Organic Chemistry — Free IB MYP5 Chemistry Questions

1QuestionCovalent bonding in organic moleculesConcept Practice

3 marks~5 minCriterion A

The graph below shows the boiling points of four straight-chain alkanes: methane (

\text{CH}_4

), ethane (

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

), propane (

\text{C}_3\text{H}_8

), and butane (

\text{C}_4\text{H}_{10}

).

a

State the trend in boiling point as the number of carbon atoms increases from methane to butane. [1]

b

Identify the type of intermolecular force responsible for this trend. [1]

c

Explain why longer carbon chains produce stronger intermolecular forces, resulting in higher boiling points. [1]

Solutions

2QuestionMultiple substituents (di, tri, tetra…)Concept Practice

2 marks~3 minCriterion A

The structural formula below shows a straight-chain alkane with four carbon atoms. A methyl group (

\text{CH}_3

) is attached to carbon-2 and another methyl group is attached to carbon-3. Each carbon satisfies tetravalency.

(a) Deduce the IUPAC name of this compound. [2]

Solutions

3QuestionIdentifying isomers from formulasConcept Practice

4 marks~6 minCriterion A

Two organic compounds, both with molecular formula

C_3H_6O

, are shown below.

Compound X:

\text{H–C(=O)–CH}_2\text{–CH}_3

Compound Y:

\text{CH}_3\text{–C(=O)–CH}_3

a

Identify which compound is an aldehyde and which is a ketone. [1]

b

Explain the difference in the bonding arrangement of the carbonyl carbon that distinguishes an aldehyde from a ketone. [2]

c

A student claims that Compounds X and Y are isomers. Evaluate this claim using evidence from their molecular and structural formulas. [1]

Solutions

4QuestionSaturated vs unsaturated hydrocarbonsConcept Practice

4 marks~6 minCriterion A

When ethene (C2H4) reacts with bromine water, the time for complete decolourisation was recorded at three temperatures.

Temperature (°C)	20	30	40
Time (s)	120	60	30

Use the relationship

\text{rate} = \dfrac{1}{\text{time}}

throughout.

a

Calculate the reaction rate at 20°C. [1]

b

Calculate the reaction rates at 30°C and 40°C. Present all three rates in the format:

Temperature (°C)	20	30	40
Reaction rate (s $^{-1}$ )	___	___	___ [1]

c

The time halves with each 10°C rise. Explain, using collision theory, why increasing temperature increases the reaction rate of ethene with bromine water. [2]

Solutions

5QuestionCommon functional groups:Alkane (-C-C-) , Alkene (-C=C-), Alcohol (-OH), Carboxylic acid (-COOH), Ester (-COO-)Concept Practice

2 marks~3 minCriterion A

The displayed formula below shows a molecule containing two carbon atoms.

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

Solutions

6QuestionALCOHOLS Functional Group (-OH) / General FormulaConcept Practice

2 marks~3 minCriterion A

The structural formula of ethanol is shown below, with a group of atoms highlighted.

a

State the name of the highlighted functional group and write its chemical formula. [1]

b

Explain why the presence of this functional group makes ethanol an alcohol rather than an alkane. [1]

Solutions

7QuestionFunctional group (-COOH) / General FormulaConcept Practice

2 marks~3 minCriterion A

Propanoic acid has the following structural formula:

\begin{array}{ccccc}H & H & O & & \\| & | & \| & & \\H-C & - & C-C-O-H & & \\| & & | & & \\H & & H & & \\\end{array}

a

Identify the carboxyl functional group in the structure above by circling or labelling it clearly. [1]

b

Deduce the molecular formula of propanoic acid from its structural formula, and explain how the presence of the carboxyl group accounts for the acidic behaviour of carboxylic acids in aqueous solution. [1]

Solutions

8QuestionNaming esters: Alcohol part (alkyl) + acid part (oate)Concept Practice

2 marks~3 minCriterion A

The structural formulas of methanol (

CH_3OH

) and butanoic acid (

C_3H_7COOH

) are shown below.

[Structural formula diagram]

a

State the complete IUPAC name of the ester formed when methanol reacts with butanoic acid in a condensation reaction. [1]

b

Deduce which part of each reactant molecule contributes to the ester name, and explain the order in which those parts are combined to produce the IUPAC name. [1]

Solutions

9QuestionMonomers and polymerizationConcept Practice

2 marks~3 minCriterion A

The diagram below shows a section of the addition polymer polyethene. The repeat unit is indicated by the brackets.

\text{---}\left[\begin{array}{c} \text{H} \quad \text{H} \\ | \quad\quad | \\ \text{---C---C---} \\ | \quad\quad | \\ \text{H} \quad \text{H} \end{array}\right]_n\text{---}

a

State the name and molecular formula of the monomer used to produce polyethene. [1]

b

Explain why the monomer's structure differs from the repeat unit shown in the diagram. [1]

Solutions

10QuestionEnvironmental impacts like Fossil fuels, Pollution, Climate changeConcept Practice

4 marks~6 minCriterion A

During the combustion of octane (

C_8H_{18}

), bonds in the reactants are broken and new bonds are formed in the products, as shown in the diagram.

C_8H_{18} + \tfrac{25}{2}\,O_2 \rightarrow 8\,CO_2 + 9\,H_2O

a

State what happens to energy during bond breaking and during bond forming. [1]

b

Identify the bonds broken in the reactants and the bonds formed in the products during this combustion reaction. [1]

c

Explain why the combustion of octane releases a net amount of energy, referring to the relative energy changes involved in breaking and forming the bonds identified in part (b). [2]

Solutions

11QuestionTetravalency 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

12QuestionOrganic vs inorganic compounds (comparison)Assessment Practice

3 marks~5 minCriterion D

A student investigates the environmental persistence of two pesticides: DDT (

\text{C}_{14}\text{H}_9\text{Cl}_5

), an organic compound, and copper sulfate (

\text{CuSO}_4

), an inorganic salt. Each is dissolved in a separate

1.0\ \text{L}

water sample at an initial concentration of

1.0\ \text{g/L}

. After 30 days under controlled conditions (

25°\text{C}

, constant light, aeration), the concentrations measured are:

DDT:

0.95\ \text{g/L}

Copper sulfate:

0.50\ \text{g/L}

a

Deduce which pesticide is more persistent, using quantitative evidence from the data. [1]

b

Discuss TWO limitations of this experiment that may prevent the results from accurately predicting the ecological impact of these pesticides in a real river ecosystem. In your discussion, refer to the organic or inorganic nature of each pesticide. [2]

Solutions

13QuestionSaturated vs unsaturated compoundsAssessment Practice

5 marks~8 minCriterion C

A student tests four liquid samples — W, X, Y, and Z — with bromine water to investigate saturation. Decolorization times are recorded:

Sample W: no decolorization after 120 s
Sample X: decolorizes in 15 s
Sample Y: no decolorization after 120 s
Sample Z: decolorizes in 18 s

W is hexane (saturated), X is hex-1-ene (unsaturated), and Y is cyclohexane (saturated). Z is unknown.

A hypothesis states: "Sample Z contains a carbon–carbon double bond."

a

State what is observed when bromine water reacts with a compound containing a

C{=}C

bond, and identify the type of reaction occurring. [1]

b

Using the data from W, X, and Y, explain why bromine water is a reliable test for distinguishing saturated from unsaturated compounds. [2]

c

Evaluate the hypothesis using all four samples' data, identifying one limitation of this conclusion. [2]

Solutions

14QuestionNaming cyclic compounds (basic)Assessment Practice

5 marks~8 minCriterion D

Three isomers of

\text{C}_8\text{H}_{16}

have the following experimentally measured boiling points:

1,1-dimethylcyclohexane: 119.7 °C
1,2-cis-dimethylcyclohexane: 129.7 °C
1,3-trans-dimethylcyclohexane: 124.5 °C

a

Draw the structural formula of each isomer using wedge-dash notation to show the position and stereochemistry of the methyl groups. [2]

b

Explain how the position of the methyl groups affects the symmetry and polarity of each isomer. [1]

c

Evaluate which isomer's structure best accounts for the observed order of boiling points, justifying your answer in terms of intermolecular forces. [2]

Solutions

15QuestionNaming cyclic compounds (basic)Assessment Practice

5 marks~8 minCriterion B

The standard enthalpy of combustion per

\text{CH}_2

group for four cycloalkanes is given below.

Cycloalkane	cyclopropane	cyclobutane	cyclopentane	cyclohexane
Enthalpy per $\text{CH}_2$ / kJ mol $^{-1}$	$-697$	$-683$	$-664$	$-659$

a

Identify the trend in combustion enthalpy per

\text{CH}_2

as ring size increases from cyclopropane to cyclohexane. [1]

b

Deduce the combustion enthalpy per

\text{CH}_2

for cycloheptane (

\text{C}_7\text{H}_{14}

), showing your reasoning from the data. [2]

c

Justify the trend identified in (a) using Baeyer strain theory, and explain why the values approach a limiting enthalpy as ring size increases. [2]

Solutions

16QuestionNaming compounds with functional groups like Alcohols (-ol) and Carboxylic acids (-oic acid)Assessment Practice

5 marks~8 minCriterion C

An unknown organic compound has the molecular formula

\text{C}_3\text{H}_6\text{O}_2

. Its infrared (IR) spectrum shows a strong, broad absorption at approximately

3300 \ \text{cm}^{-1}

and a strong, sharp absorption at approximately

1710 \ \text{cm}^{-1}

.

Two students propose different identities for the compound:

Student 1: "The compound is propan-1-ol."
Student 2: "The compound is propanoic acid."

a

Identify the functional groups responsible for each IR absorption band. [2]

b

State the IUPAC name and structural formula of the correct compound. [1]

c

Evaluate both students' claims, explaining why one is supported by the spectral data and the other is not. [2]

Solutions

17QuestionDefinition of isomers / PropertiesAssessment Practice

3 marks~5 minCriterion B

The boiling points of three structural isomers of

\text{C}_5\text{H}_{12}

are given below.

Isomer: pentane, 2-methylbutane, 2,2-dimethylpropane
Boiling point (°C): 36, 28, 9

a

State the trend in boiling point as branching increases among these three isomers. [1]

b

Identify the type of intermolecular force present in all three isomers and explain why only this type is present. [1]

c

Explain how increasing branching affects the strength of these intermolecular forces and, therefore, the boiling point. [1]

Solutions

18QuestionInterpreting skeletal diagramsAssessment Practice

6 marks~9 minCriterion D

A pharmaceutical company identifies two skeletal isomers of a painkiller: Compound X and Compound Y. Both bind identically to pain receptors, providing equal therapeutic efficacy. Compound X is synthesised using dichloromethane (

CH_2Cl_2

), a chlorinated solvent toxic to aquatic organisms that persists in the environment. Compound Y is synthesised via a water-based green chemistry route producing no toxic by-products, but costs 50% more to manufacture than Compound X.

a

Identify the immediate societal benefit provided by both compounds. [1]

b

Analyse the environmental impact of using dichloromethane in the synthesis of Compound X compared to the green chemistry route used for Compound Y. [3]

c

Evaluate the trade-offs a regulatory agency must consider when selecting one compound for commercial production, including the economic implications and the limitations of comparing only these two synthesis routes. [2]

Solutions

19QuestionDrawing displayed structuresAssessment Practice

5 marks~8 minCriterion C

A chemist hypothesises that two compounds with molecular formula

C_4H_{10}O

are structural isomers. Combustion of 1.00 g of each compound gives:

Compound A: 2.41 g

CO_2

and 1.18 g

H_2O

Compound B: 2.39 g

CO_2

and 1.20 g

H_2O

The chemist identifies Compound A as butan-1-ol and Compound B as diethyl ether.

a

Deduce the empirical formula of each compound from the combustion data. Show all working. [2]

b

Draw the displayed structure of each compound. [1]

c

Evaluate whether the experimental data supports the hypothesis that Compound A and Compound B are structural isomers. In your answer, consider the significance of any differences in the combustion data. [2]

Solutions

20QuestionAlkenes Reactivity compared to alkanesAssessment Practice

4 marks~6 minCriterion C

The graph below shows the time taken for bromine water to decolorize when added to five different alkenes (A–E) and one alkane (F) under the same conditions.

Interpret the graph and answer the following questions.

a

Describe the overall trend shown in the graph regarding the reactivity of alkenes compared to the alkane.

b

Identify which alkene data point is an anomaly and explain why it is considered an anomaly.

c

State a conclusion about the role of the carbon-carbon double bond in the reactivity of alkenes, referencing the graph data.

d

Suggest one reason why the anomalous alkene might react more slowly than expected.

Solutions

21QuestionAlkenes Double bonds / General formula (CₙH₂ₙ)Assessment Practice

6 marks~9 minCriterion D

A fruit-ripening facility uses ethene (

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

) gas to accelerate banana ripening. The room measures

10\ \text{m} \times 8\ \text{m} \times 3\ \text{m}

. In a controlled process,

0.50\ \text{kg}

of ethene is released. Assume ideal gas behaviour, room temperature

25\ ^\circ\text{C}

, and atmospheric pressure

1.00 \times 10^5\ \text{Pa}

.

Molar mass of ethene:

28.0\ \text{g mol}^{-1}

;

R = 8.31\ \text{J mol}^{-1}\text{K}^{-1}

; room volume:

240\ \text{m}^3

.

a

Calculate the volume of ethene released under these conditions. [2]

b

Show that the ethene occupies less than 1% of the room volume, and explain what this suggests about oxygen availability for workers. [2]

c

Evaluate the reliability of the ideal gas law for predicting safe ethene concentration levels in this facility. [2]

Solutions

22QuestionUses of hydrocarbons (fuels, plastics)Assessment Practice

4 marks~6 minCriterion B

The table below shows the standard enthalpy of combustion (

\Delta H_c

) for six consecutive alkanes.

Alkane	methane	ethane	propane	butane	pentane	hexane
Number of carbon atoms ( $n$ )	1	2	3	4	5	6
$\Delta H_c$ (kJ mol $^{-1}$ )	−890	−1560	−2220	−2877	−3536	−4194

a

Construct a graph of

\Delta H_c

(kJ mol

^{-1}

) against

n

. Describe the relationship shown. [2]

b

Deduce the average increase in

\Delta H_c

per additional

CH_2

group. Use this value to predict

\Delta H_c

for heptane (

C_7H_{16}

). Show your working. [1]

c

Justify why

\Delta H_c

becomes more negative as chain length increases, with reference to the bonds broken and bonds formed during combustion. [1]

Solutions

23QuestionCommon functional groups:Alkane (-C-C-) , Alkene (-C=C-), Alcohol (-OH), Carboxylic acid (-COOH), Ester (-COO-)Assessment Practice

7 marks~11 minCriterion B

The table below shows balanced combustion equations for four organic compounds from different homologous series.

Compound — Balanced combustion equation

Methane (

CH_4

):

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

Ethene (

C_2H_4

):

C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O

Ethanol (

C_2H_5OH

):

C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O

Ethanoic acid (

CH_3COOH

):

CH_3COOH + 2O_2 \rightarrow 2CO_2 + 2H_2O

a

Calculate the ratio of

CO_2

molecules produced per carbon atom for each compound, and deduce the pattern. [2]

b

Explain why the number of

H_2O

molecules produced per carbon atom differs between ethene, ethanol, and methane, linking your answer to molecular composition. [2]

c

Methyl ethanoate (

CH_3COOCH_3

) is an ester used as a solvent in nail-polish remover. Construct the balanced combustion equation for methyl ethanoate and justify each step using the patterns identified above. [3]

Solutions

24QuestionCommon functional groups:Alkane (-C-C-) , Alkene (-C=C-), Alcohol (-OH), Carboxylic acid (-COOH), Ester (-COO-)Assessment Practice

3 marks~5 minCriterion C

The table below shows the time taken for bromine water to decolourise when added to five hydrocarbon samples.

Hydrocarbon A (s): 120
Hydrocarbon B (s): 115
Hydrocarbon C (s): 118
Hydrocarbon D (s): 8
Hydrocarbon E (s): 6

Hydrocarbons A, B, and C are alkanes; D and E are alkenes.

a

Identify the trend shown in the data. [1]

b

Explain how the functional groups present in alkanes and alkenes account for this trend. [1]

c

A student claims that alkanes do not react with bromine water at all. Evaluate this claim using your knowledge of the reactions of alkanes and alkenes. [1]

Solutions

25QuestionCommon functional groups:Alkane (-C-C-) , Alkene (-C=C-), Alcohol (-OH), Carboxylic acid (-COOH), Ester (-COO-)Assessment Practice

2 marks~3 minCriterion D

A poorly maintained gas heater produces a yellow, sooty flame, indicating incomplete combustion of the alkane fuel.

Describe one environmental impact of incomplete combustion of alkanes in this appliance. [2]

Solutions

26QuestionCombustion of alcoholsAssessment Practice

3 marks~5 minCriterion B

The table below shows data for the complete combustion of four primary alcohols.

Alcohol	Carbon atoms	Oxygen consumed (mol)	Carbon dioxide produced (mol)
Methanol	1	1.5	1
Ethanol	2	3.0	2
Propanol	3	4.5	3
Butanol	4	6.0	4

a

State the trend in oxygen consumption as the number of carbon atoms increases. [1]

b

Write the general combustion equation for a primary alcohol of molecular formula

C_nH_{2n+2}O

, showing the stoichiometric coefficients in terms of

n

. [1]

c

Explain why each additional carbon atom in the alcohol chain requires exactly 1.5 mol of oxygen for complete combustion. [1]

Solutions

27QuestionALCOHOLS Functional Group (-OH) / General FormulaAssessment Practice

4 marks~6 minCriterion C

Experimental standard combustion enthalpies for four isomeric alcohols (molecular formula

C_4H_{10}O

) are given below.

Butan-1-ol:

-2676

kJ mol

^{-1}

Butan-2-ol:

-2660

kJ mol

^{-1}

2-Methylpropan-1-ol:

-2645

kJ mol

^{-1}

2-Methylpropan-2-ol:

-2630

kJ mol

^{-1}

a

Identify which alcohol does not follow the expected trend in combustion enthalpy as branching increases, and justify your answer with reference to the position of the

-

OH group and hydrogen bonding. [2]

b

Analyse how the position of the

-

OH group in butan-2-ol influences the strength of intermolecular forces and explain how this accounts for the deviation in its combustion enthalpy. [2]

Solutions

28QuestionNaming alcohols (IUPAC)Assessment Practice

6 marks~9 minCriterion D

Three alcohols are compared below.

Name	Methanol	Ethanol	Propan-1-ol
Structure	$CH_3OH$	$CH_3CH_2OH$	$CH_3CH_2CH_2OH$
$LD_{50}$ oral, rat (mg/kg)	5628	7060	1870
Common use	fuel/solvent	beverage/fuel	hand sanitiser/solvent

a

Explain why ethanol is considered safer than methanol for human consumption. In your answer, identify the metabolic products of each alcohol and link their toxicities to the enzymes involved. [2]

b

Evaluate the limitations of using

LD_{50}

data alone to establish safe human exposure limits for these alcohols. [2]

c

Discuss one significant limitation of relying exclusively on IUPAC naming to predict the health effects of a substance, using evidence from the data above to support your answer. [2]

Solutions

29QuestionFunctional group (-COOH) / General FormulaAssessment Practice

2 marks~3 minCriterion B

The molecular formulas of the first four carboxylic acids are given below.

Carboxylic acid	Methanoic	Ethanoic	Propanoic	Butanoic
Number of carbon atoms ( $n$ )	1	2	3	4
Molecular formula	$CH_2O_2$	$C_2H_4O_2$	$C_3H_6O_2$	$C_4H_8O_2$

a

Deduce the general formula that relates the number of carbon atoms

n

to the molecular formula of these carboxylic acids. [1]

b

Justify the prediction that pentanoic acid (

n = 5

) has the molecular formula

C_5H_{10}O_2

, by referring to the structure of the carboxylic acid functional group

-COOH

. [1]

Solutions

30QuestionReactions:With metals and With bases (neutralization) and With carbonates (CO₂ production)Assessment Practice

5 marks~8 minCriterion C

When

0.10

mol of each carboxylic acid reacts with excess sodium carbonate at room temperature and pressure, the following volumes of

CO_2

are collected.

Acid	methanoic	ethanoic	propanoic	butanoic
Molar mass (g/mol)	46	60	74	88
Volume of $CO_2$ (cm³)	2400	2400	2400	1200

At room temperature and pressure, 1 mol of gas occupies 24 000 cm³.

a

Construct the balanced chemical equation, with state symbols, for the reaction of ethanoic acid with sodium carbonate. [1]

b

Deduce the expected volume of

CO_2

produced when 0.10 mol of a monoprotic carboxylic acid reacts with excess sodium carbonate, and show your reasoning. [2]

c

Analyse the data to identify the anomalous result and evaluate whether the trend in acid strength across the homologous series can account for the anomaly. [2]

Solutions

31QuestionNaming carboxylic acidsAssessment Practice

5 marks~8 minCriterion D

Methanoic acid (

HCOOH

, 1 carbon) is found in ant venom and causes skin irritation. Butanoic acid (

C_3H_7COOH

, 4 carbons) is responsible for the smell of rancid butter and can cause nausea. In the IUPAC naming system for carboxylic acids, the prefix indicates the number of carbon atoms in the chain: methanoic = 1C, ethanoic = 2C, propanoic = 3C, butanoic = 4C.

a

State the IUPAC name of the carboxylic acid with 5 carbon atoms in its chain. [1]

b

Explain how the chain length indicated by an IUPAC name can be used to predict the volatility and health effects of a carboxylic acid. Use methanoic acid and butanoic acid as examples. [2]

c

Evaluate the reliability of using an IUPAC name alone to assess the health risks of a carboxylic acid, identifying at least one specific limitation. [2]

Solutions

32QuestionStructure 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

33QuestionHydrolysis of esters (basic idea)Assessment Practice

4 marks~6 minCriterion D

Aspirin (acetylsalicylic acid) undergoes hydrolysis in the stomach according to the equation:

\text{acetylsalicylic acid} + \text{water} \rightarrow \text{salicylic acid} + \text{acetic acid}

The stomach maintains a pH of 1.5–3.5. Aspirin is used to relieve pain and reduce inflammation, but it is also associated with stomach irritation and ulcers.

a

Explain how the two products of aspirin hydrolysis account for both its therapeutic effect and the side effect of stomach irritation. [2]

b

A simplified model of this reaction assumes constant pH and ignores enzyme activity throughout the digestive tract. Evaluate one limitation of this model in predicting the actual behaviour of aspirin in the human body. [2]

Solutions

34QuestionHydrolysis of esters (basic idea)Assessment Practice

2 marks~3 minCriterion C

Ethyl ethanoate (

CH_3COOCH_2CH_3

) is an ester used as a solvent in nail-varnish remover. When ethyl ethanoate is warmed with water in the presence of a dilute acid catalyst, the ester linkage (

-COO-

) breaks.

a

State the two organic products formed. [1]

b

Deduce which reactant provides the oxygen atom that becomes part of the carboxylic acid product, and explain how the position of the ester linkage in the structural formula supports your answer. [1]

Solutions

35QuestionBiodegradable polymers (basic idea)Assessment Practice

3 marks~5 minCriterion D

The graph below shows the percentage of original mass remaining over 30 days for two biodegradable polymers — polylactic acid (PLA) and polyhydroxyalkanoate (PHA) — composted at 58°C. Both polymers begin at 100% mass at day 0. By day 30, PLA retains approximately 85% of its original mass, while PHA retains approximately 20%.

a

Describe the trend in mass loss shown by each polymer over the 30-day period. [1]

b

Identify which polymer biodegrades faster and calculate the percentage of mass lost by each polymer over the 30-day period. [1]

c

Explain what the difference in mass loss between PLA and PHA suggests about their suitability for use in single-use packaging that must break down quickly in industrial compost facilities. [1]

Solutions

36QuestionNatural vs synthetic polymersAssessment Practice

4 marks~6 minCriterion C

The diagram below shows a section of a polyethene chain and a section of a cellulose chain.

Polyethene repeating unit:

-\text{CH}_2-\text{CH}_2-

connected by C–C single bonds.

Cellulose repeating unit: glucose monomers linked by glycosidic (C–O–C) bonds.

a

State the type of bond found in the backbone of each polymer. [1]

b

Explain why C–C bonds in polyethene resist attack by enzymes in the environment. [1]

c

Discuss how the bond type in cellulose makes it susceptible to enzymatic breakdown, and evaluate why this difference in bond type means polyethene persists in ecosystems while cellulose does not. [2]

Solutions

37QuestionNatural vs synthetic polymersAssessment Practice

4 marks~6 minCriterion B

A diagram shows the setup for synthesizing nylon 6,10: a beaker contains two immiscible layers—an aqueous solution of 1,6-diaminohexane (top) and a hexane solution of sebacoyl chloride (bottom). At the interface, nylon 6,10 forms. The polymer chains are long because each monomer has a 6-carbon or 10-carbon chain. In a modified experiment, the 1,6-diaminohexane is replaced with 1,2-diaminoethane (which has only a 2-carbon chain). All other conditions remain the same.

a

[2 marks] Predict how the chain length of the nylon produced in the modified experiment would compare to that of nylon 6,10.

b

[2 marks] Predict how the flexibility and tensile strength of the modified nylon would compare to those of nylon 6,10. Justify your prediction by referring to intermolecular forces and chain packing.

Solutions

38QuestionChain length vs boiling pointAssessment Practice

6 marks~9 minCriterion B

The table below shows the molecular formula and boiling point of five straight-chain alkanes.

Alkane	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

Explain the relationship between carbon chain length and boiling point for these alkanes. [2]

b

Deduce the boiling point of hexane (

C_6H_{14}

), justifying your value using the pattern in the data. [2]

c

A student claims that atmospheric pressure is the most important variable to control when measuring boiling points experimentally. Evaluate this claim, identifying one other variable that must be controlled and explaining why each affects the measurement. [2]

Solutions

39QuestionEnvironmental impacts like Fossil fuels, Pollution, Climate changeAssessment Practice

6 marks~9 minCriterion D

Diesel engines burn hydrocarbons obtained from the fractional distillation of crude oil. The table below shows exhaust gas composition at three air-fuel ratios.

Air-fuel ratio	14.5:1 (stoichiometric)	12:1 (rich)	16:1 (lean)
$CO$ (ppm)	500	2000	200
$CO_2$ (%)	12	8	14
$NOx$ (ppm)	300	100	600
Soot (mg/m³)	10	80	5

a

Describe what happens during incomplete combustion in a rich air-fuel mixture, and identify two pollutants produced. [2]

b

Explain how

CO

and

NOx

each cause a different type of harm — one to human health and one to the environment. [2]

c

Using the data, discuss whether switching from a rich to a lean air-fuel ratio is an effective overall solution to reducing diesel engine pollution. [2]

Solutions

40QuestionViscosity and flammability trendsAssessment Practice

5 marks~8 minCriterion C

A student hypothesises that viscosity of crude oil fractions increases with carbon chain length. Five fractions (A–E) are collected by fractional distillation and tested at 25 °C using a standard viscometer. Flow time for 50 mL of each fraction is recorded below.

Fraction	A	B	C	D	E
Flow time (s)	12	20	35	55	80

Fractions are ordered from lightest (A) to heaviest (E), corresponding to increasing carbon chain length.

a

Identify the trend in flow time across fractions A to E and state what this indicates about viscosity. [1]

b

Explain how intermolecular forces account for the trend observed in part (a). [2]

c

Evaluate whether the experimental evidence supports the student's hypothesis, discussing at least two limitations that affect confidence in the conclusion. [2]

Solutions

Organic Chemistry — Free MYP5 Chemistry Practice Questions