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Introduction

Contents Planning Page number * Background Information---------------------------------------- 3 * Aim---------------------------------------------------------------- 4 * Plan - (choices of equipment)--------------------------------- 5 - 15 - (risk assessment) * Synoptic grid----------------------------------------------------- 16 Implementing * Preparation of Aspirin------------------------------------------ 18 - 19 * Melting point determination---------------------------------- 20 * Forward titration------------------------------------------------ 21 - 24 * Back titration---------------------------------------------------- 25 - 28 Analysing * Calculations----------------------------------------------------- 30 - 35 * Conclusion------------------------------------------------------ 36 - 37 Evaluating * 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. ...read more.

Middle

Using a pipette 10cm3 of 95% ethanol was added to a 100cm3 conical flask followed by 3 drops of phenolphthalein indicator. Aspirin was then added to the flask (as much as possible) and swirled gently to dissolve it. Care was taken so that no solution splashed out of the flask. (Aspirin is not very soluble in water therefore ethanol is used to help it dissolve) Performing a rough titration A rough titration was carried in order to distinguish an approximate endpoint In order to perform a rough titration a note of the burette reading was recorded to the nearest 0.05cm3. The conical flask was placed on a white tile under the burette (white tile was used to view the end point clearly) Then from the burette the 0.1 mol dm-3 sodium hydroxide solution was added 1cm3 at a time, until there was a colour change from colourless to the first tinge of pale pink. This indicated the end point of the reaction. A note of the new burette reading was then recorded. To work out the volume of the solution added a calculation was made whereby the initial reading was subtracted from this end point value. The value calculated was the titre. The first titre was only a guide; therefore it was not included when the average value was calculated. Performing an accurate titration In order to perform an accurate titration, the whole titration method was carried out again. As the rough end point was approached, the 0.1 mol dm-3 sodium hydroxide solution was added a drop at a time and the flask was shaken. Each drop was added until one drop caused the colour to change. The titration was repeated to get concordant results within 0.1cm3 of each other. Results obtained were recorded in a table format. The whole experiment was repeated again, but this time using pure aspirin. Results Re-crystalised aspirin Volume cm3 Accurate 1 Accurate 2 Accurate 3 Final 16.10 cm3 16.15 cm3 16.05 cm3 Start 0.00cm3 0.00cm3 0.00cm3 NaOH used ...read more.

Conclusion

The solution was mixed thoroughly to make it homogenous. - The burette was washed with distilled water first to clean it and then washed with the acid solution. The burette was washed with the acid to get rid of any water present in the burette and any air bubbles. If water was present in the burette it would make the acid weaker and therefore more acid is needed to neutralise the sodium hydroxide. If air bubbles were present it would affect the final reading of the burette. - The pipette was firstly washed with distilled water to clean it. It was then washed with the sodium hydroxide to get rid of any water that may be present in the pipette. If water was present in the pipette it would have made the sodium hydroxide solution more dilute and therefore more acid would have been needed to neutralise it. - The conical flask was washed thoroughly with distilled water before each titration to get rid of any previous solution present. - A rough titration was carried out to give an approximate value of acid added to the flask to reach the endpoint. The titrations were repeated to obtain two or three concordant results and then an average was calculated. - To avoid overshooting of the endpoint, acid solution was added from the burette drop by drop. The conical flask was swirled to mix the solutions thoroughly when the acid was being added. Care was taken when doing so, so that no liquid was lost through splashing. - Three drops of indicator were added for each titration to make it a fair investigation, because different amounts of indicator give different endpoints. Other experiments could be carried out such as colorimetry, thin layer chromatography and Iron (III) chloride test. Acknowledgements Many thanks to my project supervisors Dr Knutton and Mr Gallagher at the Huddersfield Technical College for supporting me throughout my project. I would also like to thank Sheila our Technician at the Huddersfield Technical College for preparing all the apparatus, chemical and solutions for my project. ...read more.

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