A Store Of Old Aspirin Tablets Biology Essay

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A doctor has came across a store of old aspirin tablets and wants to know if they have the correct amount of the active ingredient so that he can use them, or donate them for use by charity organisations.

Aspirin is an anti inflammatory drug that is also used as a fever reducer. If it often used for mild irritation or pain, giving quick relief to head aches, colds and flu.

Using an acid/base titration is a straightforward way of determining how much acetyl salicylic acid they contain by adding a solution to neutralize the acid.

2 hydroxybenzoic acid now called salicylic acid is a plant

hormone, which can also be used in cosmetics as a preventer of acne.

Aspirin was first discovered in ancient Greece where willow tree extracts were made into a drink to treat labour pains. The different strengths of aspirin depend on the amount of acetyl salicylic acid they have in them. It has also been tested as it is thought that aspirin can decrease the chances of people getting heart attack and strokes etc this is because it reduces the production of the prostaglandin thromboxane which is involved in clotting blood.

Nowadays we don't get aspirin from willow trees but make it artificially by the synthesis of acetylic acid. Aspirin has been synthesised from the reaction

Salicylic acid + acetic  aspirin + acetic acid

Over time, Aspirin can "go off" by reacting with moisture in the air and revert back to salicylic acid, this process is called hydrolysis.

The purity of aspirin can be seen by doing a acid/base titration.

The properties of the compounds that may be involved in my investigation are;

Acetic Acid


Salicylic acid

Melting point

16.5 °C







Molar mass

60.05 g mol−1

180.15 g mol−1

138.12 g mol−1


1.08x 10-3

2.72x 10-5

There are one or two solutions that I will be using that require me to think about safety:

Hydrochloric acid risk assessment

Hydrochloric acid is a toxic and corrosive acid, there for it should not come in contact with skin or eyes. Therefore it is best to handle it with neoprene gloves, safety glasses and good ventilation as the fumes can be harmful. If it does get into a persons eye then it must be flushed immediately with water and then medical help will be needed. And if it is swallowed lots of water should be drunk and then medical is needed. And if it comes in contact with skin it should be washed off immediately.

Sodium hydroxide risk assessment

Is a harmful and corrosive alkali, it is a damaging substance that can cause physical damage, if it gets on the skin it should be washed immediately and if it gets on your clothes these should be removed immediately. Therefore you should always wear safety glasses when handling sodium hydroxide, if it has been swallowed then you should not try to get the victim to vomit.

1st Experiment

Weighing boat- 25.55g

Aspirin- 0.62

Ethanol- 10ml

Distilled water- 25ml

3 drops of Phenolphthalein

2.7 ml to turn pink

2nd Experiment

Weighing boat- 25.55g

Aspirin- 0.62

Ethanol- 10ml

Distilled water- 25ml

3 drops of Phenolphthalein

6.32 ml to turn pink

3rd Experiment

Weighing boat- 25.55g

Aspirin- 0.62

Ethanol- 10ml

Distilled water- 25ml

3 drops of Phenolphthalein

9.1 ml to turn pink

I am going to carry out an experiment to test this aspirin. I am going to do this by setting up a titration and making a standard solution of aspirin and titrating it until I see a colour change which will determine how much active ingredient is in the aspirin (acetyl salicylic acid).

My experiment

I ground a aspirin tablet using a pestle and mortar, making it into a powder. I then weighed the weighing boat it weighed 25.55g this was the same boat I was going to use all thought the experiments, I then candled it and weighed the ground aspirin, it weighed 0.62g. I then put the aspirin into a conical flask and added 10ml of ethanol and 25ml of distilled water to make a solution. This solution was then mixed until the aspirin dissolved into the solution, however I found that not all of the bits dissolved. I then measured 25ml of the solution using a pipette and then put it into a clean conical flask and then added 3 drops of Phenolphthalein

Into the solution this was to act as a indicator, I filled the pipette with sodium hydroxide this was then to be titrated into the solution of aspirin, I then titrated it until the solution turned pink. I realised I had don't the first experiment wrong when the solution turned pink immediately; this was because I had used a too strong mole of sodium hydroxide. So I repeated the experiment using 0.30g of aspirin, 10ml of ethanol and 25ml of distilled water into a beaker then stirred it until it had dissolved I then added 3 drops of Phenolphthalein.

To make the sodium hydroxide I used 0.20g of sodium hydroxide pellets and 500ml of distilled water and mixed it until it was dissolved I then put the sodium hydroxide solution into a 500ml conical flask with a lid for later use.

I am going to use Phenolphthalein as an indicator because it goes pink if the PH is above 8.5 there for when I titrate the solution I will be able to stop as soon as the solution turns pink.

How I made the standard solution

I made a standard solution because I am going to use it in my titration to see the concentration I need to turn the solution pink. I made my standard solution from 0.2g of sodium hydroxide pellets with 500ml of distilled water, I used this amount of the pellets because I wanted to make 0.1 moles of NaOH (Sodium Hydroxide). After I dissolved the pellets into the solution I put it into a volumetric flask to make sure the solution was exactly 500ml and they have tops on them so if I left it wouldn't evaporate.


1. 0.1 Mdm-3 NaOH

2. Ethyl alcohol C2H5OH

3. Aspirin from the cupboard

4. 150 mL flask

5. Burette

6. Mortar and pestle

7. Phenolphthalein indicator

8. Goggles

9. Pipette

Pure aspirin = 1:1

Main of aspirin = 0.62

= 3.44 x 10-3 moles

0.1m NaOH = 40

.2 = 40 x .2 = 8g in 1 dm3

4g in 500 cm3

Main = 4.0g

.1m pure 3.44 x 10-3 = 0.1 x V


3.44 x 10-3 = 1 x 10-2 v 34.4cm3 = V

3.44 x 10-3 x 10-3 = 34.4

1 x 10-2

So in theory I should need 34.4 cm3 of NaOH

But mine are only

6.2 = 18%


Weight of aspirin 6.2

Number of moles of aspirin = 6.2 = 0.0344062


Concentration of aspirin = 0.344062 x 1000 = 0.093mdm-3


Weight if NaOH

1mole of NaOH = 23+16+1 = 40

No of moles of NaOH = 0.005 moles

Concentration = 0.0005 x 1000 = 0.01m NaOH


Results from the 3 titrations:

Titration 1


40 = 0.005

2 x 0.005 = 0.01 moles NaOH

= 0.01 x 2.7


2.7x 10-6 aspirin

2.7x 10-6 x 180.2 (molecular mass of aspirin)= 0.0049g


= 0.007% purity of aspirin

Titration 2


40 = 0.005

2 x 0.005 = 0.01 moles NaOH

0.01 x 6.32

1000 = 6.32x10-5

6.32x10-5 x 180.2 = 0.01



Titration 3


40 = 0.005

2 x 0.005 = 0.01 moles NaOH

0.01 x 9.1

1000 = 9.1 x 10-5

9.1 x10-5 x 180.2 = 0.01




This isn't a very good way of finding out the purity of aspirin because it isn't very accurate and the results were all different and quite far away from each other.