Agata Łuszczyńska 5.01.2008

II Lo. im. Stefana Batorego I ib 2.5 h

Titration of aspirin

DCP		CE
1 asp		1 asp
2 asp		2 asp
3 asp		3 asp

In this experiment we tried to determine the amount of aspirin in one gram of a pill.

Collecting raw data:

the best way to collect data from this experiment will be a table.

	Initial Reading [±0.05 ml]	Final reading [[±0.05 ml] the indicator changed color from pink to colourless	Mass of the titrated aspirin pill [± 0.0001 g]
Probe 1	0.00 ml	29.40 ml	1.0112 g
Probe 2	0.00 ml	24.10 ml	1.0001 g
Probe 3	0.00 ml	23.00 ml	1.0010 g
Probe 4	0.00 ml	24.20 ml	1.0008 g

Processing raw data:

1.

V₁ = [29.40 ± 0.05] ml - [0.00 ± 0.05] ml = 29.40 ml ± 0.10 ml

V₂ = [24.10 ± 0.05] ml - [0.00 ± 0.05] ml = 24.10 ml ± 0.10 ml

V₃ = [23.00 ± 0.05] ml - [0.00 ± 0.05] ml = 23.00 ml ± 0.10 ml

V₄ = [24.20 ± 0.05] ml - [0.00 ± 0.05] ml = 24.20 ml ± 0.10 ml
V_average = (29.40+24.10+23.00+24.20)/4 = [25.18 ± 0,40] ml

2. Reactions:

C₉H₈O₄ + 2NaOH → NaC₉H₇O₄ + H₂O

NaOH + HCl → NaCl + H₂O

3. 
   I assume that the solutions (NaOH and HCl) are perfect (no uncertainity)

C_HCl = 0.2 M

V_HCl = [25.18 ± 0,40] ml = [0,02518 ± 0,0004] dm³

n = C x V

So:

n_NaOH = n_HCl = 0.2 M x [0,02518 ± 0,0004] dm³ =[0.005 ± 0.0008] mol

nⁱ _NaOH = n^titrated _NaOH + n^asp _NaOH

nⁱ _NaOH = 0.5 M x 0.045 dm³ = 0.023 mol

n^asp _NaOH = n _asp

n^asp _NaOH = 0.023 - 0.005

n^asp _NaOH = 0.015 mol = n _asp

5.

m_asp = n x M

m_asp = 0.015 x 180 = 2.7 g

Conclusion and evaluation:

The amount of aspirin in one gram of aspirin tablet, from the formulas, is 2.7 gram.

Of course it is wrong.

The main cause of the error can be the improper concentration of the hydrochloric acid or of the sodium hydroxide.

Also, this could indicate that the aspirin didn't react with the sodium hydroxide, because of lack of time.

The best way to improve the experiment would be to heat the aspirin/NaOH mixture to speed up the reation and then do the backtitration with the hydrochloric acid.

The other way for improvement is also to use a different type of pill wich also contains the needed aspirin (ex. sparkling tablet) that will enable the aspirin in the tablet to dissolve in water.

---