Chemistry
posted by Rachel .
Can someone please check my work?
Calculate the mass of (NH4)2S2O8 needed to prepare 250mL of a 0.100M solution.
I got 5.705 g.
Calculate the volume of 2.00M KI needed to prepare 250mL of a 0.200M solution.
I got 0.025L or 25mL.
Calculate the volume of 0.100M Na2S2O3 needed to prepare 250mL of a 0.0100M solution.
I got 0.025L or 25mL.

5.705 is a correct number for the first one; however, you can't have that many significant figures. You are allowed three; therefore, I would round to 5.70 g. Your prof may not round a 5 the same way and could round to 5.71 g.
The second one is correct also; however, you are allowed 3 s.f. and I would give the answer as 25.0 mL.
Same thing for the third one. 25.0 mL.