Work Book -Alkanes, Alkenes, Alcohols & Acids

Work Book/Organic Chemistry

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1

Name of the student …………………………………. Grade : …………………

Mahatma Gandhi School, Jakarta

By: Manoj K. Agnihotri


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2

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. B.P (oC)

Mr 16 30

-160 -89

44 58

-42 -0.5

72 86

36 69

100

98

114

126

150

100

Temp. in OC

200

50

Mr

-50 -100 Mahatma Gandhi School, Jakarta -150 - 200



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Question 3. The structural formula of pentane is

3

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 l CH3

or

CH3 – CH –CH2 – CH3 l CH3

or

or

CH3 l CH3 – CH2 –CH – CH3

CH3

CH3 l – CH –CH2 – 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

………………………………………………………………………………………………………………. Mahatma Gandhi School, Jakarta



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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

H H

H

C

C

C

H

H

H

+ hydrogen REACTION A

C H

+ bromine REACTION B

+ steam REACTION C

(b)

What other substance is needed in reaction A?

(c)

Name the product of reaction A.




Answer

Page

(a)

5

H

H

H H

C

C

C

H

H

H

+ hydrogen REACTION A

H

H H C

C H

H

H

H

H

Addition of H2 will take place across the double bond

Answer

(c)

+ steam REACTION C

H

C

(b)

H

+ bromine REACTION B

H C

Answer

C

H H

Br

H C

C

C

C H

H

H

Br H

H

H

H H

OH

H C

C

C

C H

H

H

H

H

Addition of H2O will take place across the double bond

Addition of Br2 will take place across the double bond Other substance needed is a catalyst Ni 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) (b) (c)

an alkane with 6 carbon atoms and an alkene molecule; 8 ethene molecules and one other alkene molecule and hydrogen; an alkene with 12 carbon atoms, one other alkene molecule and hydrogen.

Answer

cracking

(a)

C20H42

C6H14

+

Alkane

C14H28 Alkene

cracking

(b)

C20H42

8 C2H4

+

Ethene

C4H10 Butane

Cracking

(c)

C20H42


………..+

……………

+

H2



Question 9

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Complete the following table.

Name of the homologous series

alkanes

Name of the first member

Structural formula of the first member

methane

Molecular Formula of the first member

H l H–C–H l H H

General formula of the series

Cn H2n +2

H C

C

H

H H

silanes

silane

H

Si

H

SiH4

Sin H2n +2

H

Question 10

(a)

Answer

Formula

A

CH4

−162

B

C2H4

−104

C

C2H6

−89

D

C3H6

−48

E

C3H8

F

C4H10

(i)

0

The hydrocarbons in the table above belong to two homologous series. Name these two series

Alkane series ………………………………………

(ii)

Answer

Boiling point/oC

Compound

Alkene series ……………………………………

State which compound belongs to each series

CH4, C2H6, C3H8, C4H10

(Alkane series)

C2H4, C3H6,

(Alkene series)




(b)

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State one method that could be used to separate a mixture of the six hydrocarbons

Answer

7

………………………………………………………………………………………….

(c)

Answer

Which hydrocarbon is the main component of the natural gas?

………………………………………………………. (Hint lower hydrocarbons from C1 to C4) (d)

Answer

Is compound F is a solid, liquid or gas at a room conditions?

…………………………………………………………………………

(e)

Answer

From the table predict the boiling point of compound E

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)

Answer

Reddish-brown colour of bromine water will de-colourise.

(iii)

Answer

State what is seen in the test with compound E.

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)

Answer

State what it seen in the test with compound D

Compound B and D belong to the same homologous series. Calculate the relative molecular mass, Mr of the next member of the series C4H10


Mr =58



Question 11.

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Study the reaction scheme below and then answer the following questions.

Process I

Petroleum

C10H22

C2H5NH2

Cracking reaction VI ammonia

Reaction V Hydrogen chloride

Reagent Z

Compound X

C2H5OH

C2H5Cl

Reaction II

bromine

Hydrogen Reaction IV Chlorine

Compound Y

C2H6

Reaction III

CO2 and water

(a)

Answer

Write the name and formula of the organic compound X

……………………………………………………………………………………………… (b) (i)

Answer

What is the name used for process I?

………………………………………………………………………………… (ii)

Answer

What other substance is needed for reaction II? ………………………………………………………………………………………………

(iii) Answer

What type of reaction is reaction II? ………………………………………………………………………….

(iv)

What type of reaction is reaction III?

Answer Mahatma Gandhi School, Jakarta

…………………………………………………………………………. By: Manoj K. Agnihotri


(v)

Answer

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What type of reaction is reaction IV?

………………………………………………………………………….

(c)

Answer

Suggest the type of reaction that takes place in (i) reaction V?

………………………………………………………………………………………………. (ii)

reaction VI?

Answer

…………………………………………………………………………………… (d)

Answer

Write the formula of the compound Y?

…………………………………………………………………………………………….. (e)

Answer

Name reagent Z …………………………………………………………………………………………

(f) (i) Answer

Name the homologous series to which C10H22 belongs …………………………………………………………………………………………

(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)

Answer

the number of moles of gas in 2.88 dm3 of CO2.

From the formula Volume of the gas = Number of moles × Molar volume

………………………………………………………………………………………………………..

………………………………………………………………………………………………………. (ii)

Answer

the number of moles of CO2 produced by the combustion of 1 mole of Z

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 By: Manoj K. Agnihotri


(iii)

Answer

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the number of carbon atoms in one molecule of Z

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)

Answer

It means maximum amount of the hydrocarbon in a given amount of the substance. (ii)

Answer

Explain what is meant by the term saturated.

Deduce the molecular formula of the hydrocarbon and give one possible structural formula for it.

By assuming that total mass of the hydrocarbon is 100 g

Element C

H

5

12

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

The molecular formula of the hydrocarbon is The structural formula of hydrocarbon is ……………………………………………………… Mahatma Gandhi School, Jakarta



(b)

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Saturated hydrocarbons undergo cracking in industry to produce smaller molecules, including alkenes. These alkenes are used to make useful chemicals by addition reactions (i)

Answer

What is meant by the term cracking. Write a balanced equation for a cracking reaction and name the alkene products ……………………………………………………………………………………………………

………………………………………………………………………………………………. (ii)

Explain what is meant by the term addition reaction.

………………………………………………………………………………………

(iii)

Answer

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.

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)

Answer :

Deduce the value of x in the general formula.

……………………………………………………………………………………………… (i)

Write the formula of the second member of this homologous series.

Answer :

………………………………………………………………………………………………

(b)

The hydrocarbon, C6H6 is poisonous and non biodegradable.

(i)

Answer :

What is meant by non -biodegradable?

……………………………………………………………………………………………. (ii)

Suggest the equation for a chemical reaction in which you would attempt to destroy unwanted C6H6.

Answer :

Combustion reaction 2C6H6 + 15O2 → 12CO2 + 6H2O …………………………………………………………………………………………….




(c)

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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 :

Cl +

Cl2

FeCl3

+ 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)

Answer

…………………………………………………………………………………………………………

(i)

Answer

Write molecular formula of the first member of this other series of the hydrocarbons.

Sketch a diagram to show the possible electronic structure of a molecule of this hydrocarbon (outer shells only).

…………………………………………………………………………………………………………

(ii)

The hydrocarbons in (i) can be produced by the reaction of water with calcium carbide, CaC2. Deduce the equation for the reaction

CaC2 +

Answer

2H2O

→

C2H2

+

Ca(OH)2

…………………………………………………………………………………………………………




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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)

Answer:

Calculate the value of n for the hydrocarbon which contains 82.76 % by mass of carbon.

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 Mass of each element (g)

C 82.76

H 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) Simplest whole number atomic ratio

6.89 ------- = 1.0 6.89

17.24 -------- = 2.50 6.89

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) 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)

Answer:

Give one full structural formula for this hydrocarbon.

Suggest the name of one of the alkenes which may be present in the mixture formed by cracking in the hydrocarbon in (a).

From the molecular formula of the hydrocarbon as calculated above the name of the alkenes is ascertained.

C4H10


Cracking -------------

C2H4 Ethene

+

C2H6



(ii)

Answer:

Explain what is meant by

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14

synthetic macromolecules?

Those macromolecules/ polymers prepared by synthetic method called synthetic macromolecules. These are synthetic polymers like polyethene, PVC, Nylon etc. (ii)

Answer:

Question 1

Name a type of macromolecules which occurs naturally. Give one use named example of this type of macromolecules.

………………………………………………………………………………………. ……………………

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 + Ethene

H2O

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



Question 3

H

O

C

H

H

H

C

C

C

H

H

H

H

C

O

H

H

H

C

C

C

H

H

H

H

This part came from the acid Conclusion:

Answer

H

From the structural formula given above, the following conclusions can be made. Ester is always made by the combination of acid and alcohol together.

O

Question 4

15

Write a chemical names and formulas of the two organic compounds from which the ester below is made. O

Answer

Page

This part came from the alcohol

The acid molecule contains only one carbon atom. HCOOH (methanoic acid) The alcohol molecule has three carbon atoms. CH3-CH2-CH2-OH (Propanol)

Write the structural formula of the ester produced by reacting ethanol with propanoic acid.

CH3-CH2-CH2-COOH

+ OH- CH2-CH3

…………………………………………………………………………………….




Question 5

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16

The structural formulas of eight organic compounds, A to H are shown Below. Use the letters for your answers.

H

O

H

H

H

C

C

C H

H

H

H

H

H

O

C

C

O

H

H

C

C

H

H

H

B

A

H H

H

C

C

C

H

H

H

H

H

H

H

H

C

C

C H

H

O

H

H

C

D

H H

C

C

H

O

O H

H

H

H

H

C

C

C H H

H

C H

H

H

E

H

C

F

O

H

O

Answer

Answer (c)

Answer

C

C

H

Cl

Cl

Which compounds are (i) alcohols and (ii) acids

(i) (ii)

(b)

Cl

H

G

(a)

H

H

Alcohols are ………………………………….. Acids are ………………………………………

Which two compounds are members of the same homologous series?

…………………………………………………………………………………………………………… Which two compounds are isomers?

Isomers have same molecular formula but different structural formula. The compound …………………….and ……………………. has same molecular formula.

Therefore, they are isomers. Mahatma Gandhi School, Jakarta



(d) Answer

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Which compound quickly decolourizes a solution of bromine in water? This is called unsaturation test. This test given by the olefins/ unsaturated hydrocarbons i.e. alkenes or alkynes. ……………………………………………………………………………………………………………………..

(e)

Answer (f)

Answer

(g)

Answer

(h)

Answer

Which compound has a sweet smell?

………………………………………………………………………………………. Which compound is produced by the oxidation of the ethanol?

……………………………………………………………………………………….

Choose two compounds which would react together to form an ester?

……………………………………………………………………………………….

Which compound can be made from an alkane by a substitution reaction? Suggest a use for this compound

………………………………………………………………………………………. Use; Trichloroethane is an important organic solvent.

Question 6

Following figures shows the sources of the ethanol manufactured in three countries. 30%

70%

1 2

Brazil (100%)

Singapore (100%)

USA Fermentation Petroleum

(a)

Ethanol is made from petroleum by cracking, followed by reaction with stem. (i)

Answer

Lower alkanes, lower alkenes or be hydrogen

(iii)

Answer

What organic compounds made in the cracking?

Write a balanced chemical equation for the reaction with steam.

…………………………………………………………………………………………………….




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(b) (i)

Answer (ii)

Answer

(iii)

Answer (c)

Name the organic compound from which ethanol is produced in Brazil.

………………………………………………………………………………………………………. A major use of ethanol is produced in Brazil is in motorcars. Write a balanced chemical when ethanol is used.

……………………………………………………………………………………………………….

State one other important use of ethanol.

……………………………………………………………………………………………………….

Suggest one reason why the diagram for Singapore is different from that of Brazil

Answer

(d)

Because source of ethanol is different ……………………………………………………………………………………………………….

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)

Calculate the relative molecular mass, Mr of butanol

(i)

Answer (ii) Answer (iii)

Answer

………………………………………………………………………………………………………. Calculate the number of moles of butanol used in the experiment. ………………………………………………………………………………………………………. Calculate the relative molecular mass, Mr of butanoic acid.

……………………………………………………………………………………………………….




(iv)

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19

Calculate the maximum mass of butanoic acid that could be obtained from the butanol in the experiment.

Answer C4H9OH Mr = 74 g

C3H7CO2H 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 H

C H

O

H

C

+

H

O

H

H

C

C

H

H

O

H

Ethanol

Ethanoic acid

H H

C

O

C

H

H

C

C

H

H

H

O

+

H

H H

O

Water

Ethyl ethanoate The table gives the relative molecular masses for the reactants and products in the reaction. Substance

Relative molecular mass (Mr)

Ethanoic acid Ethanol Ethyl ethanoate water

60 46 88 18

(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 −−−−−−−−−−−−−−−− Mr of ethanoic acid 3.0 = −−−−− 60

Number of moles of ethanoic acid =




(ii)

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20

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.

H

H

H

C

C

H

H

O C O

H

Draw the structural formula of the ester formed when propanoic acid reacts with ethanol.

Answer

……………………………………………………………………………………………………….

Question 9 (a)

Olive oil contains oleic acid which is unsaturated. (i) By naming the reagent and giving the observation, describe a simple test to confirm that olive oil contains an acid.

Answer

Reagent …………………………………………………………………………..

Observation ………………………………………………………………………..




(ii)

Answer

21

Explain what is meant by the term unsaturated.

……………………………………………………………………………………………………….

(iii)

Answer

Page

By naming the reagent and giving the observation, describe a simple test to confirm that oleic acid is unsaturated.

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.

glucose Fermentation P Dehydration

Ethene C2H4 Polymerization

Q


1,2 - dibromoehtane

Hydrogen and a catalyst

R



(a)

(i)

Answer

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22

Give the name of the substances and the conditions needed to ferment glucose.

Substances needed …………………………………………………………..

Conditions needed …………………………………………………………..

(ii)

Answer

(b)

(i)

Answer

Give the name of the gas that is also produced during the fermentation of glucose Describe a chemical test for this gas.

Name of the gas …………………………………………………………..

Test for the gas

…………………………………………………………..

Observation

………………………………………………………………….

Give the name and molecular formula for the substance P.

Name ……………………………………………………………………………….

Molecular formula …………………………………………………………..

(ii)

Answer

Give the names of substances Q and R.

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)

Answer

Describe how cane sugar can be converted by the process of fermentation.

. ……………………………………………………………………………………………………..

. ……………………………………………………………………………………………………..




(ii)

Answer

Page

What is the name of the gas produced during this fermentation? How would you test for this gas.

23

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)

Answer (ii)

Answer

Construct the balanced equation for the burning of ethanol.

C2H5OH

+

3O2

→

2CO2

+

3H2O; ∆Η = - 1370 kj

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?

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)

Answer

(ii)

Answer.

One advantage of using ethanol rather than gasoline.

using ethanol as a fuel will meet the increasing demand for the petrol, moreover One advantage of using gasoline rather than ethanol.

Same mass of the gasoline on combustion produces more heat than same mass of ethanol. Therefore, gasoline is a better fuel than ethanol.




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Question 12

Cold Water

Organic Compound X

Ethanol + Compound Y + acid A

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. From the formula the compound X, CH3CH2CO2CH2CH3 It is concluded that it is an ester.

Answer

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 from alcohol

This part came From acid Compound X Compound Y

→ →

Ester Organic acid (CH3CH2COOH)

Compound A (Acid) → H2SO4

H2SO4 (ii)

CH3CH2COOH +

HOCH2CH3

CH3CH2COOCH2CH3 + H2O

(iii)

(b)

Cold water will reduce the rate of evaporation of the molecular substance (ester).

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 Mahatma Gandhi School, Jakarta



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25

Element O

C

H

Mass of each element (g) 53.3

40.0

16g

12g

6.7

Molar Mass (i.e. Ar in grams)

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

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 30

= 2 =n

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.




(b)

Answer

(c)

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Compound B: a liquid with relative molecular mass of 32; the liquid can be oxidized to produce a compound with molecular formula HCOOH.

26

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

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

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Work Book -Alkanes, Alkenes, Alcohols & Acids

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