When 22.50 mL of aqueous NaOH were added to 1.311 g of cyclohexylaminoethanesulfonic acid (FM 207.29, structure in the pKa values of common buffers table) dissolved in 41.18 mL of water, the pH was 9.25. Calculate the molarity of the NaOH.
pH of acidic buffer = pka + log(NaOH/cyclohexylaminoethanesulfonic acid)
no of mole of NaOH = x
no of mole of cyclohexylaminoethanesulfonic acid = 1.311/207.29 = 0.00632 mol
pka of cyclohexylaminoethanesulfonic acid = 9.3
pH = 9.25
9.25 = 9.3 +log(x/(0.00632-x))
x = 0.00298
no of mole of NaOH = x = 0.00298 mol
concentration of NaOH added = n/v*1000
= 0.00298/22.5*1000
= 0.1324 M
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