Salicylic Acid

Result
Table: Shows the absorbance value of different solution at pH1.
Solution Volume of Salicylic acid (ml) Volume of pH 1 buffer solution (ml) Absorbance
A 25 25 0.508
B 20 30 0.415
C 15 35 0.193
D 10 40 0.189
E 5 45 0.088
X (unknown) 0.534

Table: Shows the absorbance value of different solution at pH8.
Solution Volume of Salicylic acid (ml) Volume of pH 8 buffer solution(ml) Absorbance
A 25 25 0.370
B 20 30 0.298
C 15 35 0.214
D 10 40 0.138
E 5 45 0.066
X (unknown) 0.903

Calculation
Stock solution of Sodium Salicylate is 0.0005% (w/v) = 0.005g/100ml
Convert this into a molar concentration, using the following equation:
Molarity (M) = Fraction of 1L x (weight (g))/MW
= 1000/100 x 0.005/160.1
= 0.000312 M
Now, to calculate the concentration of the standards using: C1V1 = C2V2
Where,
C1 = concentration of the stock solution of sodium salicylate, 0.000312M as calculated above. This case C1 is kept the same throughout each calculation.
V1 = the volume of stock solution of salicylic acid, which would be different for each calculation being either 25, 20, 15, 10 or 5 cm3
C2 = the concentration of stock solution of salicylic acid
V2 = the total volume which is 50 cm3. This is kept constant throughout each calculation.
Solution A
C1=0.000312M V1=25 C2=? V2=50