- I attached a condenser to the top of the flask and heated the contents gently until they boiled. I then refluxed the contents for 15 minutes.
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I allowed the flask to cool and poured the solution slowly into a beaker leaving the anti-bumping granules in the flask. I added 10 drops of methyl orange indicator to the solution. The solution turned from colourless to orange. I then added 20cm3 of 2.0 moldm-3 hydrochloric acid to the solution. The solution turned pink and a precipitate formed immediately. I then filtered the solution under reduced pressure. This left white, needle shaped crystals, which I washed with a minimal amount of distilled water.
- I then placed these carefully into a boiling tube and added a small amount of distilled water. I heated the tube until the crystals disappeared and then placed the boiling tube in a beaker of cold water to cool. I filtered the product again under reduced pressure.
- I placed the crystals on a piece of filter paper and left them to dry in the oven over night.
- I weighed a small pot, then added the crystals to the pot and weighed it again. The pot had a mass of 15.92g and with the crystals had a mass of 16.92g, meaning the crystals had amass of 1.00g.
- I sealed one end of a melting point tube using a Bunsen burner. I put a few crystals into the tiny tube and forced them to the bottom. I then attached this tube to a thermometer and placed them in a small beaker of liquid paraffin. I gently heated the beaker while stirring the paraffin. At the point when the white crystals disappeared I recorded the temperature. My result was 121°C.
Calculations:
1 mole methyl benzoate (C6H5COOCH3) 1 mole benzoic acid (C6H5COOH)
RMM (methyl benzoate) = 136
RMM (benzoic acid) = 122
Density (methyl benzoate) = 1.09gcm-3
2cm3 used: mass = 2 x 1.09 = 2.18g
% Yield = (actual yield / theoretical yield) x 100
Theoretical yield is 100%.
Therefore: theoretical yield = ((2.18 / 136) x 122) g
Actual yield = 1.00g
% Yield = 1.00 / ((2.18 / 136) x 122) = 51.1 % (to 3 s.f.)
Melting point = 121°C
Hazards:
Methyl benzoate: This is a harmful chemical, so it was used in a fume cupboard to prevent inhalation and a pipette was used to extract it to avoid contact with skin.
Ethanol: This is highly flammable so I did not have a Bunsen burner alight while I was measuring it out.
Hydrochloric acid (2.0 moldm-3): This concentration is irritant, so I wore eye protection and a lab coat at all times and handled the solution with extreme care.
Sodium hydroxide (2.0 moldm-3): This concentration is corrosive and reacts violently with water. I, therefore, wore eye protection and a lab coat and did not mix it with water.
Methyl orange: To avoid contact with skin I used a pipette to measure out the methyl orange indicator.
General precautions: I wore a lab coat and goggles at all times.