How do I make 100 milliliters of 100mM H2O2 using 3% H2O2? [closed]








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I need to make 100 milliliters of 100mM H2O2 using 3% H2O2.


Do I: 


1. add X milliliters of distilled water to the 3% H2O2? How many ml?


or


2. add X milliliters of 3% H2O2 to the distilled water? How many ml?




It seems that this is some sort of reagent solution so +/- 25% is probably no problem.


Assume density 1 g/ml for 3% solution which gives 0.03 g $\ce{H2O2}$ per ml, or 30 g $\ce{H2O2}$ per liter.


The molecular weight of $\ce{H2O2}$ is about 34 g/mol so:


$\dfrac{30}{34} \approx 1$ molar. 


You want 100 mMolar which is 0.100 molar. Thus you need a 10 fold dilution. 


So add 10 ml of the 3% to 90 ml water to get 100 ml of solution. 


*Typically add the chemical solution to pure water.*


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