Cobalt, rhodium and iridium are metals in the same group of the Periodic Table. （d）Hydrated rhodium（III）chloride， $$$\mathrm{RhCl}_{3} \cdot \mathrm{xH}_{2} \mathrm{O}$$$ ，catalyses the conversion of ethene to but－2－ene． Both stereoisomers of but－2－ene are formed in the reaction．（i）Hydrated rhodium（III）chloride contains $$$20.5 \%$$$ by mass of water of crystallisation． Deduce the integer value of $$$x$$$ in $$$\mathrm{RhCl}_{3} \cdot \mathrm{xH}_{2} \mathrm{O}$$$ ． Show your working． $$$x=$$$ .......................... ［2］（ii）Define stereoisomers． ....................................................................................................................................... . ................................................................................................................................. ［1］（iii）Explain how the conversion of ethene to but－2－ene can be described as an addition reaction． ....................................................................................................................................... . ................................................................................................................................. ［1］（iv）Draw the two stereoisomers of but－2－ene．

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w24_qp_21 Year：2024 Question No：1(d)

Answer:

Knowledge points:

13.2.1.1 homologous series

13.2.1.2 saturated and unsaturated

13.2.1.3 homolytic and heterolytic fission

13.2.1.4 free radical, initiation, propagation, termination (the use of arrows to show movement of single electrons is not required)

13.2.1.5 nucleophile, electrophile, nucleophilic, electrophilic

13.2.1.6 addition, substitution, elimination, hydrolysis, condensation

13.2.1.7 oxidation and reduction (in equations for organic redox reactions, the symbol [O] can be used to represent one atom of oxygen from an oxidising agent and the symbol [H] one atom of hydrogen from a reducing agent)

13.2.2.1 free-radical substitution

13.2.2.2 electrophilic addition

13.2.2.3 nucleophilic substitution

13.2.2.4 nucleophilic addition (in organic reaction mechanisms, the use of curly arrows to represent movement of electron pairs is expected; the arrow should begin at a bond or a lone pair of electrons)

13.4.1 describe structural isomerism and its division into chain, positional and functional group isomerism

13.4.2 describe stereoisomerism and its division into geometrical (cis/trans) and optical isomerism (use of E, Z nomenclature is acceptable but is not required)

13.4.3 describe geometrical (cis/trans) isomerism in alkenes, and explain its origin in terms of restricted rotation due to the presence of π bonds

13.4.4 explain what is meant by a chiral centre and that such a centre gives rise to two optical isomers (enantiomers) (Candidates should appreciate that compounds can contain more than one chiral centre, but knowledge of meso compounds, or nomenclature such as diastereoisomers is not required)

13.4.5 identify chiral centres and geometrical (cis/trans) isomerism in a molecule of given structural formula including cyclic compounds

13.4.6 deduce the possible isomers for an organic molecule of known molecular formula

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