Syllabus Edition

First teaching 2023

First exams 2025

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Electron Pair Sharing Reactions (HL IB Chemistry)

Exam Questions

4 hours62 questions
1a1 mark

A reaction scheme for propene is shown below.

10-2-ib-sl-sq-easy-q1a-reaction-scheme-of-propene

State the condensed structural formula of propene.

1b3 marks

State the IUPAC names for compounds A, B and C shown in the reaction scheme in part (a)

1c3 marks

Propene will also react to form an alcohol. State the reagents and conditions required for the formation of an alcohol from propene. 

1d1 mark

State the colour change when compound B is formed from propene. 

1e2 marks

Propene can form polypropene. Draw the repeating unit that will be formed via the addition polymerisation of propene. 

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2a2 marks

Benzene undergoes substitution reactions. State the equation for the reaction of benzene with nitric acid to produce nitrobenzene and water.

2b2 marks

The structure of methylbenzene is shown below.

a2c33069-43fc-46b0-af04-465fc1e6e6d1

Draw the structures of the two isomers of choromethylbenzene formed from the reaction of methyl benzene and Cl2 in the presence of AlCl3

2c1 mark

State the type of reaction that benzene will typically undergo. 

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3a2 marks

The structure of but-1-ene is shown below. But-1-ene IB SL SQ 10.2 E Q5a

Draw and state the name of the secondary halogenoalkane formed when but-1-ene reacts with HCl. 

3b2 marks

Explain why halogenoalaknes are more reactive than alkanes.

3c3 marks

State the reagents and conditions required for the formation of propan-1-ol from 1-bromopropane. 

3d1 mark

The type of reaction outlined in part (c) is nucleophilic substitution. State the meaning of the term nucleophile

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4a1 mark

A complex ion contains one Fe3+ ion, four ammonia molecules and two chloride ions.

State the formula of this complex ion.

4b2 marks

State two characteristic properties of transition elements.

4c1 mark

Transition metals can be used as successful catalysts in a range of reactions.

State what is meant by the term homogeneous catalyst.

4d2 marks

Transition metals can form complexes with different ligands.

Identify one species from the following list that does not act as a ligand and explain your answer.


CO         H2O         SCN-          H2

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5a3 marks

Define the terms Lewis acid and Lewis base and state the type of bond formed between a Lewis acid and base.

5b5 marks

Identify which of the following are Lewis acids, Lewis bases or neither:

NH3, K+, SO42-, CH4, BCl3
5c2 marks

Explain why aqueous ions of transition metals can act as Lewis acids.

5d1 mark

State an alternative name for a species that acts as a Lewis base in organic chemistry mechanisms.

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6a2 marks

Define the term nucleophile

6b2 marks

Explain why the hydroxide ion, OH, is a stronger nucleophile than water. 

6c1 mark

State the two ways a nucleophilic substitution reaction can occur. 

6d1 mark

State the the name of the mechanism occurring in the image below which will form ethanol in one step. 

ib-hl-sq-e-20-1-chem-q1d-sn2-mechanism

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7a6 marks

The start of the electrophilic addition mechanism for the addition of hydrogen bromide to ethene is shown below:

7

Complete the mechanism by:

i)
Adding two curly arrows and the partial charges, δ+ / δ-, to the reactants.
[3]
ii)
Adding the correct charge to the carbocation intermediate, adding the anion, including its lone pair, and one curly arrow to the intermediate step.
[3]
7b1 mark

Draw the product of the reaction in part a).

7c2 marks

The electrophilic addition of hydrogen bromide to but-1-ene results in two isomeric products - one is a major product and one is a minor product. The first steps of the electrophilic addition mechanism are shown below:

9

 

i)
Draw the displayed formula of the secondary carbocation intermediate that forms the major product.
[1]

ii)
Draw the displayed formula of the primary carbocation intermediate that forms the minor product.
[1]

7d1 mark

Explain why the secondary carbocation is more stable than the primary carbocation.

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8a1 mark

Name the type of mechanism that benzene will undergo in order to form nitrobenzene.

8b1 mark

State the reagents required to form nitrobenzene from benzene.

8c3 marks

Outline the mechanism for the formation of nitrobenzene from benzene.

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9a3 marks

2-chloro-2-methylpropane is reacted with aqueous sodium hydroxide in ethanol and heated under reflux.

i)
Deduce the class of halogenoalkane that 2-chloro-2-methylpropane belongs to.
[1]

ii)
State the name of the product formed in this reaction.
[1]

iii)
State the type of mechanism that this reaction will favour.
[1]
9b4 marks

Outline the mechanism for the reaction given in part a).

9c1 mark

State the type of bond breaking that occurs in this mechanism.

9d3 marks

A student stated that changing the halogenoalkane for the reaction in part a) to 2-iodo-2-methylpropane, the reaction would be quicker. Is the student correct? Explain your answer. 

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10a3 marks

Propan-1-ol can be synthesised from alkene P in the following synthetic route:

       alkene P rightwards arrow with Step space 1 on top halogenoalkane Q rightwards arrow with Step space 2 on top propan-1-ol

i)
State the identity of halogenoalkane Q.

[1]

ii)
Give the reagents and conditions needed for Step 2.

[2]

10b2 marks

Give the name and structure of alkene P.

10c3 marks

Give a reagent that could be used to convert P to Q and outline why this synthesis of propan-1-ol might not be very efficient.

10d4 marks

This question is about alkene P and Step 1.

i)
Give the empirical formula of P.

[1]

ii)
Give the reagents and conditions needed for Step 1.

[2]

iii)
State the type of reaction mechanism.

[1]

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1a4 marks

Benzene, C6H6, typically undergoes electrophilic substitution

i)
State the meaning of the term electrophile.
[1]
ii)
Write an equation for the reaction between benzene and concentrated nitric acid.
[1]
iii)
Identify the electrophile in the reaction and show, by means of an equation, how it is generated.
[2]
1b5 marks

Benzene is a highly unsaturated molecule.

i)
Discuss why benzene undergoes substitution reactions rather than addition reactions.
[3]
ii)
Show, by means of an equation, the reaction of benzene with chlorine and state any necessary conditions.
[2]
1c3 marks

An aromatic organic compound with molecular formula C7H8 reacts with bromine in the presence of UV light to produce a compound with molecular formula C7H7

i)
Name the type of reaction taking place.
[1]
ii)
Deduce the structures of the reactant and product.
[1]
iii)
Give the formula of an additional organic product that could be obtained in the reaction.
[1]
1d3 marks

The same aromatic compound in part (c), C7H8, can be reacted with concentrated nitric acid to produce a multiple substituted product, with molecular formula C7H5N3O6.

i)
Deduce the systematic IUPAC name for this compound. 
[1]
ii)
Draw the structure of C7H5N3O6.
[1] 
iii)
Name a use for the product.
[1]

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2a2 marks

Iron(III) ions can react with cyanide ions to form ferricyanide ion via the following equation

Fe3+ + 6CN- → [Fe(CN)6]3-  

State which of the reactants is behaving as a Lewis base and justify your answer.

           

2b2 marks

State the definition of a Brønsted-Lowry acid and the equation which demonstrates how ethanoic acid, CH3COOH (aq) , behaves as a Brønsted-Lowry acid when reacting with ammonia, NH3 (aq).

2c2 marks

Sketch a graph to indicate the change in pH during a titration of 25.0 cm3 of 0.100 mol dm-3 hydrochloric acid, HCl (aq) , with 0.100 mol of ammonia, NH3 (aq).

q1c_18-1_ib_hl_medium_sq

2d5 marks

The endpoint in a titration can be identified using a suitable indicator.

i)
Using Section 18 of the Data Booklet, select a suitable indicator that could be used for this titration and justify your choice.
[2]
ii)
Describe how an acidic indicator works.

[3]

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3a3 marks

The results of a series of experiments performed to determine the order of reaction between an isomer of bromobutane, C4H9Br, and aqueous sodium hydroxide are shown.

Experiment

[C4H9Br]

/ mol dm-3

[OH-]

/ mol dm-3

Initial rate

/ mol dm-3 s-1

1

0.10

0.20

2.90 x 10-4

2

0.15

0.20

4.35 x 10-4

3

0.30

0.40

8.70 x 10-4

                        

Determine, explaining your method, the rate expression for the reaction of the bromobutane isomer with aqueous sodium hydroxide.

3b2 marks

Use your answer to (a) to deduce the type of mechanism for the reaction of the bromobutane isomer with aqueous sodium hydroxide, explain your reasoning.

3c4 marks

Sketch the mechanism, using curly arrows to represent the movement of electrons.

3d1 mark

State, giving your reason, the role of the hydroxide ion in the nucleophilic substitution.

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4a1 mark

The starting materials for many products are alkenes such as propene.

State the type of reaction that occurs when propene is converted into chloropropane.

4b1 mark

Two possible isomeric products can be formed in the conversion of propene to chloropropane. 

State the type of isomerism that is exhibited by these chloropropane products.

4c4 marks

Explain the mechanism of the reaction that forms the major product when propene is converted to chloropropane using curly arrows to represent the movement of electron pairs.

4d1 mark

Outline why the major product is formed.

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5a3 marks

Kekulé proposed the following structure of benzene.q3a_20-1_ib_hl_medium_sq

Discuss the physical and chemical evidence to suggest that the Kekulé structure of benzene is incorrect.

5b2 marks

State the reagents and the name of the mechanism used to convert benzene into nitrobenzene.

5c1 mark

Using your answer to (b), formulate the equation for the formation of the nitronium ion.

5d4 marks

Using curly arrows to indicate the movement of electron pairs, explain the mechanism for the nitration of benzene.

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6a1 mark

State a halogenoalkane reactant that can be used to slowly produce butan-1-ol by reacting with aqueous sodium hydroxide.

6b1 mark

Butan-1-ol can also be formed by the catalytic reduction of butanal. State the reagents for this reduction to occur

6c1 mark

State the reagent required to reduce butanoic acid to butan-1-ol. 

6d1 mark

Using your answer to (c), write the equation for the reduction reaction of butanoic acid.

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7a2 marks

1-bromobutane and 2-bromo-2-methylpropane are isomers. State the type of structural isomerism that they exhibit, explaining your reasoning.

7b4 marks

Using curly arrows to indicate the movement of electron pairs, explain the mechanism for the reaction of 1-bromobutane with aqueous sodium hydroxide.

7c3 marks

Consider the reactions of 1-bromobutane and 2-bromo-2-methylpropane with aqueous sodium hydroxide.

Compare and contrast the mechanisms for these reactions.

7d1 mark

Explain why an inversion of configuration occurs during the reaction described in (c).

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1a2 marks

The following scheme shows reactions of Compound A. 

10-2-ib-sl-sq-hard-q4a-reaction-scheme
i)
Deduce the structural formula of compound A.
[1]
ii)
Apply IUPAC rules to name compound B.
[1]
1b2 marks

Reaction 1 forms an alcohol when reacted with concentrated sulfuric acid, H2SOand steam. 

i)
State the conditions required for this reaction.
[1]

ii)
Deduce the structure of the intermediate in this reaction. 
[1]
1c3 marks

Butan-2-ol can also be directly formed from a halogenoalkane. 

i)
State the name of of the type of reaction occurring in this conversation.
[2]
ii)
State the conditions for this reaction. 
[1]
1d1 mark

Identify the structure of the repeating unit of poly(but-2-ene).

1e1 mark

Compound A reacts with hydrogen bromide to form compound C. A student suggested a possible formula of compound C is CH2(Br)CH2CH2CH3.

State whether the student is correct and justify your answer. 

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2a2 marks

A student investigated two reactions of phenylethene, C6H5CHCH2. First she reacted phenylethene with excess bromine at room temperature to form Compound A. She then added aluminium bromide, AlBrto the reaction mixture to form Compound B.

Draw the structure of Compound A and identify one the isomers of C8H7Br3 formed in the second reaction. 

10-2-ib-sl-sq-hard-q5a-reaction-pathway

2b2 marks

2,4,6-trinitrotoluene (TNT) can be manufactured from benzene as shown below.

Chem OCR A2 6.1 Q5c

5.00 g of benzene was used in step 1. Use section 6 of the data booklet to determine the theoretical yield for step 1.

2c3 marks

Step 2 involves the formation of a nitronium ion for the nitration of Toluene, as shown in the following equation:

HNO3 + 2H2SO4 → NO2+ + 2HSO4- + H3O+

i)
Explain the role of the nitric acid in the formation of the electrophile.
[2]
ii)
Explain the role of the sulphuric acid in the overall nitration reaction.
[1]
2d1 mark

Explain why the product of step 2 is most likely to have the nitro group bonded to the second or fourth carbon atom. 

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3a2 marks

Chromium (III) picolinate, shown below, is often used in tablets as a nutritional supplement for chromium.

chromium-piccolate

i)
Draw the structure of the ligand in chromium(III) picolinate.
[1]
ii)
State the coordination number of chromium in chromium(III) picolinate.
[1]
3b3 marks

A complex of cobalt has the following composition by mass:

Co, 21.98%; N, 31.35%; H, 6.81%; Cl, 39.86%

i)
Calculate the empirical formula of this complex.
[2]

ii)
The formula of this cobalt complex can be expressed in the form [Co(L)m]x+(Cl)n.
Suggest the chemical formula of [Co(L)m]x+.

[1]

3c2 marks

Ni(ClO4)2 reacts with water to form the complex ion [Ni(H2O)6][ClO4]2.

Explain this reaction in terms of an acid-base theory.

3d2 marks

Nickel(II) forms a complex ion with water, [Ni(H2O)6]2+

i)
Outline how the bond is formed between Ni2+ and H2O during the formation of the complex.

[1]

ii)        State the geometry of the complex formed.

[1]

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4a2 marks

Ammonia reacts with boron trifluoride to form an adduct, a molecule made from the combination of two others.

NH3 + BF3 →  NH3BF3

Identify the Lewis acid and base and the type of bond formed between a Lewis acid and base.

4b2 marks

Explain the role of water, in terms of Lewis acid-base theory, in the following equations:

NH3 (aq) + H2O (l) rightwards harpoon over leftwards harpoon  NH4+ (aq) + OH- (aq)
HCl (aq) + H2O (l) →  H3O+ (aq) + Cl- (aq)
4c4 marks

'All Brønsted-Lowry acids are Lewis acids but not all Lewis acids are Brønsted Lowry acids.'

Evaluate whether this statement is true, giving an appropriate example.

4d1 mark

In the nitration of benzene, identify a species which acts as a Lewis base.

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5a2 marks

Halogen molecules can react with alkenes to produce halogenoalkanes which contain two halogen atoms. Explain why halogen molecules can react with alkenes.

5b3 marks

Outline the mechanism for the reaction between 1-methylcyclohex-1-ene and hydrogen bromide, HBr, to form the major product. 

5c3 marks

Explain why a major product and minor product are produced in the reaction outlined in part b).

5d2 marks

The major product from the reaction of part b) forms an alcohol when reacted with water. Predict the type of mechanism for this reaction and the structure of the alcohol. 

i)
State the type of mechanism that will occur. 
[1]
ii)
Give the structure of the alcohol formed.
[1]

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6a2 marks

C5H11Cl is a chiral molecule.

Draw the three-dimensional shape of each enantiomer of this isomer showing their spatial relationship to each other

6b3 marks

One of these enantiomers undergoes alkaline hydrolysis and approximately 75 % of the product formed shows an inversion of configuration.

Outline the mechanism that causes approximately 100% of the inversion of configuration. 

6c2 marks

Explain why the inversion of configuration is 75%.

6d1 mark

Explain what would happen to the rate of the mechanism in part b) if the concentration of alkali is doubled.

 
6e2 marks

Comment on the rate if ammonia was reacted with C5H11Cl compared to alkaline hydrolysis. 

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7a3 marks

The theoretical molecule cyclohexa-1,3,5-triene reacts differently with bromine than benzene. 

Benzene will react with bromine in the presence of aluminium bromide. Outline the mechanism for this reaction.

7b1 mark

State the name of the mechanism that occurs during the reaction between cyclohexa-1,3,5-triene and bromine. 

7c3 marks

The nitration of benzene is the first important step in the manufacture of dyes and explosives.

i)
Outline the generation of the electrophile for the nitration of benzene by writing an equation. 
[1]

ii)
Indicate in your equation which reactant is acting as a Brønsted Lowry base. 
[1]

iii)
Explain your answer and identify the conjugate acid and base pairs in the reaction.
[1]
7d3 marks

Explain why benzene can only undergo substitution reactions.

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8a2 marks

Benzene and cyclohexene are two hydrocarbons that are able to react with bromine. State the type of reactions in each case.

8b2 marks

Benzene can be converted into nitrobenzene in a one step reaction. State the names of the reagents needed for the reaction and the formula of the electrophile in the reaction.

8c4 marks

Outline the mechanism of the reaction between benzene and the electrophile in part c)

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