1.002g/ml is 1,002 g/L, so divided by 90.12 g/mol = 11.12 mol/L (M) for the undiluted liquid.
To make 5 ml of a 1M solution, you would mix 1M/11.12M * 5 ml = 0.450 ml of your chemical plus water to 5 ml. I would normally just dilute that 1M stock to 10 mM with a 1:100 (50 ul + 4.95 ml water) dilution, then make the 1 mM stock by making a 1:10 dilution of the 10 mM stock (500 ul + 4.5 ml water), then another 1:10 dilution of the 1 mM stock to get the final 0.1 mM solution (again, 500 ul + 4.5 ml water). I don't like pipetting really small volumes (because of poor accuracy of pipettes at those volumes), so I'd avoid doing dilutions straight from your 11.12M solution to get the 1 mM and 0.1 mM solutions (those would be 1:1,112 and 1:11,120 dilutions, with 4.5 ul and 0.45 ul of your undiluted chemical in 5 ml water).
Edited by John Forsberg, 30 November 2012 - 05:23 PM.