13.0 Alkenes exam q's

4 (a) Name the homologous series that both C2H4 and C4H8 belong to. Draw a functional group isomer of C4H8 that does not belong to this homologous series.

(a) Alkene

5 (a) In a trial experiment, the student failed to fill the burette correctly so that the gap between the tap and the tip of the burette still contained air. Suggest what effect this would have on the measured volume of bromine water in this trial. Explain your answer.

(a) Measured volume would be greater as level in burette falls as tap is filled before any liquid is delivered

5(b) Other than incorrect use of the burette, suggest a reason for the inconsistency in the student's results.

(b) Drop sizes vary

5 (c) Outline how the student could improve this practical procedure to determine the number of C=C double bonds in a molecule of the oil so that more consistent results are obtained.

(c) Use a larger single volume of oil Dissolve this oil in the organic solvent Transfer to a conical flask and make up to 250 cm3 with more solvent Titrate (25 cm3) samples from the flask

7. Which statement about E-1,2-dichloroethene is correct? A It has the same boiling point as Z-1,2-dichloroethene. B It forms a polymer with the same repeating unit as Z-1,2-dichloroethene. C It has the same IR spectrum as Z-1,2-dichloroethene in the range 400-1500 cm−1. D It has a molecular ion peak different from that of Z-1,2-dichloroethene in its mass spectrum.

B

10. What is the major product of the reaction between but-1-ene and DBr? (D is deuterium and represents 2H)

C

6. Consider the reaction between propene and hydrogen bromide to form the major product. Which species is formed in the mechanism of this reaction?

C

8. Which statement about ethene is correct? A It has no geometric isomers because there is free rotation around the C=C bond. B It reacts with HBr in a nucleophilic addition reaction. C It burns in excess oxygen to produce carbon dioxide and water. D The C=C bond is twice as strong as the C-C bond in ethane.

C

2. There is a repeating unit of polymer. Which of the following molecules would form a polymer containing this repeating unit? A But-1-ene B E-but-2-ene C Z-but-2-ene D Methylpropene

D

3. Alcohols can be prepared from alkenes in various ways. (a) On a laboratory scale, a mixture of propan-1-ol and propan-2-ol can be prepared from propene in two steps. In step 1, propene reacts with cold, concentrated sulfuric acid to form intermediate compounds. In step 2, the intermediate compounds react with water to form the mixture of alcohols. Name and outline the mechanism for the reaction between propene and concentrated sulfuric acid to form the intermediate compound which gives propan-2-ol in step 2. Explain why propan-2-ol is the major product of this preparation.

Electrophilic addition Major product- propan-2-ol formed via most stable carbocation- secondary carbocation which is more stable than primary.

9. But-1-ene reacts with a reagent of the form HY to form a saturated compound. (a) Suggest a reagent of the form HY which reacts with but-1-ene. (b) Name and draw a mechanism for the reaction in part (a) c) Explain how three isomeric products are formed when HY reacts with but-1-ene.

HBr OR HCl OR H2SO4 (c) The major product exists as a pair of enantiomers The third isomer is 1-bromobutane (minor product) Because it is obtained via primary carbocation

3. (b) On an industrial scale ethanol can be produced from ethene by direct hydration or from glucose by fermentation. State the conditions for the direct hydration reaction. State two advantages and two disadvantages of the fermentation method compared with the direct hydration method.

High temperatures and pressures. Silicon dioxide covered with phosphoric acid catalyst advantages of fermentation • Low(er) T and P / lower energy use • Less use of non-renewable fossil fuels/renewable/sustainable (resources) • Low(er) equipment/plant/capital costs Disadvantages- • Slow(er) reaction • Low atom economy • Impure product/extra purification/distillation required • Batch process/labour intensive/difficult to automate • Land used for sugar crops (so not available for food crops)

4. (b) Identify compound X. (c) Name polymer Y. (d) Reaction 1 is an example of thermal cracking and is carried out at a temperature of 750 °C. State one other reaction condition needed.

b) C6H14 c) Polybutene d) High pressures 7000kpa

4. (e) Reaction 2 is exothermic. A typical compromise temperature of 200 °C is used industrially for this reaction. Explain the effect of a change of temperature on both the position of equilibrium and the rate of reaction, and justify why a compromise temperature is used industrially.

e) Le chaterliers principle predicts that equilibrium shifts to oppose any increase in temperature. Exothermic reaction so equilibrium shifts in endothermic direction (left) so a higher temperature will reduce yield. At a higher temperature, there are more high energy molecules so there are more collisions that have E>Ea. So rate of reaction increases. Industrial conditions chosen to achieve cost-effective balance of suitable yield at reasonable rate

1. (b) Name and outline the mechanism for the formation of 3-bromo-3-methylpentane from this reaction of 3-methylpent-2-ene with hydrogen bromide. Explain why more 3-bromo-3-methylpentane is formed in this reaction than 2-bromo-3-methylpentane.

electrophilic addition 3-bromo-3-methylpentane is formed from 3y carbocation 2-bromo-3-methylpentane is formed from 2y carbocation 3y carbocation more stable than 2y