The diagram shows the structure of a propene molecule - Edexcel - GCSE Chemistry - Question 3 - 2011 - Paper 1

To represent the polymerization of propene, draw two propene monomers:

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

Then, connect the monomers into a polymer:

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

This diagram shows the part of the poly(propene) molecule formed.

A typical test to confirm the presence of carbon to carbon double bonds (i.e., alkenes) is the bromine water test. When bromine water (an orange solution) is added to propene, the solution decolorizes, indicating that a reaction occurred, and confirming the presence of double bonds. The bromine adds across the double bond, forming a dibromide compound.

To find the total mass of products formed when 17 g of decane is cracked:

1. Calculate the molar mass of decane (C₁₀H₂₂) = 10(12) + 22(1) = 142 g/mol.
2. For every 1 mole of decane (142 g), 1 mole of propene (C₃H₆) and 1 mole of butane (C₄H₁₀) are produced.
3. Calculate the total moles of decane cracked: $moles = \frac{mass}{molar \ mass} = \frac{17}{142} ≈ 0.1196 \ ext{moles}$
4. Therefore, total mass of products = moles × (molar mass of propene + molar mass of butane) = $0.1196 \times (42 + 58) = 0.1196 \times 100 = 11.96 \text{g}$

Cracking is a chemical process used to break down large hydrocarbon molecules, usually derived from crude oil, into smaller, more useful molecules, such as alkenes and alkanes. This process increases the yield of valuable products like gasoline and chemical feedstocks.

Cracking is necessary because large hydrocarbon molecules from crude oil fractions are less valuable; they are typically less efficient as fuels, and have limited uses in the chemical industry. By cracking these large molecules, we can produce smaller, more useful ones, such as alkenes that can serve as monomers for polymer production or are used as fuel for vehicles.