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May 5, 2016

Homework Help: Chem Lab Math!

Posted by Morgan M on Sunday, March 18, 2012 at 9:41pm.

A liquid solution of formaldehyde is 37.0% pure. This solution has a specific gravity of 1.037. The molecular weight of formaldehyde is 30.0. to 1.00 ml of this impure stock solution is added quantity sufficient to take the total volume to 500ml. If 1.00 ml of this solution is added to 4ml of water in a final reaction, what is the molarity of formaldehyde in this final reaction tube?

Thank you!!!!
• Chem Lab Math! - DrBob222, Sunday, March 18, 2012 at 10:09pm

What's the molarity of the solution?
1,000 mL x 1.037 g/mL x 0.37 = ?g HCHO.
?g HCHO/molar mass = moles and that is the molarity since the solution is 1 L.Abut 13M but you need to do that more accurately than I.

final M = about 13M x (1.00/500) x (1.00/5.00) = ?
(Note: Technically we can't calculate the final M since the final dilution takes 1.00 mL and ADDS 4.00 mL water. The last step of the above calculation depends upon the 1.00 mL adding to 4.00 mL to give 5.00 mL. The way dilutions are made is that you would add 1.00 mL to enough water to make the total volume equal to 5.00 mL. In reality, I'm not sure we would be able to measure the difference.