Organic Chemistry — Free IB MYP4 Chemistry Questions

1QuestionCovalent bonding in organic moleculesConcept Practice

2 marks~3 minCriterion A

A poorly maintained gas stove produces a yellow, sooty flame, indicating incomplete combustion of methane (

CH_4

).

Explain one environmental impact of the incomplete combustion of methane. [2]

Solutions

2QuestionAlphabetical order of substituentsConcept Practice

2 marks~3 minCriterion A

In IUPAC nomenclature, the compound 3-ethyl-2-methylpentane contains two substituents: an ethyl group (

-CH_{2}CH_{3}

) and a methyl group (

-CH_{3}

).

a

State the IUPAC rule that determines the order in which substituents are listed in an organic compound's name. [1]

b

Apply this rule to explain why "ethyl" is listed before "methyl" in 3-ethyl-2-methylpentane. [1]

Solutions

3QuestionStructural/displayed formulaConcept Practice

3 marks~5 minCriterion A

The diagram below shows the structural formula of a hydrocarbon molecule.

a

Deduce the total number of carbon atoms and the total number of hydrogen atoms present in this molecule. [2]

b

Explain, using the bonds shown in the diagram, why this molecule is classified as saturated. [1]

Solutions

4QuestionCombustion reactions / Environmental ImpactConcept Practice

2 marks~3 minCriterion A

In cities with heavy traffic, incomplete combustion of fuel in car engines produces carbon monoxide (

CO

) rather than carbon dioxide (

CO_2

). During idling or cold starts, engines run at lower temperatures with fuel-rich mixtures.

a

State one difference between complete and incomplete combustion of a hydrocarbon fuel. [1]

b

Explain how idling or cold-start driving conditions lead to increased production of

CO

rather than

CO_2

. [1]

Solutions

5QuestionHomologous Series Definition and characteristicsConcept Practice

2 marks~3 minCriterion B

The table below shows the first five alkanes.

Name	Methane	Ethane	Propane	Butane	Pentane
Molecular formula	$CH_4$	$C_2H_6$	$C_3H_8$	$C_4H_{10}$	$C_5H_{12}$
Boiling point (°C)	−162	−89	−42	−1	36

a

Analyse the pattern in the molecular formulas as the carbon chain length increases. [1]

b

Deduce the molecular formula and name of the next alkane in the series. [1]

Solutions

6QuestionHomologous Series Definition and characteristicsConcept Practice

2 marks~3 minCriterion A

Car engines burn alkanes such as octane as fuel. When the oxygen supply is insufficient, incomplete combustion occurs.

Describe one environmental or health impact resulting from the incomplete combustion of alkanes in car engines. [2]

Solutions

7QuestionCombustion of alcoholsConcept Practice

2 marks~3 minCriterion A

A hiker uses a poorly maintained camping stove burning ethanol in an enclosed tent. The stove produces a yellow, flickering flame.

a

Identify one product of incomplete combustion of ethanol that is not produced during complete combustion. [1]

b

Explain one environmental impact of releasing this product into the atmosphere. [1]

Solutions

8QuestionPhysical properties:High boiling point and SolubilityConcept Practice

2 marks~3 minCriterion A

The table below shows data for two substances.

Substance: ethanoic acid ( $\text{C}_2\text{H}_4\text{O}_2$ )	Boiling point: 118 °C	Functional group: carboxyl (–COOH)
Substance: propane ( $\text{C}_3\text{H}_8$ )	Boiling point: –42 °C	Functional group: none

a

State which substance has the higher boiling point. [1]

b

Explain why these two substances have significantly different boiling points, with reference to the intermolecular forces present in each. [1]

Solutions

9QuestionProperties: Pleasant smell and VolatilityConcept Practice

2 marks~3 minCriterion A

The structural formula of ethyl ethanoate is shown below.

[Structural formula diagram]

a

State the IUPAC name of the small molecule eliminated when ethanol and ethanoic acid undergo a condensation reaction to form ethyl ethanoate. [1]

b

Explain how concentrated sulfuric acid increases the yield of ethyl ethanoate in this reaction. [1]

Solutions

10QuestionNatural vs synthetic polymersConcept Practice

2 marks~3 minCriterion A

Two segments of polymer chains are shown in the diagram. Polymer X has a repeating unit containing a peptide bond (

-\text{CO}-\text{NH}-

) in its backbone. Polymer Y has a repeating carbon–carbon backbone with chlorine atoms attached to alternate carbon atoms.

a

Identify which polymer is natural and which is synthetic. [1]

b

Deduce one structural feature visible in the diagram that explains why Polymer X is classified as natural rather than synthetic. [1]

Solutions

11QuestionNatural vs synthetic polymersConcept Practice

2 marks~3 minCriterion B

Outline the steps of a simple experiment to compare the biodegradability of natural and synthetic polymers, using the apparatus shown in the diagram. The diagram shows two identical glass jars, each half-filled with soil and a small piece of polymer (one labeled 'Cellulose (natural)', the other labeled 'Nylon (synthetic)'). Both jars are sealed with a lid and placed in a warm, dark cupboard.

Solutions

12QuestionCrude oil as a mixture of hydrocarbonsConcept Practice

2 marks~3 minCriterion A

The diagram shows a fractional distillation column used to separate crude oil. Crude oil is fed into the column continuously as a hot vapour–liquid mixture.

a

Identify the substance fed into the bottom of the column. [1]

b

State one property of this substance that makes fractional distillation an effective method of separation. [1]

Solutions

13QuestionBasic classification like Aliphatic compounds and Aromatic compounds (basic idea only)Assessment Practice

2 marks~3 minCriterion D

Polyethylene is a polymer produced from ethene, a non-renewable petrochemical feedstock. It is widely used in single-use packaging and is classified as an aliphatic compound.

a

State one environmental impact caused by the accumulation of polyethylene waste. [1]

b

Explain one reason why recycling alone cannot fully resolve this environmental impact. [1]

Solutions

14QuestionBasic classification like Aliphatic compounds and Aromatic compounds (basic idea only)Assessment Practice

5 marks~8 minCriterion C

Three unknown hydrocarbons are tested. Results are summarised below.

Hydrocarbon — Formula — Combustion flame — Bromine water — Nitration (conc. HNO3 / H2SO4)
X — C6H12, ring of single bonds — clean blue — no change — no reaction
Y — C6H6, ring with alternating double bonds — yellow, sooty — no change — yellow oily product
Z — C5H10, straight chain with one double bond — clean blue — decolourises — no reaction

a

Deduce the classification (aliphatic saturated, aliphatic unsaturated, or aromatic) of each hydrocarbon X, Y, and Z, using the experimental results as evidence. [3]

b

Explain why Y does not decolourise bromine water, even though its formula suggests unsaturation. [1]

c

Evaluate the hypothesis: "All hydrocarbons with a ring structure are aromatic," using evidence from the results for X and Y. [1]

Solutions

15QuestionTetravalency of carbon/ CatenationAssessment Practice

5 marks~8 minCriterion B

The table below shows data for four organic compounds.

Compound — Molecular formula — C–C bond length (pm) — C–C bond enthalpy (kJ/mol)

Methane —

CH_4

— 154 — 348

Ethene —

C_2H_4

— 134 — 612

Ethyne —

C_2H_2

— 120 — 837

Benzene —

C_6H_6

— 140 — 518

a

State the relationship between C–C bond length and bond enthalpy shown by methane, ethene, and ethyne. [1]

b

Using the data, deduce why benzene's bond length (140 pm) and bond enthalpy (518 kJ/mol) are anomalous compared to the pattern in (a). [2]

c

Analyse whether benzene violates the tetravalency rule, using the concept of delocalized electrons to support your reasoning. [2]

Solutions

16QuestionWriting structures from IUPAC namesAssessment Practice

3 marks~5 minCriterion B

The boiling points of three

C_6H_{12}O

isomers are: hexan-2-one (127 °C), 3-methylpentan-2-one (118 °C), and 2,3-dimethylbutan-2-one (106 °C).

a

Draw the displayed formula of 3-methylpentan-2-one, clearly showing all bonds. [1]

b

Explain how the branched structure of 3-methylpentan-2-one affects the intermolecular forces between its molecules compared with hexan-2-one. [1]

c

Using the boiling point data for all three isomers, analyse the relationship between the degree of branching and boiling point, and justify why 2,3-dimethylbutan-2-one has the lowest boiling point of the three. [1]

Solutions

17QuestionNaming alkenes / alkanes / alkynesAssessment Practice

4 marks~6 minCriterion C

Three chlorinated alkanes are used as industrial solvents. Data for each compound is given below.

Compound: 1,2-dichloroethane / 1,1,1-trichloroethane / carbon tetrachloride (

CCl_4

)
Number of Cl atoms: 2 / 3 / 4
Biodegradability: moderate / low / very low

LD_{50}

(mg/kg): 670 / 5000 / 200

a

Explain how the number of chlorine atoms influences the biodegradability of these compounds. Use data from the table in your answer. [1]

b

The

LD_{50}

values do not follow a simple trend with increasing chlorination. Interpret the toxicity data to identify which compound poses the greatest acute health risk, and suggest one structural reason why chlorination alone does not determine toxicity. [2]

c

Discuss the limitations of IUPAC names as a tool for predicting the environmental persistence of chlorinated alkanes. [1]

Solutions

18QuestionNaming compounds with functional groups like Alcohols (-ol) and Carboxylic acids (-oic acid)Assessment Practice

2 marks~3 minCriterion D

Ethanoic acid (

CH_3COOH

) is produced industrially via the carbonylation of methanol, a process requiring high temperatures, pressures, and fossil-fuel-derived energy. Vinegar, a dilute aqueous solution containing approximately 5% ethanoic acid, is marketed as a household cleaning agent.

a

Outline one environmental impact of producing ethanoic acid on an industrial scale. [1]

b

Explain one limitation of using vinegar as a cleaning agent, referring to the chemical properties of ethanoic acid. [1]

Solutions

19QuestionStructural/displayed formulaAssessment Practice

6 marks~9 minCriterion B

The molecular formula

C_4H_{10}O

represents several structural isomers containing a hydroxyl group (

-OH

).

a

Construct the displayed formulas for all structural isomers of

C_4H_{10}O

, ensuring every bond and atom is clearly shown. [2]

b

Describe the pattern in how the carbon skeleton and the position of the

-OH

group vary across the isomers drawn in part (a). [2]

c

Using the pattern identified in part (b), deduce the number of structural isomers of

C_5H_{12}O

that contain an

-OH

group. Justify your answer by systematically accounting for each carbon skeleton and each possible

-OH

position. [2]

Solutions

20QuestionStructural/displayed formulaAssessment Practice

8 marks~12 minCriterion D

A chemical company produces a plastic using 2-methylpentane, a branched-chain alkane. To improve biodegradability, they propose substituting it with n-hexane, its straight-chain isomer. However, n-hexane poses greater toxicity risk to aquatic organisms. Both compounds share the molecular formula

C_6H_{14}

.

a

Draw the structural formula for each compound, clearly showing all bonds. [2]

b

Explain why n-hexane is expected to biodegrade more readily than 2-methylpentane. [2]

c

Evaluate the environmental and societal trade-offs of this substitution, including the limitations of assuming that all straight-chain alkanes biodegrade at the same rate under real landfill conditions. [4]

Solutions

21QuestionInterpreting skeletal diagramsAssessment Practice

2 marks~3 minCriterion C

The skeletal diagram below shows 3-methylpentane.

a

Deduce the condensed structural formula of 3-methylpentane from the skeletal diagram. Show your working by identifying each carbon group in the main chain and at the branch point. [1]

b

A student claims that

CH_3CH_2CH(CH_3)CH_2CH_3

and

CH_3CH(CH_3)CH_2CH_2CH_3

represent different compounds. Evaluate this claim. [1]

Solutions

22QuestionUses of hydrocarbons (fuels, plastics)Assessment Practice

6 marks~9 minCriterion B

When five hydrocarbons are burned in excess oxygen, the following results are observed.

Hydrocarbon — C:H atomic ratio — Combustion products

Methane (

CH_4

) — 1:4 —

CO_2

and

H_2O

only

Ethene (

C_2H_4

) — 1:2 —

CO_2

and

H_2O

only

Cyclohexane (

C_6H_{12}

) — 1:2 —

CO_2

and

H_2O

only

Benzene (

C_6H_6

) — 1:1 —

CO_2

,

H_2O

, and soot

Ethanol (

C_2H_5OH

) — 1:3 —

CO_2

and

H_2O

only

a

Identify the pattern linking the C:H atomic ratio to the tendency to produce soot during combustion. Support your answer with evidence from the data. [2]

b

Propyne has the molecular formula

C_3H_4

. Deduce whether propyne would produce soot when burned in excess oxygen, and explain your reasoning using the pattern identified in part (a). [2]

c

Justify why a higher C:H ratio increases the likelihood of incomplete combustion. Your answer must refer to oxygen demand per carbon atom and to the relative strengths of

C-H

,

C-C

,

C=C

, and

C \equiv C

bonds. [2]

Solutions

23QuestionAlkanes Single bonds and saturationAssessment Practice

5 marks~8 minCriterion C

Four hydrocarbons — W, X, Y, and Z — were tested with bromine water under identical conditions.

Decolourisation time (s)	W: no decolourisation	X: 45	Y: 60	Z: no decolourisation
Final colour	W: orange	X: colourless	Y: colourless	Z: orange

One hydrocarbon is an alkane, one is an alkene, and two are unidentified. A student proposes the hypothesis: "All hydrocarbons containing only single bonds will not decolourise bromine water."

a

State what the bromine water test indicates about the bonding in hydrocarbons X and Y. [1]

b

Deduce which hydrocarbon — W or Z — is more likely to be the alkane, and justify your reasoning using the experimental data. [2]

c

Evaluate the student's hypothesis. In your evaluation, identify one limitation of using this dataset alone to fully support the hypothesis. [2]

Solutions

24QuestionCombustion reactions / Environmental ImpactAssessment Practice

3 marks~5 minCriterion D

A Bunsen burner can produce two flame types. Setting A has the air hole fully open, producing a blue flame. Setting B has the air hole partially closed, producing a yellow, smoky flame. The fuel burned is methane (

CH_4

).

a

State the products of combustion for each setting and explain why different products are formed. [2]

b

A city authority is considering banning the use of equipment that produces Setting B-type combustion in indoor workshops. Evaluate whether this decision is justified, using evidence from the chemistry of incomplete combustion. [1]

Solutions

25QuestionHomologous Series Definition and characteristicsAssessment Practice

5 marks~8 minCriterion D

A student investigates methane (

CH_4

) and methanol (

CH_3OH

) as alternative fuels. Their complete combustion equations are:

CH_4 + 2\,O_2 \rightarrow CO_2 + 2\,H_2O

2\,CH_3OH + 3\,O_2 \rightarrow 2\,CO_2 + 4\,H_2O

Molar masses:

CH_4 = 16\ \text{g/mol}

,

CH_3OH = 32\ \text{g/mol}

,

CO_2 = 44\ \text{g/mol}

.

a

Calculate the mass of

CO_2

produced per gram of each fuel burned. [2]

b

Deduce, using your results from (a), which fuel produces less

CO_2

per gram, and explain why the fuel with the lower molar mass does not automatically produce less

CO_2

per gram. [1]

c

Discuss two factors beyond

CO_2

emissions that must be considered to fully evaluate the environmental impact of these fuels. [2]

Solutions

26QuestionFunctional Groups Importance in determining propertiesAssessment Practice

5 marks~8 minCriterion C

The structural diagrams of ethanol (

\text{C}_2\text{H}_6\text{O}

) and ethanoic acid (

\text{C}_2\text{H}_4\text{O}_2

) are shown below.

a

Identify the functional group present in each molecule. [2]

b

Ethanoic acid has a boiling point of 118 °C, while ethanol has a boiling point of 78 °C. Both molecules are miscible with water. Explain how the functional groups account for the difference in boiling points between the two molecules. [2]

c

Evaluate whether boiling point alone is sufficient evidence to conclude that ethanoic acid forms stronger intermolecular forces than ethanol. [1]

Solutions

27QuestionNaming alcohols (IUPAC)Assessment Practice

6 marks~9 minCriterion B

The table below summarises four alcohols and their reactions with acidified potassium dichromate (

\text{K}_2\text{Cr}_2\text{O}_7

) under reflux.

Alcohol — Structure — Product after reflux

ethanol —

\text{CH}_3\text{CH}_2\text{OH}

— ethanoic acid

propan-1-ol —

\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}

— propanoic acid

butan-2-ol —

\text{CH}_3\text{CH(OH)CH}_2\text{CH}_3

— butanone

2-methylpropan-2-ol —

(\text{CH}_3)_3\text{COH}

— no reaction

a

Deduce the relationship between the classification of an alcohol (primary, secondary, or tertiary) and the type of product formed when reacted with acidified

\text{K}_2\text{Cr}_2\text{O}_7

under reflux. [2]

b

Predict the organic product(s) formed when pentan-1-ol and pentan-3-ol are each reacted with acidified

\text{K}_2\text{Cr}_2\text{O}_7

under reflux. [2]

c

Justify why tertiary alcohols cannot be oxidised under these conditions, while primary alcohols undergo two successive oxidation steps, by analysing the role of hydrogen atoms on the carbon bearing the

-\text{OH}

group. [2]

Solutions

28QuestionNaming alcohols (IUPAC)Assessment Practice

2 marks~3 minCriterion D

Brazil blends ethanol (

\text{C}_2\text{H}_5\text{OH}

) with petrol to power vehicles, reducing dependence on fossil fuels.

a

Explain one reason why ethanol is considered a more sustainable fuel than petrol. [1]

b

Explain one limitation of using ethanol instead of petrol in vehicles, linking your answer to the chemical structure of

\text{C}_2\text{H}_5\text{OH}

. [1]

Solutions

29QuestionOxidation (basic concept)Assessment Practice

5 marks~8 minCriterion C

When four alcohols are heated with acidified potassium dichromate (

K_2Cr_2O_7 / H_2SO_4

), the following products are obtained:

Alcohol	ethanol ( $CH_3CH_2OH$ )	Product: ethanoic acid
Alcohol	propan-1-ol ( $CH_3CH_2CH_2OH$ )	Product: propanoic acid
Alcohol	butan-2-ol ( $CH_3CH_2CH(OH)CH_3$ )	Product: butanone
Alcohol	2-methylpropan-2-ol ( $(CH_3)_3COH$ )	Product: no reaction

a

Deduce the relationship between the class of alcohol (primary, secondary, or tertiary) and the type of product formed. [2]

b

Justify the prediction that pentan-3-ol (

CH_3CH_2CH(OH)CH_2CH_3

) produces a single organic product when treated with acidified potassium dichromate, by explaining how the number of hydrogen atoms on the carbon bearing the

OH

group determines both the product type and why no further oxidation occurs. [3]

Solutions

30QuestionPhysical properties:High boiling point and SolubilityAssessment Practice

3 marks~5 minCriterion B

The table below shows the boiling points of four organic compounds.

Compound	Boiling point (°C)
Methanoic acid	101
Ethanol	78
Propanoic acid	141
Propan-1-ol	97

a

Identify the pattern in boiling points between the carboxylic acids and the alcohols shown in the table. [1]

b

Deduce the boiling point of butanoic acid, using the data in the table to support your reasoning. [1]

c

Analyse why carboxylic acids have higher boiling points than alcohols of comparable molar mass, referring to intermolecular forces and molecular structure. [1]

Solutions

31QuestionReactions:With metals and With bases (neutralization) and With carbonates (CO₂ production)Assessment Practice

5 marks~8 minCriterion C

A student investigates the reaction of ethanoic acid (

CH_3COOH

) with magnesium (

Mg

), zinc (

Zn

), and copper (

Cu

). Each metal (0.10 g) is placed in 50 cm³ of 1.0 mol dm

^{-3}

ethanoic acid at 25 °C. Mass loss (due to gas escape) and temperature change are recorded after 5 minutes.

Metal	Mass loss (g)	Temperature change (°C)
Magnesium	0.082	+4.2
Zinc	0.045	+2.1
Copper	0.000	0.0

The student hypothesises: "All metals react with carboxylic acids to produce hydrogen gas."

a

State the gas produced when magnesium reacts with ethanoic acid and write a balanced chemical equation for this reaction. [1]

b

Interpret the data for magnesium and zinc to compare the relative reactivity of these two metals with ethanoic acid. [2]

c

Evaluate whether the experimental evidence supports or refutes the hypothesis. In your answer, explain the copper result using the reactivity series. [2]

Solutions

32QuestionReactions:With metals and With bases (neutralization) and With carbonates (CO₂ production)Assessment Practice

6 marks~9 minCriterion D

A student spills vinegar (a dilute solution of ethanoic acid,

CH_3COOH

) on a limestone (

CaCO_3

) kitchen counter. Bubbles of

CO_2

form immediately.

a

Construct a balanced chemical equation, including state symbols, for the reaction between ethanoic acid and calcium carbonate. [2]

b

The student considers two clean-up options:
- Option 1: baking soda (

NaHCO_3

)
- Option 2: sodium hydroxide (

NaOH

)

Construct a balanced equation, including state symbols, for the reaction of excess ethanoic acid with each option. [2]

c

Evaluate which clean-up option poses a lower risk to aquatic life if the solution is washed down the drain. Refer to the products formed in each reaction. [2]

Solutions

33QuestionStructure of estersAssessment Practice

6 marks~9 minCriterion B

A student reacted methanoic, ethanoic, propanoic, butanoic, and pentanoic acids separately with ethanol under identical conditions (same temperature, concentration, catalyst, and reaction time). Results are shown below.

Carboxylic acid	methanoic	ethanoic	propanoic	butanoic	pentanoic
Carbon chain length	1	2	3	4	5
Yield (\%)	92	85	78	72	67

a

Describe the pattern in percentage yield as carbon chain length increases. [2]

b

Deduce the percentage yield for the reaction of hexanoic acid with ethanol under the same conditions, using the pattern you identified. [2]

c

Explain, using collision theory, why percentage yield decreases as carbon chain length increases. [2]

Solutions

34QuestionUses: Perfumes and Food flavoringAssessment Practice

3 marks~5 minCriterion D

The graph below shows the hydrolysis of ethyl ethanoate (

CH_3COOC_2H_5

) at three pH values over time. The y-axis shows ester concentration remaining; the x-axis shows time. Curve A (pH 1) declines steeply; Curve B (pH 7) remains high throughout; Curve C (pH 13) declines steeply, similar to Curve A.

a

Identify which pH condition(s) produce the fastest hydrolysis of ethyl ethanoate and describe the trend shown by Curve B. [1]

b

Explain why both strongly acidic and strongly basic conditions accelerate ester hydrolysis compared to neutral conditions. [1]

c

Discuss the significance of ester stability at neutral pH for their use as food flavourings, referring to shelf life and flavour integrity. [1]

Solutions

35QuestionReaction:Alcohol + Carboxylic acid → Ester + WaterAssessment Practice

5 marks~8 minCriterion C

A student investigates the esterification of ethanol and ethanoic acid using a reflux apparatus with concentrated sulfuric acid as a catalyst. Equal amounts of each reactant (0.50 mol) are used.

\text{CH}_3\text{CH}_2\text{OH} + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COOCH}_2\text{CH}_3 + \text{H}_2\text{O}

Mass of water collected at 10-minute intervals:

Time (min)	10	20	30	40	50	60
Water (g)	4.1	6.8	7.2	7.2	7.2	7.2

The student hypothesises that "the reaction reaches completion after 30 minutes."

a

Calculate the theoretical mass of water produced if the reaction goes to completion. [2]

b

Deduce whether the experimental data support the student's hypothesis. [1]

c

Evaluate the claim that the reaction reaches completion, using your knowledge of the nature of esterification reactions. [2]

Solutions

36QuestionCondensation polymerization (basic)Assessment Practice

5 marks~8 minCriterion C

A student hypothesises that two unknown polymers,

X

and

Y

, are both formed by condensation polymerisation. The following evidence was collected.

Elemental analysis (mass percent):
Polymer

X

: C 54.5%, H 9.1%, O 36.4%
Polymer

Y

: C 85.7%, H 14.3%

IR spectroscopy:
Polymer

X

: strong peak at

1735\ \text{cm}^{-1}

; broad peak at

3200

–

3500\ \text{cm}^{-1}

Polymer

Y

: no peaks in the

1700

–

1750\ \text{cm}^{-1}

or

3200

–

3500\ \text{cm}^{-1}

regions

a

State two features that define a condensation polymer at the molecular level. [1]

b

Explain how the elemental analysis and IR data together support classifying polymer

X

as a condensation polymer. [2]

c

Evaluate whether the full dataset supports the hypothesis that both

X

and

Y

are condensation polymers, identifying which evidence is most decisive for polymer

Y

and justifying your conclusion. [2]

Solutions

37QuestionEnvironmental issues like Non-biodegradability, MicroplasticsAssessment Practice

6 marks~9 minCriterion D

A city has banned single-use polyethylene shopping bags due to concerns about their persistence in landfills. Polyethylene is formed from repeating ethene (

\text{C}_2\text{H}_4

) units, producing long chains held together by strong carbon–carbon (

\text{C–C}

) and carbon–hydrogen (

\text{C–H}

) covalent bonds. These bonds are resistant to hydrolysis. Studies suggest polyethylene bags may persist in landfills for 500–1000 years, though this estimate assumes uniform decomposition conditions across all sites.

a

Explain why polyethylene bags persist in landfills for centuries, referring to polymer bonding and landfill conditions. [2]

b

Discuss one limitation of assuming decomposition rates are uniform across all landfill environments. [2]

c

Evaluate one environmental or health implication of microplastics formed when polyethylene fragments into tiny particles over time. [2]

Solutions

38QuestionRefinery gasesAssessment Practice

6 marks~9 minCriterion B

Refinery gases from the fractional distillation of crude oil consist of methane (

CH_4

), ethane (

C_2H_6

), propane (

C_3H_8

), and butane (

C_4H_{10}

).

a

Construct balanced chemical equations, including state symbols, for the complete combustion of each of the four alkanes listed above. [4]

b

Using your equations from part (a), deduce how the molar ratio of

CO_2

produced to

H_2O

produced changes as the number of carbon atoms in the alkane increases. [1]

c

The general formula for alkanes is

C_nH_{2n+2}

. Explain, using this formula, why the

CO_2 : H_2O

molar ratio approaches but never reaches

1:1

as

n

increases. [1]

Solutions

39QuestionRefinery gasesAssessment Practice

6 marks~9 minCriterion D

Refinery gases — methane (

CH_4

), ethane (

C_2H_6

), propane (

C_3H_8

), and butane (

C_4H_{10}

) — are burned as fuel in homes and industry. When oxygen supply is limited, incomplete combustion occurs, producing carbon monoxide (

CO

) and soot (carbon particles) alongside water, rather than the

CO_2

and

H_2O

predicted by complete combustion. Environmental models of urban air quality frequently assume combustion is 100% complete.

a

Construct balanced chemical equations for both the complete combustion and the incomplete combustion of methane (

CH_4

), clearly identifying the products in each case. [2]

b

Discuss two health or environmental implications arising specifically from the products of incomplete combustion of refinery gases. [2]

c

Evaluate the limitations of assuming 100% complete combustion when modelling air quality in urban areas. [2]

Solutions

40QuestionViscosity and flammability trendsAssessment Practice

4 marks~6 minCriterion C

Three alkane molecules are compared: pentane (

C_5H_{12}

), decane (

C_{10}H_{22}

), and octadecane (

C_{18}H_{38}

).

Observed viscosities: pentane flows like water; decane flows like cooking oil; octadecane flows like honey.

Boiling points: pentane

36°C

; decane

174°C

; octadecane

317°C

.

a

State the trend in viscosity as hydrocarbon chain length increases. [1]

b

Explain how molecular structure influences the strength of London dispersion forces in these three molecules. [1]

c

Using the boiling point data, analyse how the intermolecular force strength accounts for both the boiling point trend and the viscosity trend across these three hydrocarbons. [2]

Solutions

Organic Chemistry — Free MYP4 Chemistry Practice Questions