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Transcript
Complete the table
Name
Formula
Structure
+ O2
Miscibility
in water
methane
CH4
CO2 + H2O Immiscible
ethane
C2H6
CO2 + H2O Immiscible
propane
C3H8
CO2 + H2O Immiscible
butane
C4H10
CO2 + H2O Immiscible
Alcohols
•
•
•
•
What does the word alcohol mean to you?
Like the alkanes the alcohols are a series of related compounds
They all contain an –OH group – a functional group
The –OH group allows them to ‘hydrogen bond’ like water does
– so boiling points are higher than for the equivalent alkane
Structures
ethanol C2H5OH
propanol C3H7OH
butanol C4H9OH
Reactions
• + oxygen:
burn to give CO2 and H2O
C2H5OH (l) + 3 O2 (g)  2 CO2 (g) + 3 H2O (l)
• + water:
miscible
• + sodium:
reacts slowly producing hydrogen gas and sodium
ethoxide
2 C2H5OH + 2 Na  2 C2H5O-Na+ + H2
c.f. 2 Na + 2 H2O  2 NaOH + H2
Learning objective:
28/04/2017
• To illustrate the practical importance of carboxylic acids
• To demonstrate that carboxylic acids in solution show the
characteristic reactions of acids
• To introduce the –COOH functional group in carboxylic acids
• To practise writing balanced equations to describe the reactions of
carboxylic acids
• To introduce esters as products of the reactions of alcohols with
carboxylic acids
• To observe properties of esters
Carboxylic acids
• Include the –COOH functional group
• -C=O
O
H
• Dissolves in water to form:
e.g. CH3COOH
CH3COO- + H+
• Carboxylic acids react in the same way as acids –
but because they are only partially ionised at any
one time they react more slowly – the concentration
of [H+] is less than with, for example, HCl. They are
weak acids
Practical
Test
Observations
Notes
Smell
e.g. vinegar
Shows that there are volatile
molecules i.e. does not separate
fully into ions as HCl (aq) does.
Weakly acidic
 3-4
pH of a
solution of the
carboxylic acid
solution
2 HCOOH (aq) + Mg (s) 
Reaction with Slow fizzing
magnesium
Produces hydrogen
(HCOO)2Mg (aq) + H2 (g)
metal
gas & salt
Reaction with Produces coloured 2 CH3COOH (aq) + CuO (s) 
copper oxide
salt
(CH3COO)2Cu (aq) + H2O (l)
Reaction with
sodium
carbonate
Fizzes
Produces carbon
dioxide
2 HCOOH (aq) + Na2CO3 (s) 
2HCOONa (aq) + H2O (l) +
CO (g)
Salts of carboxylic acids
•
•
•
•
Called carboxylates
Contain RCOO- group
Sodium ethanoate dissolves to give
CH3COONa (s)  CH3COO- (aq) + Na+ (aq)
sodium ethanoate  ethanoate ions + sodium ions
REMINDER
• Parents’ Evening – Thursday 10th February
• Coursework due – Monday 14th February
Learning objective:
28/04/2017
To introduce esters as products of the reactions of alcohols with carboxylic acids
To observe properties of esters
To demonstrate the procedure for making an ester on a laboratory scale
To explain the purposes of practical techniques involved in the preparation of an ester
Complete first section of carboxylic acids and esters sheet
Making Esters
•
•
•
•
Why is it necessary to heat the test tubes? Why should
you heat them in a water bath, not directly in a flame?
What is the purpose of adding concentrated sulfuric acid
to the mixture of the organic acid and the alcohol?
Suggest why you poured the mixture into sodium
carbonate solution, not just water.
Use the example of esters and water to explain what the
work ‘immiscible’ means.
1.
2.
3.
4.
5.
6.
Add 10 g ethanoic acid and 8 g ethanol to
the distillation flask. Swirl and carefully
add 2 cm3 concentrated sulfuric acid.
Fit a reflux condenser and heat gently for
10 minutes. Cool.
Rearrange the apparatus for distillation.
Distil off everything up to 82 °C. (Clean
the distillation apparatus for step 6.)
Transfer the distillate to a tap funnel.
Taking the usual precautions to release
gases, shake first with sodium carbonate
solution to remove acids and then with
calcium chloride solution to remove
unchanged ethanol. In both instances run
off and discard the lower, aqueous layer.
Transfer to a small flask. Add a few
granules of anhydrous calcium chloride.
Stand for a few minutes until the liquid is
clear.
Redistil from the clean distillation
apparatus and collect the fraction boiling
in the range 74–79 °C.
Structure and naming
acid + alcohol  ester + water
ethanoic acid + methanol  methyl ethanoate + water
propanoic acid + butanol  butyl propanoate + water
I
C=O
I
O
I
H-C-H
I
Ester Functional group
• The oxygens are not directly bonded to the
hydrogens
• The molecule does not form hydrogen bonds so
do not mix well with water
• Esters are much more volatile (evaporate more
easily) than the alcohol and acid that form them
ethanol
propanoic acid
ethyl propanoate
water
1.
Heat under
reflux preparation
Separating
aqueous
layer purification
2.
3.
Fractional
distillation purification
Drying with
anhydrous
CaCl2 purification Fractional
distillation purification
4.
5.
6.
Add 10 g ethanoic acid and 8 g ethanol to
the distillation flask. Swirl and carefully
add 2 cm3 concentrated sulfuric acid.
Fit a reflux condenser and heat gently for
10 minutes. Cool.
Rearrange the apparatus for distillation.
Distil off everything up to 82 °C. (Clean
the distillation apparatus for step 6.)
Transfer the distillate to a tap funnel.
Taking the usual precautions to release
gases, shake first with sodium carbonate
solution to remove acids and then with
calcium chloride solution to remove
unchanged ethanol. In both instances run
off and discard the lower, aqueous layer.
Transfer to a small flask. Add a few
granules of anhydrous calcium chloride.
Stand for a few minutes until the liquid is
clear.
Redistil from the clean distillation
apparatus and collect the fraction boiling
in the range 74–79 °C.
Fats and oils
Fats and oils
Naturally occuring
Animal fat
Vegetable oil
Marine oil
lard
suet
sunflower oil
coconut oil
cod liver oil
whale oil
Homework
Find out about the issues around trans fats.
• You need to make bullet points on:
– The sources, structure and properties of saturated and
unsaturated fats
– The difference between cis and trans fats in terms of
molecular structure
– A description and explanation of the effect that cis and
trans structures have on properties
– Explain how oils are hardened
– Explain the problems with the trans fats formed when
oils are hardened
Fats and oils
Fats and oils are built from an alcohol with three -O-H groups.
glycerol
Systematic name is propane-1,2,3-triol
Fats and oils
The other components of fat molecules are carboxylic acids
such as
Stearic acid
Systematic name is octadecanoic acid
Fats and oils
Fats and oils are ESTERS of
glycerol and
long chain carboxylic acids
Fats and oils
Removal of water in the condensation reaction gives -
The molecular formula shown above suggests that the fat
molecule is shaped like an E, but the molecule is actually
shaped more like this:
Fats and oils
Fats are mainly built from carboxylic acids with
C-C single bonds.
Stearic acid in beef fat
Oils have some C=C bonds in the carboxylic acids
from which they are made.
Carbon –
carbon
(>C=C<)
double
bond here
Oleic acid in olive oil
Fats and oils
Oil
Double bonds in oil make the molecule less compact.
Less tightly packed molecules make oils liquid.
Fat
Fat molecules pack together more tightly,
making fats solid at room temperature.
This is like he difference between ldpe and hdpe last year
Testing for unsaturation
• Carbon-carbon double bonds (>C=C<)
decolourise bromine water
Fats and oils
• that fats and oils are esters of glycerol with
fatty acids.
• that unsaturated compounds can be
recognised by the presence of C= C double
bonds.