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Calculating mL in a M concentration with litres and moles problems
ngofine
#1 Posted : Wednesday, July 23, 2014 2:29:11 AM
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Can anyone explain this concept to me? I know it looks so simple but I am confused and cant seem to figure it out and its always coming up in past questions with mcat. I will appreciate your prompt response as my mcat is this friday.

Thanks
finolahackett
#2 Posted : Wednesday, July 23, 2014 6:53:12 PM
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Concentration in terms of M (molarity) = moles solute/volume of solution.
M is usually given in units of mol/L.
To calculate volume, divide the number of moles by the concentration.
M = n/V so V = n/M

Ex. What is the volume of 2 M NaOH needed to react with 3 moles of H+ ions?
V = n/M = 3 moles / 2 mol/L = 1.5 L

To convert L to mL, multiply by 1000.
Ex. 1.5 L = 1500 mL

Don't forget to use the stoichiometric coefficients (mole ratio) of the balanced reaction when converted between chemical species!
(the ratio above is 1:1 since 1 OH- reacts with 1 H+)

Hope this helps.

Finola
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