Calculations

This 5 moles is now in a final volume of 20 mL ( 5 mol/20 mL ( 250 M or 0.25 mM. The key to doing this problem is to convert the concentration to sensible units i.e. M ( mol/mL. Then it is easy to see how many moles you would have in 0.5 mL and then very easy to calculate the diluted concentration, given that the 5 moles will now be in 20 mL. ................
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