You received a water sample to determine its "hardness", expressed as the total amount of carbonates (such as CaCO₃). The sample solution is approximately 5 times more diluted than the EDTA solution.

a) Based on this information, and knowing that you have at your disposal volumetric pipettes of 10, 25, and 100 mL and graduated pipettes of 5, 20, and 50 mL, state the volume of the sample (Vs) that you would use for the determination (the burette used for the titration is 50 mL). Justify your answer.

I know that M_{EDTA}XV_{EDTA}=M_{s}xV_{s}

Let y be the molarity of the water sample:

5yx50=yxV_{s}

So it gives me that V_{s}= 250 ml

What am I doing wrong?