[Tripping0ut-]

hey having some issues with my calculations, im noob chemistry student, we dissociated a 325mg asa tablet int 30ml of methanol, then titrated with NaOH, my concentration for NaOH comes out to be 0.15, but for some reason when i add in my NaOH concentration on my mass calculation for asa i keep getting 10 mg over,

Here are my calculations:

C NaOH= 0.010L KC7H4O2COOH x 0.150mol KC7H4O2COOH/1L KC7H4O2COOH x 1/0.010L NaOH x 1molNaOH/1mol KC7H4O2COOH = 0.15



M ASA= 0.0124L NaOH x 0.15 mol NaOH/1L NaOH x 1mol ASA/1mol NaOH x 180.17g ASA/1mol ASA =0.3351162

?

O.o

[Mitch]

asa?

[Tripping0ut-]

KHP Balanced formula

KC7H4O2COOH(AQ) + NaOH(AQ)  KNaC7H4O2COO(AQ) + H2O(L)   

C=0.150 mol/L            m=?
V=0.100L                   M=40.00g/mol
M=204.23 g/mol

mNaOH = 0.150mol/1L x 204.23g/1mol x 0.1L = 3.06g

proceeded with titration, used 3 drops of indicator(phenolphthalein) solution turned light pink at 10ml of NaOH
added.

C NaOH= 0.010L KC7H4O2COOH x 0.150mol KC7H4O2COOH/1L KC7H4O2COOH x 1/0.010L NaOH x 1mol NaOH/1 mol KC7H4O2COOH =0.15

ASA Tablet balanced

C8H7O2COOH(AQ) + NaOH(AQ)  NaC8H7O2COO(AQ) + H2O(L)

M=180.17g/mol           C=0.15mol/L
V=30.0mL (methanol)  V=12.4 mL

teach told us not to include the methanol into our calculation, we crushed a 325mg tablet of ASA into 30mL of methanol, took 10ml of the crushed asa solution with a pipette, and proceeded with titration with NaOH, solution turned light pink at 12.4 mL (same indicator for KHP 3 drops)

m C8H7O2COOH=0.0124L NaOH x 0.15mol NaOH/1L NaOH x 1mol C8H7O2COOH/1 mol NaOH x 180.17g C8H7O2COOH/1 mol C8H7O2COOH

i keep getting 0.33511 something and im not sure where i could have gone wrong, perhaps an error with my dimensional analysis *scratches head*

[Borek]

Actually looks like you forgot to multiply by 3 (10 mL of methanol solution out of 30 mL), which will make your result even worse.

Assuming by ASA you mean an acetylsalicylic acid titrating it with NaOH is asking for troubles, as it hydrolyzes consuming more base than expected.

But your calculations are impossible to follow, you haven't told us the procedure nor the volumes of titrant, and trying to guess what you are doing only makes me confused. How much KHP have you used? 100 mL of 0.15 M solution? Really that high volume? Why do you calculate mass of NaOH, when the only thing you really need to know is its molar concentration? Why do you use 0.15 M for the molar concentration of NaOH later, wasn't 0.15 M concentration of KHP?