Organic 1 Section 3 - Unit 15: Alcohols
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Explain what is meant by the term dehydration (1 mark)
• Removal of water
State the type of compound formed by dehydration of alcohols (1 mark)
• Alkenes
Suggest suitable reagent(s) and condition(s) for the dehydration of alcohols (2 marks)
• Concentrated sulphuric acid/concentrated phosphoric acid • High temperatures/150 – 200°C • Catalyst - aluminium oxide
State what must be added to an aqueous solution of glucose so that ethanol is formed (1 mark)
• Yeast
Outline the essential conditions for hydration and fermentation. State the equation for the fermentation reaction. Compare the relative rates and the purity of the product obtained in each case by these two manufacturing processes. (5 marks)
Hydration reaction: - Water Fermentation reaction: - Yeast - C6H12O6 → 2C2H5OH + 2CO2 Comparison of reactions: - The rate of fermentation is slower than hydration - The product of fermentation is less pure than the product of hydration
Ethanoic acid can be formed from bromoethane in two steps. Give reagents and conditions for each step. Include in your answer the name of the mechanism for the first step and an equation for the second step (9 marks)
General Equation: - CH3CH2OH + 2[O] → CH3COOH + H2O (1) CH3CH2Br (1) to CH3CH2OH (1): • NaOH (1) • Aqueous or warm (1) • Nucleophilic substitution (1) CH3CH2OH to CH3COOH (1): • K2Cr2O7 or H2SO4 (1) • Reflux (1)
State the equation and two necessary conditions for a fermentation reaction (3 marks)
• C6H12O6 → 2C2h5OH + 2CO2 • Yeast • 30°C
State the reagent that you would use in the laboratory to oxidise ethanol to ethanoic acid (2 marks)
• Acidified potassium or sodium dichromate - Orange to green
State the meaning of the term carbon-neutral (1 mark)
An activity which has no overall carbon emissions to the atmosphere
State and explain the type of bond between H-C-H bond, its shape (3)
• 109.5° • Tetrahedral • 4 bonding pairs of electrons are repelling
State and explain the type of bond between C-O-H bond, its shape (3)
• 104.5° • Bent Line • 2 bonding pairs and 2 lone pairs of electrons
Explain why alcohols have high boiling points (3)
• They form hydrogen bonds between other alcohol molecules • And this bond is strong • So high amount of energy is needed to overcome it
Partial oxidation of Primary Alcohols (5) • Conditions • Reagents • Colour Change
• Aldehyde produced • K2Cr2O7 • Dilute H2SO4 • Distillation • Orange to green
Full oxidation of Primary Alcohols (5) • Conditions • Reagents • Colour Change
• Carboxylic Acid produced • K2Cr2O7 • Dilute H2SO4 • Heat under reflux • Orange to green
Oxidation of Secondary Alcohols (4) • Conditions • Reagents
• Ketone produced • K2Cr2O7 • Dilute H2SO4 • Heat under reflux
Tollens Reagent (5) • How it works (3) • Colour changes (2)
• Contains silver nitrate in NH3 • So oxidises aldehydes • Not ketones • So in aldehydes a silver mirror forms • No change in ketones • [Ag(NH3)2]+ + e– → Ag + 2NH3
Fehling’s Solution (4)
- Contains blue copper (II) ions (gentle oxidising agent) - Reduced to Cu+ ions (brick red) - Aldehydes - colour change to brick red - Ketones - no visible change
Write a half equation for the overall oxidation of ethanol into ethanoic acid (1 mark)
CH₃CH₂OH + H₂O –> CH₃COOH + 4H+ + 4e-