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August 23, 2014

Homework Help: Chemistry

Posted by Chris on Monday, October 9, 2006 at 12:13pm.

In a lab we are trying to find the percent yield of NaCl collected after evaporating the water off an NaCl solution. We made up a .100 M NaCl solution, and used 10. mL of it in our experiment.
We know that the empty evaporating dish and cover mass 68.9132 +/- .0003 g, and after our final trial our evaporating dish, cover, and NaCl mass 68.9695 +/- .0003 g.

We calculated our theoretical yield as such..
10. mL +/- .2% x (.100 sub 0 mol +/- .6 % / 1 L) x ( 1 L/ 1000 mL) x (58.77 g / 1 mol) = .058 +/- .001 g

I calculated our actual yeild as such..
68.9695 +/- .0003 g -> 68.9695 +/- .0004 sub 3 %
- 68.9132 +/- .0003 g -> 68.9132 +/- .0004 sub 4%
= .0563 +/- .00008 sub 7 %

Going by these calculations, I calculate the percent yield to be
(.0563 +/- .0008 sub 7 %) / (.058 +/- 1.sub 7 %) = 97 +/- 2 (absolute) %

However, my partner got 97 +/- 3%, and since I haven't done error calculations in a while I'm trusting that her answer is correct. Can someone help me find what I did wrong?


I get one percent error on the measured mass, and two percent on the theoretical.

Stick with your three percent. The precision of the known solutions (molarity and volume) as you have cited is beyond what most college labs do.

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