how do you convert mL to mmol?

Question

im having issues setting up the conversions.. and issues with knowing where to put the liters portion in the conversion table.

Need to find how much mmol is in concertion of 0.30 M Pb 2+ in 5 mL.

Thank you!

Answer 1

This is really a problem in using dimensional analysis. If you don't quite get it, you should probably look it up and read a little about it. It's really quite simple once you understand the principle. We want to put units in the numerator or denominator in order that they cancel and leave us with the units we want. So, in the present problem, we have M which has units of moles/liter and we have mls which we will convert to liters. Then we will also have to change moles to millimoles (mmole) since that's what the question asks for.

I'll do it in individual steps first, and then show you how to do it all in one calculation:

step 1: convert 5 ml to liters. 5 ml x 1 L / 1000 ml = 0.005 L (note ml cancel leaving us with L)

step 2: write 0.30 M Pb²⁺ in units of mol / L. 0.30 M = 0.30 moles Pb²⁺ / L

step 3: find moles by using moles / L and L: 0.30 moles Pb²⁺ / L x 0.005 L = 0.0015 moles Pb²⁺ (note L cancel leaving us with moles)

step 4: convert moles to mmoles: 0.0015 moles Pb²⁺ x 1000 mmoles / mole = 1.5 mmoles Pb²⁺ (moles cancel leaving mmoles)

Single calculation:

5 ml x 1 L / 1000 ml x 0.30 mol Pb²⁺ / L x 1000 mmoles / mole = 1.5 mmoles Pb²⁺