UNIT 3: SECTION 3 - ALKENES & ALCOHOLS

Question 1

What is an alkene?

Answer 1

Unsaturated hydrocarbon with at least one double bond.

Question 2

What is electrophilic addition?

Answer 2

Where electrophiles are attracted to the high electron charge density of an alkenes double bond; they open up the double bond.

Question 3

Describe the test for unsaturation.

Answer 3

Sample added to test tube of bromine water.
Orange-brown —> colourless.

Mechanism is A

Question 4

What is a carbocation?

Answer 4

Positive Carbon ion; very reactive.

Question 5

How does carbocation stability determine product?

How is stability determined?

Answer 5

The more stable the carbocation, the more likely that becomes the major product.

Stability determined by number of R-Groups feeding electrons to the +charge on cation.

Question 6

Conditions required to make
Alkyl Hydrogen Sulfate?

Conditions to make Ethanol from this?

Overall equation?

Answer 6

Cold, concentrated H2SO4

Then, add cold water and warm up to produce alcohol.

H2C=CH2 + H2O (+H2SO4) —> C2H5OH (H2SO4)

Question 7

What are addition polymers?

What are alkene addition polymers called?

Answer 7

Addition polymers are formed from monomers.

Addition polymers which are formed from alkenes are called polyalkenes.

Question 8

What does the properties of polyalkenes rely on?

How?

Answer 8

Properties depend on IMF’s;
Longer the chain, closer molecules lie -> Stronger the London Forces are!
-> long straight chains = strong & rigid.
-> branched, weaker & more flexible.

Question 9

What is a plasticiser and how does it work?

Answer 9

Plasticisers are polymer property modifiers;
they do this by getting in between polymer chains and pushing molecules apart;
this reduces strength of IMF’s making it easier to slide and bend.

Question 10

What is PVC?

What can we use regular PVC for?

What can we use plasticised PVC for?

Answer 10

• Poly(chloroethene)
• drainpipes, window frames.
• cable insulation, clothing.

Question 11

How can we produce polymers from sustainable resources?

Answer 11

Polymers = alkenes.
Dehydration reaction of alcohol -> alkene (+H2O).

E.g. Ethanol -> Ethene + H2O
^heat w/ conc. sulfuric acid! (catalyst)

Question 12

Describe the mechanism for dehydration of alcohol.

Answer 12

H+ (from acid) forms bond with free electron pair on Oxygen (in alcohol).

Oxygen now has +charge; Electrons in C-O bond move towards Oxygen to satisfy +charge.

Carbon dissociates with Oxygen; left with Carbocation. Hydrogen from carbocation leaves to satisfy carbocation (leaves its electrons).

Alkene formed, H2O removed
and also H+ from acid not used up.

Question 13

3 step process to obtain polymers?

Answer 13

• Cracking
• Fractional distillation
• Polymerisation.