoethane is created when the reaction with ethene occurs.

When bromine and propene interact, the double bond dissolves and a bromine atom is joined to each carbon. The product of this reaction with propene is 1,2-dibromopropane. The reaction is an example of electrophilic addition. The bromine is a very "polarizable" molecule and the approaching pi bond in the proene induces a dipole in the bromine molecule.
Chemical reaction involved:
CH₃-CH=CH₂ + Br₂ → CH₃-CH₂Br-CH₂

One mole of propene reacts with 1 mole of Br₂ to give 1 mole of 1,1 dibromopropane. From the mole concept, 21 grams of propene means moles of propene. Therefore, we need 0.5 moles of Br₂ gas. That is, we need 80 gms of bromine.
The correct answer is A.

Note: Apart from fluorine, the other halogens exhibit comparable behaviour. Each carbon now has a halogen atom connected to it when the double bond dissolves. All hydrocarbons, including alkenes, react violently with fluorine to produce carbon and hydrogen fluoride.