Concentrated sulfuric acid reacts with alkenes, alcohols and sodium halides - AQA - A-Level Chemistry - Question 2 - 2017 - Paper 3

1. Protonation of Propene: The pi bond of propene attacks a hydrogen ion (H+) from sulfuric acid, forming a carbocation.

2. Carbocation Formation: The more stable secondary carbocation is formed when the H+ attaches to the terminal carbon, leading to either a primary or a secondary carbocation in branching scenarios.

3. Nucleophilic Attack: The bisulfate ion (HSO4-) then attacks the carbocation, leading to the formation of the major product—alkyl hydrogen sulfate.

4. Product Formation: The alkyl hydrogen sulfate can further undergo hydrolysis to give the corresponding alcohol.

The minor product can be represented as follows:

     H   O  
      \  |  
       C--C
      /   
     H

This product arises from the formation of a different carbocation due to the protonation site.

The product shown is the major product due to the greater stability of the secondary carbocation formed during the reaction process. Secondary carbocations are more stable than primary ones due to hyperconjugation and inductive effects from adjacent carbon groups.

1. Isomer 1:

  H   H  
   \  | 
    C=C
   /  
  H   C
      | 
      H

Name: 2-butene

2. Isomer 2:

  H H
   \| 
    C=C
   / 
  H   C
      | 
      H

Name: E-but-2-ene (trans)

3. Isomer 3:

  H H  
   \ | 
    C=C
   /   
  H H 

Name: Z-but-2-ene (cis)

1. By-product: The by-product is butanol (C4H10O).

2. Role of sulfuric acid: The sulfuric acid acts as a dehydrating agent, facilitating the conversion of alcohol to alkene and producing water as a by-product.

3. Name of separation method: Distillation could be used to separate the products of this reaction.

1. Observation with sodium chloride: The reaction produces white fumes of hydrogen chloride gas and may form a solid residue.

2. Role of sulfuric acid: It acts as a catalyst and proton donor, enabling the reaction of sodium chloride to produce HCl.

1. Black solid: This is typically elemental iodine.

2. Yellow solid: This refers to sulfur.

3. Gas: The gas observed is hydrogen sulfide (H2S), which is known for its characteristic smell of rotten eggs.