what are the errors in the double-indicator titration of (sodium carbonate and sodium hydrogen carbonate) against hydrochloric acid, using Phenolphthalein and Methyl orange as indicator?
how can I improve the it?
1 answer
The phenolphthalein end point is difficult to see AND it goes from very pink to colorless with just a drop (or less) of titrant; therefore, it is easy to over shoot the end point. Add to that that the end point is not very sharp. For the m.o. end point, the solution in the area of the equivalence point is buffered with excess CO2 from the titration product which makes that end point not very sharp either. That can be alleviated by adding HCl to the m.o. end point, boiling th solution (being careful not to lose any of the contents by spattering), let the solution cool, then finish the titration. The end point for the second go around is much sharper. The need to perform the heating step a second time can be obviated by adding a SLIGHT excess of HCl after reaching the tentative end point, then begin the heating step and finish the titration. I hope this gives you some insight into the experiment.
1 answer