Chapter 16

• What is the purpose of greasing the joints in a Quickfit apparatus?

  To ensure a tight seal and prevent leaks
• Why is it necessary to have a continuous water flow around the condenser in a distillation setup?

  To keep the water cool for effective distillation
• What is the method to separate immiscible liquids using a separating funnel?

  • Pour the mixture into a separating funnel with distilled water
  • Invert the funnel to mix and equalize pressure
  • Shake until no 'whistle' sound is heard
  • Open the stopper to collect the lower layer in a beaker
  • Use another beaker for the desired organic layer
  • Shake with a drying agent
• Name two drying agents used in organic chemistry.

  Magnesium sulphate and calcium chloride
• How do you use drying agents in organic chemistry?

  • Add drying agent to the organic product
  • If clumps form, add more until they move freely
  • Use gravity filtration to collect the dry product
  • The filtrate is the final product
• What does re-distillation mean?

  Purifying a liquid using multiple distillations
• How can unsaturated hydrocarbons be tested and what are the observations?

  • Use bromine water
  • Add drops to the sample and mix
  • Positive test: bromine water turns colourless
• What reagents are used to test haloalkanes and what are the observations?

  • Reagents: silver nitrate, ethanol, and water
  • Observations:
  • Chloro-: white precipitate
  • Bromo-: cream precipitate
  • Iodo-: yellow precipitate
• What are the three reagents that can be used to test carbonyls?

  • Acidified potassium dichromate
  • Fehling’s solution
  • Tollens’ reagent
• What are the observations when acidified potassium dichromate reacts with ketones and aldehydes?

  • Ketones: no change
  • Aldehydes: turns from orange to green
• What are the observations when Fehling’s solution is reacted with ketones and aldehydes?

  • Ketones: no change
  • Aldehydes: dark red precipitate
• What are the observations when Tollens’ reagent is reacted with ketones and aldehydes?


  • Ketones: no silver mirror
  • Aldehydes: silver mirror
• What reagents can be used to test carboxylic acids and what are the corresponding observations?

  • Universal indicator: pH of weak acid
  • Reactive metal: hydrogen effervescence
  • Metal carbonate: carbon dioxide effervescence
• What is the purpose of distillation in organic chemistry?

  • To separate compounds by their boiling point
  • To isolate desired products from reactions that do not go to completion
  • To remove unwanted chemicals produced during reactions
• What is the common practical application of distillation mentioned in the notes?

  Oxidation of primary and secondary alcohol to aldehydes and ketones
• Describe the distillation process for producing an aldehyde from a primary alcohol.

  1. Mix primary alcohol with acidified potassium dichromate in a flask.
  2. Add anti-bumping granules.
  3. Set up Quickfit apparatus with a still head and condenser.
  4. Grease joints for better sealing.
  5. Use a thermometer to monitor vapors.
  6. Heat the mixture until boiling.
  7. Collect distillate at +/- 2°C of the boiling point.
• Why are anti-bumping granules added during distillation?

  To promote smooth boiling
• What is the purpose of using silicon grease on the joints of the Quickfit apparatus?

  To provide a better seal and ease disassembly
• How does the water jacket in the condenser function during distillation?

  It allows a steady stream of water to cool the condenser
• What type of heating apparatus is recommended for distillation due to safety concerns?

  Electric heating mantle
• What should be done if the temperature rises above +/- 2°C of the boiling point during distillation?

  Stop collecting the distillate
• Why can the aldehyde product be distilled off as soon as it forms?

  Because it has a lower boiling point than the alcohol
• What is the purpose of heating under reflux in organic reactions?

  • To allow reactions to occur fully without losing reactants or products
  • To maintain all chemicals inside the reaction vessel
  • To increase the reaction rate by applying heat
• What is an example of a reaction that can be completed by heating under reflux?

  Production of a carboxylic acid from a primary alcohol
• Describe the heating under reflux process.

  1. Place reaction mixture in a flask.
  2. Add anti-bumping granules.
  3. Set up Quickfit apparatus with a vertically clamped condenser.
  4. Heat the mixture until boiling.
  5. Allow the mixture to cool back to room temperature after heating.
• What is the recommended duration for heating under reflux when preparing ethyl ethanoate?

  About 15 minutes
• What are some health and safety considerations when performing distillation and reflux?

  • Use electric heating mantles instead of Bunsen burners
  • Handle corrosive, irritant, flammable, and toxic liquids carefully
  • Ensure proper ventilation in the laboratory
• What are the methods to purify organic liquids?

  • Use of a separating funnel
  • Use of drying agents
  • Redistillation
• How can you identify the organic layer when using a separating funnel?

  By adding water and observing which layer increases in volume
• What should be done if neutralization occurs before purifying organic liquids?

  Add sodium carbonate solution to the reaction vessel
• What is the procedure for using a separating funnel?

  Transfer contents, invert, release pressure, allow layers to separate, drain layers
• Why is it important to open the stopcock slowly after neutralization in a separating funnel?

  To avoid losing any product
• What factors determine the position of the organic layer in a separating funnel?

  • Density of the organic layer compared to the aqueous layer
  • If denser, it will be the bottom layer; if less dense, it will be the top layer
• What are drying agents used for in organic chemistry?

  To remove traces of water from an organic product
• What is a common drying agent used for hydrocarbons?

  Anhydrous calcium chloride
• How can you tell if there is still water in the organic liquid when using a drying agent?

  If the drying agent clumps together
• What indicates that the organic liquid is dry after using a drying agent?

  It appears clear
• What is the purpose of redistillation in organic chemistry?

  • To remove traces of other liquids from the desired organic liquid
  • To achieve a narrower boiling point range for increased purity
  • To ensure the final product is free from by-products
• Why is a narrower boiling point range important during redistillation?

  It indicates a more pure organic liquid
• What should be done with the distillation apparatus before redistillation?

  Clean and dry it