Practical_1_Aspirin_Titration by xiaopangnv

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									                               Practical 1 – Aspirin Titration


In this experiment you will determine the percentage purity of aspirin in two different
strengths of over the counter aspirin tablets by performing a titration with sodium
hydroxide.
The chemical name for aspirin is acetylsalicylic acid. The fact that it is an acid allows us
to quantify the amount of aspirin in a solution by using an acid-base titration. In this
experiment the base used is sodium hydroxide (NaOH). The chemical structure of aspirin
is shown below:




Preparation


       Make sure that your lab coat is fully fastened at all times.
       Make sure you wear gloves and safety goggles at all times.


Methodology


In all titration experiments careful measurements are essential for accurate results.


   1.        Fill the burette with 0.1M NaOH solution using the funnel provided.
                Fill to the Zero mark.
                Ensure there are no bubbles by tapping the side of the burette.


                                                                                          1
2.    Grind up ONE aspirin tablet to a fine powder using the pestle and mortar.
3.    Place a clean, dry conical flask on a top balance.
         Zero the reading.
         Add all the powder to the conical flask using a spatula and record the
          weight of the powder on the table on page 4.
4.    Measure out accurately 10ml of 95% ethanol and transfer to the conical flask.
      Note: Ethanol is used in this case as aspirin does not easily dissolve in water.
5.    Add 25ml of distilled water to the conical flask.
6.    Add 4 drops of phenolphthalein indicator solution.
7.    Swirl the conical flask carefully until the powder is fully dissolved.
         Swirl for at least 3 minutes.
8.    Titrate carefully with sodium hydroxide.
         Swirl the flask continuously.
         The NaOH solution should be added very slowly.
         The end point is reached at the first instance of the pink colour persisting.
9.    Record the volume of the sodium hydroxide used on the table on page 4.
10.   Repeat this procedure twice for each tablet type.




                                                                                          2
To determine the percentage purity of aspirin in each tablet you will need the
following information:


At room temperature 1 mole of aspirin reacts with 1 mole of sodium hydroxide.


Mass of 1 mole of aspirin = 180.2g


Formula 1:
% Aspirin in tablet          =       Mass of aspirin calculated by titration    X 100
                                     Mass of weighed aspirin tablet


Formula 2:
% Aspirin in tablet          =       Mass of aspirin stated by manufacturer     X 100
(Manufacturer)                       Mass of weighed aspirin tablet




                                                                                        3
Results
Aspirin Type                            A       B

Measurement                         1   2   1   2
Mass of Powder (g)


Volume of NaOH added (ml)
=Y

Moles of NaOH added to flask
(mol) = Y x 0.1

           1000
Moles     of     aspirin    which

reacted with NaOH (mol) = Z
(1:1 reaction so Z is the same as
the number of moles of NaOH
added     to    flask   –   above
calculation).
Mass of aspirin which reacted
with NaOH (g) = Z x Mass of 1
mole of aspirin (180.2g)


% aspirin in tablet calculated
by titration = Formula 1 (on
previous page)


% aspirin in tablet according
to manufacturer = Formula 2
(on previous page)




                                                    4
Questions:


   1.    What was the average percentage of aspirin within each tablet type?




   2.    For each tablet type was the percentage aspirin the same as that stated by
         the manufacturer? Explain why your results may be different.




                                                                                 5
                                        Practical 2


In this experiment you will determine the amount of iron present in an iron tablet by
performing a titration with potassium permanganate.
Iron is used to prevent and treat anaemia.          It is essential for the production of
haemoglobin, which is the pigment that makes red blood cells red. Haemoglobin is very
important as it carries oxygen from the lungs to the rest of the body and also carries the
waste product carbon dioxide back to the lungs.
If someone has an iron deficiency it means that there is not enough oxygen being carried
around the body. This can cause tiredness, breathlessness, palpitations, dizziness and
headache and is known as anaemia.
Iron is found naturally in certain foods, but for some people who do not get enough iron
from their normal diet an iron supplement can be useful. Some conditions can also cause
iron deficiency, such as pregnancy or heavy periods.
Iron supplements can also be known as ferrous sulphate, ferrous fumarate, ferrous
succinate, ferrous gluconate, sodium feredetate or sodium ironedetate. You may notice
the use of one of these names on the packaging of your medicine.


Preparation


      Make sure that your lab coat is fully fastened at all times.
      Make sure you wear gloves and safety goggles at all times.


Methodology
In all titration experiments careful measurements are essential for accurate results.


   1. Place a clean, dry beaker on a top balance.
              Zero the reading.
              Crush THREE iron tablets using a mortar and pestle and add all the
               powder to the beaker and record the weight of the powder on the table
               on page8.


                                                                                        6
2. Add 50ml dilute sulphuric acid to the beaker.
          Carefully stir with a spatula for 3 minutes
3. Using a funnel pour this solution into a 250ml volumetric flask.
          Add a small amount of dilute sulphuric acid to the beaker and swirl.
          Add this to the volumetric flask ensuring that all the powder is transferred
           from the beaker to the volumetric flask.
          Add another 50ml dilute sulphuric acid to the volumetric flask.
4. Add water to make up to the 250ml line (carefully) and shake carefully for 1
   minute.
5. Allow this solution to settle for 10 minutes.
          Complete step 6 during this 10 minutes, then continue onto step 7.
6. Fill the burette with the potassium permanganate solution using the funnel
   provided.
          Fill to the Zero mark (carefully – the dark colour will mask the markings
           on the burette).
          Ensure there are no bubbles by tapping the side of the burette.
7. Accurately transfer 25ml of the solution into a conical flask.
          Take care not to disturb the sediment at the bottom of the flask.
          If the sediment is disturbed allow it to settle before continuing.
8. Titrate carefully with the potassium permanganate.
          Swirl the flask continuously, until there is a permanent pink colour.
          The potassium permanganate solution should be added slowly and the end
           point is reached at the first instance of the pink colour persisting for 10
           seconds.
9. Record the volume of the potassium permanganate used on the table on page 8.
10. Repeat this titration, adding the potassium permanganate drop wise near the end
   point, until 2 concordant results are obtained.




                                                                                     7
To determine the amount of iron in each tablet you will need the following
information:


The ratio in which iron (II) and potassium permanganate react is 5 to 1.


              -     +        2+                                 2+                 3+
      MnO4 + 8H + 5Fe                       =              Mn        + 4H2O + 5Fe


Molecular mass of iron (II) sulphate         =       152




Results


Mass of the iron tablet powder =_________________(g)


                        1st Burette Reading 2ndBurette Reading Titre (ml)
1st attempt


2nd attempt


3rd attempt


4th attempt




Formula 1
Moles of potassium permanganate        =     Volume X Molarity


                                       =     Titre   X     0.005
                                             1000                     =    ___________mol


                                                                                        8
Formula 2
            2+
Moles of Fe                         =   Moles of permanganate X 5
                                                              =_____________mol


Formula 3
                                                   2+
Mass of iron in the 25ml solution   =   Moles of Fe     X Molecular mass
                                                              =______________(g)


Formula 4
Mass of iron in the 250ml flask     =   Mass of iron in 25ml solution X 10
                                                              =______________(g)


Formula 5
% of iron sulphate in the tablet    =   Mass of iron in 250ml flask   X    100
                                        Mass of powder
                                                              =______________%


Formula 6
Mass of iron in each tablet         =   Mass of iron in 250ml flask
                                                   3
                                                              =______________(g)




                                                                                 9
Questions:


   1.    According to the manufacturer each tablet contains 200mg of iron
         sulphate.   Work out the percentage accuracy of your final result
         compared to the manufacturers 200mg.




   2.    List some reasons why your result may differ from the manufacturers.




                                                                                10
                                    Technician’s List
                                 Quantitative Practicals


Apparatus: Each group will have
Practical 1                                        Practical 2
0.1M NaOH (300ml)                                  Potassium permanganate (0.05M)
95% Ethanol (100ml bottle)                         3 Iron tablets
1 Burette & Stand                                  Dilute 2M Sulphuric Acid (200ml)
White Tile                                         1 Burette & Stand
Pipettes (1ml & 10ml)                              White Tile
Pipette filler (green)                             1 Beaker
6 Conical flasks                                   Volumetric Flask (250ml)
Pestle & Mortar                                    Top pan balance
Measuring cylinder (10ml)                          1 spatula
1 Filter funnel                                    1 Filter funnel
Phenolphthalein solution (dropper bottle)          4 Conical flasks
1 Wax pencil                                       Measuring cylinder (25ml)
Top pan balance                                    Pestle & Mortar
1 spatula
3 types of aspirin tablet (labelled A, B & C)




Practical 2
The         students      are      supplied       with         0.05M    Potassium
Permanganate but the bottles should be labelled as 0.005M
Potassium Permanganate.



                                                                                      11

								
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