Calculate how much Na2S2O3*5H2O (FW= 248) should be weighed, if that is what is available in the lab, to be dissolved in DI water to prepare 500 mL of a 0.07 M Na2S2O3 (FW=158) solution.
What would you weigh if you have pure anhydrous sodium sulfate available instead of the pentahydrate material?