Posted by **Rachel** on Saturday, January 22, 2011 at 1:55pm.

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.

- Chemistry -
**DrBob222**, Saturday, January 22, 2011 at 2:14pm
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.

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