Procedure :
1. 20 Ibuprofen tablets which
were selected randomly are weighted and powdered.
2. A quantity of powder
containing 0.5g Ibuprofen is extracted with 20ml chloroform for 15 minutes and
is filtered through normal filter paper.
3. The residue is washed with 3 x
10ml chloroform and is gently evaporated the combined filtrate just to dryness
in a current air.
4. The residue is dissolved in
100 ml with ethanol (96%) and three drops of phenolphthalein is dropped into the
solution.
5. The solution is titrated with
0.1M sodium hydroxide to end point.
6. The content of ibuprofen is
calculated with each ml of 0.1M sodium hydroxide is equivalent to 0.02063g of C13H18O2.
Result and
Calculation :
Total weight of powder of 20 tablets of Ibuprofen + weighting boat
|
12.486 g
|
Weight of weighting boat
|
3.200 g
|
Weight of powder of Ibuprofen
|
9.286 g
|
1 tablet of
Ibuprofen à
400mg of Ibuprofen
20 tablets
of Ibuprofen à
20 x 400mg = 8000mg = 8g of Ibuprofen
To obtain 0.5g of Ibuprofen
|
8g of Ibuprofen = 9.286g of total weight (Ibuprofen + excipient)
0.5g of Ibuprofen = x g
(0.5g/8g) x 9.286 g = 0.5803 g of powder of Ibuprofen
Therefore, 0.58 g of powder of
Ibuprofen are take out to obtain 0.5 g of Ibuprofen.
|
Volume of NaOH needed to achieve the end point of titration
|
7.60 ml
|
The content of Ibuprofen in solution
|
NaOH + C13H18O2 à
C13H17ONa + H2O
From equation, 1 mol of NaOH = 1 mol of C13H18O2
No. of mole of NaOH = MV = (0.1)(7.6x10-3) = 7.6x10-4
mol
Hence, 7.6x10-4 mol of NaOH =
7.6x10-4 mol mol of C13H18O2
If each ml of NaOH is equivalent to 0.02063g of C13H18O2
,
7.60ml x 0.02063 = 0.1567g of Ibuprofen
Therefore, The content of
Ibuprofen is 0.1567g.
|
Calculation for assay (standard deviation)
|
=
(Experimental value) / (Theoretical value) x 100%
= 0.1567/0.5 x 100%
= 31.34%
|
Discussion :
In theory, the
amount of Ibuprofen is 0.5g. Meanwhile in experiment, after the calculation the
amount of Ibuprofen is only 0.1567g. There is quite huge different in amount of
active ingredient. This may be due to some wrong techniques that used during
experiment. The resulted deviation may be due to several errors which occurred
while the experiment was carried out. These errors may affect the accuracy of
the experiment data.
One of the
possible errors detected may due to the ibuprofen that we used for the
experiment may have expired, causing the loss of active ingredients in the
tablets as the active ingredients might have decomposed. Therefore, to increase
the accuracy of the experiment, we should use ibuprofen tablets that are not
expired. Next, the solution may not completely dry during the drying process.
Other possible
errors are, the active ingredient in the tablet might loss when the crushing of
the tablets are done. This is because when we were using mortar and pestle to
crush the tablets, some of them would drop out of the pestle. Thus, to prevent
this to happen, we should try to crush the tablet gently so that the loss of
the active ingredient can be reduced.
Besides, the
solution are not filtered through a sintered glass crucible but using filter
funnel and filter paper. This will cause some of the powder that are not
dissolved in the chloroform will pass through into the conical flask. Lastly,
the error might happen due to the titration of the solution with sodium
hydroxide. We might mis the actual end-point of the solution to turn from
colourless to pale pink in colour.
Conclusion :
The content of Ibuprofen is 0.1567g which
differ from the theoretical value due to many factors.
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