Organics Questions 2008 - 2010

Click the question to get the solutions, including videos.


Exemplar 2008

5 Alcohols are used in a variety of chemical reactions and as preservatives in certain medicines. All alcohols are toxic. Although ethanol is the least toxic of all alcohols, it is still a poisonous substance. It is rapidly absorbed into the blood. High blood alcohol levels can cause brain poisoning. The body can reduce high blood alcohol levels by oxidising the alcohol. Contrary to what people believe, alcohol is a depressant and not a stimulant.

The following table indicates the effects of various blood alcohol levels:



The liver enzyme, ADH, catalyses the oxidation of ethanol to ethanal and then to non-toxic ethanoic acid. The liver is able to remove only 28 grams of pure alcohol per hour.

5.1Write down the NAMES of the homologous series to which the compounds ethanal and ethanoic acid respectively belong. (2)

5.1
ethanal – aldehydes
ethanoic acid – carboxylic acids  

5.2 Write down the structural formula of ethanal. (2)

5.2


5.3 Alcohols are prepared by the hydration of alkenes. Use structural formulae to write down the equation which represents the formation of ethanol. (3)

5.3


5.4 The warning on the labels of certain medicines reads as follows:

The effect of this medicine is aggravated by the simultaneous intake of alcohol.

Use the information in the passage above to justify this warning. (4)

5.4 Any additional intake of alcohol will increase the blood alcohol level which may then lead to either loss of coordination / severe poisoning / damage to organs e.g. the liver. 


6. The first six members of the alkanes occur as gases and liquids at normal temperatures. Alkanes are currently our most important fuels, but the use of alcohols as renewable energy sources is becoming more important. Alcohols are liquids that might be a solution to the energy crisis.
Answer the following questions.

6.1. Which chemical properties of alkanes and alcohols make them suitable to be used as fuels. (2)

highly exothermic
high energy of combustion
combustion releases huge amounts of energy


6.2. The table shows the boiling points of the first six alkanes and the first six alcohols.



Draw a graph of boiling points versus number of carbons atoms for the first six ALCOHOLS. Choose 500C and 1 carbon atom as origin and use an appropriate scale. Plot the points and draw the best curve through the points. (5)



Examiner will look for these following criteria for the graph:
• Appropriate heading
• Appropriate scale on both axes
• Both axes labelled correctly
• Points correctly plotted
• Best curve drawn through points 

6.3. What trend in boiling point can be observed from the graph? (2)
Boiling point increases with increasing number of carbon atoms

6.4. Provide a reason for the trend mentioned in QUESTION 6.3. by referring to the type of intermolecular forces. (2)

Van der Waals forces between alcohol molecules increase with increase in molecular size
THe larger the molecule, the greater the surface area for Van der Waals forces to act.

6.5. Explain, referring to the type of intermolecular forces, why the boiling points of alcohols are higher than the boiling points of alkanes. (2)

Hydrogen bonds between alcohol molecules are stronger than Van der Waals forces between molecules of alkanes.
The hydrogen bonds are brought about by the presence of the -OH in the alcohols

6.6. People are always cautioned to keep liquids such as petrol (a mixture of alkanes) out of reach of children. Use the boiling points of alkanes and justify this precaution. (2)

• Petrol has a low boiling point, thus it vapourises easily
• Is volatile (vapourises easily, produces a lot of vapour)
• Vapours have a high rate of reaction
• Hence it is explosive
• Flammable
• Easily combustible
• Vapours have a higher density than oxygen and when swallowed vapours can cause suffocation.

6.7. Briefly explain why ethanol is a renewable energy source, while the alkanes are non-renewable. (2)

Ethanol can be produced through industry by fermentation of plant material e.g. maize and sugar cane.
Alkanes are fossil fuels which are non-renewable. (actually, will take a few million years, but we call it non-renewable.)


7. Consider the organic compounds labelled A – E.

Answer the following questions.

7.1. Write a balanced chemical equation for the preparation of compound D using an alkane as one of the reactants.(3)

CH4 + Cl2 → CH3Cℓ + HCℓ

7.2. Write down the IUPAC name for compound B. (2)

4,4-dimethyl-2-hexanone

7.3. Write down the structural formula of an isomer of compound A that has only FOUR carbon atoms in the longest chain. (2)



or

7.4. Write down the structural formula for compound C. (2)



or



(This compound is benzene.)


Additional Exemplar 2008

5.Hydrocarbons are simple organic compounds. The homologous series called alkanes is one group of hydrocarbons. One physical property of alkanes is shown in the table below.

Answer the followng questions.

5.1. Define the concept homologous series. (2)

A group of organic compounds that can be represented by the same general formula.

5.2. Explain the change in boiling points of the alkanes from methane to hexane. (2)

Molecular mass / size of molecules increase therefore Van der Waals forces increase.
(due to the larger available surface areas for bonding.)

5.3. How do the boiling points of the straight chain compounds differ from that of their corresponding isomers? Give a reason for this difference. (3)

Straight chain alkanes have higher boiling points than that of corresponding branched chains.

Branched chains become more compact and spherical
• surface contact decreases
• therefore intermolecular forces are weaker
• less energy needed to break bonds
• hence lower boiling point.

5.4. Write down the structural formula of the isomer of hexane shown in the table. (2)

5.5. The human body secretes oils that maintain the moisture of the skin. Alkanes, such as petrol and paint thinner, dissolve non-polar organic material such as fats and oils. Explain why people must minimise contact with hydrocarbon solvents such as paint thinner. (2)

The thinners will dissolve the fats and oils in the skin, and leave the skin dry and damaged.

5.6. Petroleum jelly (Vaseline) is a soft semi-solid mixture of hydrocarbons that provides a protective film when used on the skin. It is hydrophobic (water repelling) and is, for example, used on burns or to prevent nappy rash on babies.

Answer the followng questions.

5.6.1. Which physical property of Vaseline explains why it does not flow like petrol? (1)

Viscosity
It has a high viscosity, which means it does not flow very well.

5.6.2. Boiling water is accidentally spilled on a child. Explain why Vaseline should not be used on the child's skin immediately after sustaining burns. (2)

The Vaseline will form a layer on the skin that traps heat and increase the pain from the burns.


6. Four organic compounds, labelled A, B, C and D, are shown below.

Answer the followng questions.

6.1. Write down the structure of the functional group and the IUPAC name for compound A. (3)

Functional Group


Name of entire compound
2-pentanone
pentan-2-one

6.2. Write down the IUPAC name of compound C. (2)

N-Ethylpropylamine (not in syllabus for this exams!)

6.3. Write down the structural formula for compound B. (2)

6.4. Describe a test that can be used to distinguish compound D from 4-methylhexane. (2)

• Compound D (unsaturated, alkyne, addition reaction) will decolorise bromine water quickly.
• 4-methylhexane (saturated, alkane) will not decolorise bromine water unless placed in sunlight or heated. (substitution reaction)

6.5. Esters are a group of organic compounds widely known for their pleasant odours. The fruity smell of apple is, for example, due to the presence of ethyl butanoate. Write down the condensed structural formula of ethyl butanoate. (2)


7. Some organic reactions are shown in the flow diagram below.

7.1. Name the type of reactions illustrated by A, B, C and D. (4)

A: Substitution
B: Substitution
C: Substitution
D: elimination OR dehydrohalogenation

7.2. Use condensed structural formulae and write a balanced equation for reaction C. (3)

CH3CH2CH2Br + H2O → CH3CH2CH2OH + HBr

CH3CH2CH2Br + OH- → CH3CH2CH2OH + Br-

react with dilute base in ethanol

7.3. Write down the structural formula for compound X. (2)

7.4. In order to obtain product Y, C3H7Br is heated with a concentrated solution of KOH under reflux. Use condensed structural formulae to write a balanced equation for the reaction. (3)

CH3CH2CH2Br + KOH → CH2═CHCH3 + KBr + H2

7.5. A group of learners decided to heat C3H7Br with dilute sodium hydroxide, instead of the concentrated potassium hydroxide, under reflux. Write down the IUPAC name of the organic compound that they will obtain. (2)

propan-1-ol


Prep Exams 2008

5.1. Write down the structural formulae and IUPAC names for the product(s) formed when the following compounds react with each other:
Answer the following questions.

5.1.1. cyclohexene and HCl


chlorocyclohexane

5.1.2.


3-bromo-3-methylpentane

5.2. The following equations represent chemical reaction:

Answer the following questions.

5.2.1. Name the type of reaction in reaction 2. (1)

substitution

5.2.2. Write down the structural formula for the organic compound A. (2)

5.3. Cracking is a process that is generally used in the oil industry.

Answer the following questions.

5.3.1. What is meant by cracking? (2)

• dividing longer chains of hydrocarbons into shorter ones
• shorter chains burn more freely
• shorter chains are blended with fuel to enrish fuel

When chains are long, due to their larger molar masses, they have stronger Van der Waals forces. Hence they do not vapourise easily, and do not make good fuels. By cracking them into smaller molecules, this then decreases their molar masses, resulting in weaker Van der Waals forces. They are now able to vapourise easily and become good fuels.

5.3.2. Why is cracking used in the fuel industry? (2)

to obtain a larger percentage of usable products from larger fractions of crude oil

5.3.3. Give a reason for the difference in the melting and boiling points of the following two compounds, produced from a specific cracking process: (2)

• boiling points increase with increasing molar masses
• Van der Waasl forces increase with increasing molare masses

5.3.4. In which phase (gas, liquid or solid) is each of the following when used as a fuel: (2)
(a) Butane
(b) Heptane

(a) gas
(b) liquid

As humans, we operate at "typical temperatures" around 200C.
Notice that butane would have already boiled into a gas at -10C.
But heptane becomes a liquid at -910C, and remains a liquid for "typical temperatures". It changes into a gas only at 890C.


Jana wants to investigate how molecular mass influences the boiling points of the first eight straight chain alcohols.

6.1 Which property of the alcohols could make this investigation dangerous?

6.1 Alcohols are flammable

Structural isomers can influence the outcome of this investigation. Alcohols with more than two carbon atoms have more than one structural isomer.

6.2.1 Write down the structural formulae and IUPAC names of the structural isomers of the alcohol containing three carbon atoms.

6.2.1

propan-1-ol


propan-2-ol

6.2.2 Jana uses heptan-1-ol as one of the compounds in the investigation. Which ONE of the isomers named in QUESTION 6.2.1 must she use for a fair test?

6.2.2 propan-1-ol

6.2.3 Explain the need for this choice in QUESTION 6.2.2

6.2.3 The position of the -OH group in the chain will affect the intermolecular forces.

Design an investigation than Jana can conduct. USe the following headngs in your design.

6.3.1 Hypothesis

6.3.1
The boiling point of the alcohols will increase with molcular mass.
The larger the molecular mass of a member of the same homologous series (alcohol), the higher the boiling point.

6.3.2 Precautions

6.3.2 Don't heat alcohols over an open flame.

6.3.3 Apparatus

6.3.3
• Measuring cylinder
• Thermometer
• 8 containers e.g. test-tubes / beakers / flasks
• Heat source e.g. Hot plate, Bunsen burner

6.3.4 Method

6.3.4
Measure equal volumes of the eight alcohols and transfer it to separate containers.
Heat samples of each compound (in a water bath) until it boils.
Measure the temperature with a thermometer at boiling point.


November Finals 2008

5. Ethene is a gaseous hormone associated with the ripening of fruit. It also contributes to the ageing and distortion of plants. In industry, the artificial ripening of fruit takes place when ethene is passed over the fruit in large rooms. After a while the ripening fruit releases its own ethene.
Answer the following questions.

5.1. Write down the structural formula of ethene. (2)

5.2. Why is it not advisable to place a banana that has been artificially ripened alongside a cabbage and lettuce? (2)

The ethene liberated by the banana ages the cabbage and lettuce.


In industry ethene is also used to synthesise a variety of organic compounds. The flow diagram below illustrates some of the many reactions ethene undergoes.



5.3. Write down the general formula for the homologous series to which ethene belongs. (1)
CnH2n

5.4. Name the type of reaction represented by each of the letters A, B, D and H. Write down the letters A, B, D and H and next to each the type of reaction. (4)

A: substitution
B: addition (hydrogenation)
D: addition (hydration)
H: substitution

5.5. Use structural formulae to write down a balanced equation for reaction B. (3)

5.6. Apart from ethene, which other reactant is needed for reaction F? Write down the FORMULA only. (2)

HBr

5.7. Both reactions E and G occur in the presence of a base. Reaction E is an elimination reaction and reaction G is a substitution reaction.

Answer the following questions.

5.7.1. How is the base in reaction E different from the base in reaction G? (2)

E: concentrated
G: dilute

OR

• Base is more concentrated in reaction E than in reaction G
• or base is less concentrated in reaction G than in reaction E

5.7.2. Name the type of elimination reaction represented by E. (1)

Dehydrohalogenation


7. More than 90 million organic compounds are known to man today. In the table below the letters A to E represent a few of these compounds.

Answer the following questions.

7.1. Write down the IUPAC name of compound A. (1)

butanoic acid

7.2. Write down the structural formula of compound D. (2)

7.3. To which homologous series does compound E belong? (1)

amides (not in this years exams)

7.4. Write down the IUPAC name of an isomer of compound C. (2)

propan-1-ol
or
1-propanol

7.5. Compound B is one of the substances responsible for the fishy odour (smell) of fish. Explain why serving lemon slices with fish reduces the odour. (2)

(not in this years exams)
Amines are (weak) bases, and lemon juice is an acid
Therefore a neutralisation reaction takes place to mask the smell (odour).

The base (amine) neutralises the acid


March 2009

5. There are two structural isomers for the organic compound with molecular formula C2H4O2 .
Answer the following questions.

5.1. Define the term structural isomer. (2)

Compounds that have the same molecular formula but different structural formulae.

5.2. Write down the structural formula of these two isomers and next to each its IUPAC name. (3 x 2) (6)


methylmethanoate


ethanoic acid

5.3. State with reason which ONE of these isomers:

Answer the following questions.

5.3.1. Has the higher boiling point. (3)

Ethanoic acid has the higher boiling point

• The hydrogen bonds (-OH) from the (intermolecular forces) between ethanoic acid molecules are stronger than the Van der Waals forces (intermolecular forces) between the ester molecules.
• Thus more energy needed to break bonds between ethanoic acid molecules, hence the higher boiling point.

5.3.2. Has the higher vapour pressure. (3)

Methylmethanoate has the higher vapour pressure.

The Van der Waals forces (intermolecular forces) between the ester molecules are weaker than the hydrogen bonds (intermolecular forces) between ethanoic acid molecules.
Thus less energy needed to break bonds between the ester molecules, resulting in them vapourising easily.

5.4. Will the vapour pressure of carboxylic acids increase or decrease if the number of carbon atoms in the chain increases? Give a reason for your answer. (3)

Decrease
• Van der Waals forces increase with molecular size.
• The molecules bond (stick to each other) more strongly and thus tends to remain as liquid
• Hence less vapour, and less vapour pressure.


6. Rubber is a naturally occurring compound. The diene, 2-methyl-1,3-butadiene, is one of the repeating units found in rubber. Over 20 million families depend on rubber cultivation for their livelihood. Tens of thousands of hectares of tropical forests have been cleared to make way for rubber plantations.
Chemists have been able to combine other dienes to obtain synthetic rubbers. Some rubber products include latex products such as hand gloves, raincoats and other products used in the battle against HIV/Aids.
The world's largest use of rubber is in tyres, and most tyres contain both natural rubber, which withstands heat better, and one or more kinds of synthetic rubber.

Answer the following questions.

6.1. Is 2-methyl-1,3-butadiene an example of a saturated or an unsaturated hydrocarbon?
Give a reason for your answer. (3)

Unsaturated
Contains C=C double bonds

Not all C-C bonds are single bonds

6.2. Write down the structural formula of 2-methyl-1,3-butadiene. (2)

6.3. With regard to the environment, name TWO disadvantages of rubber and the production of rubber. (2)

Any TWO:
• Destruction of indigenous forests (leading to global warming)
• Rubber is not biodegradable – disposal impacts negatively on environment
• Burning of rubber releases toxic gases

6.4. With regard to human life, name TWO benefits of rubber and the production of rubber. (2)

Any TWO:
• Job creation
• Tyres for cars/gloves for medical industry/raincoats etc.
• Protective devices – insulation


7. Most organic compounds can undergo substitution or addition or elimination reactions to produce a variety of organic compounds. Some incomplete organic reactions are represented below.

Answer the following questions.

7.1. Name the type of reaction represented by reaction III. (1)

III - elimination / dehydration

7.2. Both reactions I and II are examples of addition reactions. Name the type of addition that is represented by each reaction. (2)

I – hydration
II – hydrohalogenation

7.3. Write down the structural formula and IUPAC name of the major product formed in reaction I. (3)

7.4. Reaction I only takes place in the presence of a catalyst. Write down the formula of the catalyst used in reaction I. (1)

H2SO4

7.5. Write down the structural formula and IUPAC name of the major product formed in reaction II. (3)


2-bromo-2-methylpentane

7.6. To which homologous series does the organic product formed in reaction III belong? (2)

Alkenes


November Finals 2009

5. The table below shows the results obtained during a practical investigation. Two experiments were performed to determine the boiling points of compounds from three different homologous series under the same conditions. Each letter A to F represents the organic compound written in the block next to it.

Answer the following questions.

5.1. Name the homologous series to which each of the following pairs of compounds belong:

Answer the following questions.

5.1.1. A and D (1)

Carboxylic acids

5.1.2. B and E (1)

Alcohols

5.1.3. C and F (1)

Aldehydes

5.2. Write down the IUPAC name for:

Answer the following questions.

5.2.1. Compound C (1)

Propanal

5.2.2. Compound E (1)

Pentan-1-ol

5.3. Formulate an investigative question for this practical investigation. (2)

OPTION 1
Relationship: Boiling point and type of functional group/homologous series
• What is the relationship between boiling point and the type of functional group / type of homologous series?

or

• How does the boiling points of the carboxylic acid, aldehyde and alcohol compare? or

• How do the boiling points of compounds from the three homologous series differ / compare?
OPTION 2
Relationship: Boiling point and chain length / molar mass/ molecular size (of compounds with same functional group / from same homologous series).
• What is the relationship between boiling point and chain length / molar mass / molecular size?
• How does chain length / molar mass / molecular size influence boiling point?

5.4. Which other variable, apart from the conditions for determining boiling points, was kept constant? (1)

IF OPTION 1
Molar mass / molecular mass / formula mass

IF OPTION 2
Type of functional group / homologous series

5.5. What conclusion can be drawn from the results in Experiment II? (2)

Boiling point of carboxylic acids > alcohols > aldehydes

5.6. Refer to intermolecular forces to explain the trend in boiling points, as shown in the table. (3)

Option 1
Relationship: Boiling point and type of functional group/homologous series
Carboxylic acids
highest boiling points due to strongest / more hydrogen bonding / formation of dimers.

Alcohols – lower boiling points than carboxylic acids due to weaker / less hydrogen bonding
higher boiling points than aldehydes due to strong hydrogen bonds between molecules.

Aldehydes – lowest boiling points due to weak Van der Waals forces / weak intermolecular forces between molecules.
Option 1
Relationship: Boiling point and chain length / molar mass (of compounds with same functional group / from same homologous series)
Compounds in Exp. 2 have higher boiling points than compounds in Exp. 1.
Chain length of compounds in Exp. 2 longer than in Exp. 1.
Van der Waals forces / intermolecular forces increase with increase in chain length / molecular size (number of electrons).


6. The flow diagram below shows the conversion of propene to a secondary alcohol.

Answer the following questions.

6.1. Give a reason why propene is classified as an unsaturated organic compound. (1)

Contains a double bond (between two carbon atoms).

6.2. Use structural formulae to write a balanced equation for the formation of compound X. (4)

6.3. Name the type of reaction that takes place when propene is converted to compound X. (1)

Addition / hydrohalogenation / hydrobromination

6.4. Write down the structural formula and IUPAC name for the secondary alcohol that is formed. (3)



propan-2-ol

6.5. Name the type of substitution reaction that takes place when compound X is converted to the secondary alcohol. (1)

hydrolysis

6.6. With the aid of a catalyst, propene can be converted directly to the secondary alcohol, without the formation of the intermediate compound X.

Answer the following questions.

6.6.1. Besides propene, write down the NAME of the reactant needed for this direct conversion. (1)

water

6.6.2. Write down the FORMULA of a catalyst that can be used. (1)

H3PO4 / H2SO4 / HCl / HBr

6.6.3. Name the type of reaction that will take place during this direct conversion. (1)

Addition / hydration

6.7. Instead of adding water to compound X, concentrated sodium hydroxide is added and the mixture is heated.

Answer the following questions.

6.7.1. Write down the IUPAC name of the organic product that is formed. (1)

prop-1-ene

6.7.2. Name the type of reaction that takes place. (1)

Dehydrohalogenation

or

Elimination


November 2009 Unused

4. The environmental effects of CFCs and their substitutes
The ozone layer protects the earth and its inhabitants from the dangerous ultraviolet rays of the sun. It was discovered that gases such as chlorofluorocarbons (CFCs) had damaged the ozone layer, creating a huge hole through which dangerous ultraviolet light could reach the earth.
CFCs were widely used as cooling agents in air conditioners and refrigerators and as propellants in aerosol cans because of their special physical properties. CFCs can be produced by the reaction of alkanes with chlorine, followed by the reaction of the resulting product with fluorine.
Since the banning of CFCs in the year 2000, hydrocarbons such as propane and 2-methylpropane are now used as more environmentally friendly alternatives to CFCs. Both these hydrocarbons and CFCs are greenhouse gases. However, CFCs have greater global warming potential.
Answer the following questions.

4.1. The structural formula for a commonly used CFC is given below.



Write down the IUPAC name for this CFC. (2)

dichlorodifluoromethane

4.2. Which physical property of CFCs makes them suitable for use as cooling agents and propellant gases? (1)

Low boiling point
OR
High volatility / high vapour pressure

(we can conclude that they have weak intermolecular forces (Van der Waals forces) between their molecules from the fact that they have low boiling points or from the fact that they have a high vapour pressure)

4.3. CFCs have a negative impact on the environment.

Answer the following questions.

4.3.1. State this negative impact. (1)

Damages the ozone layer

4.3.2. Describe how this negative impact also affects human health. (2)

Increase in (dangerous) UV rays that reaches earth

4.4. Use condensed structural formulae to write a balanced equation for the preparation of chloroethane from ethane. (3)

4.5. State ONE reaction condition needed for the reaction in QUESTION 4.4 to occur. (1)

Heat
OR
Ultraviolet light
OR
Sunlight

4.6. Write down a structural formula of an isomer of 2-methylpropane. (2)

4.7. Give TWO reasons why propane and 2-methylpropane are considered more environmentally friendly than CFCs.(2)

No harm to the ozone layer
Less potent greenhouse gas – contributes less to global warming


5. The table below shows data collected for four organic compounds, represented by the letters A – D, during a practical investigation.

5.1. Is compound A a saturated or an unsaturated hydrocarbon? Give a reason for your answer. (2)

Saturated
Contains only carbon-carbon single bonds

OR

No carbon-carbon double or triple bonds

OR

Each carbon bonded to four other atoms

5.2. To which homologous series does compound B belong? (1)

aldehydes

5.3. Write down the IUPAC name for each of the following compounds:

5.3.1. B (1)

ethanal

5.3.2. C (1)

ethanamine (not in this years exams)

5.3.2. Write down the structural formula of a secondary amine that is a structural isomer of compound C. (2)


(not in this years exams)

5.5. Which variable was controlled during this investigation? (1)

relative molecular mass / molecular size

5.6. Name the following in this investigation:

5.6.1. The dependent variable (1)

boiling point

5.6.2. The independent variable (1)

type of organic compound / type of homologous series / type of functional group

5.7. Refer to intermolecular forces to explain the difference in boiling points between compounds A and D. (3)

Between alkane molecules (molecules of compound A / propane molecules) there are weak Van der Waals forces (intermolecular) forces

Between alcohol molecules (molecules of compound D / ethanol molecules) there are (weak Van der Waals forces as well as) strong hydrogen bonds.

More energy needed to overcome intermolecular forces between alcohol molecules (ethanol molecules / molecules of compound D)due to their stronger hydrogen bonds.

OR

Less energy needed to overcome intermolecular forces between alkane molecules (molecules of compound A / propane molecules) due to their weaker Van der Waals forces. oorkom

5.8. Which ONE of compound B or C will have the highest vapour pressure at a specific temperature? Give a reason for your answer. (2)

Compound C
Lower boiling point / weaker intermolecular forces
vapourises easily, creating higher vapour pressures.


6. The flow diagram below shows the conversion of an alcohol into haloalkanes.

Answer the following questions.

6.1. Name the type of organic reaction of which dehydration is an example. (1)

elimination

6.2. To which homologous series do compounds P and Q belong? (1)

alkenes

6.3. What type of reaction takes place when compound P is converted to compounds X and Y as illustrated above? (1)

Addition / hydrohalogenation / hydrobromination

6.4. Use structural formulae to write a balanced equation for the preparation of compound Q as illustrated above. (4)

6.5. Which compound, P or Q, will be the major product? Give a reason for your answer. (2)

Q
The major product is the one in which the H-atom is removed from the least substituted C-atom (the C-atom with the least number of hydrogen atoms)

6.6. Write down the structural formula and the IUPAC name for compound X. (3)



2-bromobutane

6.7. A learner indicates that he can convert butan-2-ol directly into compound X. Name the type of reaction that will take place during a direct conversion. (1)

substitution


March 2010

4. Consider the following terms/compounds in organic chemistry.

Choose from the above terms/compounds: (Write down the question number only and next to each the correct term/compound.)
Answer the following questions.

4.1. The homologous series that has a carbonyl group as functional group. (1)

ketones

4.2. A saturated hydrocarbon. (1)

butane

4.3. The product formed when an alkane reacts with a halogen. (1)

haloalkane

4.4. The homologous series to which propanal belongs. (1)

aldehydes

4.5. The homologous series to which 2-bromobutane belongs (1)

haloalkane

4.6. The reaction of 2-bromobutane with water. (1)

hydrolysis

4.7. The homologous series with a –NH2 group as functional group. (1)

amines (not in this years exams)

4.8. An unsaturated compound that has isomers (1)

but-1-ene

4.9. A compound which belongs to the homologous series with the general formula CnH2n-2. (1)

ethyne

4.10. The type of organic reaction during which hydrogen chloride reacts with ethene (1)

hydrohalogenation


5. Petrol is a complex mixture of hydrocarbons such as hexane. Compounds such as 2,2,4-trimethylpentane are added to petrol to change its combustion properties.

5.1. Explain the term hydrocarbon. (2)

an organic compound that consists of hydrogen and carbon only. 

5.2. Complete the following equation that represents the complete combustion of hexane in a car engine. (Balancing of the equation is not required.)

C8H14 + O2 → CO2 + H2O

5.3. Write down the structural formula for 2,2,4-trimethylpentane. (2)

5.4. Petrol requires alkanes in the range from C 5 to C 10 . Cracking is the process that is used to convert longer chains into shorter chains.
The diagram below illustrates one of the possible cracking reactions of C15H32 .



Write down the STRUCTURAL FORMULA and NAME for the hydrocarbon represented by Y. (3)



prop-1-ene


November 2010

3. The chemical properties of organic compounds are determined by their functional groups. The letters A to F in the table below represent six organic compounds.

3.1 Write down the LETTER that represents the following:
3.1.1 An alkene (1)
3.1.2 An aldehyde (1)

3.1.1 A
3.1.2 D

3.2 Write down the IUPAC name of the following:
3.2.1 Compound B (2)
3.2.2 Compound C (2)

3.2.1     1-bromo-2-methylpropane        
3.2.2     2,4-dimethylhexane

3.3 Write down the structural formula of compound D. (2)

3.4 Write down the IUPAC name of the carboxylic acid shown in the table. (2)

ethanoic acid

3.5 Write down the structural formula of compound F. (2)

4 Five alcohols represented by the letters A – E are listed in the table below.

4.1 Which ONE of the above alcohols is a SECONDARY alcohol? Write down only the LETTER that represents the alcohol. (1)

D

4.2 The letter E represents 2-methylpropan-2-ol. For this alcohol, write down the following:
4.2.1 Its structural formula (2)
4.2.2 The LETTER in the table that represents one of its structural isomers (1)

4.2.1.

4.2.2. D

4.3 Viscosity is a measure of a fluid's resistance to flow. Learners conduct an investigation to compare the viscosities of the first three alcohols (A – C) in the table above. They use the apparatus shown below.



The learners use the stopwatch to measure the time it takes a FIXED VOLUME of each of the alcohols to flow from the pipette. They record this flow time, which is an indication of the viscosity of each alcohol, as given in the table below.

4.3.1 Formulate an investigative question for this investigation. (2)

What is the relationship between viscosity / flow time and chain length / number of C atoms / molecular mass / molecular size / molar mass / surface area / number of electrons / alcohols? (or vice versa.)

4.3.2 Which ONE of the alcohols (A, B, or C) has the highest viscosity? Use the data in the table to give a reason for the answer. (2)

C
Longest flow time Viscosity is like "resistance" for liquids. Since C had the longest flow time, its molecules must be "stuck" (strongly bonded) to each other. C had the strongest intermolecular forces. High voscosity means the liquid is "thick" due to stronger bonds, and cannot flow very well.

4.3.3 Refer to the intermolecular forces of the three alcohols (A, B and C) to explain the trend in viscosities as shown in the table. (2)

Increase in chain length / molecular mass / molar mass / molecular size / surface area from A to C.

Increase in (strength of) intermolecular / Van der Waals / dispersion / London / forces

4.3.4 Lubricants reduce friction. Which one of alcohols, A, B or C, will be the best lubricant? (1)

C
This answer can be debatable!

4.4 Which ONE of 2-methylpropan-2-ol and butan-2-ol has the higher viscosity? (1)

D butan-2-ol

4.5 Refer to intermolecular forces to explain the answer to QUESTION 4.4. (2)

The more branched (more compact, more spherical) alcohol E (2-methylpropan-2-ol) has a smaller surface area (over which the intermolecular forces act).
Thus there is a decrease in strength of intermolecular forces.
This reduces resistance to flow and thus lowers the viscosity.

Compound D (butan-2-ol) is straight chained. This creates a larger surface area over which intermolecular forces can act.
Thus there is an increase in strength of intermolecular forces.
This increases resistance to flow and thus increases the viscosity.


5 Prop-1-ene is a flammable alkene.

5.1 Why is prop-1-ene considered to be a dangerous compound? (1)

Prop-1-ene is highly flammable.

Through addition reactions, prop-1-ene can be converted to other compounds, such as alkanes and alcohols.

5.2 Which part of the structure of an alkene allows it to undergo addition reactions? (1)

Any ONE:
Alkenes contain a double carbon – carbon / (C=C) / bond.
The presence of the pi bond.
They are unsaturated.
Contains an sp2 hybridised C atom.
All the carbon atoms are not bonded to the max. number of atoms.

5.3 In one type of addition reaction, prop-1-ene can be converted to an alcohol.
5.3.1 Use structural formulae to write a balanced equation for the formation of the alcohol during this addition reaction. (4)
5.3.2 Name the type of addition reaction that takes place. (1)
5.3.3 Write down the name or formula of the catalyst used in this reaction. (1)

5.3.1

5.3.2. hydration

5.3.3. sulphuric acid /hydrogen sulphate/H2SO4/phosphoric acid / H3PO4 / hydrogen phosphate

5.4 Use molecular formulae to write down a balanced chemical equation for the complete combustion of propane. (3)

Prop-1-ene can be produced from an alcohol by an elimination reaction.

5.5 Use structural formulae to write a balanced chemical equation for the formation of prop-1-ene from a PRIMARY alcohol. (4)

5.6 Name the type of elimination reaction that takes place. (1)

dehydration

Copyright ©
V. Gokal
academic@afrihost.co.za