Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
1
Name of the student ………………………………….
Grade : …………………
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
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Question 1 Write the molecular formula of the alkane molecules with 10 carbon atoms.
What is the physical state likely to be at r.t.p?
Answer 1. The molecular formula of the alkane molecule with 10 carbon atoms is C10H22
This formula is obeying the general formula of alkane, which is Cn H2n +2
The structural formula will be different.
……………………………………………………………………………………………………………..
Question 2. From the table of homologous series the molecular formula of nonane is C9H20.
(a) Write the molecular formula, relative molecular mass and structural
formula of nonane. (b) Draw a graph of the boiling point (vertical axis) against the Mr of the
alkanes.
Use your graph to find the approximate boiling point of the nonane.
Answer2. (a) From the table of homologous series
The molecular formula of nonane is C9H20
The relative molecular mass (Mr) =
The structural formula is CH3-(CH2)7-CH3
Or
……………………………………………………………………………………………………
(b) From the table, as B. P. increases Mr also ncreases.
Mr B.P (oC)
16 -160
30 -89
44 -42
58 -0.5
72 36
86 69
100 98
114 126
Tem
p. in
OC
Mr
200
- 200
-150
-100
-50
150
100
50
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
3Question 3. The structural formula of pentane is
CH3 – CH2 –CH2 – CH2 − CH3
Write structural formula of two hydrocarbons which are isomer of pentane.
Answer. The structural formula of the isomer of pentane are:
First structural formula
CH3 – CH2 –CH – CH3 or CH3 – CH –CH2 – CH3
l l
CH3 CH3
or or
CH3
CH3 l
l CH3 – CH –CH2 – CH3
CH3 – CH2 –CH – CH3
Name : Isopentane
* It does not matter whether the alkyl group (CH3) attached above or below.
Just one structural formula (All are similar)
Second structural formula
CH3
l
CH3 – C– CH3
l
CH3
Name ; Neo pentane (Only one possible way to write)
Question 4. Write the structural formulas of two isomers with molecular formula C2H4Br2.
Answer The structural formula of C2H4Br2 are:
………………………………………………… ………………………………………………
Question 5. Write molecular formula and structural formula of the next member of the C2H4, C3H6, C4H8 this series.
Answer. Three alkenes; C2H4, C3H6, C4H8 forms the homologous series.
The molecular formula of the next member is C5H10.
(This molecular formula is obeying the general formula for alkenes, CnH2n)
The structural formula is CH3-CH2-CH2-CH =CH2
Also write its structural formula in the flat form
……………………………………………………………………………………………………………….
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Question 6. Decene is an alkene containing ten carbon atoms in one molecule. Write its
molecular formula. Answer. The molecular formula of decene is …………………………………. Question 7.
(a) Some reactions of butene are shown in the following diagram. Write
the structural formulas of the products in the three boxes.
H C
H
H
C
H
H
C
H
C
H
H
+ hydrogen REACTION A
+ bromineREACTION B
+ steam REACTION C
(b) What other substance is needed in reaction A?
(c) Name the product of reaction A.
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
5Answer (a)
H C
H
H
C
H
H
C
H
C
H
H
+ hydrogen REACTION A
+ bromineREACTION B
+ steam REACTION C
H C
H
H
C
H
H
C
Br
C
H Br
H
H
Addition of Br2
will take place
across the
double bond
H C
H
H
C
H
H
C
H
C
H H
H
H
Addition of H2
will take place
across the
double bond
H C
H
H
C
H
H
C
H
C
H OH
H
H
Addition of H2O
will take place
across the
double bond Answer (b) Other substance needed is a catalyst Ni
Answer (c) The product of reaction A is alcohol (Butanol)
Question 8. Write a balanced chemical equation in each case to show the cracking of C20H42, to produce
(a) an alkane with 6 carbon atoms and an alkene molecule;
(b) 8 ethene molecules and one other alkene molecule and hydrogen;
(c) an alkene with 12 carbon atoms, one other alkene molecule and
hydrogen. Answer cracking (a) C20H42 C6H14 + C14H28
Alkane Alkene
cracking (b) C20H42 8 C2H4 + C4H10
Ethene Butane
Cracking (c) C20H42 ………..+ …………… + H2
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Question 9 Complete the following table.
Question 10
Compound
Formula
Boiling point/oC
A CH4 −162
B C2H4 −104
C C2H6 −89
D C3H6 −48
E C3H8
F C4H10 0
(a) (i) The hydrocarbons in the table above belong to two homologous
series.
Name these two series
Alkane series Alkene series
Answer ……………………………………… ……………………………………
(ii) State which compound belongs to each series
Answer CH4, C2H6, C3H8, C4H10 (Alkane series)
C2H4, C3H6, (Alkene series)
Name of the homologous series
Name of the first member
Structural formula of the first member
Molecular Formula of the first member
General formula of the series
alkanes
methane
H l
H – C – H
l
H
Cn H2n +2
C C
H
HH
H
silanes
silane
Si
H
HH
H
SiH4
Sin H2n +2
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
7 (b) State one method that could be used to separate a mixture of
the six hydrocarbons
Answer ………………………………………………………………………………………….
(c) Which hydrocarbon is the main component of the natural gas?
Answer ……………………………………………………….
(Hint lower hydrocarbons from C1 to C4)
(d) Is compound F is a solid, liquid or gas at a room conditions?
Answer …………………………………………………………………………
(e) From the table predict the boiling point of compound E
Answer The boiling point of this compound should be close to C3H6
Since it also contains three carbon atoms, since the number
Of hydrogen atoms are higher in case of C3H8 comparatively to C3H6,
therefore,its boiling point must be higher than C3H6 and lower than
00C.
−30 or −20 or −10
(f) Compound D and E can be distinguished by a chemical test.
(i) Name a reagent used for the test.
Bromine water (unsaturation test)
Answer ……………………………………………………………
(ii) State what it seen in the test with compound D
Answer Reddish-brown colour of bromine water will de-colourise.
(iii) State what is seen in the test with compound E.
Answer The compound E is an ‘alkane’ (saturated aliphatic hydrocarbon)
Therefore, no de-colourisation of bromine water will take place
in case of compound E.
(g) Compound B and D belong to the same homologous series.
Calculate the relative molecular mass, Mr of the next member of
the series
Answer C4H10 Mr =58
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Question 11. Study the reaction scheme below and then answer the following
questions.
Petroleum C10H22
Cracking
Compound XC2H5OH
Reagent Z
bromine
Compound Y
C2H6
Reaction II
Hydrogen
CO2 and
water
Reaction III
C2H5Cl
Reaction V
Hydrogen chloride
Reaction IV
Chlorine
C2H5NH2
reaction VI
ammonia
Process I
(a) Write the name and formula of the organic compound X
Answer ………………………………………………………………………………………………
(b)
(i) What is the name used for process I?
Answer …………………………………………………………………………………
(ii) What other substance is needed for reaction II?
Answer ………………………………………………………………………………………………
(iii) What type of reaction is reaction II?
Answer ………………………………………………………………………….
(iv) What type of reaction is reaction III?
Answer ………………………………………………………………………….
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(v) What type of reaction is reaction IV?
Answer ………………………………………………………………………….
(c) Suggest the type of reaction that takes place in
(i) reaction V?
Answer ……………………………………………………………………………………………….
(ii) reaction VI?
Answer ……………………………………………………………………………………
(d) Write the formula of the compound Y?
Answer ……………………………………………………………………………………………..
(e) Name reagent Z
Answer …………………………………………………………………………………………
(f) (i) Name the homologous series to which C10H22 belongs
Answer …………………………………………………………………………………………
(ii) Write the formula of the next member of this series
Answer …………………………………………………………………………………………
Question 12 In an experiment, 0.04 mole of hydrocarbon Z was completely burnt in
oxygen, producing 2.88 dm3 of CO2 measured at room conditions.
(a) Calculate
(i) the number of moles of gas in 2.88 dm3 of CO2.
Answer From the formula
Volume of the gas = Number of moles × Molar volume
………………………………………………………………………………………………………..
……………………………………………………………………………………………………….
(ii) the number of moles of CO2 produced by the combustion of 1
mole of Z
Answer From the above result,
0.04 mole of hydrocarbon Z produces 0.12 moles of CO2
Therefore,
1 mol of hydrocarbon Z will produce 0.12
-------- = 3.0 moles of CO2
0.04
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(iii) the number of carbon atoms in one molecule of Z
Answer It is important to note that all carbon atoms present in any
hydrocarbon will
change into carbon dioxide.
Therefore same numbers of carbon atoms are present in the
CO2 on complete combustion of any hydrocarbon.
For example, C2H4 on complete combustion produces 2 carbon
atoms in the form of CO2
C2H4 + 3O2 → 2CO2 + 2H2O
2 moles of CO2 contains 2 carbon atoms in CO2 as well as 2
carbon atoms in C2H4
……………………………………………………………………………………………………………………………..
………………………………………………………………………………………………………………………………
Question 13 (a) A saturated hydrocarbon contains 83.33 % by mass of carbon.
(i) Explain what is meant by the term saturated.
Answer It means maximum amount of the hydrocarbon in a given amount of the
substance.
(ii) Deduce the molecular formula of the hydrocarbon and give one
possible structural formula for it.
Answer By assuming that total mass of the hydrocarbon is 100 g
Element
C H Mass of each element (g)
Molar mass (i. e. Ar in grams)
Number of moles
Mass = ----------------- Molar mass
Simplest atomic ratio
(It is obtained by dividing
each number of moles by the
smallest number)
Simplest whole number
atomic ratio
5 12
The molecular formula of the hydrocarbon is
The structural formula of hydrocarbon is ………………………………………………………
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(b) Saturated hydrocarbons undergo cracking in industry to produce smaller
molecules, including alkenes. These alkenes are used to make useful
chemicals by addition reactions
(i) What is meant by the term cracking.
Write a balanced equation for a cracking reaction and name the
alkene products
Answer ……………………………………………………………………………………………………
……………………………………………………………………………………………….
(ii) Explain what is meant by the term addition reaction.
………………………………………………………………………………………
(iii) Give the chemical name, formula and one important use of an organic
compound produced by an addition reaction of the alkene named in (i)
above.
Answer Chemical name: …………………………………………………………………
Chemical Formula: ………………………………………………….
Use: ……………………………………………………
Question 14 A Hydrocarbon, C6H6 is the first member of the homologous series with the
general formula CnH2n −x, where n is the number of carbon atoms in the
molecule.
(a) (i) Deduce the value of x in the general formula.
Answer : ………………………………………………………………………………………………
(i) Write the formula of the second member of this homologous
series.
Answer : ………………………………………………………………………………………………
(b) The hydrocarbon, C6H6 is poisonous and non biodegradable.
(i) What is meant by non -biodegradable?
Answer : …………………………………………………………………………………………….
(ii) Suggest the equation for a chemical reaction in which you
would attempt to destroy unwanted C6H6.
Answer : Combustion reaction
2C6H6 + 15O2 → 12CO2 + 6H2O
…………………………………………………………………………………………….
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(c) The hydrocarbon, C6H6 undergoes a substitution reaction with chlorine
under the right conditions. One of the products of the reaction is
hydrogen chloride
Construct a balanced chemical equation for the reaction and use it to
explain the meaning of the substitution reaction.
Answer :
Cl2FeCl3
Cl
HCl+ +
C6H6
Chlorobenzene
Benzene
Question 15 (a) The hydrocarbon, C6H14 forms isomers.
Explain the meaning of the term isomers, using two isomers of the
hydrocarbon as examples.
Suggest one difference in the physical properties of these isomers.
Answer …………………………………………………………………………………………………………
……………………………………………………………………………………………………….
……………………………………………………………………………………………………….
(b) Methane is the first member of the alkane homologous series.
Another homologous series of hydrocarbons has the general formula
Cn H2n−2 (where n is the greater than 1).
(i) Write molecular formula of the first member of this other series
of the hydrocarbons.
Answer …………………………………………………………………………………………………………
(i) Sketch a diagram to show the possible electronic structure of a
molecule of this hydrocarbon (outer shells only).
Answer …………………………………………………………………………………………………………
(ii) The hydrocarbons in (i) can be produced by the reaction of
water with calcium carbide, CaC2. Deduce the equation for the
reaction
CaC2 + 2H2O → C2H2 + Ca(OH)2
Answer …………………………………………………………………………………………………………
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
13 Question 16 (a) The general formula of the alkane series of is CnH2n+2. One member of this
series contains 82.76% by mass of carbon.
(i) Calculate the value of n for the hydrocarbon which contains 82.76 % by
mass of carbon. Answer: In order to calculate the value of n for the hydrocarbon, the molecular formula
of the hydrocarbon is to be calculated first. Then from the molecular formula
the value of n can be obtained.
By assuming that total mass of the hydrocarbon is 100 g
Element
C H Mass of each element (g)
82.76 17.24
Molar mass (i. e. Ar in grams)
12 1
Number of moles
Mass = ----------------- Molar mass
82.76
---------- = 6.89 12
17.24
-------- = 17.24
1.0
Simplest atomic ratio
(It is obtained by dividing
each number of moles by the
smallest number)
6.89 ------- = 1.0
6.89
17.24
-------- = 2.50
6.89
Simplest whole number
atomic ratio
1
2 or 4
2.5
5 or 10
The molecular formula of the hydrocarbon is C2H5 is not acceptable because it is
Given in the question that it belongs to the general formula CnH2n+2. Therefore,
Acceptable molecular formula is C4H10
This molecular formula belongs to this alkane series.
Therefore, the value of n is 4……
(ii) Give one full structural formula for this hydrocarbon.
Answer: …………………………………………………………………………………………………….
(b) One of the industrial uses of hydrocarbons involves ‘cracking’ them into
mixtures of smaller molecules which involves various alkenes.
These alkenes are then used to make synthetic macromolecules.
(i) Suggest the name of one of the alkenes which may be present in the
mixture formed by cracking in the hydrocarbon in (a).
Answer: From the molecular formula of the hydrocarbon as calculated above the
name of the alkenes is ascertained.
Cracking C4H10 -------------���� C2H4 + C2H6
Ethene
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(ii) Explain what is meant by synthetic macromolecules?
Answer: Those macromolecules/ polymers prepared by synthetic method called
synthetic macromolecules.
These are synthetic polymers like polyethene, PVC, Nylon etc.
(ii) Name a type of macromolecules which occurs naturally. Give one use
named example of this type of macromolecules.
Answer: ………………………………………………………………………………………. ……………………
Question 1 Propanol reacts with a hot mixture of sulphuric acid and potassium dichromate
(VII). Write the molecular formula and structural formula of the organic
compound that you would except to be formed.
What type of organic compound is this product?
H2SO4 + K2Cr2O7
(Hot)
Answer CH3-CH2-CH2-OH CH2 = CH2 + H2O
Ethene
Molecular formula of this (ethane ) is …………………..
Structural formula of ethene is CH2 = CH2
The structural formula of ethane in flat form is ……………………………………..
This is an alkene organic compound.
Question 2 Write the molecular formula and structural formula of the acid with 5 carbon
atom in one molecule.
Answer Molecular formula is ……………………………………………………………………………
Structural formula is ……………………………………………………………………………
Question 3 Construct an equation for the reaction of ethanoic acid with copper (II) oxide .
Answer CH3COOH + CuO Cu (CH3COO)2
Copper acetate / Copper ethanoate
SALT
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
15 Question 3 Write a chemical names and formulas of the two organic compounds from
which the ester below is made.
H C
O
O C
H
H
C
H
H
C
H
H
H
Answer From the structural formula given above, the following conclusions can be
made. Ester is always made by the combination of acid and alcohol together.
H C
O
O C
H
H
C
H
H
C
H
H
H
This part came
from the acidThis part came from
the alcohol
Conclusion: The acid molecule contains only one carbon atom.
HCOOH (methanoic acid)
The alcohol molecule has three carbon atoms.
CH3-CH2-CH2-OH (Propanol)
Question 4 Write the structural formula of the ester produced by reacting ethanol with
propanoic acid.
Answer CH3-CH2-CH2-COOH + OH- CH2-CH3 …………………………………………………………………………………….
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
16 Question 5 The structural formulas of eight organic compounds, A to H are shown
Below. Use the letters for your answers.
H O C
H
H
C
H
H
C
H
H
H
A
H C
H
H
C
H
H
C
H
H
HC O
O
B
C
H
C C
H
H
H
H
H
C
H C
H
H
C
O
H
C
H
H
H
H
D
H C
H
H
C
O
O H
E
H C
H
H
C
H
C
H
H
H
C
H
HH
F
H C
O
O H
G
H C
H
H
C
Cl
Cl
Cl
H
(a) Which compounds are (i) alcohols and (ii) acids
Answer (i) Alcohols are …………………………………..
(ii) Acids are ………………………………………
(b) Which two compounds are members of the same homologous series?
Answer ……………………………………………………………………………………………………………
(c) Which two compounds are isomers?
Answer Isomers have same molecular formula but different structural formula.
The compound …………………….and ……………………. has same molecular formula.
Therefore, they are isomers.
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(d) Which compound quickly decolourizes a solution of bromine in water?
Answer This is called unsaturation test. This test given by the olefins/ unsaturated
hydrocarbons i.e. alkenes or alkynes.
……………………………………………………………………………………………………………………..
(e) Which compound has a sweet smell?
Answer ……………………………………………………………………………………….
(f) Which compound is produced by the oxidation of the ethanol?
Answer ……………………………………………………………………………………….
(g) Choose two compounds which would react together to form an ester?
Answer ……………………………………………………………………………………….
(h) Which compound can be made from an alkane by a substitution reaction?
Suggest a use for this compound
Answer ……………………………………………………………………………………….
Use; Trichloroethane is an important organic solvent.
Question 6 Following figures shows the sources of the ethanol manufactured in three countries.
Fermentation
Petroleum
(a) Ethanol is made from petroleum by cracking, followed by reaction with stem.
(i) What organic compounds made in the cracking?
Answer Lower alkanes, lower alkenes or be hydrogen
(iii) Write a balanced chemical equation for the reaction with steam.
Answer …………………………………………………………………………………………………….
Brazil (100%) Singapore (100%)
1
2
USA
30%
70%
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(b) (i) Name the organic compound from which ethanol is produced in Brazil.
Answer ……………………………………………………………………………………………………….
(ii) A major use of ethanol is produced in Brazil is in motorcars.
Write a balanced chemical when ethanol is used.
Answer ……………………………………………………………………………………………………….
(iii) State one other important use of ethanol.
Answer ……………………………………………………………………………………………………….
(c) Suggest one reason why the diagram for Singapore is different
from that of Brazil
Because source of ethanol is different
Answer ……………………………………………………………………………………………………….
(d) How do you think the diagram for the United States will look 100 years from
now?
Explain your answer.
Answer
After 100 years most of the petroleum reserves will get exhausted
……………………………………………………………………………………………………….
so,
…………………………………………………………………………………………………………….
………………………………………………………………………………………………………………….
Question 7
Butanoic acid, C3H7CO2H, can be made by oxidizing butanol, C4H9OH. In an
experiment, 3.3 g of butanoic acid was produced from the oxidation of
3.7 g of butanol.
(a) (i) Name a suitable oxidizing agent for this reaction.
Answer ……………………………………………………………………………………………………….
(ii) State one observation you would make in this experiment
Answer The purple colour of KMnO4 (an oxidizing agent) will decolourise
or
The colour of K2Cr2O7 (an oxidizing agent) will change from orange to
green.
(b) (i) Calculate the relative molecular mass, Mr of butanol
Answer ……………………………………………………………………………………………………….
(ii) Calculate the number of moles of butanol used in the experiment.
Answer ……………………………………………………………………………………………………….
(iii) Calculate the relative molecular mass, Mr of butanoic acid.
Answer ……………………………………………………………………………………………………….
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(iv) Calculate the maximum mass of butanoic acid that could be obtained
from the butanol in the experiment.
Answer
C4H9OH → C3H7CO2H
Mr = 74 g Mr = 88 g
74.0 g of butanol produces butanoic acid = 88.0 g
∴ 1.0 g of butanol will produce butanoic acid =
∴ 3.7 g of butanol will produce butanoic acid =
…………………………………………………………………………………………….
(iv) Calculate the percentage yield of butanoic acid in the experiment.
Answer ……………………………………………………………………………………………………….
Question 8 Ethyl ethanoate is made by esterification.
H C C
O
H
H
O H
+ H C C
H
H
O H
H
H
H C C
O
H
H
C C
H
H
H
H
H
O +
H
O
H
Ethanoic acid Ethanol
Ethyl ethanoate
Water
The table gives the relative molecular masses for the reactants and products in the reaction.
(a) In an experiment, 3.0 g of ethanoic acid and 4.6 g of ethanol were heated
together with a catalyst.
(i) How many moles of ethanoic acid were used?
Answer 3.0
Number of moles of ethanoic acid = −−−−−−−−−−−−−−−− Mr of ethanoic acid
3.0
= −−−−− 60
Substance Relative molecular mass (Mr)
Ethanoic acid
Ethanol
Ethyl ethanoate
water
60
46
88
18
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(ii) How many moles of ethanol were used?
Answer ……………………………………………………………………………………………………….
(iii) Which reactant (ethanol or ethanoic acid) was in excess?
Answer ……………………………………………………………………………………………………….
(iv) What mass of ethyl ethanoate would be made if there was 100 %
conversion?
Answer CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
Ratio of number of moles,
1
Number of moles of ethyl ethanoate = −−−−−− Number of moles of ethyl ethanoic acid 1
For 100 % conversion →
Number of moles of ethyl ethanoate = 0.05 mol
Mass of the ethyl ethanoate = number of moles × Mr of
Ethyl ethanoate
= 0.05 × 88 = 4.4 g
(v) In the experiment, only 2.20 g of ethyl ethanoate were obtained. What
was the percentage yield of ethyl ethanoate?
Answer ……………………………………………………………………………………………………….
(b) Propanoic acid has the following structural formula.
CH
H
H
C
H
H
H
C
O
O
Draw the structural formula of the ester formed when propanoic acid reacts
with ethanol.
Answer ……………………………………………………………………………………………………….
Question 9 Olive oil contains oleic acid which is unsaturated.
(a) (i) By naming the reagent and giving the observation, describe a
simple test to confirm that olive oil contains an acid.
Answer Reagent …………………………………………………………………………..
Observation ………………………………………………………………………..
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(ii) Explain what is meant by the term unsaturated.
Answer ……………………………………………………………………………………………………….
(iii) By naming the reagent and giving the observation, describe a simple
test to confirm that oleic acid is unsaturated.
Answer Reagent …………………………………………………………………………..
Observation ………………………………………………………………………..
(b) The molecular formula of oleic acid is C17H31CO2H.
How many double bonds between carbon atoms are present in one molecule
of oleic acid?
Explain your answer.
Answer ……………………………………………………………………………………………………….
CH3−(CH2)12(C2H2)2 • COOH
Question 10
Carefully study the reaction scheme below and use it answer the questions
that follow.
P
Fermentation
Ethene C2H4
R 1,2 - dibromoehtane Q
Polymerization
Dehydration
Hydrogen and a catalyst
glucose
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(a) (i) Give the name of the substances and the conditions needed to
ferment glucose.
Answer Substances needed …………………………………………………………..
Conditions needed …………………………………………………………..
(ii) Give the name of the gas that is also produced during the fermentation
of glucose
Describe a chemical test for this gas.
Answer Name of the gas …………………………………………………………..
Test for the gas …………………………………………………………..
Observation ………………………………………………………………….
(b) (i) Give the name and molecular formula for the substance P.
Answer Name ……………………………………………………………………………….
Molecular formula …………………………………………………………..
(ii) Give the names of substances Q and R.
Answer Substance Q ……………………………………………………………………………….
Substance R ……………………………………………………………………………..
(c) Write the equation for the addition reaction between ethane and bromine
Answer . ……………………………………………………………………………………………………..
Question 11
Ethanol, C2H5OH, is used in Brazil as a liquid fuel instead of gasoline (petrol). The
ethanol is manufactured by a fermentation process from sugar cane.
(a) (i) Describe how cane sugar can be converted by the process of
fermentation.
Answer . ……………………………………………………………………………………………………..
. ……………………………………………………………………………………………………..
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
23 (ii) What is the name of the gas produced during this fermentation?
How would you test for this gas.
Answer Name of the gas……………………………………………………………………………..
Test for the gas ………………………………………………………………………..
(b) When ethanol is completely burnt in air, it forms CO2 gas and water. One
mole of ethanol will release 1370 kj of heat energy during this reaction
(i) Construct the balanced equation for the burning of ethanol.
Answer C2H5OH + 3O2 → 2CO2 + 3H2O; ∆Η = - 1370 kj
(ii) The mass of 1 litre of ethanol is 780 g. How much heat energy will
be released when 1 litre (1 dm3) ethanol is completely burnt?
Answer one mole of ethanol on produces heat 1370 kj (From above)
C2H5OH + 3O2 → 2CO2 + 3H2O; ∆Η = - 1370 kj
From the chemical equation, the mass of one mole of C2H5OH
is = 46 (Mr)
46 g of ethanol produces heat = - 1370 kj
1.0 g of ethanol will produce heat = - 1370 kj/ 46
- 1370 × 780 ∴ 780 g (1 litre/1 dm3 ) will produce heat = −−−−−−−−−−−−−− kj 46
= - 23230 kj
(c) When completely burnt, 1 litre of gasoline releases 38000 kJ of heat energy.
Comparing ethanol and gasoline as a liquid fuels, suggest
(i) One advantage of using ethanol rather than gasoline.
Answer using ethanol as a fuel will meet the increasing demand for the
petrol, moreover
(ii) One advantage of using gasoline rather than ethanol.
Answer. Same mass of the gasoline on combustion produces more heat than
same mass of ethanol.
Therefore, gasoline is a better fuel than ethanol.
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
24 Question 12
Ethanol
+
Compound Y
+ acid A
Organic Compound X
Cold Water
Heat (a) Above figure shows an experiment to make organic compound X by reacting
ethanol with organic compound Y in the presence of acid A. Compound X has the formula CH3CH2CO2CH2CH3
(i) Name the compounds X, Y and A.
Answer From the formula the compound X, CH3CH2CO2CH2CH3
It is concluded that it is an ester.
An ester is formed by the reaction of an acid and an alcohol.
Therefore, total number of carbon atoms an acid and total number of
carbon atoms in alcohol can be found out from the molecular formula
of an ester.
CH3CH2CO OCH2CH3
This part came
This part came from alcohol
From acid
Compound X → Ester
Compound Y → Organic acid (CH3CH2COOH)
Compound A (Acid) → H2SO4
H2SO4
(ii) CH3CH2COOH + HOCH2CH3 CH3CH2COOCH2CH3
+
H2O
(iii) Cold water will reduce the rate of evaporation of the molecular
substance (ester).
(b) The same apparatus was used to make organic compound Z,by reacting
ethanol with compound B in the presence of acid A. Compound Z has the composition by mass: 53.3 % oxygen,40.0 % carbon and
6.7% hydrogen.
(i) Find the empirical formula of compound Z
By assuming that total mass of the hydrocarbon is 100 g
Answer
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
25
The empirical formula of the compound Z is …….CH2O
(ii) The relative molecular mass of compound Z is 60. Find the molecular
formula of the compound Z and write its structural
formula.
Answer
The relative molecular mass
= n
Relative mass of the empirical formula
60 = 2 =n
30
molecular formula of the compound Z is …..2 × CH2O = C2H4O2
The structural formula of the compound is
……………………………………………………………………………………………
Question 13 Some information is given below on four organic compounds. A,
B, C and D. In each case, suggest the identity of the compound by writing a full
structural formula. Explain your reasoning.
(a) Compound A: a liquid with relative molecular mass 60; the liquid is neutral
and soluble in water; under right conditions, it reacts with ethanoic acid and
to give a sweet smelling product.
Answer A sweet smelling product is formed by the reaction of ethanoic acid
with compound A. Therefore, the compound A could be an acid.
Because, an ester (a sweet smelling compound) is only formed by the
reaction of an acid with alcohol, in presence of acid (right conditions)
This organic acid (A) has molecular mass 60 (given)
So. The molecular formula of A will be CH3COOH
It is water soluble, because it is capable of forming H-bonding with
water molecule.
Element
O C H
Mass of each element (g)
53.3
40.0
6.7
Molar Mass (i.e. Ar in grams)
16g
12g
1.0 g
Number of moles
Mass
= ------------------
Molar mass
53.3
----- = 3.33
16
40.0
----- = 3.33
12
6.7
--- = 6.7
1.0
Simplest atomic ratio (it is
obtained by dividing each
number of moles by the
smallest number)
3.33
----- = 1.0
3.33
3.33
----- = 1.0
3.33
6.7
---- = 2.0
3.33
Simplest whole number atomic
ratio
1
1
2
Work Book/Organic Chemistry Page
Mahatma Gandhi School, Jakarta By: Manoj K. Agnihotri
26(b) Compound B: a liquid with relative molecular mass of 32; the liquid can
be oxidized to produce a compound with molecular formula HCOOH.
Answer The given compound, HCOOH is an acid. If oxidation of any compound
can produce an acid, it means that compound is an alcohol.
It is important to note that the number of carbon atoms in alcohol and
acid remains same. Therefore, alcohol is CH3OH, which has the molar
mass 32
(c) Compound C: a liquid with relative molecular mass of 74; a dilute solution
of the compound has a pH less than 7 and reacts with magnesium ribbon to
produce a gas which burns in air.
Answer If, the liquid has pH less than 7, it means the liquid is an acid, acid also
reacts with magnesium ribbon & produces H2 gas. H2 gas burns in the
air.
The possible compound is:-
HCOOH Mr = 32
CH3COOH Mr = 60
√ CH3CH2COOH Mr = 72
***************