I am trying to make and titrate a very dilute solution of HCl.
My process is to use KHP as primary standard, calibrate an NaOH solution against KHP (approximately 0.03M NaOH) then use the NaOH to titrate HCl, which is about 0.004M.
The problem that i am running into is that my pH curve does not look like a strong acid / strong base curve should look. I get a very slow and drawn out linear fall. I am also seeing pH value drift if i stop for a while. This tells me that the reaction rate between such dilute solutions is very slow, hence my pH readings are wrong. I tried magnetic stirrer and it makes pH fall, but if i turn stirring off pH rises as much as 0.3pH points within the few minutes i observed it for. Is there a trick / proper technique in titration of such dilute solutions? Or is leaving solution to settle for 30 minutes at every point is my only choice?