[nini2]

titration with pH meter
Sample solution which contains 5g in total weight of Na2CO3 and NaOH in 1000cm3 solution (Clue 1: Weight of Na2CO3 (g) + NaOH (g) =5g in 1 liter solution

1.calculate the respective concentration of Na2CO3 and NaOH in the sample solution.
2. calculate the weight percentage (wt%) of each alkali in the sample solution
volume(cm3)   pH   
0.0   12.89   9.0   12.58   18.0   11.45
0.5   12.86   9.5   12.56   18.5   11.24
1.0   12.86   10.0   12.53   19.0   10.99
1.5   12.85   10.5   12.50   19.5   10.73
2.0   12.83   11.0   12.47   20.0   10.58
2.5   12.82   11.5   12.44   20.5   10.39
3.0   12.81   12.0   12.40   21.0   10.14
3.5   12.80   12.5   12.37   21.5   9.98
4.0   12.78   13.0   12.31   22.0   9.82
4.5   12.77   13.5   12.28   22.5   9.62
5.0   12.75   14.0   12.22   23.0   9.27
5.5   12.73   14.5   12.16   23.5   8.60
6.0   12.71   15.0   12.11   24.0   8.44
6.5   12.69   15.5   12.03   24.5   6.99
7.0   12.66   16.0   11.96   25.0   6.73
7.5   12.65   16.5   11.85   25.5   6.46
8.0   12.63   17.0   11.73   26.0   6.29
8.5   12.60   17.5   11.60   26.5   6.13
pls help me to solve this problem....
pls....

[Borek]

http://www.titrations.info/acid-base-titration-sodium-hydroxide-and-carbonate

Determine both end points from the titration curve.

[nini2]

http://www.titrations.info/acid-base-titration-sodium-hydroxide-and-carbonate

Determine both end points from the titration curve.

this is found b4 too..
but now is mixture of Na2CO3 and NaCl..
no seperate...
and is used pH meter to find the equivalent ponit..
so cant find the volume 1 and volume 2

[Borek]

Method described on the lnked page is for determination of mixture composition, so it perfectly fits your case.

Make a plot of your titration curve.

Could be you have finished your titration too early, and there is no second end point - it is visible around pH 4, your data end at 6.13.