Alkanes and Alkenes

Question 1

What’s a Hydrocarbon?

Answer 1

A molecular compound that contains ONLY hydrogen and carbon

Question 2

What’s a saturated hydrocarbon?

Answer 2

• All bonds with other atoms are single bonds
• Alkanes

Question 3

What are the properties/uses of Alkanes?

Answer 3

• Low reactivity
• Combusts well making them good for fuel

Question 4

What’s the general formula for Alkanes?

Answer 4

C(n)H(2n+2)

Question 5

What are the features of Alkenes?

Answer 5

• reactive
• unsaturated (carbon to carbon double bond)

Question 6

What’s a homologous series?

Answer 6

A series of compounds with the same functional group and similar chemical properties

Question 7

What are the 4 shortest alkenes?

Answer 7

Ethene (c2h4)
propene
butene
pentene

Question 8

What’s the structure of alkanes?

Answer 8

• One carbon is bonded to 4 other atoms

Question 9

What can alkenes be used for?

Answer 9

• Making plastics (polymers)
• Can undergo addition reactions to make new compounds

Question 10

What’s a functional group?

Answer 10

A functional group is an atom or group of atoms that is mainly responsible for a molecule’s chemical properties

Question 11

Describe how alkanes and alkenes are oxidised during complete combustion

Answer 11

The alkanes and alkenes react with oxygen. Their carbon atoms and hydrogen atoms gain oxygen.

Question 12

Why do hydrocarbons make great fuels?

Answer 12

• During combustion reactions when you burn them in oxygen, they give out lots of energy (exothermic)

Question 13

How does complete combustion occur? - what are the products?

Answer 13

• Hydrocarbons are burnt in plenty of oxygen, all the atoms are fully oxidised, so, the only products are carbon dioxide and water

Question 14

When does incomplete combustion occur?

Answer 14

• Insufficient reaction means that full oxidation does not occur
• So, carbon monoxide (CO) and carbon in the form of soot can be formed as well

Question 15

What’s the functional group of alkenes?

Answer 15

C=C

Question 16

What happens during addition reactions?

Answer 16

ALKENES
C=C bond can open up and allow the two carbons to bond to atoms of another molecule
So, the reactants combine to form one larger product molecule and no other products

Question 17

What process can alkenes go through to become alkanes?

Answer 17

Addition reactions

Question 18

What test could you do to determine if something is an alkane or alkene?

Answer 18

Bromine water

Question 19

Explain the bromine water test

Answer 19

• Bromine water goes from orange-brown to colourless when mixed with alkenes because a chemical reaction occurs
• This works because the C=C double bond reacts with bromine to form a colourless product
• The bromine is therefore removed from the solution, which loses its colour
  (alkanes do not have any double bonds so no colour change would occur)

Question 20

What is formed when an alkene reacts with hydrogen?

Answer 20

Alkane

Question 21

How many atoms are found in the formula C6H12?

Answer 21

18