2. Alkanes, alkanes and polymers Flashcards Preview

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What is a alkane.

Hydrocarbon with no double bond. Saturated.


What is a alkene

Hydrocarbon with a double bond. unSaturated.


Explain the halogenation of the alkanes.

Alakanes react with haolgens in UV (or 300deg) to produce Halogenoalkane and Hydrogen halide. This is a radical substitution. Cov bonds broken by homolytic fusion to make halogen radicals. A H atom gets substituted by this. Then the H and Br react.


Mechanism for the chlorination.

  • initiation: C2--->2Cl*   with UV by homolytic fision.
  • Propagation 1: CH4+Cl* ---> *CH3+HCL   (could gets di,tri etc here)
  • Propagation 2:*CH3+Cl2--> CH3Cl +Cl*   (and here)
  • Terminations: any of the previus radicals combiing



How is the pi bond formed.

above and below the the plane of the cabon atoms by sideways/latteral overlap of p-orbitals. Each carbon atom contributes 1 e- from the P orbital.


ractivity of alkanes v alkenes

alkenes are more reactive, becuase the double bond becuase the pi bond is weaker then the sigma bond and this is what breaks.


Addidition oif hydrogen to a alkene


Nickle catalyst, 150 deg , high pressure.


test for a double bond.

add bromine water. If a double bond is present it will decolourise, as the Br has reacted.


Why would you get different products with a alke unsymmetric alkene + HBr(or other thing) substitution reaction.

If the original alkene isit makes two different products in the substitution


Alkene + steam.

becomes a alcohol

H3PO4 catalyst, high temp and pressure.


Alkene + halogen halide.

The delta + on the hydrogen is attracted to the E- dense region around thedouble bond.

A carbon cation, and a halide ion form as the double bond has bonded with the H and the Hhalide has heterolytically fissioned.

The Halide ion then bondes the the + carbon atom.


Alkane + diatomic halide.

The Halide gets an induced dipole thanks to the e- rich region.

The double bond breaks and form with one Halide, the other becomes a halide ion by heterolytic fision. (forming a carbocation)

The halide ion then bonde with the +ve carbon.


What are unstaurated compounds used for?

Make polymers (plastics)

Make margarine


What is etene used for?

The chloretene used as a paint remover

The dialcohol is used as antifreeze,or in polyesters.

etanoic acid is vinegar. 


How do you make margerine?

Hydrogenation of unsaturated molecules.

This means that it partly solidifies and hardens which efeects the spreadabilty.



BP of ene v ane.

very similar but the alkene is a bit lower as vanderwaals are lower.


Polymer reaction?9radical)

Via radical polymerisation. (200 deg, high pressure) . The radical breaks the double bond (and bonds)wich creates a radical monomer this contiues to break more , and join with them, creating a variety of polymer lengths and branchings.



polymer reaction (ziegler natta)

us ea ziegler natta catalysr. The alkane gets passed over the catalyst, continually, at abolut 60 deg, produces unbranched polymers.


Uses of polymer waster?

as a fuel source- for heat to be turne d into electricity.

In feedstock recycling- converting into Hydrogen and carmon monokide to be used to make more useful stuff.

Reforming the plastic



How are PVC';s recycled.

dissolved in a solution (to stop Cl going into the atmosphere), then precipitated out.


what are biodegradable and compostable polymers.

When disposed they will be broken down naturally by the envionment to carbon dioxide and water, inorganic compounds, and biomass.