Emilia Hawkins
Unit 4: Laboratory Techniques and their Application
C: Explore manufacturing techniques and testing methods for an organic solid.
Hazards
Ethanoic anhydride is flammable and corrosive. Phosphoric acid is corrosive. 2-hydrobenzoic acid is
corrosive.
Method:
Stage 1: Make the product under reflux
1. Take about 2 g of 2-hydroxobenzioc acid (salicylic acid). Weigh and record the exact mass in
a round bottom flask.
2. Add 4 cm3 of ethanoic anhydride, followed by a few drops of phosphoric acid. This needs to
be done in a fume cupboard.
3. Clamp your flask, attach the condenser and check the water flow. Make sure the quick fir
apparatus is watertight.
4. Warm and swirl the mixture in an isomantle (electric heater) until all the solid has dissolved.
Heat for a further 10 minutes.
5. Do not excessively boil the mixture. Keep the isomantle (electric heater) on low. The mixture
should not change colour.
Stage 2: Separate the impurities using filtration
6. Allow the mixture to cool before dismantling the condenser.
7. Carefully add 5 cm3 of cold water to your solution.
8. Leave in an ice bath until all the solid has formed. You may need to stir with a glass rod.
9. Filter the product using a Buchner filter and wash with ice cold water. Use double filter
paper and moisten it before filtering.
10. Re crystalise the product from the smallest possible amount of hot water.
11. The product can be left in an overnight oven to dry.
Stage 3: Determine the yield of aspirin
12. Weigh your product.
13. Determine the theoretical yield based on the moles of 2-hydroxybenzoic acid used.
14. Calculate your percentage yield.
Stage 4: Check the purity by TLC and melting point
15. Put a sample amount of the product into a sealed capillary tube and use the melting point
apparatus to determine the melting point.
16. Run a TLC plate of your sample against a sample of pure aspirin.
Melting point
Melting point = 137oC
, Emilia Hawkins
The range at which aspirin melts at is between 135 oC – 136oC. You can test for impurities in the
aspirin sample by observing if all the aspirin melts at the temperature that it should. Salicylic acid
can be used to make aspirin and melts at a temperature of between 138 oC and 140oC. If the aspirin is
fully melted at this temperature then it may mean that the sample is impure and the reaction was
incomplete. The aspirin sample that I tested was fully melted at 137 oC which could mean that my
sample was impure or that the temperature was measured incorrectly. To check if my results are
correct and reliable I could measure the melting point again using the same sample and then take an
average.
Thin layer chromatography
Calculated Rf Values:
Rf = distance travelled by the spot / distance travelled by solvent
Weight of aspirin in small glass beaker: 0.25g
o SA = Sample aspirin
o A = Aspirin
1: Solvent front = 6.2cm
2: Solvent front = 6.3cm
Aspirin
A1 = 5.8cm
A2 = 6.1cm
A1 Rf = 5..2 = 0.935
A2 Rf = 6..3 = 0.968
Sample Aspirin
SA1 = 5.9cm
SA2 = 6.2cm
SA1 Rf = 5..2 = 0.951
SA2 Rf = 6..3 = 0.984
When looking at the differences between the R f values of aspirin and the sample aspirin you can
calculate the purity of the aspirin I produced. The R f values are close together meaning that the
sample of aspirin I produced must be close to pure aspirin. If the sample I produced was
contaminated or the reaction was incomplete, the R f values would have a large difference between
them. Due to the sample aspirin and aspirin having different R f values means that the aspirin I
produced may not have been 100% purified. This could have been due to an error when making it or
an error when measuring the aspirin spots on the chromatography paper.
Unit 4: Laboratory Techniques and their Application
C: Explore manufacturing techniques and testing methods for an organic solid.
Hazards
Ethanoic anhydride is flammable and corrosive. Phosphoric acid is corrosive. 2-hydrobenzoic acid is
corrosive.
Method:
Stage 1: Make the product under reflux
1. Take about 2 g of 2-hydroxobenzioc acid (salicylic acid). Weigh and record the exact mass in
a round bottom flask.
2. Add 4 cm3 of ethanoic anhydride, followed by a few drops of phosphoric acid. This needs to
be done in a fume cupboard.
3. Clamp your flask, attach the condenser and check the water flow. Make sure the quick fir
apparatus is watertight.
4. Warm and swirl the mixture in an isomantle (electric heater) until all the solid has dissolved.
Heat for a further 10 minutes.
5. Do not excessively boil the mixture. Keep the isomantle (electric heater) on low. The mixture
should not change colour.
Stage 2: Separate the impurities using filtration
6. Allow the mixture to cool before dismantling the condenser.
7. Carefully add 5 cm3 of cold water to your solution.
8. Leave in an ice bath until all the solid has formed. You may need to stir with a glass rod.
9. Filter the product using a Buchner filter and wash with ice cold water. Use double filter
paper and moisten it before filtering.
10. Re crystalise the product from the smallest possible amount of hot water.
11. The product can be left in an overnight oven to dry.
Stage 3: Determine the yield of aspirin
12. Weigh your product.
13. Determine the theoretical yield based on the moles of 2-hydroxybenzoic acid used.
14. Calculate your percentage yield.
Stage 4: Check the purity by TLC and melting point
15. Put a sample amount of the product into a sealed capillary tube and use the melting point
apparatus to determine the melting point.
16. Run a TLC plate of your sample against a sample of pure aspirin.
Melting point
Melting point = 137oC
, Emilia Hawkins
The range at which aspirin melts at is between 135 oC – 136oC. You can test for impurities in the
aspirin sample by observing if all the aspirin melts at the temperature that it should. Salicylic acid
can be used to make aspirin and melts at a temperature of between 138 oC and 140oC. If the aspirin is
fully melted at this temperature then it may mean that the sample is impure and the reaction was
incomplete. The aspirin sample that I tested was fully melted at 137 oC which could mean that my
sample was impure or that the temperature was measured incorrectly. To check if my results are
correct and reliable I could measure the melting point again using the same sample and then take an
average.
Thin layer chromatography
Calculated Rf Values:
Rf = distance travelled by the spot / distance travelled by solvent
Weight of aspirin in small glass beaker: 0.25g
o SA = Sample aspirin
o A = Aspirin
1: Solvent front = 6.2cm
2: Solvent front = 6.3cm
Aspirin
A1 = 5.8cm
A2 = 6.1cm
A1 Rf = 5..2 = 0.935
A2 Rf = 6..3 = 0.968
Sample Aspirin
SA1 = 5.9cm
SA2 = 6.2cm
SA1 Rf = 5..2 = 0.951
SA2 Rf = 6..3 = 0.984
When looking at the differences between the R f values of aspirin and the sample aspirin you can
calculate the purity of the aspirin I produced. The R f values are close together meaning that the
sample of aspirin I produced must be close to pure aspirin. If the sample I produced was
contaminated or the reaction was incomplete, the R f values would have a large difference between
them. Due to the sample aspirin and aspirin having different R f values means that the aspirin I
produced may not have been 100% purified. This could have been due to an error when making it or
an error when measuring the aspirin spots on the chromatography paper.
