Organics Questions 2011 - onwards

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March 2013

3 The letters A to F in the table below represent six organic compounds.



3.1 Write down the letter representing the compound which:
(A compound may be used more than once.)
3.1.1   Is an aldehyde (1)
3.1.1   E

3.1.2   Has the general formula CnH2n (1)
3.1.2   A

3.1.3   Is unsaturated (1)
3.1.3   A

3.1.4   Is a ketone (1)
3.1.4   F

3.1.5   Is a hydrocarbon (1)
3.1.5   A or D

3.1.6   Can be prepared by the reaction of an alcohol with a carboxylic acid (1)
3.1.6   C


3.2. Write down the structural formula of:
3.2.1 Compound A (2)
3.2.1.


3.2.2 Compound D (2)
3.2.2.



3.3. Write down the:
3.3.1 NAME of the functional group of compound F (1)
3.3.1   Carbonyl (group)

3.3.2 IUPAC name of compound B (2)
3.3.2   2-methyl propan-1-ol

OR
2-methyl-1-propanol

4 The table below shows the boiling points of four organic compounds, represented by the letters A to D, of comparable molecular mass.



4.1 Compound A is used as a fuel in gas burners.
4.1.1 Is compound A in the GAS, LIQUID or SOLID phase at 250C? (1)
4.1.1   Gas


4.1.2 How will the boiling point of an ISOMER of compound A compare to that of compound A?
Write down HIGHER THAN, LOWER THAN or EQUAL TO. Refer to MOLECULAR STRUCTURE, INTERMOLECULAR FORCES and the ENERGY needed to explain the answer. (4)
4.1.2   LOWER THAN

Isomers of A:
MOLECULAR STRUCTURE
Isomer has more branching / Molecules more compact / Smaller surface area (over which the intermolecular forces act.)

INTERMOLECULAR FORCES
Weaker / less intermolecular forces.

ENERGY
Less energy needed to overcome intermolecular forces.

Due to the lower energy requirement, the boiling temperature decreases.

OR

LOWER THAN

A itself

MOLECULAR STRUCTURE
A is less branched / has less compact molecules / has larger surface area (over which intermolecular forces act)

INTERMOLECULAR FORCES
Stronger/more intermolecular forces.

ENERGY
More energy needed to overcome intermolecular forces.


4.1.3 Using molecular formulae, write down the balanced equation for the combustion of compound A in excess oxygen. (3)

4.1.4 Compound A has a lower boiling point than compound B. Give reasons for this difference in boiling points by referring to the following:
• Structural differences between the two compounds
• Polarity (2)
Structural
Compound B contains a carbonyl group / O atom (bonded to C atom). It is an aldehyde.

Polarity
Hence B is a polar molecule (dipole).

Thus molecules of B are able to bond more strongly with each other, resulting in a higher boiling point.
Molecules of A are not strong dipoles, and hence do not have strong bonding capabilities. Hence A has a lower boiling point.

4.2 Consider the boiling points of compounds C and D.
4.2.1 Give a reason for this difference in boiling points by referring to the intermolecular forces present in EACH of these compounds. (2)
4.2.1   Compound D:
Two sites for hydrogen bonding / forms dimers
Compound C: One site for hydrogen bonding

Both compounds have hydrogen bonding (between molecules).
Compound D has two sites for/stronger/more hydrogen bonding.


4.2.2 Which ONE of compound C or D has a higher vapour pressure?
Refer to their boiling points to give a reason for the answer. (2)
4.2.2   Compound C
Lowest boiling point

Due to its low boiling point, it boils easily producing a lot of vapour. And it boils easily because of its weak intermolecular forces.

5 Some of the reactions of BUTAN-1-OL are represented in the flow diagram below. P, Q and R represent the organic products formed.



5.1 Is butan-1-ol a PRIMARY, SECONDARY or TERTIARY alcohol? (1)
5.1 Primary


5.2 Product P is formed when butan-1-ol is heated in the presence of concentrated sulphuric acid. Write down the:
5.2.1 Name of the type of reaction that takes place (1)
5.2.1 Elimination/dehydration

5.2.2 Balanced equation for the reaction that takes place using structural formulae.



5.3 Product R is formed when butan-1-ol reacts with ethanoic acid in the presence of an acid catalyst. Write down the:
5.3.1 Name of the type of reaction that takes place (1)
Esterification / (Acid catalysed) condensation

5.3.2 Structural formula of the organic product formed (2)



5.4 When HBr reacts with butan-1-ol, compound Q, a haloalkane, is formed. Write down the:
5.4.1 Name of the type of reaction that takes place (1)
5.4.1 Substitution

5.4.2 IUPAC name of the haloalkane formed (2)
1-bromobutane


March 2012

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



Write down the:
3.1 Homologous series to which compound A belongs (1)
3.1 Alkanes

3.2 IUPAC name of compound A (2)
3.2   2,4-dimethylhexane

3.3 IUPAC name of compound B (2)
3.3   4-fluoro-3-methylcyclopentene

3.4 IUPAC name of compound C (2)
3.4   4-methyl pent-2-yne

3.5 Structural formula of compound D (2)



4.1 In the petroleum industry smaller, more useful hydrocarbons are obtained from larger ones by a process called cracking. (2)
4.1.1 Define the term hydrocarbon. (2)
4.1.1 (An organic) compound/substance/ molecule which contains/consists of carbon and hydrogen (atoms only).


The compound C10H22 is cracked to obtain alkane X and another hydrocarbon. The cracking reaction is represented by the following incomplete equation:


4.1.2 Write down the molecular formula of compound X. (1)
4.1.2   C5H12


The cracking process requires very high temperatures. Therefore engineers use a catalyst in the reaction.
4.1.3 Give TWO reasons why they use a catalyst. (2)
4.1.3 Any TWO:
Speeds up the reaction / Increase reaction rate.
Reaction runs at a lower temperature / energy.
Cost is reduced / better safety.


2-methylbut-1-ene (C5H10) is one of the compounds formed in this reaction.
4.1.4 Write down the structural formula of 2-methyl-but-1-ene. (2)
4.1.4


4.1.5 Name the type of reaction that occurs when 2-methylbut-1-ene reacts with hydrogen. (1)
4.1.5   Addition / hydrogenation


4.2 Consider the structural isomers represented by A, B and C shown below.



4.2.1 Give a reason why the above compounds are considered to be structural isomers. (2)
4.2.1 Compounds have the same molecular formula, but different structural formulae.

4.2.2 Describe the trend in the boiling points from A to C, as shown in the table. Explain this trend by referring to molecular structure, intermolecular forces and energy involved. (4)
4.2.2.
From A to C:
Boiling points decrease from A to C.

molecular structure
Branching increases. Molecules become more compact. Molecules become more spherical. Decrease in surface area (over which the intermolecular forces act.)

intermolecular forces
Decrease in (strength) of intermolecular forces.

energy
Less energy needed to overcome intermolecular forces.
From C to A:
Boiling points increase from C to A. molecular structure
Less branching. Molecules become less compact. Molecules become less spherical. Increase in surface area (over which intermolecular forces act.)

intermolecular forces
Increase in (strength) of intermolecular forces.

energy
More energy needed to overcome intermolecular forces.
4.2.3 Give a reason why branched hydrocarbons are preferred to straight chain hydrocarbons as fuel. (2)
4.2.3 Branched chains have weaker intermolecular forces therefore they (burn) react faster.
or
Branched chains have higher vapour pressures (more easily in the vapour form, burnw faster)


5.1 In the flow diagram below, X, Y and Z represent three different types of organic reactions. P represents an organic compound.



5.1.1 Name the type of reaction represented by X. (1)
5.1.1   elimination / dehydrohalogenation / dehydrobromination

5.1.2 State TWO reaction conditions needed for reaction X. (2)
5.1.2
• Heat
• concentrated sodium hydroxide (NaOH) / concentrated potassium hydroxide (KOH) / concentrated strong base
OR
sodium hydroxide (NaOH) / potassium hydroxide (KOH) / strong base dissolved in ethanol / alcohol
Hot ethanolic sodium hydroxide / potassium hydroxide / KOH / NaOH

5.1.3 Reaction Y represents a substitution reaction. Write down the structural formula of compound P formed in this reaction. (2)
5.1.3


5.1.4 Apart from the organic reactant, write down the NAME or FORMULA of the other reactant needed in reaction Z. (1)
5.1.4   H2O / water


5.2 Hexanoic acid is responsible for the unique odour associated with goats. When it reacts with alcohol X, ethyl hexanoate, which is used commercially as a fruit flavour, is formed. Learners set up the apparatus shown below to prepare ethyl hexanoate in a laboratory.

5.2.1 Write down the IUPAC name of alcohol X. (2)
5.2.1   ethanol

5.2.2 What is the role of the sulphuric acid in the above reaction? (1)
5.2.2 Catalyst
(also Dehydrating agent)

5.2.3 Use structural formulae to write down a balanced equation for the preparation of ethyl hexanoate. (6)
5.2.3


5.2.4 Give a reason why the test tube and its contents are heated in a water bath and not directly over the flame. (1)
5.2.4   alcohols are flammable / volatile / catch fire easily.

5.2.5 Write down ONE use of esters in the food manufacturing industry. (1)
5.2.5 (Food) flavourant


Nov 2012

3. The letters A to F in the table below represent six organic compounds



3.1 Write down the letter(s) that represent(s) each of the following: (A compound may be used more than once.)
3.1.1 An alkyne (1)
3.1.1 A

3.1.2 Two compounds that are structural isomers (2)
3.1.2 D & F

3.1.3 A compound containing a carboxyl group (1)
3.1.3 D

3.1.4 An aldehyde (1)
3.1.4 E

3.1.5 An alcohol (1)
3.1.5 B


3.2 Write down the:
3.2.1 IUPAC name of compound C (2)
3.2.1   2-methyl-but-1-ene

3.2.2 Structural formula of compound D (2)
3.2.2.



3.3 Compound F is prepared in the laboratory.
3.3.1 How can one quickly establish whether compound F is indeed being formed? (1)
3.3.1 Pleasant odour

3.3.2 Write down the IUPAC name of the alcohol needed to prepare compound F. (2)
3.3.2 Ethanol

3.3.3 Write down the IUPAC name of compound F. (2)
3.3.3 ethyl propanoate



4. During a practical investigation the boiling points of the first six straight-chain ALKANES were determined and the results were recorded in the table below.



4.1 Write down the:
4.1.1 Most important use of the alkanes in the above table (1)
4.1.1 Fuels

4.1.2 General formula of the alkanes (1)
4.1.2   CnH2n + 2

Refer to the table to answer QUESTION 4.2 and QUESTION 4.3 below.
4.2 For this investigation, write down the following:
4.2.1 Dependent variable (1)
4.2.1 Boiling point

4.2.2 Independent variable (1)
4.2.2 Chain length / Molecular size / Molecular mass

4.2.3 Conclusion that can be drawn from the above results (2)
4.2.3 any one
• Boiling point increases with increase in chain length/molecular size/molecular mass.
• Boiling point decreases with decrease in chain length/ molecular size/molecular mass.
• Boiling point is proportional to chain length/molecular size/molecular mass.

4.3 Write down the NAME of an alkane that is a liquid at 250C.
4.3 Pentane

4.4 Alkanes burn readily in oxygen. Write down a balanced equation, using molecular formulae, for the combustion of propane in excess oxygen. (3)
4.4.

4.5 Will the boiling points of the structural isomers of hexane be HIGHER THAN, LOWER THAN or EQUAL TO that of hexane? Refer to MOLECULAR STRUCTURE, INTERMOLECULAR FORCES and ENERGY NEEDED to explain the answer. (4)
Lower than
Structure:
Isomers have more branching / more compact or spherical molecules / smaller surface areas over which the intermolecular forces act.

Intermolecular forces:
Weaker intermolecular forces / less intermolecular forces results due to the above

Energy:
Less energy needed to overcome these weaker intermolecular forces.

5 The flow diagram below shows how three organic compounds can be prepared from 2-bromo-3-methylbutane.



5.1 Write down the:
5.1.1 Homologous series to which 2-bromo-3-methylbutane belongs (1)
5.1.1 Haloalkanes

5.1.2 Structural formula of 2-bromo-3-methylbutane (2)
5.1.2

5.2 Reaction 2 takes place in the presence of a dilute sodium hydroxide solution.
Write down the:
5.2.1 Name of the type of reaction which takes place (1)
5.2.1 substitution or hydrolysis

5.2.2 Structural formula of compound B (2)
5.2.2

5.3 Reaction 1 takes place in the presence of concentrated sodium hydroxide.
Write down:
5.3.1 Another reaction condition needed for this reaction (1)
5.3.1 Heat strongly

5.3.2 The name of the type of reaction which takes place (1)
5.3.2 Elimination / dehydrohalogenation / dehydrobromination

5.3.3 The structural formula of compound A, the major product formed (2)
5.3.3

5.4 Reaction 3 takes place when compound B is heated in the presence of concentrated sulphuric acid. Write down the IUPAC name of the major product formed. (2)
5.4   2-methyl-but-2-ene


March 2011

3. Millions of organic compounds are known to date. Four of these compounds, represented by the letters P, Q, R and S, are shown in the table below.



3.1 Write down the following:
3.1.1 Structural formula of the functional group of P (2)
3.1.1


3.1.2 Homologous series to which Q belongs (1)
3.1.2 Ketones

3.1.3 Structural formula of an isomer of Q (2)
3.1.3


or



3.1.4 IUPAC name of R (2)
1-bromo-2-chlorocyclopentane

3.2 S represents an alcohol. Classify this alcohol as primary, secondary or tertiary. (1)
3.2 Tertiary

4. Knowledge of boiling points can be used to identify chemical compounds. The boiling points of four organic compounds, represented by the letters A, B, C and D, are given in the table below/



4.1 Define the term boiling point. (2)
4.1 The temperature at which the vapour pressure of a liquid is equal to the external (atmospheric) pressure.

4.2 Which ONE of A or B has the higher vapour pressure? (1)
4.2 A (propane)
It has the lowest boiling point, hence vapourises easily, producing lots of vapour, hence highest vapour pressure.

4.3 An unknown STRAIGHT CHAIN ALKANE has a boiling point of -0,50C. Use the information in the table to identify this alkane and write down its IUPAC name.
4.3 Butane

4.4 B and C are structural isomers.
4.4.1 Define the term structural isomer. (2)
4.4.1 Compounds with the same molecular formula, but different structural formulae.

4.4.2 Explain why B has a higher boiling point than C. Refer to structure, intermolecular forces and energy in your explanation.
4.4.2 Structure
Compound C (2-methylbutane) is more branched / more compact / more spherical / has a shorter chain / has a smaller surface area.

Intermolecular forces Weaker intermolecular forces / Van der Waals forces / dispersion forces / London forces.

Energy Less energy needed to overcome intermolecular forces.

OR

Structure
Compound B / Pentane is less branched/has a longer chain / less compact / less spherical / has a larger surface area.

Intermolecular forces Stronger intermolecular forces / Van der Waals forces.

Energy More energy needed to overcome intermolecular forces.
4.5 Explain the difference in the boiling points of B and D. Refer to intermolecular forces and energy in your explanation. (4)
4.5 The Van der Waals forces in B (pentane) are weaker than the hydrogen bonds in D (pentan-1-ol) and hence requires less energy to break.


5.1 Prop-1-ene, an UNSATURATED hydrocarbon, and compound X, a SATURATED hydrocarbon, react with chlorine, as represented by the incomplete equations below.



5.1.1 Give a reason why prop-1-ene is classified as unsaturated. (1)
5.1.1 It contains a double bond / C=C) between two carbon atoms in its hydrocarbon chain.
OR All carbon atoms not bonded to the maximum number of atoms / four atoms.

5.1.2 What type of reaction (ADDITION or SUBSTITUTION) takes place in the following:
(a) Reaction I (1)
(a) Addition

(b) Reaction II (1)
(b) Substitution

5.1.3 Write down the structural formula of the product formed in Reaction I. (2)
5.1.3


5.1.4 Write down the reaction condition necessary for Reaction II to take place. (1)
5.1.4 Heat / sunlight / ultraviolet light / hf

5.1.5 Write down the IUPAC name of reactant X. (1)
5.1.5 Butane

5.1.6 Write down the name or formula of product Y. (1)
5.1.6 hydrogen chloride / HCl
hydrochloric acid is correct as well.


5.2     2-chlorobutane can either undergo ELIMINATION or SUBSTITUTION in the presence of a strong base such as sodium hydroxide.
5.2.1 Which reaction will preferably take place when 2-chlorobutane is heated in the presence of CONCENTRATED sodium hydroxide in ethanol? Write down only SUBSTITUTION or ELIMINATION. (1)
5.2.1 Elimination

5.2.2 Write down the IUPAC name of the major organic compound formed in QUESTION 5.2.1. (2)
5.2.2 but-2-ene

5.2.3 Use structural formulae to write down a balanced equation for the reaction that takes place when 2-chlorobutane reacts with a DILUTE sodium hydroxide solution. (6)
5.2.3


5.2.4 Write down the name of the type of substitution reaction that takes place in QUESTION 5.2.3. (1)
5.2.4 Hydrolysis


5.3 Haloalkanes are used in insecticides (insect killers).
5.3.1 Write down ONE POSITIVE impact of insecticides on human development. (2)
5.3.1 ANY ONE:
• Diseases like malaria are contained.
• Provide food security through healthy crops.

5.3.2 Write down ONE NEGATIVE impact of insecticides on humans. (2)
5.3.2 ANY ONE:
• Contaminates fruit and vegetables that can lead to illness, e.g. cancer
• Spraying of crops can result in respiratory problems.
• Inhaling (while spraying) can result in illness.


Nov 2011

3. 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 A ketone (1)
3.1.1 D

3.1.2 A compound which is an isomer of prop-1-ene (1)
3.1.2 C

3.2 Write down the IUPAC name of the following:
3.2.1 Compound A (2)
3.2.1 4-methylpentanal

3.2.2 Compound B (2)
3.2.2 prop-1-yne
propyne is accepted

3.3 Write down the NAME or FORMULA of EACH of the TWO products formed during the complete combustion of compound E. (2)
3.3   H2O /
CO2 / carbon dioxide

3.4 Compound F is the organic product of the reaction between a carboxylic acid and ethanol. Write down the following:
3.4.1 The name of the homologous series to which compound F belongs (1)
3.4.1 Esters

3.4.2 The structural formula of the FUNCTIONAL GROUP of carboxylic acids (1)


3.4.3 The IUPAC name of the carboxylic acid from which compound F is prepared (2)
3.4.3 Butanoic acid

3.4.4 The structural formula of compound F (2)



4. Three hydrocarbons (A, B and C) with molecular formula C5H12 are used to investigate the effect of BRANCHING on the BOILING POINTS of hydrocarbons. The results obtained are shown in the table below.



4.1 Write down the term used to describe compounds with the same molecular formula, but with different structural formulae. (1)
4.1 (Structural) isomers

4.2 Write down for this investigation the following:
4.2.1 Dependent variable (1)
4.2.1 Boiling point

4.2.2 Independent variable (1)
4.2.2 Branching

4.2.3 Controlled variable (1)
4.2.3 Number of C atoms

OR

molecular or molar mass or molecular formula / C5H12

4.3 Are these hydrocarbons saturated or unsaturated? Explain the answer. (3)
Saturated
No carbon-carbon double (or triple) bonds

OR

Saturated
Only single bonds between C atoms. OR

Saturated
No multiple bonds.

4.4 One of the hydrocarbons (A, B or C) has a straight chain with no branches. Write down the following:
4.4.1 The letter (A, B or C) that represents this hydrocarbon (1)
4.4.1 A
This compound has the highest boiling point. Therefore, it must the straight chain compound. Branched chain compounds have lower boiling points.

4.4.2 Its IUPAC name (2)
4.4.2 Pentane

4.5 Consider hydrocarbon C and its boiling point.
4.5.1 Write down the structural formula of hydrocarbon C. (2)
4.5.1


4.5.2 Explain why hydrocarbon C has the lowest boiling point. In your explanation, refer to its structure, intermolecular forces and the energy involved. (3)
4.5.2
Structure
Most branching present / Molecules most compact or spherical / Smallest surface area (over which intermolecular forces act.)

Intermolecular Forces
Least / Weakest intermolecular forces.

Energy
Least energy needed to overcome intermolecular forces.

Hence lowest boiling point

4.6 Which ONE of hydrocarbons (A, B or C) has the highest vapour pressure? Refer to the data in the table to give a reason for the answer. (2)
4.6   C
Lowest boiling point
Due to the low boilong point, it easily forms vapour, cretaing a highest vapour pressure.


5. In the flow diagram below R, P and Q represent different types of reactions.<



5.1 Name the type of reaction represented by:
5.1.1 P (1)
5.1.1 Addition

5.1.2 Q (1)
5.1.2 Substitution

5.1.3 R (1)
5.1.3 Elimination

5.2 Using structural formulae, write down a balanced equation for reaction P. (4)


5.3 Write down the IUPAC name of alcohol Y. (2)
5.3 Propan-2-ol

5.4 Reaction Q takes place in the presence of a BASE. Write down TWO reaction conditions for this reaction. (2)
5.4 Dilute base
      Mild heat



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