How to Mix a 2mM solution of EtOH?
Answer:
you need 0.002 moles of ethanol in 1 L of water. 0.002 moles of ethanol is 0.002*molecular weight (24+5+17)=0.092g. density is 0.789 g/ml so you need 0.092/0.789=0.117 ml and add water to 1 L
Use dimentional analysis
2 mM EtOHx...1 mole....x 45.1688g= 0.090g
..1 L water..1000mmoles....1 mole
The density of ethanol is 0.789g/mL therefore:
0.090g/0.789=0.114mL or 114 uL
Use a 150 or 250uL syringe and draw up 114uL of ethanol and place it in a 1L volumetric flask and dilute to volume with water.
**If I can add a little sidenote. When you are determining this type of problem it is important to be as accurate you can with the calculation, such as the molecular weight of ethanol. This is basically because there is some error involved when preparing the solution. If you use zero places after the decimal for the determination of the molecular weight and then take the error involved while preparing the solution you have compounded the error twofold rather than one fold.
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