MAI Haloalkanes and Alcohols
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A student records the following observations: - X, a yellow precipitate forms almost instantly - Y, white precipitate forms after several minutes - Z, cream precipitate forms within 1 minute Explain observed order of reactivity of the three halogenoalkanes, XYZ. Refer to the relevant C-X bonds in your answer (3)
• bond enthalpy decreases as you go down the group from Cl to I • C-I bond is the weakest due to having lowest bond enthalpy and C-Cl bond is strongest due to having highest bond enthalpy • low bond enthalpy means bond breaks more easily which increases rate
Explain the different roles of the 2 ammonia molecules reacting with a haloalkane to form an amine
• One acts as a nucleophile by attacking the electron-deficient carbon • Other acts as a base by accepting a proton
The reaction to form alkene X from bromoalkane Y is an elimination reaction Explain the role of the hydroxide ion in this elimination reaction, describing the key bond-breaking and bond-forming steps (3)
• hydroxide ion acts as a base and attacks a hydrogen • C-H bond breaks, electrons form C=C double bond • C-Br bond breaks, Br ion leaves
tertiary alcohol + hydrochloric acid. After the reaction, the crude organic product is separated from the aqueous layer using a separating funnel. The crude organic product is washed with sodium hydrocarbonate solution. Explain the purpose of this step. (1)
the sodium hydrocarbonate will neutralise any unreacted acid
Explain the purpose of adding anyhdrous calcium chloride to the organic layer and describe the visual change that indicates enough has been added.
• anhydrous calcium chloride acts as a drying agent to remove water from the organic layer • liquid turns from cloudy to clear
Explain in terms of molecular structure, why but-2-ene exhibits E/Z isomerism but but-1-ene does not
• restricted rotation around the C=C double bond • ## in but-2-ene each carbon is attached to two different groups (hydrogen and methyl)
Explain the role of adding the drying agent in purification process and state 2 observations that would be made (3)
• The drying agent is used to remove dissolved water from the ester • The liquid turns from cloudy to clear • The solid drying agent moves freely when the flask is swirled because it is no longer clumped together