Assessing The Purity Of An Aspirin Sample Biology Essay

The purpose of my probe is to happen the most accurate method of mensurating the pureness of the acetylsalicylic acid through the usage of quantitative analysis methods, including ( 1 ) :

– Acid-base titration

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

– Back titration

– Colorimetry

The most likely drosss present in an aspirin sample are salicylic acid ( un-reacted or as a consequence of hydrolysis ) or ethanoic acid ( or other acerb accelerators ) .

Introductrion to aspirin

What is aspirin?

Aspirin ( 2-ethanoylbenzoic acid or Acetylsalicylic acid ) is likely the most normally used hurting alleviation medical specialty in the universe today and is described as holding analgetic ( pain-killing ) , anti-inflammatory and antipyretic ( fever-reducing ) actions. The Ca salt is now marketed as a soluble solution, and the Na salt as effervescent ( fizzing ) acetylsalicylic acid. 4000 million aspirin tablets are sold in the UK every twelvemonth ( 2 ) . Pure acetylsalicylic acid is a white, crystalline pulverization that is synthesised unnaturally in the reaction:

( 3 )

The find and unreal synthesis of acetylsalicylic acid

The usage of willow bark and leaves for hurting alleviation day of the months abck to 400BC, when Hippocrates recommended it for easing the paing of childbearing. In 1763, Reverend Edmund Stone used a will bark brew to cut down febrilities. The utile chemical in willow bark is salicin, which has no pharmocological consequence by itself. However, when salicin is ingested it is converted through oxidization and hydrolysis to salicylic acid ( or 2-hydroxybenzoic acid ) , and active chemical.

In order to synthetically synthesize salicylic acid in a Labratory a chemical of similar construction can be converted through a simple chemical reaction. The construction of phenol merely differs from salicylic acid by one functional group, a carboxylic acid group. Initially salicyclic acid was marketed by Bayer as a febrility cutting hurting alleviation medcine, nevertheless the bad side effects of utilizing salicylic acid became known non long after.

Felix Hoffman was the first individual to synthesize acetylsalicylic acid ( 2-ethanoylhydroxybenzoic acid or acetylsalicylic acid ) in 1897. He did this by changing the construction of salicylic acid and proving the effectivity of the new compound on his male parent, who suffered from chronic rheumatism. Hoffman successfully prepared a derivitive of salicylic acid that was every bit effectual as effectual as pure salycilic acid but without the unpleasant side effects. The usage of acetylsalicylic acid ( acetylsalicylic acid ) as hurting alleviation began. Aspirin was ab initio sold in sachets but Bayer deicded to pellet the pulverization and acetylsalicylic acid became the first medical specialty to be sold a a tablet. ( 4 )

Acid-base titration

Aim ( s )

i?? To happen out how accurate acid-base titration ( and the undermentioned computations ) are at finding the pureness of a sample of acetylsalicylic acid of a known concentration.

i?? To happen out which index would be best to utilize for this reaction

What is an acid-base titration?

An acid-base titration is an analytical method used to find the concentration of an acid or base in aqueous solutions by neutralizing the acid/base in solution by a basic/acidic reagent. ( 5 )

The concentration of a solution is how much of a chemical substance is dissolved in a given volume of solution. The equation for happening concentration is shown ( left ) .

One solution is bit by bit added to another until the reaction between the two is complete. The point where the reaction ends is called the terminal point of the reaction and depends on the comparative strengths of the acids and bases used. If a weak acid reacts with a weak base, a impersonal solution can be obtained. However, any other combination will switch the end point either in the acidic way or the basic way. The completion of the reaction is normally shown by an index, added to the solution being titrated, through a color alteration.

This method of analysis is appropriate for happening the concentration of acetylsalicylic acid because it is a weak acid and therefore can be neutralized utilizing a base. In my experiment a known concentration of a strong base, sodium hydrated oxide of concentration 0.1moldm-3, is used. The reaction that takes topographic point between the acetylsalicylic acid and the Na hydrated oxide can be used to find the concentration of acetylsalicylic acid in the sample, through the usage of a simple computation with the assistance of the undermentioned reaction equation:

Acetylsalicylic Acid ( Aspirin ) + Sodium Hydroxide? Sodium Acetylsalicylate + Water

( C9H8O4 ) ( NaOH ) ( C9H7O4Na ) ( H2O )

( 3 )

Hazard appraisal

Name of substance Quantity and/or concentration Risk Potential jeopardies Safety safeguards taken

Sodium hydrated oxide ( NaOH )

( 7 ) 0.1moldm-3 Exothermic reaction with water-could eject hot solution.

Could be splashed into the eyes, onto the tegument or apparels. Caustic

Irritant Labratory coat

Labratory spectacless

Acetylsalicylic acid ( acetylsalicylic acid )

( 7 ) Small sums at one time-one tablet. Accretion on fingers or pulverization inhaled. Harmful, particularly if swallowed pure.

Annoying to eyes, respiratory system and tegument. Labratory coat

Labratory spectacless

Phenolphthalein index

( 7 )

Small sums at one clip, ne’er coming into contact with tegument. Can stain clamber on contact. Irritant to eyes and respiratory system Labratory spectacless

Labratory coat

Ethyl alcohol

( 7 ) Small volumes at one clip, ne’er coming into contact with tegument. Vapour will readily catch fire at temperatures above 13oC. Methanol is toxic by inspiration, if swallowed and by skin soaking up so spills to be cleaned up rapidly. Highly flammable

Contains methanol-toxic No naked fires

Labratory coat

Labratory spectacless

Baseball gloves ( if in high concentration )

Preliminary work

Choosing an index

An acid-base index is a compound that changes colour depending on the pH of the solution it is placed in. There are many different acid-base indexs avaiLabratoryle and taking which is appropriate for the reaction you are transporting out depends on a figure of different things, such as:

i?? The comparative strength of the acid and base used

This affects the place of equilibrium harmonizing to Le Chatiliers rule, which states that when a alteration is made to a system in equilibrium, the place of equilibrium will travel in such a manner to understate the effects of the alteration. This is relevent to the equilibrium nowadays in the index and the manner in which a coloring material alteration is brought approximately.

i?? The equivilance point of the reaction

This is the point at which the figure of moles of H+ ions is equal to the figure of moles of OH- ions in a solution. In an acid-base titration this equivilance point will merely be impersonal if a strong acid and strong base are reacted together. However, in the acid-base titration of acetylsalicylic acid and Na hydrated oxide, there is a weak acid and strong base reacting. This shifts the place of equilibrium to the basic side of the equation because the solution contains an acetylsalicylic acid salt which is basic. This means that the equivileance point will be above pH 7.0.

i?? The pH scope on the index

Each index is capable of covering a specifc pH scope. This means that depending on the comparative strength of the acid and base used and the equivilance point of the reaction an index can be chosen which covers the needed pH scope. In the instance of acetylsalicylic acid and Na hydrated oxide, the equivilance point is above 7.0 and the indexs phenolphthalein and bromothymol blue are both active above this pH. Phenolphthalein, for illustration, has two signifiers. In acidic conditions, it is in the acerb signifier, which is colourless. In basic conditions, a H+ ion is removed from each phenolphthalein molecule, change overing it to its base signifier, which is pink. ( 9 )

i?? The easiness of sensing of the coloring material alteration

For both phenolphthalein and bromothymol blue there is an easy noticeable color alteration:

Indicator Low pH High pH

Bromothymol blue xanthous Blue

Phenolphthalein Colourless Pink

Chemicals and Equipment

Aspirin of known concentration ( tablets )

Ethanol ( 95 % )

Sodium hydroxide solution ( 0.1moldm-3 )

Phenolphthalein index

Pestle and howitzer

3 ten Specimen bottle

2 ten 250cm3 beaker

Access to electronic balance

3 ten 100cm3 conelike flask

10cm3 mensurating cylinder

Burette ( clinch and base )

White tile

Glass funnel

Droping pipette

Diagram

Method

1. Crunch up one acetylsalicylic acid tablet utilizing a stamp and howitzer.

2. Transfer as much of the pulverization as possible to a specimen bottle, utilizing a spatula. Weigh the specimen bottle to an truth of 0.01g and enter the mass.

3. Using a measurement cylinder topographic point 10cm3 of 95 % ethyl alcohol into a 100cm3 conelike flask. Add 5 beads of chosen index.

4. Transfer as much of the aspirin pulverization as possible from the specimen bottle to the conelike flask. Re-weigh the specimen bottle and record the mass.

5. Twirl the conelike flask until all the acetylsalicylic acid pulverization has dissolved. Make non allow any of the solution splash out of the flask.

6. Titrate the solution in the flask with 0.1moldm-3 NaOH solution from a burette record the volume needed to bring forth the first touch of pale pink coloring material in the index. This measures the terminal point of the titration.

7. Repeat the process until a lower limit of three consequences within 0.01cm-3 is found. Find the mean titer.

Final work

Chemicals and Equipment

Aspirin sample of known concentration ( tablet signifier )

Sodium hydrated oxide ( 0.1moldm-3 )

Ethanol ( 95 % )

Phenolphthalein index

Bromothymol bluish index

250cm3 volumetric flask

2 ten 250cm3 beaker

6 ten 250cm3 conelike flask

100cm3 mensurating cylinder

Specimens bottle

Volumetric pipette ( and safety filler )

Burette ( clinch and base )

Volumetric flask spile

Distilled H2O

Access to an electronic balance

Glass funnel

Droping pipettes

White tile

Pestle and howitzer

Diagram

Making the aspirin solution

1. Using pestle and mortar crush one acetylsalicylic acid tablet and reassign as much of the pulverization as possible to the specimen bottle. Weigh specimen bottle and record mass.

2. Transfer as much of the pulverization as possible from the specimen bottle to a 250cm3 beaker. Reweigh specimen bottle and record mass. Find the mass of aspirin pulverization used ( transferred to beaker )

3. Repeat steps 1 and 2 until the pulverization of 10 aspirin tablets has been added to the beaker. Find the entire mass of aspirin pulverization used.

4. Add 100cm3 ethyl alcohol to the beaker incorporating the acetylsalicylic acid, utilizing a 100cm3 measurement cylinder ( mensurating cylinder is accurate plenty for this because the solution does non hold to be precisely 50 % ethyl alcohol, 50 % distilled H2O, but about ) and swirl to fade out the acetylsalicylic acid pulverization. Using a clean measurement cylinder add 100cm3 distilled H2O to the beaker and whirl. Add another 25cm3 ethyl alcohol to the beaker and whirl.

5. Transfer this solution to a 250cm3 volumetric flask, with lavations, utilizing a clean funnel. Make up to the grade with distilled H2O. This should make a dissolved aspirin solution of 50 % ethanol 50 % distilled H2O.

Titration method

1. Rinse the burette with a little sum of 0.1moldm-3 NaOH solution. Fill the burette with the 0.1moldm-3 NaOH, overfill somewhat so that some solution can run into a waste beaker make fulling the burette tip. Take the initial burette reading to the nearest 0.05cm3 and record this in a tabular array.

2. Rinse a 25cm3 volumetric pipette with a little sum of your aspirin sample solution and run out into a waste beaker. Fill the volumetric pipette up to the grade, guaranting that the underside of the semilunar cartilage rests precisely on the grade.

3. Carefully run the aspirin solution sample into a clean 250m3 conelike flask. Once the pipette is empty, touch the tip against the interior of the conelike flask. This ensures that the last bead is transferred from the pipette to the conelike flask. The pipette has delivered precisely 25cm3 of the aspirin solution.

4. Add five beads of index ( phenolphthalein or Bromothymol bluish index i?? dependant on consequences from preliminary work ) , and whirl to blend.

5. Slowly run the NaOH from the burette into the conelike flask twirling invariably and looking for the first intimation of color alteration given by the index. This first titration is called a unsmooth titration so it does non count if the terminal point is over shooting. The intent of the unsmooth titration is to give an indicant of the sum of NaOH. Record the concluding burette reading and happen the volume of NaOH used ( the titer ) .

6. If necessary, replenish the burette and record the initial burette reading. It is best to get down on a whole figure.

7. Using the volumetric pipette transportation 25cm3 of the aspirin solution to a clean conelike flask. Add the same sum of index as the first clip, 5 beads.

8. Run the NaOH easy into the conelike flask, twirling invariably, until you are within 5cm3 of the unsmooth titer. Then add 0.5cm3 of NaOH to the conelike flask, twirling after every add-on until within 1cm3 of the unsmooth titer.

9. Add the NaOH to the conelike flask bead by bead, twirling after every add-on, until a lasting alteration of coloring material is shown by the index. The coloring material should stay for 30s, if it does non go on to add NaOH to the conelike flask until this occurs.

10. Record the terminal burette reading and cipher the titer. Repeat steps 6-9 until a lower limit of 3 consequences within 0.10cm3 of each other is obtained. Find the mean titer and record.

Back-titration

Purpose

The purpose of this experiment is to find the per centum of acetylsalicylic acid in an aspirin tablet. The consequence will let me to cipher the sum of aspirin nowadays in each tablet and compare this to the sum of acetylsalicylic acid stated on the box. In finishing this analysis utilizing a back titration method I will be able to compare the truth of back titration against acid-base titration and colorimetric analysis.

What is a back titration?

Back titratioin undergoes a similar method to a forward titration, the difference is in that it is non carried out with the solution whose concentration is required to be known ( the analyte ) but with extra volume of reactant which has been left over after the completion of a reaction with the analyte.

When ingested, aspirin base on ballss unchanged through the acidic conditions of the tummy but is hydrolysed in the alkalic juices of the bowels. This hydrolysis is mimacked in the labratory by hydrolyzing acetylsalicylic acid with NaOH ( 1.0 moldm-3 ) and the equation for this reaction is shown below:

CH3COOC6H4 + NaOH? CH3COONa + HOC6H4COONa + H2O

The fresh Na hydrated oxide which ramains after the hydrolysis can be titrated against a standard acid, in this experiment HCl ( 0.1moldm-3 ) is used. The sum of base required for the hydrolysis can now be calculated from the above equation, the figure of moles of acetyl-salicylic acid which have been hydrolysed can be found.

Hazard appraisal

Risk appraisal available on page 3 for most chemicals used in this experiment. Those that are non listed in the old hazard appraisal can be found below:

Chemical Quantity and/or concentration Risk Possible jeopardies Safety safeguards

Hydrochloric acid 1.0moldm-3

Small sums, normally less than 50cm3 used at one clip.

Could be splashed into the eyes, onto the tegument or apparels.

Vapors could be inhaled if left exposed. Irritant

Highly annoying to respiratory system Baseball gloves

Labratory coat

Labratory spectacless

Hydrochloric acid 0.1 moldm-3

Small volumes used with volumetric pipettes. No more than 50cm3 at one clip. Could be splashed into the eyes, onto the tegument or apparels.

Vapors could be inhaled if left exposed. Irritant

Highly annoying to respiratory system Labratory coat

Labratory spectacless

Sodium hydrated oxide

( NaOH ) 0.1moldm-3

Small sums, normally less than 50cm3 used at one clip.

Exothermic reaction with water-could eject hot solution.

Could be splashed into the eyes, onto the tegument or apparels. Caustic

irritant Labratory coat

Labratory spectacless

Baseball gloves ( if in high concentration )

Chemicals and Equipment

Aspirin of a known concentration ( aspirin tablets )

NaOH ( 1.0moldm-3 )

HCl ( 0.1moldm-3 )

HCl ( 0.05moldm-3 )

Phenolphthalein index

Anti-bumping granules

Volumetric pipette ( and pipette filler )

Burette ( clinch and base )

2 ten 250cm3 beaker

12 ten 250cm3 conelike flask

Distilled H2O

Funnels

White tile

100cm3 Pear shaped flask

Capacitor

Bunsen burner

Tripod

Gauze

Heat immune bench mat

Clamp base and clinch

Entree to running H2O

Spatula

Access to an electronic balance

Making hydrolysed aspirin solution

1. Using pestle and mortar crush one acetylsalicylic acid tablet and reassign as much of the pulverization as possible to the specimen bottle. Weigh specimen bottle and record mass.

2. Transfer as much of the pulverization as possible from the specimen bottle to a 100cm3 pear shaped flask. Reweigh specimen bottle and record mass. Find the mass of aspirin pulverization used ( i.e. sum transferred to beaker ) .

3. Repeat steps 1 and 2 until a entire mass of between 1.3 -1.7g has been added to the pear shaped flask.

4. Add 25cm3 ethyl alcohol to the pear-shaped flask, utilizing a 25cm3 volumetric pipette and whirl to fade out the acetylsalicylic acid pulverization. Using a clean 25cm3 volumetric pipette add 25cm3 1.0 NaOH to the pear shaped flask and whirl. Finally add 25cm3 distilled H2O to the pear shaped flask utilizing a 25cm3 measurement cylinder.

5. Add a spatula of anti-bumping granules. ( Do non stopple the flask )

Hydrolysis of the aspirin solution

Diagram

Method

1. Put up a Bunsen burner with tripod and gauze.

2. Attach a capacitor vertically to a clinch base, so that it i??hangsi?? over the gauze and straight above the Bunsen burner.

3. Connect the capacitor to a cold H2O supply with the H2O come ining at the underside and running out into a sink from the top.

4. Attach the pear-shaped flask to the underside of the capacitor in such a manner that the underside merely rests on the gauze.

5. Using the Bunsen burner ( on a blue-flame ) heat the reactants so that they boil gently. The distilling vapor should ideally make no more than half manner up the capacitor and the vapor should drip back into the pear-shaped flask no faster than 1 bead per second.

6. After 10-15 proceedingss turn off the Bunsen burner and let the solution to chill. Once cool take the pear-shaped flask from the capacitor and carefully reassign the solution, with lavation, to a 250cm3 volumetric flask taking attention to go forth the anti-bumping granules behind.

7. Make up to the grade with distilled H2O and stopped the flask.

Standardization titration

Diagram

Method

1. Rinse the burette with a little sum of 1.0moldm-3 NaOH solution. Fill the burette with the 1.0moldm-3 NaOH, overfill somewhat so that some solution can run into a waste beaker make fulling the burette tip. Take the initial burette reading to the nearest 0.05cm3 and record this in a tabular array.

2. Rinse a 25cm3 volumetric pipette with a little sum of 1.0moldm-3 HCl solution and run out into a waste beaker. Fill the volumetric pipette up to the grade, guaranting that the underside of the semilunar cartilage rests precisely on the grade.

3. Carefully run the HCl solution sample into a clean 250m3 conelike flask. Once the pipette is empty touch the tip against the interior of the conelike flask, this ensures that the last bead is transferred from the pipette to the conelike flask. Therefore the pipette has delivered precisely 25cm3 of the HCl solution.

4. Add five beads of phenolphthalein index and whirl to blend.

5. Slowly run the NaOH from the burette into the conelike flask twirling invariably and looking for the first intimation of color alteration given ( colourless to tap ) by the index. This first titration is called a unsmooth titration so it does non count if the terminal point is over shooting. The intent of the unsmooth titration is to give an indicant of the sum of NaOH required. Record the concluding burette reading and happen the volume of NaOH used ( the titer ) .

6. If necessary, re-fill the burette and record the initial burette reading. It is best to get down on a whole figure.

7. Using the volumetric pipette transportation 25cm3 of HCl solution to a clean conelike flask. Add the same sum of index as the first clip, 5 beads.

8. Run the NaOH easy into the conelike flask, twirling invariably, until you are within 5cm3 of the unsmooth titer. Then add 0.5cm3 of NaOH to the conelike flask, twirling after every add-on until within 1cm3 of the unsmooth titer.

9. Add the NaOH to the conelike flask bead by bead, twirling after every add-on, until a lasting alteration of coloring material is shown by the index. The coloring material should stay for 30s, if it does non go on to add NaOH to the conelike flask until this occurs.

10. Record the terminal burette reading and cipher the titer. Repeat steps 6-9 until a lower limit of 3 consequences within 0.10cm3 of each other is obtained. Find the mean titer and record.

Hydrolysis of aspirin titration

Diagram

Method

1. Rinse the burette with a little sum of 0.1moldm-3 HCl solution. Fill the burette with the 0.1moldm-3 HCl, overfill somewhat so that some solution can run into a waste beaker make fulling the burette tip. Take the initial burette reading to the nearest 0.05cm3 and record this in a tabular array.

2. Rinse a 25cm3 volumetric pipette with a little sum of your hydrolysed aspirin solution and run out into a waste beaker. Fill the volumetric pipette up to the grade, guaranting that the underside of the semilunar cartilage rests precisely on the grade.

3. Carefully run the hydrolysed aspirin solution sample into a clean 250m3 conelike flask. Once the pipette is empty, touch the tip against the interior of the conelike flask, this ensures that the last bead is transferred from the pipette to the conelike flask. Therefore the pipette has delivered precisely 25cm3 of the hydrolysed aspirin solution.

4. Add five beads of phenolphthalein index, and whirl to blend. The solution should turn a pink coloring material.

5. Slowly run the HCl from the burette into the conelike flask twirling invariably and looking for the first intimation of the index coloring material attenuation. This first titration is called a unsmooth titration so it does non count if the terminal point is over shooting. The intent of the unsmooth titration is to give an indicant of the sum of HCl. Record the concluding burette reading and happen the volume of HCl used ( the titer ) .

6. If necessary, replenish the burette and record the initial burette reading. It is best to get down on a whole figure.

7. Using the volumetric pipette transportation 25cm3 of the aspirin solution to a clean conelike flask. Add the same sum of index as the first clip.

8. Run the HCl easy into the conelike flask, twirling invariably, until you are within 5cm3 of the unsmooth titer. Then add 0.5cm3 of HCl to the conelike flask, twirling after of all time add-on until within 1cm3 of the unsmooth titer.

9. Add the HCl to the conelike flask bead by bead, twirling after every add-on, until a there is a lasting alteration ; tap to colourless shown by the index. The coloring material should non return for 30s, if the coloring material returns within this clip go on to add HCl to the conelike flask until it is colorless.

10. Record the terminal burette reading and cipher the titer. Repeat steps 6-9 until a lower limit of 3 consequences within 0.10cm3 of each other is obtained. Find the mean titer and record.