WJEC A Level Chemistry Alkenes Past Paper PDF

WJEC Okay, here are 20 multiple choice questions based on topic 2.5 Hydrocarbons, focusing speci cally on the information about *alkenes* provided in the WJEC A Level Chemistry document, and excluding any questions about alkanes: Questions: 1. What is the general formula for alkenes (with one C=C...

WJEC Okay, here are 20 multiple choice questions based on topic 2.5 Hydrocarbons, focusing speci cally on the information about *alkenes* provided in the WJEC A Level Chemistry document, and excluding any questions about alkanes: Questions: 1. What is the general formula for alkenes (with one C=C bond)? * A) CnH2n+2 * B) CnH2n * C) CnH2n-2 * D) CnHn 2. Which term best describes the bonding in alkenes? * A) Saturated * B) Unsaturated * C) Ionic * D) Metallic 3. The C=C double bond in alkenes is a region of: * A) Low electron density * B) High electron density * C) No electron density * D) Neutral charge 4. What type of species are attracted to the C=C double bond in alkenes? * A) Nucleophiles * B) Electrophiles * C) Free radicals * D) Cations 5. What is the most common type of reaction that alkenes undergo? * A) Electrophilic substitution * B) Nucleophilic substitution * C) Electrophilic addition * D) Free radical substitution 6. How does the solubility of alkenes in water compare to alkanes? fi * A) Alkenes are more soluble * B) Alkenes are less soluble * C) Similar solubility * D) alkenes are highly soluble 7. A pi (π) bond is formed by the overlap of which type of orbitals? * A) s orbitals * B) p orbitals * C) sp hybrid orbitals * D) sp2 hybrid orbitals 8. Which is weaker: a sigma (σ) bond or a pi (π) bond? * A) Sigma (σ) bond * B) Pi (π) bond * C) They are equally strong * D) neither, they are both equally weak 9. What type of stereoisomerism can alkenes exhibit? * A) Optical isomerism * B) E/Z isomerism * C) Chain isomerism * D) Functional group isomerism 10. What prevents free rotation around the C=C double bond in alkenes? * A) The sigma (σ) bond * B) The pi (π) bond * C) Hydrogen bonding * D) Induced dipole-dipole forces 11. What are the two requirements for E/Z isomerism in alkenes? * A) a c=c double bond, with one different groups attached to each carbon atom * B) a c=c single bond, with two different groups attached to each carbon atom * C) a c=c double bond, with two different groups attached to each carbon atom * D) a c=c triple bond, with two different groups attached to each carbon atom 12. In E/Z notation, what does the "E" represent? * A) The priority groups are on the same side of the double bond. * B) The priority groups are on opposite sides of the double bond. * C) The molecule is an enantiomer. * D) The molecule contains a triple bond. 13. What is the rst step in determining E/Z con guration using the Cahn-Ingold-Prelog (CIP) rules? * A) Identify groups of highest molecular mass * B) Identify atoms with highest atomic mass * C) identify groups with lowest atomic number * D) Identify the atoms directly bonded to each C of the C=C with the highest atomic number. 14. What is the colour change when bromine water is added to an alkene? * A) Colourless to orange * B) Orange to colourless * C) Purple to colourless * D) Colourless to purple 15. What is the colour change when potassium manganate(VII) solution is added to an alkene? * A) Colourless to orange * B) Orange to colourless * C) Purple to colourless * D) Colourless to purple 16. In the electrophilic addition of HBr to an alkene, what is the electrophile? * A) Br- * B) HBr * C) H+ * D) the c=c double bond 17. What is the intermediate formed during the electrophilic addition of HBr to an alkene? * A) A carbanion * B) A carbocation * C) A free radical fi fi * D) An alkoxide 18. What is the product of the reaction between ethene and Br2? * A) Bromoethane * B) 1,2-Dibromoethane * C) 1,1-Dibromoethane * D) 2,2- dibromoethene 19. Markovnikov's rule applies to the addition of HX to which type of alkene? * A) Symmetrical alkenes * B) Unsymmetrical alkenes * C) All alkenes * D) Only cyclic alkenes 20. According to Markovnikov's rule, when HBr adds to propene, which carbon atom does the hydrogen atom *more likely* bond to? * A) The carbon atom with fewer hydrogen atoms already attached. * B) The carbon atom with more hydrogen atoms already attached. * C) Both carbon atoms are equally likely. * D) neither carbon atom, the bromine bonds to both. Answers and Explanations: 1. B) CnH2n - This is the general formula for alkenes with one double bond. 2. B) Unsaturated - Alkenes contain a C=C double bond. 3. B) High electron density - The double bond has four electrons. 4. B) Electrophiles - Electrophiles are attracted to negative charge/ electron density. 5. C) Electrophilic addition - This is the characteristic reaction of alkenes. 6. C) Similar solubility - Both are relatively non-polar and insoluble in water. 7. B) p orbitals - p orbitals overlap sideways to form a pi bond. 8. B) Pi (π) bond - Pi bonds are weaker and more easily broken. 9. B) E/Z isomerism - Due to restricted rotation around the C=C bond. 10. B) The pi (π) bond - The pi bond prevents rotation. 11. C) a c=c double bond, with two different groups attached to each carbon atom This is the correct de nition. 12. B) The priority groups are on opposite sides of the double bond. - "E" stands for "entgegen," meaning "opposite." 13. D) Identify the atoms directly bonded to each C of the C=C with the highest atomic number. - This is the rst step in applying CIP rules. 14. B) Orange to colourless - Bromine is decolourised in the reaction. 15. C) Purple to colourless Correct de nition. 16. C) H+ - The partially positive hydrogen atom acts as the electrophile. 17. B) A carbocation - A positively charged carbon intermediate is formed. 18. B) 1,2-Dibromoethane - Both Br atoms add across the double bond. 19. B) Unsymmetrical alkenes - Markovnikov's rule predicts the major product. 20. B) The carbon atom with more hydrogen atoms already attached. - This leads to the more stable carbocation intermediate (secondary in this case). fi fi fi