Student Doctor Network Forums > Pre-Medical Forums > MCAT Discussions > MCAT Study Question Q&A > Kaplan Titration Question! PDA View Full Version : Kaplan Titration Question! RHC198705-11-2008, 09:56 PMMethyl red (pKA = 5.0) is a pH indicator dye that is red when protonated and yellow when deprotonated. A student chose to use methyl red as an indicator in her titration of an unknown concentration of HCl into a 250mL solution of 10-2 M NaOH. What will be the color of the solution before the titration begins, at the equivalence point of the titration and at the end point of the titration? (Assume the temperature of the solution remains constant at 25°C) Answer: The solution will be yellow before the titration, yellow at the equivalence point and red at the end point. (I'm having a hard time understanding whats going on at the equivalence point of the titration... Any feedback will be awesome!) BloodySurgeon05-11-2008, 10:44 PMI am going to say the short version: pOH= -log [OH] pOH=2 pH + pOH = 14 pH = 12 pKa = 5.0 start: pH = 12 .......... deprotonated (yellow) Equivalence pt: pH about 7 b/c OH- + H+ --> H2O ..... deprotonated (yellow) end pt: pH 2 b/c nearly all HCl ................ protonated (red) pH>pKa : deprotonated (yellow) pH=pKa : half protonated, half deprotonated (orange) pH