Nature's Chemistry

1
Unit 2 Nature's Chemistry Homologous Series
2
How do you know these people are related? Who
stands out? Why?
3
How do you what you are buying? What stands out?
Why?
4
Homologous Series (family)

• Each series has a general formula.
• All members possess the same functional group. It
  is the functional group that gives the series its
  characteristic reactions.
• There is a gradual change in physical properties
  from one member to the next. The most common
  example of this is the increasing melting and
  boiling points as we go up a series. The reason
  for this is that the molecules get larger and
  therefore harder to break.
• Members of the same homologous series have
  similar chemical properties.

5
Question How many different ways can be count
up to 8?

• Number of carbons in the hydrocarbon compound
• One Meth Five Pent
• Two Eth Six Hex
• Three Prop Seven Hept
• Four But Eight Oct

6
Prefixes
M onkeys (meth... 1 carbon) E at (eth
2 carbons) P eanut (prop 3 carbons) B
utter (but 4 carbons) P andas (pent 5
carbons) H ate (hex 6 carbons) H
airy (hept 7 carbons) O ranges (oct 8
carbons)
7
Alkanes

• Important characteristics of the alkane
  homologous series
• The names of all alkanes end in ane
• All bonds are single (saturated)
• All alkanes follow the general formula

Important
8
Isomers and Naming
Isomers have the same chemical formula (same
amount of stuff) but a different structural
formula (different layout) For the first
three members of the alkanes only one structure
is possible but butane, C4H10, has two isomers
white board example
9

• Rules for naming branched alkanes
• Find the longest carbon chain in the molecule
• the name is based on the alkane with this
• number of carbon atoms.
• 2. Number the chain to give any branches the
• lowest possible number(s).
• 3. Name the branches methyl (-CH3), ethyl (-
• C2H5), propyl (-C3H7) etc.

10

• Worked example
• Draw and name the isomers of C5H12

white board example
11
Reactions of Alkanes

• The alkanes are fairly unreactive however they do
  burn well therefore their main use is in fuels
• Combustion Example

white board example
12
Cycloalkanes
Characteristics

• The names of all cycloalkanes start with cyclo-
  and end in ane.
• All bonds in the cycloalkanes are single.
  (saturated)
• Cycloalkanes are ring structures
• First member of the series is cyclopropane.
• Used in motor fuel, kerosene, diesel, and many
  other heavy oils.
• All cycloalkanes follow the general formula

C
H
Important
n
2n
13
Alkenes

• Important characteristics of the alkene
  homologous series
• The names of all alkenes end in ene
• At least one CC double bond (unsaturated)
• Therefore 1st member is ethene.
• All alkenes follow the general formula

14
Isomers and Naming

• When naming alkenes we follow the same rules
• as for the alkanes with one major difference
• the main chain (the longest chain) must
• contain the double bond, whose position is
• indicated by a number.
• The chain is numbered to make this number
• as small as possible (the double bond takes
• priority over any branches.)

15

• Draw and name the isomers of C5H10

white board examples x6
16
Saturated and Unsaturated

• Hydrocarbons are described as either saturated or
  unsaturated.
• ____________ and ____________ are saturated.
• They have no double (or triple) carbon to carbon
  bonds.
• Every carbon atom is linked to neighbouring atoms
  by single
• bonds only (C-C)
• ________ are unsaturated hydrocarbons.
• They are unsaturated because each molecule
  contains at least
• one carbon to carbon double bond (CC)
• Alkenes are more reactive than the alkanes and
  cycloalkanes
• because of the carbon to carbon double bond.

alkanes
cycloalkanes
alkenes
17
Test for Unsaturation

• The test for unsaturation is a test to see if a
  molecule
• has a double or triple bond.
• Bromine is used to test for unsaturation as it
  rapidly
• decolourises when added to an unsaturated
  compound
• i.e. if bromine changes colour from orange to
  colourless you have an alkene.
• This is useful for identifying an alkene and a
  cycloalkane from one another if they have the
  same chemical formula.

18
Addition Reactions

• During the test for unsaturation the bromine
  adds
• on across the double bond, giving a saturated
• compound.
• This is an example of an addition reaction.
• e.g.
• Propene Bromine
  dibromopropane

white board example
19
Another Example

• Pentene Bromine
  dibromo_________
• Bromine bromo
• Chlorine chloro
• Fluorine fluoro
• Iodine iodo
• Nitrogen nitro

extra - not needed for exam
20
Another Example

• Heptene Hydrogen
  _________

An addition reaction that involves hydrogen is
called hydrogenation
21

• Butene Oxygen

This is combustion not addition... All
hydrocarbons burn to produce carbon dioxide and
water
22

• Ethene Water

An addition reaction that involves water is
called hydration
All hydrocarbons burn to produce carbon dioxide
and water
23
Consumer Products
24
Alcohols

• The names of all alcohols end in -ol
• The functional group of the alcohols is OH
  (hydroxyl group)
• Alcohols are substituted alkanes (as an -H has
  been replaced
• with an OH)
• Alcohols are made via hydration of alkenes and
  fermentation.
• Alcohols make useful industrial solvents.
• All alcohols follow the general formula

25
Isomers and Naming

• Isomers can result from both branching and
  varying the position of the -OH group.
• In naming, the main chain (longest chain) must
  contain the -OH group, whose position is
  indicated by a number.
• Example Pentan-1-ol, Pentan-2-ol,
  Pentan-3-ol

White board Example
26

• Example 2 Draw the 4 isomers of C4H9OH

White board Examples
27
Alcohols as Fuels

• Alcohols make really good fuels and burn with
• a clean flame.
• A reaction (like combustion) which gives out
• heat to the surroundings is classed as
• exothermic.
• The opposite of an exothermic reaction is an
• endothermic reaction (i.e. heat is taken in.)

White board Example
28
Carboxylic Acids

• The names of all carboxylic acids end in -oic
  acid
• The functional group of the carboxylic acids is
  -COOH
• (carboxyl group)
• This carboxyl group is always attached to the
  end
• carbon.
• Carboxylic acids react like other acids
• General Formula

Cn H2n1 COOH
29
Vinegar

• Vinegar is dilute ethanoic acid.
• Vinegar has been used for years in cooking both
  as a flavouring and as a preservative.
• Vinegar is also a useful cleaning agent and is
  found in many household products.

30
Making Esters

• Esters are compounds formed by a condensation
  reaction between alcohols and carboxylic acids.
• In a condensation reaction two molecules join and
  a small molecule (often water) is removed.
• Esters are used as flavourings in food and
  perfumes as well as industrial solvents.

White board Example
31

• Naming Esters
• The name of an ester indicates the alcohol and
  acid which go into making it.
• The first part is from the alcohol eg.
• -anol becomes -yl. (i.e. ethanol becomes
  ethyl)
• The second part is from the carboxylic acid
  e.g.
• -oic becomes -oate. (i.e. ethanoic becomes
  ethanoate)

32
Fuels Calculation

• We can calculate the energy released by a fuel
• using the following equation
• Eh c x m x ?T
• where
• c Specific heat of water, 4.18 kJ kg-1 C-1
  (data book)
• m Mass of water in kg
• ?T Temperature change of water in C
• Eh Energy (kJ)

33
Worked Example 1

• Calculate the amount of energy produced when 0.5g
  
• of methanol is burned to heat 250cm3 of water.
• The water temperature went up by 2C.

White board Example
34
Worked Example 2

• Calculate the amount of energy produced when 200g
  
• of methane is burned to heat 50cm3 of water. The
• initial temperature of water was 25C and at the
  end
• of the experiment the temperature was found to be
  
• 65C.

White board Example
35
Worked Example 3

• Calculate the amount of energy produced from the
• following results

Methanol mass before 53.65g Methanol mass after
53.46g Mass of water heated 100g Temp rise in
water 10C
White board Example