OK, so you want to make 100 ml of a solution that is 2.4 millimolar pyruvic acid. That is, its molarity (moles per liter) is 0.0024. You are starting with a stock of "98% pyruvic acid", but we don't really know what units the "%" is in. The most likely is % by weight, so let's assume that. I did not have the structure of pyruvic acid, but BladeVenom gave us Molecular Weight is 88.06 g/mol.
So you need to get to 88.06 x 0.0024 x 100 / 1000 grams of pyruvic acid in the 100 ml of final solution, and that will need
88.06 x 0.0024 x 0.100 / 0.980 = 0.02157 grams of original stock solution (the 98% stuff)
to make 100 ml. That would be impossible to measure out accurately.
You can do this in two stages. First you make 100 ml. of a solution that is 100 times stronger than you want; then you dilute some of it to get your final solution.
You will need a clean small beaker, a 100 ml volumetric flask and stopper, a funnel, two clean and dry 100 ml storage bottles, a 1.00 ml pipette, a 5 ml syringe and needle, some distilled water and a wash bottle of distilled water.
Step 1
Using the syringe and needle, withdraw from the original 98% bottle about 3 ml of the solution. Place the dry small beaker on a weigh scale that reads to at least 2 decimal places, tare it, then slowly add the stock solution from the syringe, putting 2.157 grams of it (as accurately as possible) into the beaker. Use the funnel to pour this into the 100 ml volumetric flask, rinsing the beaker many times into the flask with squirts of water from the wash bottle, so that all of the original acid solution gets into the flask. Fill that flask with distilled water exactly to the line on its neck, plug the top, and carefully tilt and mix the solution inside thoroughly. Pour this into one clean dry storage bottle - you now have 100 ml of a solution that is 0.2400M pyruvic acid. LABEL IT!
Step 2
Clean and rinse the volumetric flask thoroughly. Using the 1.00 ml pipette (you can rinse it with your intermediate solution if you want, discarding the rinsings), draw it full of your 0.2400M solution and let it drain down slowly to the line in the upper neck. Gently touch the tip of the pipette to the side of the bottle to remove any large drops, then allow the pipette to drain into the clean 100 ml volumetric flask. Do not blow out the pipette, and do not try to get its tip to drain completely - it is supposed to retain a tiny bit in its tip. Again, fill the volumetric flask with distilled water to the line and mix gently. Pour it into the second storage bottle and LABEL IT TOO! This one is your 0.0024M pyruvic acid.
Step 3
Clean up the apparatus. In future if you need more 0.0024M pyruvic acid, you can start at Step 2 since you already have the 0.2400M solution to work with.
Facebook
Twitter