Question

for each of the following explain how you would prepare 1.0L of a solution that is 0.10M in L+. repeat for concentrations of 1.0*100 ppm

Answer 1

to determine the concentration of ethanol in cognac a 5.00-mL sample of cognac is diluted 0.500L.Analysis of the diluted cognac gives an ethanol concentration of 0.0844M.what is the molar concentration of ethanol in the undiluted cognac?

Answer 2

Molar is molar the concentration of cognac in the diluted same is 0.084 mols/L as well as in the undiluted sample. You can prove this if you wish this way.
millimoles cognac in the 500 sample = mL x M = 500 x 0.084 = 42.2
millimoles cognac in the 5 mL sample is 42.2 x (5/500) = 0.422
Then M in the 5 mL sample is millimoles/mL = 0.422/5 = 0.0844 M :-)