The aim of this experiment is to produce Aspirin. This is an estrification in which an alcohol reacts with an acid and a small molecule is often eliminated. The reaction takes place under a concentrated acid catalyst which speeds up the chemical reaction.

Authors Avatar


Planning                                                                          Page number

  • Background Information----------------------------------------          3

  • Aim----------------------------------------------------------------          4


  • Plan – (choices of equipment)---------------------------------        5 - 15

  – (risk assessment)

  • Synoptic grid-----------------------------------------------------          16  


  • Preparation of Aspirin------------------------------------------        18 - 19

  • Melting point determination----------------------------------            20

  • Forward titration------------------------------------------------         21 - 24

  • Back titration----------------------------------------------------         25 - 28


  • Calculations-----------------------------------------------------          30 - 35

  • Conclusion------------------------------------------------------           36 - 37


  • Uncertainty associated with measurements---------------             39 - 46

  • Limitations of methods--------------------------------------               47

  • References----------------------------------------------------                49


Background Information

Introduction (1) (2)

Aspirin is member of a family of chemicals called salicylates. Aspirin the pain reliever also known by the chemical name acetylsalicylic acid, it is a simple molecule which was first synthesized by a German Chemist Felix Hoffman in 1893.

Aspirin is made from salicylic acid which was found in the willow tree bark and was used by many native cultures i.e. Americans and Greeks. Salicylic acid was used as a pain reliever and it is extremely bitter tasting and regular use can cause stomach irritation. Due to it causing severe stomach pain it was replaced by Aspirin.

 Aspirin is thought to have antithrombotic benefits. It is thought to work by inhibiting blood platelets. The aspirin blocks platelet enzyme called cyclo-oxygenase. This stops the product ion of an important prothrombotic agent known as thromboxane A2. Thromboxane A2 causes activation of platelets which is an early step in thrombosis.

   Studies have shown that eating half an aspirin tablet a day can reduce the risk of arterial thrombosis (Myocardial infraction, stroke).

Aspirin is the most commonly used drug as a platelet inhibitor in the category and the most cost effective antithrombotic drug.

Aspirin is used in the following conditions:

  • Inhibitor of platelet aggregation
  • Unstable angina
  • Acute myocardial infarction
  • Secondary prevention of myocardial infraction and stroke.

Aspirin is currently the first-choice drug for fever, mild to moderate pain and inflammation due to arthritis or injury like all other drugs Aspirin also has side effects such as:

  • Gastrointestinal bleeding that can over time cause iron deficiency.
  • Gastric ulcers many occur with long term use
  • Nausea, vomiting, abdominal pain
  • Dizziness, hallucinations
  • Seizures
  • Allergic reaction

Complications can be avoided by using the enteric – coated Aspirin which does not dissolve until reaching the intestine.


Aspirin is an anti-inflammatory pain killer, which is use world-wide for pain relief.

The empirical formula of Aspirin is C9H8O4

The structural formula is


The aim of the investigation was to determine the purity of synthesised aspirin, and pure aspirin. The first step was to synthesise aspirin and then compare the purity of this to pure aspirin using qualitative and quantitative method.

Whether a compound is pure or not, its purity can be qualitatively determined by examining its melting point. The smaller the temperature range the purer the compound is. This will be determined by melting point via the capillary tube technique.

To determine the purity of the synthesised aspirin and pure aspirin quantitative methods were used. These methods are back titration and forward titration.

In the forward titration the aspirin will be titrated using a dilute solution of sodium hydroxide from the results the mass of aspirin can be calculated followed by the percent purity of the sample. Using this titration it may be difficult to identify the end point because aspirin is a weak acid and the reaction may take longer to complete. Therefore the other method which will be used is back titration, which recognises the end point more easily, as it is a reaction between a strong acid and a strong base. This method will determine how much HCL is needed to neutralise the unreacted sodium hydroxide. From this the amount of aspirin that reacted with the sodium hydroxide can be determined.

  Overall the aim of this investigation was to:-

  • To make Aspirin
  • To determine the purity of Aspirin prepared by using a number of techniques such as :-
  • Melting point determination
  • Forward titration
  • Back titration

And also to determine the purity of pure aspirin using the above methods, and comparing the results with the prepared aspirin.

Preparation of Aspirin

Introduction (4) (5) (6) (7)

The aim of this experiment is to produce Aspirin. This is an estrification in which an alcohol reacts with an acid and a small molecule is often eliminated. The reaction takes place under a concentrated acid catalyst which speeds up the chemical reaction.

Aspirin (acetyl salicylic acid) can be made by a variety of methods but they all start from 2-hydroxybenzoic acid (salicylic acid). It is prepared by the reaction of salicylic acid with acid anhydride to produce acetylsalicylic acid and acetic acid.

The reaction is known as a nucleophilic addition reaction followed by elimination. The salicylic acid acts as a nucleophile, and the lone pair of electrons on the –OH group attack the carboxyl carbon atoms of acid anhydride. It is followed by elimination because a small product is lost during the process.

When the organic compound is made it may contain by-products, therefore it needs to be purified. This is done by recrystalisation by using hot water to dissolve aspirin. Boiling water is not used because it hydrolyses the aspirin back to salicylic acid. The aspirin is then cooled so that it becomes less soluble and then it is filtered using a Hirsch funnel.  



  • Salicylic acid
  • Ethanoic anhydride
  • Concentrated Sulphuric acid
  • Ethanoic acid (glacial)
  • 100 cm3 conical flask
  • Distilled Water
  • 10 cm3 pipette
  • 100 cm3 beaker
  • Hirsch funnel
  • Water bath containing crushed ice
  • Goggles
  • Laboratory coat
  • Analytical balance ( 4 d.p)

Apparatus Justification

  • Salicylic acid - contains the –OH group, which will react with the acid anhydride to produce acetylsalicylic acid.
  • Ethanoic anhydride- this is the ester that reacts with salicylic acid.
  • Concentrated Sulphuric acid- the enzyme used to speed up the chemical reaction.
  • Ethanoic acid (glacial) - this is used to dilute the crystalline mush.
  • Conical Flask 100 cm3 – This is used to react the salicylic acid with the acid anhydride.  The shape of it makes it less likely that any reactants should spill out.
  • Distilled Water – This is used to wash   equipment. Normal water will not do because of the impurities in it.
  • Pipette 10cm³ – This is used to accurately draw out the correct amount of a substance from a solution.
  • 100cm3 beaker- used to dissolve the aspirin with hot water.
  • Hirsch funnel- a small funnel for vaccum filteration.
  • Water bath containing crushed ice- used to cool the crystals.
  • Goggles – Used to protect the eyes throughout the experiment.
  • Laboratory coat – Used to protect the skin and clothing.
  • Analytical balance- used to way the salicylic acid accurately to 4 decimal places.

Results obtained were recorded in a table format:-


Safety Precautions (9)

Determine the melting point of Aspirin (10)

The purpose of this experiment is to determine the purity of the recrystalised aspirin and compare it with the purity of pure aspirin.

The melting point of a compound is the temperature at which it changes from a solid to a liquid. The purity of a substance can be determined by its melting point. A pure substance has a specific melting point. If the melting point of the same substance is measured and is found to be lower than the standard value, the substance is not pure since impurities lower the melting point of a substance. The degree at which the melting point is low depends on the concentration of the impurities.


  • Melting point apparatus
  • Capillary tubes
  • Thermometer
  • Aspirin
  • Mortar and pestle

Apparatus Justification

  • Melting point apparatus- this is used to heat the aspirin from solid to liquid so that the melting point can be determined.
  • Capillary tubes- a tube used to pack the aspirin into, and this is placed in the melting point apparatus.
  • Thermometer- this is used to measure the temperature.
  • Aspirin - contains the acetylsalicylic acid.
  • Mortar and pestle- used to grind the aspirin into fine powder so that it can be packed into the capillary tube.

Safety Precautions

  • Wear safety goggles
  • Melting point apparatus is hot while it is on. Take care otherwise it could burn you.
  • Capillary tubes break very easily, handle them with care.

Results obtained were recorded in a table format:-



Forward titration (10) (11) (12) (13)


This is a scientific analytical method used to determine the strength of a solution, or the concentration of a substance in solution. It allows you to determine the precise quantity of reactant in the titration flask. A burette is used to deliver the second reactant to the flask.

An acid – base indicator is used to show the endpoint of the reaction. Indicators are compounds that react with acid and alkalis, forming different coloured species when they are in acidic and alkaline conditions.

Join now!

Phenolphthalein indicator was used in the following reaction, because it is a suitable indicator for a titration between a weak acid and a strong alkali.


  • Aspirin
  • 100 cm3 conical flask
  • 95% ethanol
  • Pipette (10 cm3)
  • Sodium hydroxide solution 0.1 mol dm-3
  • Burette
  • Phenolphthalein indicator
  • Analytical balance (4 d.p)
  • Burette
  • Burette Stand
  • Volumetric flask 500 cm3
  • Distilled Water
  • Funnel

  • White Tile

  • Goggles

  • Laboratory coat

Apparatus Justification

  • Aspirin - contains the acetylsalicylic acid, which will react with the sodium hydroxide
  • ...

This is a preview of the whole essay