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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: zeoblade on August 10, 2010, 12:02:03 AM

Title: Making up solutions with non-water solvent
Post by: zeoblade on August 10, 2010, 12:02:03 AM

I just want to solve a stupid debate about molarity.

Solute = benzyl alcohol
Solute density at 20^oC= 1.0453g/mL
Solute molecular mass = 108.13g/mol
Needed concentration = 0.25M
Needed volume = 10mL
Solvent = CCl₄

mol solute needed = 0.25mol/L x 0.01L = 0.0025mol
A) Mass solvent needed = fill up to 10mL

OR

B) Mass solvent needed = 10mL x 1.0453g/mL = 10.4530g
This means that 10mL mark will be exceeded.

What is the correct method? If I could get the person to post you a chocolate bar for winning this bet, I would.

Title: Re: Making up solutions with non-water solvent
Post by: Borek on August 10, 2010, 04:13:02 AM

This is molarity vs molality.

Molarity is per volume, so you should fill up to 10 mL.

Molality is per solvent mass, so if preparing molal solution you should use 10.45 g of the solvent.