HIGHER CHEMISTRY REVISION.
Unit 2:- Natural Products
(a)
(i) Both reactants 1. Ethyl pentanoate is an ester. It can be prepared in the lab. As shown below.
and product are
flammable. A water
bath reduces
chance of them
catching fire.
(ii)
Acts as a
condenser.
(b)
HH O HHHH
H-C-C-O-C-C-C- C-C-H
HH
H HHH
(c) 1 mole of ethanol
(a)
(i) Why is a water bath used for heating?
(ii) What is the purpose of the wet paper towel?
(46g) will give 130g
(b) Draw the structural formula for ethyl pentanoate.
of ester at 100%
(c) Starting with a mass of 3.6 g of ethanol, and a slight excess of
yield.
pentanoic acid, a student achieved a yield of 70% of for ethyl
So 3.6g would give
pentanoate (mass of one mole = 130g)
10.17g
Calculate the mass of ester obtained.
At 70% yield = 7.12g
2. Proteins are an important part of a balanced diet.
Identify the two true statements.
A
Proteins are a more concentrated energy source than carbohydrates.
B
Proteins are made by addition polymerisation.
C
Denaturing of proteins involves changes in the structure of the molecules.
D
Globular proteins are the major structural materials in animal tissues.
E
Proteins are compounds of nitrogen, carbon, hydrogen and oxygen.
3. The structure of a molecule found in olive oil can be represented as shown
2.
C and E
3. (a) (i) Heterogeneous.
(ii) Fat is saturated,
(b) (i) Glycerol or
propane-1,2,3-triol.
(ii) Soap.
(a) Olive oil can be hardened using a nickel catalyst to produce a fat.
(i) What type of catalyst is nickel in this reaction?
(ii) In what way does the structure of a fat molecule differ from that of an
oil molecule?
(b) Olive oil can be hydrolysed using sodium hydroxide solution to produce
sodium salts of fatty acids.
(i) Name the other product of this reaction.
(ii) Give a commercial use for sodium salts of fatty acid.
4. An ester can be prepared by the following sequence of reactions.
H H H H
H– C–C–C– C–H
H H Br H
step 1
HBr removed
Compound A
CH3 – CH=CH-CH3
but-2-ene
step 2
(a)
CH3-CH2CH=CH2
(b)
Addition or hydration
(c)
Orange to green
(d)
Butanoic acid
(e)
Oily layer formed
(f)
Solvents, perfume bases.
step 2
CH3-CH2CH2CH2-OH
CH3-CH2-CH-CH3
OH
step 3
oxidation
Compound B
step 4
condensation
(a)
Draw the structural formula for compound A
Ester
(d) Name compound B.
(b)
What kind of reaction is shown by step 2?
(e) What evidence would show that an ester had been
(c)
What colour change would be seen when acidified
dichromate is used to carry out step 3.
formed in step 4?
(f) Give one use for esters.
5. Tooth enamel contains a fibrous protein called collagen.
(a) Describe the difference between a fibrous protein and a
globular protein.
(b) Name the four elements present in all proteins.
(a) Fibrous proteins are long, parallel protein chains with
occasional cross links making up fibres.
Globular proteins are folded into complex, almost spherical
shapes.
(b) Carbon, hydrogen, oxygen and nitrogen.
6. Biodiesel is a mixture of esters which can be made by heating rapeseed oil with
methanol in the presence of a catalyst.
C21H39 —C—O—CH2
O
C21H39 —C—O—CH
O
C21H39
O
+ 3CH3OH
3 C21H39 —C—O—CH3 +
X
O
—C—O—CH2
a triglyceride in
Methanol
rapeseed oil
a component
of biodiesel
(a)
Name compound X
(b)
A typical diesel molecule obtained from crude oil has the molecular formula C16H34
(hexadecane).
Other than the ester group, name a functional group present in biodiesel molecules
which is not present in hexadecane.
(c) Vegetable oils like rapeseed oil are converted into fats for use in the food industry.
What name is given to this process?
(a)
Glycerol OR propane-1,2,3-triol.
(b)
C=C double bond.
(c)
Hydrogenation.
7. All enzymes are globular proteins.
(a)
What term is used to describe proteins which are not globular?
(b)
Catalase is an enzyme, contained in potatoes.
A student was studying the effect of varying pH on the activity of catalase.
The following apparatus was set up and left for 3 minutes.
(i) What must be added to the side-arm test tube to study the enzyme activity
at this pH?
(ii) Describe how the enzyme activity at this pH can be measured.
(a)
Fibrous.
(b)
(i) Hydrogen peroxide solution.
(ii) Counting the number of bubbles of oxygen in a set time can give a
measure of the enzyme activity. The more active the enzyme o
greater the number of bubbles of oxygen gas given off.
8. Two reactions of propanoic acid are shown.
(a)
Draw a structural formula for ester X.
(b) (i) Give a name for compound Y, which reacts with propanoic acid to form
sodium propanoate.
(ii) Explain why solutions of sodium propanoate are alkaline.
(a)
O
CH3-CH2 –C-O-CH3
(b) (i)Sodium hydroxide.
(ii) Sodium propanoate dissolves to form sodium and propanoate ions
Na+CH3CH2COO-(s) + H2O(l)  Na+(aq) + CH3CH2COO-(aq)
In water there is this equilbrium
H2O(l)
 H+(aq) + OH-(aq)
As propanoic acid is a weak acid the propanoate ions and hydrogen ions
react to form molecules of propanoic acid
CH3CH2COO-(aq) + H+(aq)  CH3CH2COOH(l)
This removes hydrogen ions leaving an excess of hydroxide ions and so
the solution is alkaline.
9. Enzymes are specific biological catalysts. For example, trypsin, an enzyme produced
in the pancreas, will catalyse the hydrolysis of only certain peptide links in a protein.
(a) Draw the structure of a peptide link.
(b) Trypsin has an optimum temperature of 37oC.
Draw a curve to show how the enzyme activity varies with temperature.
(a) O H
-C–N–
(b) See graph.
(c)
The shape of the enzyme
molecule is irreversibly
changed so that it will no
longer complement the
shape of the substrate
molecule.
(c) Trypsin loses its activity if placed in a solution of very high pH.
What happens to the enzyme to cause this loss in activity?
10. Ethanol and propanoic acid can react to form an ester.
(a) Draw the structural formula for this ester.
(b) Draw a labelled diagram of the assembled apparatus that could be used to
prepare this ester in the laboratory.
(c) Due to hydrogen bonding, ethanol and propanoic acid are soluble in water
whereas the ester produced is insoluble.
In each of the boxes below, draw a molecule of water and use a dotted line
where a hydrogen bond could exist between the organic molecule and the
water molecule.
ethanol
propanoic acid
H
CH3-CH2-O-H
O H
(a)
H H
O H H
H–C–C–O–C–C–C–H
H H
(c) See opposite
(c) See boxes
H H
(a
)
Mixture of ethanol
and propanoic acid.
O
CH3-CH2-C-O-H
H
O H
11.
Pyrolysis (thermal decomposition) of esters can produce two compounds, an alkene
and an alkanoic acid, according to the following equation.
Draw a structural formula for the ester that would produce 2-methylbut-1-ene
and methanoic acid on pyrolysis.
H
H
H
H
C
C
C
H
H
C
H
H
H
O
O
C
H