Thread: Can someone please check my calculations? (pretty basic stuff)

i'm finding the concentration of OCl- by titration. I diluted 50ml of S2O3 (0.2molL-1) with 200ml H2O in a 250ml volumetric flask. So the concentration of the diluted S2O3 is:
(m1)*(v1)=(m2)*(v2)
0.2*0.05=(m1)*0.25 (volume is in litres)
(m1)= 0.04molL-1 S2O3
the volume of S2O3 in the titration is 0.02428L
moles of S2O3: n=cv
n=0.04*0.02428
n=9.712*(10^-4)mol


mole ratio of S2O3:OCl is 2:1
Therefore mo. of moles of OCl:
(9.712*(10^-4))/2=4.856*(10^-4)mol
volume OCl: 0.02L
concentration of OCl:
c=n/v
c=(4.856*(10^-4))/0.02
c=0.02428molL-1


However, I also diluted the OCl by adding 20ml OCl to 230ml H2O in a 250ml volumetric flask.
(m1)*(v1)=(m2)*(v2)
(m1)*0.02=0.02428*0.25
(m1)=(0.02428*0.25)/0.02
(m1)=0.3035molL-1
Therefore the concentration of OCl is 0.3035molL-1