posted by zoe .
in the titration between Na2CO3 and HCl...
1) at the first end point what reaction is stoiciometrically complete?
2)At the start of titration where HCl=0 is the solution acidic or basic. ExPlain?
3) At the 2nd end point what reaction is stiociometrically complete?
4)Propose a suitable indicator to use in the lab for each end point. Explain your choices.
i've tried to di it.
1)Na2CO3 + HCl---> NaCl+NaHCO3
2)Basic as Na2CO3 is a base and amount of HCl =0
4)phenolphthalein for eq pint point 1 as it will indicate change in basicity and methyl orange for secong equivalnce point as it will indicate change in acidity. (Don't know how to explain it can any one do it better than me?
All of your answers look ok to me. As for the indicator one,
The pH at the 1st equivalence point is that of a NaHCO3 solution which is pH = 1/2(k1k2) = about 8 or so and phenolphthalein changes between 8 and 10 (approximately). The second equivalence point is about pH 3.5 or 4.0 and methyl orange changes about 3-4.5. I prefer to boil the solution to expel the CO2 and that gives a sharper end point with methyl red indicator (4.2-6.3 or mid point about 5.0)