In: Chemistry
A 1 liter solution contains 0.382 M hydrofluoric acid and 0.509 M sodium fluoride. Addition of 0.191 moles of sodium hydroxide will: (Assume that the volume does not change upon the addition of sodium hydroxide.) Raise the pH slightly, Lower the pH slightly, Raise the pH by several units, Lower the pH by several units, Not change the pH ,Exceed the buffer capacity
no of moles of HF = molarity * volume in L
= 0.382*1 = 0.382moles
no of moles of NaF = molarity * volume in L
= 0.509*1 =- 0.509moles
PH = Pka + log[NaF]/[HF]
= 3.17+ log0.509/0.382
= 3.17+ 0.1246 = 3.2946
by the addition of 0.191 moles of NaOH
no of moles of HF = 0.382-0.191 = 0.191moles
no of moles of NaF = 0.509+0.191 = 0.7 moles
PH = Pka + log[NaF]/[HF]
= 3.17 + log0.7/0.191
= 3.17+ 0.564 = 3.734
Raise the pH slightly