Organic Chemistry

Notes

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(Credits to Mustafa Asif)

Organic compounds:

• • Compounds from Living Things

  • compounds found in living organisms

  • Examples: sugar, fats, plant oils, urea

Characteristics of Organic Compounds

• • All contain carbon element

  • Most come with hydrogen

  • Others with oxygen, nitrogen, or a halogen

Some uses of Organic Compounds

• • Fuels

  • plastic

  • rubber

  • detergents

  • insecticides

  • medicines

Classifying Organic Compounds

Homologeous series: a family of organic compounds with a general formula and a similar chemical properties

Functional Groups

• • Is the special group of atoms available in homologous series compounds which is responsible for the chemical properties of the compound

  • All compounds in homologous series have functional group except alkanes. Examples of functional group homologous series: alcohol

Production of Organic Compounds

a. From crude oil refinery:

• • Crude oil is a mixture of complex hydrocarbons with varying boiling points, depending on the number of carbon atoms and how they are arranged.

  • Fractional distillation uses this property to separate the hydrocarbons in crude oil.

b. From naphtha:

• • Naphtha fraction is used for production of petrochemicals, such as medicines, plastics and synthetic fibres, aside from fuels.

  • When naphtha is treated, not only it becomes a better fuel, it also contain more aromatic hydrocarbons, alkene and cyclic hydrocarbons which are important for petrochemical industry.

  • Crude oil is mostly used as fuel, though some allocated for chemical feedstock.

Saturated vs Unsaturated

Saturated hydrocarbons

• • hydrocarbons which the combining capacity of the carbon atoms is as fully used as possible in bonding with hydrogen atoms.

  • They only have single bond (–) only.

Unsaturated hydrocarbons

• • hydrocarbons which the combining capacity of the carbon atoms is not fully used, e.g. only 2 or 3 hydrogen are attached to a carbon atom.

  • usually indicated by double bond (=) or triple bond with another carbon atoms.

Alkanes

Characteristics

• • Usually in fuels, examples: natural gas, petrol, diesel

  • Are homologous series

  • Have a formula of C_nH_2n+2

    • example: propane has three carbon atom, thus n=3. Then the formula of propane is C₃H₈

  • Ends with suffix –ane

  • Next alkane formula differ by –CH₂ atoms. Eg: methane: CH₄, ethane: C₂H₆

Structure of Alkanes

• • Shows how all atoms in a molecule joined together by drawing lines between atoms to represent the bonds

  • Organic compound containing only single bond is saturated Eg: methane -

  • All alkanes are saturated

  • All alkenes are unsaturated

Physical Properties of Alkanes

• • Melting points and boiling points increase as the bonds become larger and heavier which increases the forces of attraction between molecules so more energy (from heat) is needed to separate them with the increase of strength of forces of attraction

  • insoluble in water but soluble in organic solvents such as tetrachloromethane as alkanes are organic compounds

  • density increases down the series; all alkenes are less than 1g/cm³

  • become more viscous going down the series as the longer molecules tangles together when it flows

  • become less flammable down the series as boiling point increases

  • unreactive with either metals, water, acids or bases because the C – C and C – H covalent bonds are harder to break

Reaction of Alkanes

• • Have same chemical properties – they don’t react with most chemicals

1) Combustion

• • Alkanes burn in air to ALWAYS form carbon dioxide and water.

  • When there is insufficient oxygen, the product is ALWAYS carbon monoxide and unburnt carbon.

Example: Butane is commonly used camping gas. State the chemical equation of combustion of butane in air.

2 C₄H₁₀ (g) + 13 O₂ (g) --> 8 CO₂ (g) +10 H₂O (l)

• • High alkanes burn less completely and gives soot (unburnt carbon) and CO

2) Reaction with Chlorine/Other Halogens (Alkyl Halides)

• • Chlorine molecule replaces alkane hydrogen atom with chlorine atom

  • Substitution reaction – the reaction in which one or more atoms replace other atoms in a molecule

  • Light is needed to break covalent bond between chlorine molecule --> atoms

Alkenes

Characteristics

- have general formula C_nH_2n.

- all alkene names end with –ene.

- the formula of one alkene differs from the next by –CH₂.

- have similar properties like alkane going down the series.

Structure of Alkenes

• • organic compound containing C = C double bond, said to be unsaturated

  • Reason: not all C atoms are bonded to the maximum number of 4 other atoms

The Importance of Ethene

Ethanol – solvent & fuel

Poly(ethene) – PE plastic variations

Ethanoic acid – vinegar

Reactions of Alkenes

1) Combustion

• • Burns in air to form carbon dioxide and water

Example: Ethene burns in air. Write the balanced equation for the reaction

C₂H₄ (g) + 3O₂ (g) --> 2CO₂ (g) + 2H₂O (l)

• • Incomplete combustion forms soot and CO. It’s produced more than alkane

2) Addition Reaction

• • Is the reaction of 2 or more molecules to form a single product

a. Addition of hydrogen:

• • Alkenes react with hydrogen to form alkanes, called hydrogenation. Must use nickel as catalyst and heat.

b. Addition of bromine

• • Bromine adds to C = C double bond of alkane molecules.

  • Phosphoric acid (H₃PO₄), high temperature of 300^oC and 60-70 atm pressure are needed as catalyst.

    • Eg: ethene to 1,2 – dibromoethene

c. Addition of water

• • Alkene reacts with water, in the form of steam, to produce alcohol.

  • Alkene + steam is passed over phosphoric acid (H₃PO₄) catalyst and temperature of 300^oC.

  • H₂O molecule adds to C = C bonds to form alcohol.

3) Polymerization

• • The joining of several identical alkene molecules to form a big molecule

Eg: Ethene --> poly(ethene)

Testing for Unsaturated Compounds

• • Mix bromine solution with alkene (for liquid alkenes – shake).

  • Reddish-brown colour of bromine disappears.

  • This shows that the compound is an alkene.

Characteristics of a Homologous Series

• • All members of homologous series have same general formula

  • Formula of each member differs by –CH₂ group

  • Physical properties changes gradually in the increase of carbon atoms

  • The members have similar chemical properties

The Manufacture of Margarine

• • Polyunsaturated food – food containing C=C bond in their molecules Eg: Vegetable oil

  • Hydrogen is reacted with vegetable oil with presence of nickel catalyst and heat, which adds to C=C bond, increasing the molecular mass of the compound

  • With increase in mass, the compound has higher boiling point. Therefore, margarine is solid at room temperature.

  • Since only some C=C bonds react with hydrogen, margarine is partially hydrogenated and each has different hardness, depending on the number of C=C bonds.

The Cracking of Alkanes

• • Alkanes can be cracked into shorter chain hydrocarbons because of the higher value it has that it can create more variety of products in petrochemical industries.

  • by catalytic cracking, which is, using catalyst to break alkane into simpler hydrocarbons.

  • crack alkane to get more valuable hydrocarbons.

  • The total number of carbon and hydrogen atoms from products should equal to the total number of carbon and hydrogen atoms in cracked alkane.

E.g. Octane can be cracked into simpler hydrocarbons such as the reaction below. Suggest the possible identity of product x.

C₈H₁₈ (l) --> C₂H₄ (g) + x + CH₄ (g)

Number of C atoms in x = 8 – 2 – 1 = 5

Number of H atoms in x = 18 – 4 – 4 = 10

---> Product x is C₅H₁₀

Isomers

• compounds with same molecular formula but different structural formula.

• Due to different chain length, they have different physical properties (e.g. boiling point).

• Isomerism can occur in both alkanes and alkenes.

• For alkene, double bond position can be changed.

• We therefore can’t just say that C₆H₁₄ is simply hexane because there are more variations of C₆H₁₄ and each variation has its own name.

Alcohols

Characteristics

• • Are homologous series with general formula C_nH_2n+1OH

  • They have –OH functional group (hydroxyl group)

  • All alcohols end with suffix -ol

  • First three members of the series (so that you’d have idea on the next)

- Methanol, CH₃OH

- Ethanol, C₂H₅OH or CH₃CH₂OH

- Propanol, C₃H₇OH or CH₃CH₂CH₂OH

• • For alcohol, the –OH is not of hydroxide ion, OH^-, but is covalent bond between oxygen and hydrogen, O – H

Making Ethanol

1. Fermentation of sugars with yeast

2. Reacting ethene with steam

1. Fermenting glucose

• • Fermentation is breakdown of sugars into smaller molecules by microorganisms.

  • C₆H₁₂O₆ (aq) --> 2C₂H₅OH (aq) + 2CO₂ (g)

  • Temperature is kept constant at 37^oC to prevent destruction of yeast at higher temperatures.

  • Oxygen is removed by limewater and carbon dioxide is produced during fermentation.

  • Alcohol is separated from solution by fractional distillation.

2. Reacting Ethene with Steam

• • Ethene and steam are passed over phosphoric acid H₃PO₄ (as a catalyst) under high temperature of 300^oC and pressure of 65 atm.

  • C₂H₄ (g) + H₂O (g) ⇌ C₂H₅OH (aq)

  • Since this is reversible reaction, both ethene and water are produced aside from ethanol.

  • The ethanol is separated by fractional distillation.

Uses of Alcohol

• • As organic solvent

  • alcoholic drink; preservatives

  • vehicle fuel

REACTIONS OF ALCOHOL

1) Combustion

• • Alcohols burn in air to produce carbon dioxide and water.

E.g. combustion of ethanol

C₂H₅OH (aq) + 3O₂ (g) --> 2CO₂ (g) + 3H₂O (l)

Example:

2) Oxidation

a. Alcohol can be prepared in laboratory by warming alcohol with oxidizing agent (e.g. acidified potassium chromate(VI)).

• • The product is carboxylic acid and water.

E.g. oxidation of ethanol produces water and ethanoic acid

C₂H₅OH (aq) + 2[O] {from oxidizing agent} ---> 2CH₃COOH (g) + 3H₂O (l)

2. Alcohol can be oxidized when left in air with bacterial enzymes as catalyst.

• • The products are carboxylic acid and water.

E.g. ethanol produces water and ethanoic acid when left in air.

C₂H₅OH (aq) + O₂ (g) ---> 2CH₃COOH (aq) + 3H₂O (l)

3) Esterification

Carboxylic Acids

Characteristics

• • homologous series with general formula C_nH_2n+1COOH (first series, n = 0, ascending)

  • They have –COOH functional group (carboxyl group)

  • All carboxylic acids end with suffix –oic acid

  • First three members of the series (so that you’d have idea on the next)

- Methanoic acid, HCOOH

- Ethanoic acid, CH₃COOH

- Propanoic acid, C₂H₅COOH

--> Propanoic acid

PREPARATION OF CARBOXYLIC ACIDS

1. From natural gas

• • Natural gas is passed over air and catalyst to form ethanoic acid and water.

E.g. production of ethanoic acid from methane

2CH₄ (g) + 2O₂ (g) ---> CH₃COOH (aq) + 2H₂O (l)

2. Oxidation

PROPERTIES OF CARBOXYLIC ACIDS

• Carboxylic acids are weak acids (partially ionises in water)

• Carboxylic acids react with metals to form metal ethanoate (salt) and hydrogen

E.g. Reaction between calcium and ethanoic acid forming calcium ethanoate and hydrogen

Ca (s) + 2CH₃COOH (aq) ---> Ca(CH₃COO)₂ (aq) + H₂ (g)

• Carboxylic acids react with bases to form salt and water (neutralization)

E.g. Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.

CH₃COOH (aq) + NaOH (aq) ---> CH₃COONa (aq) + H₂O(g)

• Carboxylic acids react with carbonates and bicarbonates to form salt, carbon dioxide and hydrogen.

E.g. Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and water.

2CH₃COOH (aq) + Na₂CO₃ (aq) ---> 2CH₃COONa (aq) + CO₂ (g) + H₂O (g)

ESTERIFICATION

• • Ester is organic compound made from carboxylic acid and alcohol with the removal of one molecule of water.

  • Sulfuric acid is added as catalyst then heat mixture.

  • The reaction is reversible.

  • We can add sodium hydroxide and heat mixture to obtain carboxylic acid and alcohol from ester --> This is HYDROLYSIS.

Synthetic Macromolecules

• • Macromolecule is a large molecule made by joining together many small molecules

  • Polymer is a long-chain macromolecule made by joining together many monomers

  • Polymerisation is the addition of monomers to make one large polymer

ADDITION POLYMERISATION

• small molecules (monomers) join together to form one molecule as the only product.

a. From monomer to polymer

Example: Formation of poly(ethene) from ethene

• • Ethene has double bond.

  • Another ethene molecules add to this unsaturated compound during polymerisation to form bigger compound.

  • Repeat unit is the simplest part of the polymer which is repeated many times to form the polymer.

  • We take the repeat unit to write the simplified formula of the polymer, where n is a large number.

  • From this repeat unit, to find the monomer formula, we add double bond between C – C and remove the bonds on each of their sides.

CONDENSATION POLYMERISATION

• • The joining of monomers together to form polymers along with the elimination of water molecules.

Nylon --> Dicarboxylic acid and diamine undergo condensation polymerisation to form nylon.

• • The linkage between monomers in nylon is called amide linkage.

  • Therefore we can also call nylon as polyamide.

  • we use nylon as:

- a replacement of stockings and manufacture of garments to replace silk

- make tents and parachutes due to strength

- fishing lines

- rugs and carpets

Terylene --> Dicarboxylic acid (acid with 2 –COOH groups) and diol (alcohol with 2 –OH groups) undergo condensation polymerisation to form terylene

• • The linkage between the monomers in terylene is called ester linkage.

  • Therefore we can call this polymer as polyester.

  • Terylene is used in fabrics as it is strong, resists stretching and sinking and doesn’t crumple when washed.

PROBLEMS ASSOCIATED WITH PLASTICS

• • non-biodegradable – they cannot be decomposed by bacteria --> Therefore, many plastic waste will pollute the Earth

  • produce toxic gas (such as hydrogen chloride) when burnt and this contributes to acid rain.

  • produce carbon dioxide when burnt – increases global warming.

  • Plastics that require CFC during production may contribute to global warming when the CFC is allowed to escape.

Natural Macromolecules

a. Carbohydrates

• • contain carbon, hydrogen & oxygen.

  • General formula is C_n(H₂O)_n.

  • The simplest carbohydrate is C₆H₁₂O₆ (glucose).

  • Glucose polymerise each other to form starch.

  • The overall reaction is: nC₆H₁₂O₆ ---> (C₅H₁₀O₅)n + nH₂O

  • Starch can also be broken down into glucose by heating with sulfuric acid. This is HYDROLYSIS.

b. PROTEINS

• • Proteins have similar linkage to that of a nylon.

  • Only that their monomers are only amino acids joined together.

  • formed by condensation polymerisation.

  • Proteins can be called as polyamide as it has amide linkage.

  • Proteins can also be broken down into amino acids by boiling protein with sulfuric acid.

  • This adds water molecule into the polymer.

c. FATS

• • Fats have similar linkage to that of a terylene (ester linkage).

  • Only that their monomers consists of glycerol and fatty acids; different from terylene.

  • Fats can also be broken down to sodium salts of fatty acids and glycerol by boiling it with an acid or alkali. - This is HYDROLYSIS.

MCQ

1. Which physical property of the alkanes does not increase as relative molecular mass increase?

a. boiling point

b. flammability

c. melting point

d. viscosity

2. In the polymerization of ethene to form polyethene, there is no change in

a. boiling point

b. density

c. mass

d. molecular formula

3. Which polymer has the same type of linkage between its monomers as in a fat?

a. polyamide

b. polyester

c. protein

d. starch

4. Cholesterol is an organic molecule that occurs in the blood stream. Which type of compound is cholesterol?

a. acid

b. alcohol

c. alkane

d. alkene

5. Which of the following can best be used to distinguish between ethane and ethene?

a. lighted splint

b. aqueous bromine

c. limewater

d. litmus solution

6. Methane is used as a fuel. What property is essential for this use?

a. it burns exothermically

b. it is a gas

c. it is odourless

d. it has a low boiling point

7. All the members of a homologous series have the same

a. empirical formula

b. general formula

c. molecular formula

d. physical properties

8. Yeast can be used to convert simple sugars to

a. ethanoic acid and oxygen

b. ethanol and carbon dioxide

c. ethanol and oxygen

d. starch and carbon dioxide

9. Which type of reaction occurs when soap is formed from fats?

a. hydrolysis

b. polymerisation

c. fermentation

d. substitution

10. Octane is an alkane present in petrol. What are the products when octane is completely burned in air?

a. carbon dioxide and hydrogen

b. carbon dioxide and water

c. carbon monoxide and water

d. carbon monoxide, carbon dioxide, and water

11. Which compound, on combustion, never forms soot.

a. carbon monoxide

b. ethanol

c. ethene

d. methane

12. What is produced when ethanol is boiled with an excess of acidified potassium dichromate(VI)?

a. ethane

b. ethanoic acid

c. ethene

d. ethyl ethanoate

13. Which of the following is not made from crude oil?

a. aircraft fuel

b. diesel oil

c. furniture polish

d. margarine

14. Which of the following is an ester?

a. pvc

b. soap

c. starch

d. terylene

15. Starch can be broken down into smaller molecules by heating with a dilute acid. What is this type of reaction called?

a. cracking

b. fermentation

c. hydrolysis

d. reduction

16. A margarine is described as 'high in polyunsaturates'. What does this type of margarine contain?

a. long chain alkane molecules

b. many alkene molecules joined by addition polymerization

c. molecules containing many C=C bonds

d. polymer molecules with -O=C-N-H- linkages

17. Vinegar is a solution of ethanoic acid made by the reaction of ethanol with air. Which gas in air takes part in this reaction?

a. carbon dioxide

b. nitrogen

c. oxygen

d. water vapour

18. When must a substance be an alkane?

a. when it burns easily in air or in oxygen

b. when it contains carbon and hydrogen only

c. when it has the general formula C_nH_2n+2

d. when it is generally unreactive

19. One mole of a hydrocarbon X reacted completely with one mole of hydrogen gas in the presence of a heated catalyst. What could be the formula of X?

a. C₂H₆

b. C₃H₈

c. C₅H₁₀

d. C₇H₁₆

20. Nylon (a polyamide) and Terylene (a polyester) are both man-made fibres. Which type of reaction is used to produce both of these polymers?

a. addition

b. condensation

c. fermentation

d. hydrolysis

21. Part of a polymer molecule has the following structure.

-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-

From which substance is this polymer made?

a. C₂H₄

b. C₂H₆

c. C₃H₆

d. C₃H₈

22. What type of reaction occurs when soap is formed from fats?

a. hydrolysis

b. polymerization

c. fermentation

d. substitution

23. Which of these equations does not represent an addition reaction?

a. CH₂Cl₂ + Cl₂ --> CHCl₃ + HCl

b. C₂H₄ + Br₂ --> C₂H₄Br₂

c. nC₂H₄ --> -(CH₂ - CH₂)n-

d. C₃H₆ + H₂O --> C₃H₇OH

24. Which set contains all the possible combustion products of methane, CH₄?

a. carbon, carbon dioxide, carbon monoxide, water

b. carbon, carbon monoxide, hydrogen

c. carbon dioxide, carbon monoxide, hydrogen, water

d. carbon monoxide, water

25. Octane is an alkane containing eight carbon atoms per molecule. What is its molecular formula?

a. C₈H₁₄

b. C₈H₁₆

c. C₈H₁₈

d. C₈H₂₀

26. What is produced when ethanol is boiled with an excess of acidified potassium dichromate(VI)?

a. ethane

b. ethanoic acid

c. ethene

d. ethyl ethanoate

27. What is the linkage between the units in fats and also in Terylene?

28. The structure of butan-1-ol is shown.

Which structure is an isomer of that shown above?

29. The structures of an acid and an alcohol are shown.

Which pairing of names correctly identify the two compounds?

acid alcohol

a. ethanoic butanol

b. ethanoic propanol

c. propanoic propanol

d. propanoic butanol

30. The structure of four organic compounds are shown.

Which compounds decolorise bromine water?

a. 1 and 2

b. 1, 2, and 4

c. 2 and 4

d. 3 and 4

31. Which polymer has the empirical formula CH?

32. Which is the structure of ethyl ethanoate?

33. The structures of three compounds P, Q and R are shown.

Which compounds are isomers of each other?

a. P and Q only

b. P and R only

c. Q and R only

d. P, Q and R

34. The structural formula of butenedioic acid is shown.

Which statement about butenedioic acid is not correct?

a. it decolorises aqueous bromine

b. its aqueous solution reacts with sodium carbonate

c. its empirical formula is the same as its molecular formula

d. its relative molecular mass is 116

35. The diagram represents an organic compound that contains three different elements

What could be the compound?

a. ethanoic acid

b. ethanol

c. propane

d. propene

36. Which of the following reacts with sodium carbonate to produce carbon dioxide?

37. A polymer has the structure shown.

What is the molecular formula of the monomer?

a. C₂H₄

b. C₂H₆

c. C₃H₆

d. C₃H₈

38. The structure of the monomer of Perspex is shown.

Which description of Perspex is correct?

type of polymer polymer formed by

a. carbohydrate condensation polymerization

b. ester addition polymerization

c. hydrocarbon addition polymerization

d. polyester condensation polymerization

39. Which of the following describes the ways in which isomers are identical and different?

identical different

a. chemical properties molecular formulae

b. molecular formulae structures

c. physical properties chemical properties

d. structure molecular formulae

40. When an animal fat is boiled with aqueous sodium hydroxide, a soap and glycerol are formed. This reaction is an example of

a. esterification

b. fermentation

c. hydrolysis

d. polymerization

41. In which chemical reaction does the named product formed have a lower molecular mass than the reactant?

a. formation of an ester from ethanol

b. formation of ethanoic acid from ethanol

c. formation of ethanol from glucose

d. formation of ethanol from glucose

42. In the polymerisation of ethene to form poly(ethene), which does not change?

a. boiling point

b. density

c. empirical formula

d. molecular mass

43. Why are large alkane molecules cracked to form smaller molecules?

a. alkanes with large molecules are not useful

b. small alkane molecules can be polymerised

c. crude oil does not contain small alkane molecules

d. to meet the demand for small alkane molecules

44. What is the catalyst used in the preparation of ethyl ethanoate from ethanol and ethanoic acid?

a. concentrated sulphuric acid

b. nickel

c. vanadium(V) oxide

d. yeast

45. Which of these polymers is a protein?

a. (C₂H3Cl)n

b. (C2H3NO)n

c. (C5H8O2)n

d. (C6H10O5)n

46. Which element is least likely to be found in a macromolecule?

a. carbon

b. hydrogen

c. oxygen

d. sodium

47. Which statement is true about ethanol?

a. it is formed by the catalytic addition of steam to ethene

b. it is an unsaturated compound

c. it is formed by the oxidation of ethanoic acid

d. it reacts with ethyl ethanoate to form an acid

48. Which compound has the empirical formula CH2O and reacts with sodium hydroxide?

a. ethanoic acid

b. ethanol

c. ethyl ethanoate

d. methanoic acid

49. Cholesterol is an organic molecule that occurs in the blood stream. What type of compound is cholesterol?

a. acid

b. alcohol

c. alkane

d. alkene

50.

Name the processes X, Y, Z.

X Y Z

a. respiration reduction acidification

b. respiration oxidation hydrogenation

c. cracking oxidation neutralisation

d. combustion oxidation esterification

51. Cracking is a common process in the petroleum industry. Which of the following gives the most appropriate explanation for carrying out cracking?

a. It forms more useful fractions for commercial use.

b. There is too much of the heavier fraction of petroleum present.

c. It is easier to form useful fuel fractions through this means than through fractional distillation of petroleum.

d. The reaction is exothermic.

MCQ Answers

1. b

2. c

3. b

4. b

5. b

6. a

7. b

8. b

9. a

10. b

11. a

12. b

13. d

14. d

15. c

16. c

17. c

18. c

19. c

20. b

21. a

22. a

23. a

24. a

25. c

26. b

27. a

28. d

29. d

30. c

31. d

32. b

33. d

34. c

35. b

36. b

37. c

38. b

40. c

41. d

42. c

43. d

44. a

45. b

46. d

47. a

48. a

49. b

50. d

51. a

Structured Question Worked Solutions

1. Ethyl ethanoate is made by esterification.

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

Solution

1ai. amount of acid used = 3.0/60 = 0.05 mole

1aii. amount of ethanol used = 4.6/46 = 0.1 mole

1aiii. ethanol

1aiv. amount of ester produced = 0.05 mole

mass of ester produced = 0.05 x 88 = 44 g

1av. % yield = 2.20/4.4 x 100% = 50%

1b.

2. 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.

ai. describe how cane sugar can be converted into ethanol by the process of fermentation.

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

b. When ethanol is completely burnt in air, it forms carbon dioxide 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.

ii. The mass of 1 litre of ethanol is 780 g. How much heat energy will be released when 1 litre (1dm³) of ethanol is completely burnt?

c. When completely burnt, 1 litre of gasoline releases 38000 kJ of heat energy. Comparing ethanol and gasoline as liquid fuels, suggest

i. one advantage of using ethanol rather than gasoline

ii. one advantage of using gasoline rather than ethanol

Solution

2ai. A mixture of sugar cane (which contains glucose) with some yeast is allowed to ferment in a closed container in the absence of air for some time.

C₆H₁₂O₆ --(yeast)--> 2C₂H₅OH + 2CO₂

2aii. carbon dioxide. This gas can be tested by passing it through limewater and the solution turns milky (white precipitate formed)

2bi. C₂H₅OH (l) + 3O₂ (g) --> 2CO₂ (g) + 3H₂O (l)

2bii. Mr of ethanol = 2 x 12 + 6 x 1 + 16 = 46

amount of ethanol used = 780/46 moles

amount of energy released = 780/46 x 1370 = 23230 kJ

2ci. Burning ethanol produces less carbon dioxide, which is one of the components responsible for the Greenhouse effect.

2cii. Burning gasoline produces more energy.

3. The following questions refer to compounds with the structures drawn below.

Using the letters A to F as appropriate, answer the following.

a. Which compound is an unsaturated hydrocarbon?

b. Which compounds are members of the same homologous series?

c. Which compound reacts with sodium carbonate?

d. Which compounds are isomers of each other?

Solution

3a. E

3b. B, F

3c. C

3d. A, D

4. Olive oil contains oleic acid which is unsaturated.

ai. By naming the reagent and giving the observation, describe a simple test to confirm that olive oil contains an acid.

aii. Explain what is meant by unsaturated

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

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.

Solution

4ai. reagent: sodium carbonate

observation: effervescence. Gas turns limewater milky.

4aii. An unsaturated compound is one that contains multiple bonds eg double bonds

4aiii. reagent: bromine

observation: the brown color of bromine is discharged

4b. number: 2

Explain: If oleic acid does not contain C=C double bond, its formula should be C₁₇H₃₅CO₂H (C_nH_2n+1CO₂H). Since its formula has 4 hydrogen less than 33, it should therefore contain 2 double bonds.

5. The structure of fluorochloroethane is shown below

a. Suggest a name for, and sketch the structure of, the macromolecule formed when fluorochloroethene polymerizes.

b. When 20 tonnes of fluorochloroethene polymerised, 18 tonnes of the polymer were obtained. Calculate the percentage yield.

c. Name and give a use for a commercially available polymer containing a halogen.

Solution

5a. poly(fluorochloroethene)

5b. Theoretically, 20 tonnes of products should be obtained. Therefore % yield = 18/20 x 100% = 90%

5c. polyvinylchloride (PVC). It is used as plastics.

6. Ethyne, C₂H₂, burns in oxygen to give a very hot flame. The temperature is so high that the flame can be used to cut metal.

ai. Name the two products of the complete combustion of ethyne.

aii. Describe a chemical test for one of these products

b. Calcium carbide, CaC₂, is a greyish-white solid. Ethyne can be made by the reaction of calcium carbide with water. Calcium hydroxide, Ca(OH)₂ is the other product of the reaction.

i. Construct an equation, including state symbols, for the reaction between carlcium carbide and water.

ii. The mixture obtained after this reaction was tested using Universal Indicator. What was the final color of the Universal Indicator? Explain your answer.

Solution

6ai. carbon dioxide and water

6aii. Bubble the gas through limewater. A white precipitate would be observed

6bi. CaC₂ (s) + 2H₂O (l) --> Ca(OH)₂ (aq) + C₂H₂ (g)

6bii. Blue. Ca(OH)₂ is alkaline.

7a. The following terms are used in the description of organic compounds.

alcohol

amide

alkane

hydrocarbon

alkene

polymer

From this list, choose two terms which can be applied to each of the compounds below.

i. methane

ii. hexene

iii. poly(ethene)

iv. nylon

b. One of the general characteristics of homologous series is that all the members can be represented by a general formula.

i. What is the general formula of the alkene series?

ii. Give one other general characteristics of homologous series.

Solution

7ai. alkane, hydrocarbon

7aii. alkene, hydrocarbon

7aiii. alkane, polymer

7aiv. amide, polymer

7bi. C_nH_2n

7bii. The members show similar chemical reactions.

8a. Heptane is an alkane with seven carbon atoms per molecule. It is a colorless liquid with a boiling point of 100ºC.

i. deduce the molecular formula of heptane

ii. suggest two tests you could use to decide whether a colorless liquid was heptane or water.

Predict the results of the tests for both heptane and water.

b. Fructose is a carbohydrate. One form of fructose has the following structure.

i. deduce the molecular formula of fructose

ii. suggest why the term 'carbohydrate' is used for this type of compound

iii. name another carbohydrate

Solution

8ai. C₇H₁₆

8aii. test 1: add anhydrous copper(II) sulphate

heptane: solid copper(II) sulphate remains white and insoluble

water: solid turns blue and then dissolves to give a blue solution

test 2: ignite with a flame

heptane: burns with a luminous flame

water: the flame dies off

8bi. C₆H₁₂O₆

8bii. The molecular formula seems to suggest 6 units of carbon, and hydrogen and oxygen in the ratio 2:1 just like water C₆(H₂0)₆ ie. hydrate of carbon.

8biii. glucose

9a. Hydrogen can be manufactured by the reaction between methane and steam.

i. Name a source of the methane required for this reaction.

ii. Give the equation for this reaction between methane and steam.

iii. Calculate the maximum volume of hydrogen, measured at r.t.p. which can be obtained from 16g of methane.

b. Margarine is manufactured using the addition reaction between hydrogen and a vegetable oil.

i. state the conditions used for this reaction

ii. what type of bond must be present in the vegetable oil for this reaction to take place?

c. The diagram represents the structure of a common plastic.

i. Name this plastic and draw the structure of the monomer from which it is made.

ii. This plastic is non-biodegradable. Explain the meaning of this term and describe the problems which this property creates.

d. If this plastic is burned, a thick, black smoke and a very acidic gas are produced.

i. suggest the identity of the black particles in the smoke

ii. suggest the identity of the very acidic gas.

Solution

9ai. natural gas

9aii. CH₄ (g) + H₂O (g) --> CO (g) + 3H₂ (g)

9aiii. Mr of CH₄= 16

amount of CH₄ = 16/16 = 1 mol

amount of H₂ formed = 3 mol

volume of 1 mole of gas at r.t.p. = 24dm³

volume of H₂ formed = 3 x 24 = 72 dm³ at r.t.p.

9bi. Nickel catalyst, high pressure

9bii. double bonds

9ci. polyvinylchloride (PVC)

9cii. Non-biodegradable means cannot be broken down by biochemical reactions by bacteria.

9di. carbon

9dii. hydrogen chloride

10. Ethene is an unsaturated hydrocarbon.

ai. what is meant by 'unsaturated'?

b. Ethene is made by the cracking of long chain hydrocarbon molecules such as C₁₆H₃₄.

Construct an equation to illustrate the cracking of C₁₆H₃₄ to make ethene and another hydrocarbon as the only products.

c. Ethene is bubbled through aqueous bromine to form 1,2-dibromoethane. What would you observe during the reaction?

d. Give the name of the product and the conditions needed for the reaction of ethene with water.

e. Calculate the volume of carbon dioxide, measured at r.t.p., produced by the complete combustion of 1.40g of ethene.

f. Ethene can be made into poly(ethene). Draw the structure of poly(ethene).

Solution

10a. An unsaturated compound is one that contains multiple bonds eg C=C

10b. C₁₆H₃₄ --> 3C₂H₄ + C₁₀H₂₂

10c. Decolorization of brown bromine

10d. C₂H₄ (g) + 3O₂ (g) --> 2CO₂ (g) + 2H₂O (l)

Mr of C₂H₄ = 28

25g of C₂H₄ give 48 dm³ of CO₂ at r.t.p.

--> 1.40g of C₂H₄ give 1.40 x 48/28 = 2.4dm³ of CO₂ at r.t.p.

10f.

11. The following is a list of formulae of organic compounds.

CH₃COOH

C₅H₁₂

C₂H₅OH

C₃H₆

C₇H₁₄

Which of the above formula fit the following descriptions?

a. a compound which dissolves in water to form an acidic solution

b. a compound which is not a hydrocarbon

c. two compounds which are from the same homologous series

d. two compounds which react to form an ester

e. a compound which undergoes an addition reaction with steam

f. a compound which is oxidised by acidified potassium dichromate(VI) to give ethanoic acid

Solution

11a. CH₃COOH

11b. CH₃COOH or C₂H₅OH

11c. C₃H₆ or C₇H₁₄

11d. CH₃COOH and C₂H₅OH

11e. C₃H₆ or C₇H₁₄

11f. C₂H₅OH

12. Ethanol, CH₃CH₂OH is a liquid fuel. Ethanol can be manufactured either from glucose C₆H₁₂O₆ or from ethene.

a. Briefly describe the manufacture of ethanol from glucose. Include the balanced equation in your answer.

bi. Draw the displayed formula for ethene

bii. Name the substance that reacts with ethene to make ethanol

biii. Give the conditions needed for this reaction.

Solution

12a. Yeast cells are added to a solution of glucose. The mixture is kept at 18-20ºC under anaerobic conditions. Glucose will be broken down by zymase enzyme in yeast cells to form ethanol and carbon dioxide. Ethanol is obtained by fractional distillation of the mixture.

C₆H₁₂O₆ --> 2C₂H₅OH + CO₂

12bi.

12bii. steam

12biii. 300ºC, 70 atmospheric pressure and phosphoric acid catalyst

13. Styrene-butadiene rubber is a synthetic rubber. It is made by polymerising a mixture of the monomers butadiene and styrene.

a. What type of polymerization will take place when the monomers polymerise? Explain.

One possible structure for the polymer is shown below.

b. Give the full structural formula for the repeating unit in this polymer structure.

c. When the mixture of styrene and butadiene polymerises, the polymer is unlikely to contain only this regular, repeating pattern. Explain why.

Butadiene can be made by cracking butane in a cracking tower.

di. Butane cracks to form butadiene and one other product. Write an equation to show this reaction.

dii. Give a use of the other product of this reaction.

e. 2.90kg of butane entered the cracking tower. After the reaction, 2.16kg of butadiene had been made. Calculate the percentage yield of butadiene.

Solution

13a. Addition polymerization. Addition polymerization is the joining together of two or more simple molecules, called monomers, to form a long chain compound without any loss of small molecules. The addition polymerization process can only occur when the monomer molecule is unsaturated (contain double bonds or triple bonds)

13b.

13c. Since two different monomers are mixed together before being polymerized the chain will have the different monomers distributed randomly along its length. Let styrene monomer be A and butadiene monomer be B. One possible random distribution is

-A-A-B-A-B-B-A-B-A-A-B-B-B-A-

Sometimes the same type of monomers may be polymerised to form short chains and then these chains mixed and further addition polymerization occurs. For eg.

-A-A-A-A-A-A-A-B-B-B-B-B-B-

13di. hydrogen gas

13dii. used in the manufacture of ammonia in the Haber process

13e. Mr of butane = 58

Mr of butadiene = 54

no. of moles of butane = 2900/58 = 50

From the eq, 1 mol of butane undergoes cracking to form 1 mol of butadiene.

no. of mole of butadiene formed = 50

mass of butadiene = 50 x 54 = 2700g --> 2.7kg

experimental yield of butadiene = 2.16kg

% yield of butadiene = 2.16/2.7 x 100 = 80%

14. This is the structure of an ester made in a reversible reaction between a carboxylic acid and an alcohol.

ai. State the conditions for this reaction

aii. Draw the structure of the carboxylic acid used in the reaction.

aiii. Write an equation for this reaction.

b. A student carried out some experiments to compare the relative strengths of dilute ethanoic acid with dilute hydrochloric acid.

i. Describe a test that can be used to distinguish between dilute ethanoic acid and dilute hydrochloric acid.

ii. Explain, using ideas about ions, why the two acids behave differently.

iii. Name a solid substance that will react with both acids. Describe what you will see during the reaction.

Solution

14ai. Heat the carboxylic acid with alcohol ethanol using a few drops of concentrated sulphuric acid as catalyst.

14aii.

14aiii. CH₃COOH +C₃H₇OH --> CH₃COOC₃H₇ + H₂O

14bi. Place about 2cm³ of each acid in separate test tubes. Add a few drops of silver nitrate solution to each test tube. A white precipitate will be observed in the test tube containing hydrochloric acid.

14bii. Dilute hydrochloric acid is a strong acid and ethanoic acid is a weak acid. Dilute HCl dissociates fully in water whereas a weak acid dissociates partially in water to form hydrogen ions, H⁺

HCl (aq) --> H⁺ (aq) + Cl^- (aq)

Ethanoic acid dissociates partially in water to form a solution containing H⁺ ions. There are more acid molecules in a solution of weak acid than H⁺ ions.

CH₃COOH <--> CH₃COO^- + H⁺

14biii. solid calcium carbonate.

observations: Effervescence occurs. Colorless, odourless gas formed white precipitate with limewater.