DP Chemistry (first assessment 2025)

Question 22M.2.SL.TZ1.3

Date	May 2022	Marks available	[Maximum mark: 12]	Reference code	22M.2.SL.TZ1.3
Level	SL	Paper	2	Time zone	TZ1
Command term	Apply, Deduce, Draw, Identify, Justify, Outline, State, Suggest	Question number	3	Adapted from	N/A

[Maximum mark: 12]

22M.2.SL.TZ1.3

Magnesium is a reactive metal often found in alloys.

Organomagnesium compounds can react with carbonyl compounds. One overall equation is:

Compound B can also be prepared by reacting an alkene with water.

Iodomethane is used to prepare CH₃Mg $I$ . It can also be converted into methanol:

CH₃ $I$ + HO^– → CH₃OH + $I$ ^–

(a)

Magnesium can be produced by the electrolysis of molten magnesium chloride.

Write the half-equation for the formation of magnesium.

[1]

Markscheme

Mg²⁺ + 2 e^- → Mg ✔

Do not penalize missing charge on electron.

Accept equation with equilibrium arrows.

Examiners report

Unfortunately, only 40% of the students could write this quite straightforward half equation.

(b)

Suggest an experiment that shows that magnesium is more reactive than zinc, giving the observation that would confirm this.

[2]

Markscheme

Alternative 1

put Mg in Zn²⁺(aq) ✔

Zn/«black» layer forms «on surface of Mg» ✔

Award [1 max] for “no reaction when Zn placed in Mg²⁺(aq)”.

Alternative 2

place both metals in acid ✔

bubbles evolve more rapidly from Mg
OR
Mg dissolves faster ✔

Alternative 3

construct a cell with Mg and Zn electrodes ✔

bulb lights up
OR
shows (+) voltage
OR
size/mass of Mg(s) decreases «over time»
OR
size/mass of Zn increases «over time»

Accept “electrons flow from Mg to Zn”.

Accept Mg is negative electrode/anode
OR
Zn is positive electrode/cathode

Accept other correct methods.

Examiners report

Many candidates gained some credit by suggesting voltaic cell or a displacement reaction, but most could not gain the second mark and the reason was often a failure to be able to differentiate between "what occurs" and "what is observed".

(c(i))

State the name of Compound A, applying International Union of Pure and Applied Chemistry (IUPAC) rules.

[1]

Markscheme

propanone ✔

Accept 2-propanone and propan-2-one.

Examiners report

Even though superfluous numbers (2-propanone, propan-2-one) were overlooked, only about half of the students could correctly name this simple molecule.

(c(ii))

Identify the strongest force between the molecules of Compound B.

[1]

Markscheme

hydrogen bonds ✔

Examiners report

Probably just over half the students correctly identified hydrogen bonding, with dipole-dipole being the most common wrong answer, though a significant number identified an intramolecular bond.

(d(i))

Draw the structural formula of the alkene required.

[1]

Markscheme

Examiners report

Few candidates could correctly eliminate water to deduce the identity of the required reactant.

(d(ii))

Deduce the structural formula of the repeating unit of the polymer formed from this alkene.

[1]

Markscheme

Do not penalize missing brackets or n.

Do not award mark if continuation bonds are not shown.

Examiners report

Correct answers to this were very scarce and even when candidates had an incorrect alkene for the previous part, they were unable to score an ECF mark, by deducing the formula of the polymer it would produce.

(e)

Deduce what would be observed when Compound B is warmed with acidified aqueous potassium dichromate (VI).

[1]

Markscheme

no change «in colour/appearance/solution» ✔

Examiners report

Some students deduced that, as it was a tertiary alcohol, there would be no reaction, but almost all were lucky that this was accepted as well as the correct observation - "it would remain orange".

(f(i))

Identify the type of reaction.

[1]

Markscheme

«nucleophilic» substitution
OR
SN2 ✔

Accept “hydrolysis”.

Accept SN1

Examiners report

About a quarter of the students identified this as a substitution reaction, though quite a number then lost the mark by incorrectly stating it was either "free radical" or "electrophilic". A very common wrong answer was "displacement" or "single displacement" and this makes one wonder whether this terminology is being taught instead of substitution

(f(ii))

Outline the requirements for a collision between reactants to yield products.

[2]

Markscheme

energy/E ≥ activation energy/E_a ✔

correct orientation «of reacting particles»
OR
correct geometry «of reacting particles» ✔

Examiners report

Generally well done with the vast majority of students correctly citing "correct orientation" and many only failed to gain the second mark through failing to equate the energy required to the activation energy.

(f(iii))

The polarity of the carbon–halogen bond, C–X, facilitates attack by HO^–.

Outline, giving a reason, how the bond polarity changes going down group 17.

[1]

Markscheme

decreases/less polar AND electronegativity «of the halogen» decreases ✔

Accept “decreases” AND a correct comparison of the electronegativity of two halogens.

Accept “decreases” AND “attraction for valence electrons decreases”.

Examiners report

Another question that was not well answered with probably only a quarter of candidates stating that the polarity would decrease because of decreasing electronegativity down the group.

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.2—Half-equations separate the processes of oxidation and reduction, showing the loss or gain of electrons. Deduce redox half-equations and equations in acidic or neutral solutions.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.3—The relative ease of oxidation and reduction of an element in a group can be predicted from its position in the periodic table. The reactions between metals and aqueous metal ions demonstrate the relative ease of oxidation of different metals. Predict the relative ease of oxidation of metals. Predict the relative ease of reduction of halogens. Interpret data regarding metal and metal ion reactions.

Tools » Tool 1: Experimental techniques

Structure 3. Classification of matter » Structure 3.2—Functional groups: Classification of organic compounds » Structure 3.2.5—“IUPAC nomenclature” refers to a set of rules used by the International Union of Pure and Applied Chemistry to apply systematic names to organic and inorganic compounds. Apply IUPAC nomenclature to saturated or mono-unsaturated compounds that have up to six carbon atoms in the parent chain and contain one type of the following functional groups: halogeno, hydroxyl, carbonyl, carboxyl.

Structure 2. Models of bonding and structure » Structure 2.2—The covalent model » Structure 2.2.8—The nature of the force that exists between molecules is determined by the size and polarity of the molecules. Intermolecular forces include London (dispersion), dipole-induced dipole, dipole–dipole and hydrogen bonding. Deduce the types of intermolecular force present from the structural features of covalent molecules.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.4—Electron-pair sharing reactions » Reactivity 3.4.5—Alkenes are susceptible to electrophilic attack because of the high electron density of the carbon–carbon double bond. These reactions lead to electrophilic addition. Deduce equations for the reactions of alkenes with water, halogens, and hydrogen halides.

Structure 2. Models of bonding and structure » Structure 2.4—From models to materials » Structure 2.4.5—Addition polymers form by the breaking of a double bond in each monomer. Represent the repeating unit of an addition polymer from given monomer structures.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.9—Functional groups in organic compounds may undergo oxidation. Deduce equations to show changes in the functional groups during oxidation of primary and secondary alcohols, including the two-step reaction in the oxidation of primary alcohols.

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.4—Electron-pair sharing reactions » Reactivity 3.4.9—Nucleophilic substitution reactions include the reactions between halogenoalkanes and nucleophiles. Describe and explain the mechanisms of the reactions of primary and tertiary halogenoalkanes with nucleophiles.

Reactivity 2. How much, how fast and how far? » Reactivity 2.2—How fast? The rate of chemical change » Reactivity 2.2.2—Species react as a result of collisions of sufficient energy and proper orientation. Explain the relationship between the kinetic energy of the particles and the temperature in kelvin, and the role of collision geometry.

Structure 3. Classification of matter » Structure 3.1—The periodic table: Classification of elements » Structure 3.1.4—Trends in properties of elements down a group include the increasing metallic character of group 1 elements and decreasing non-metallic character of group 17 elements. Describe and explain the reactions of group 1 metals with water, and of group 17 elements with halide ions.

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