12.1- ALKANES

Question 1

What type of hydrocarbons are alkanes?

Answer 1

saturated

Question 2

Why are alkanes described as saturated hydrocarbons?

Answer 2

contain only carbon-carbon and carbon-hydrogen single bonds

Question 3

What are alkanes among reactivity?

Answer 3

among the least reactive organic compounds

Question 4

What are alkanes used as? (3)

Answer 4

fuels and lubricants and as starting materials for a range of other compounds

Question 5

What is the main source of alkanes?

Answer 5

crude oil

Question 6

What is the general formula for alkanes?

Answer 6

CnH2n+2

Question 7

In what form can hydrocarbons be in?

Answer 7

unbranched chains, branched chains, or rings

Question 8

What are unbranched chains often called?

Answer 8

straight chains

Question 9

What is the angle of the C-C-C?

Answer 9

109.5 degrees

Question 10

As the C-C-C is 109.5 degrees what does this mean?

Answer 10

chains are not actually straight

Question 11

In an unbranched alkane how many hydrogen atoms are attached to each carbon atom?

Answer 11

each carbon atom has two hydrogen atoms except the end carbons which have one extra

Question 12

What is the general formula for ring alkanes?

Answer 12

CnH2n

Question 13

Why do ring alkanes have a general formula of CnH2n?

Answer 13

end hydrogens not required

Question 14

Where is the alkanes named from?

Answer 14

the root

Question 15

What does the root of an alkane tell us?

Answer 15

the number of carbon atoms

Question 16

What does the suffix -ane tell us?

Answer 16

denotes an alkane

Question 17

What must you first find when naming a hydrocarbon with a branched chain?

Answer 17

must first find the longest unbranched chain

Question 18

What does the longest unbranched chain of a branched hydrocarbon give?

Answer 18

gives the root name

Question 19

How are the branches/side chains named?

Answer 19

by prefixes e.g. methyl-, ethyl-, propyl-

Question 20

What do numbers tell us when naming a branched hydrocarbon?

Answer 20

which carbon atoms has side chains are attached to

Question 21

What alkanes have no isomers?

Answer 21

methane, ethane and propane

Question 22

How does the number of possible isomers change depending on the number of carbons in the alkane?

Answer 22

possible isomers increases with the number of carbons on the alkane

Question 23

What is the polarity of alkanes like?

Answer 23

almost non-polar

Question 24

Why are alkanes almost non-polar?

Answer 24

because the electronegativites of carbon and hydrogen are so similar

Question 25

As alkanes are non-polar what are the only intermolecular forces between their molecules?

Answer 25

weak van der Waals forces, larger the molecule, stronger the van der Waals forces

Question 26

What happens to boiling point of alkanes as there’s increasing intermolecular forces?

Answer 26

boiling point increases as the chain length increases

Question 27

What state are shorter chain alkanes at room temperature?

Answer 27

gases

Question 28

At about what chain length do alkanes become solids at room temperature?

Answer 28

18 carbons

Question 29

What feel do the solid alkanes have?

Answer 29

waxy feel

Question 30

What is the boiling point of alkanes with branched chains like in comparison to straight chain alkanes with the same number of carbon atoms?

Answer 30

lower melting points

Question 31

Why do alkanes with branched chains have lower melting points in comparison to straight chain alkanes with the same number of carbon atoms?

Answer 31

they cannot pack together as closely as unbranched chains so van der Waals forces not so effective

Question 32

Are alkanes soluble in water?

Answer 32

no

Question 33

Why are alkanes not soluble in water?

Answer 33

because water molecules are held together by hydrogen bonds which are much stronger than van der Waal’s forces that act between alkane molecules

Question 34

What do alkanes mix with?

Answer 34

other relatively non-polar liquids

Question 35

How reactive are alkanes?

Answer 35

relatively unreactive

Question 36

What are the bonds in alkanes like?

Answer 36

strong carbon-carbon and carbon-hydrogen bonds

Question 37

What do alkanes not reactive with?

Answer 37

acids, bases, oxidising agents and reducing agents

Question 38

What do alkanes burn and react with under suitable conditions?

Answer 38

burn and react with halogens under suitable conditions

Question 39

What do alkanes burn in a plentiful supply of and produce what?

Answer 39

burn in a plentiful supply of oxygen to form carbon dioxide and water