Mass of vial: 6.0134g
Mass of vial and Aspirin: 7.5142g
Mass of Aspirin: 1.5008g
Resulting Aspirin solution made up to: 250.0cm3
Titration I: Standardization of 0.1M sodium hydroxide solution
Titrant (in burette): Potassium Hydrogen Phthalate
Titrate (in conical flask): 25.0cm3 of Sodium Hydroxide
Indicator used: Phenolphthalein
Colour of indicator changed from: Purple to Colourless
Average volume: 24.85 cm3
Calculation:
HK(C8H4O4)(aq) + NaOH(aq) → NaK(C8H4O4)(aq) + H2O(l)
Number of mole of HK(C8H4O4) = (0.1005)(24.85/1000)
= 0.002497
∵ HK(C8H4O4) : NaOH = 1 : 1
∴ Number of mole of NaOH = Number of mole of HK(C8H4O4)
= 0.002497
Molarity of NaOH(dil) = (0.002497) / (25/1000)
= 0.09988M
~ 0.10M
Molarity of NaOH = (0.10)(250/25)
= 1.00M
Titration II: Determination of the commercial Aspirin tablet
Titrant (in burette): Potassium Hydrogen Phthalate
Titrate (in Conical flask): 25.0cm3 of Aspirin and Sodium Hydroxide Mixture Solution
Indicator used: Phenol Red
Colour of indicator changed from: Purple to Yellow
Average volume: 9.95 cm3
Calculation:
CH3COOC6H4COOH(aq) + 2NaOH(aq) → CH3COONa(aq) + HOC6H4COONa(aq) + H2O(l)
Number of mole of HK(C8H4O4) = (0.1005)(9.95/1000)
= 0.000999975
Number of mole of 25.0 cm3 NaOH(left) = Number of mole of HK(C8H4O4)
= 0.000999975
Number of mole of NaOH(left) = (0.000999975)(250/25)
= 0.00999975
Number of mole of NaOH(original) = (1)(25/1000)
= 0.025
Number of mole of NaOH(reaction) = 0.025-0.00999975
= 0.015
∵ CH3COOC6H4COOH : NaOH = 1 : 2
∴ Number of mole of CH3COOC6H4COOH = (Number of mole of NaOH) / 2
= 0.015 / 2
= 0.0075
Mass of CH3COOC6H4COOH = [(9)(12.0107)+(8)(1.00794)+(4)(15.9994)](0.0075)
= (180.15742)(0.0075)
= 1.3512
Percentage of CH3COOC6H4COOH in a Aspirin tablet = (1.3512 / 1.5008)(100%)
= 90.03%
Conclusion:
In titration I, we found out given sodium hydroxide solution was ~1.00M and is fine with the given molarity.
In titration II, we use the determined sodium hydroxide solution to react the 2-acetoxybenzoic acid which contain in 1.5g Aspirin tablet powder and found out it has 90.03% of 2-acetoxybenzoic acid in a Aspirin tablet by calculation.