I want to know the concentration of a home-made saturated aqueous solution of Bromophenol blue.
How could I know when I add unknown number of grams of the dye?
100 mg of bromophenol blue with 10 ml of ddH2O and mix. is 1% solution. Store at room temperature
1) You can use a spectrometer. because the absorbance is proportional to concentration in accordance with Beer-Lamber Law.
http://alpha.chem.umb.edu/chemistry/ch118/118%20labs/lab%204%20Beers%20Law.pdf
2) If you have an accurate 5 figure or maybe even 4 figure balance, you can take a lightweight glass petri dish, weigh it and note the dry weight ()wear gloves to stop weight increase through transfer of skin - oil etc by contact with your skin. Note the dry weight. Then add a known volume of the solution and evaporate the liquid leaving a dry mass of bromophenol blue. Re-weigh the perti dish plus dry bromophenol blue (dry it for 1 hour in a drying oven before re-weighing it). Then return the dish to the oven for another 1 hour and re-weigh it. If the weight is the same then you have the dry weight. If not, dry it for longer and keep re-weighing until the mass is constant. Subtract the mass of the dry perti dish from the mass of the dish + dry bromophenol blue. then you know the mass of bromophenol blue as well as the volume of solution added. Then you can calculate the mg/cm3 or the moles/litre.
Make a saturated solution of bromophenol blue with extra solid bromophenol blue can be seen. Let the bromophenol blue solid set down(maybe with centrifugal spinning), take 1ml/10ml (or amount you desired) of clear solution to dry down to constant weight. From the volume and weight, you should be able to find out the concentration of a home-made saturated aqueous solution of Bromophenol blue.
Or you can search the literature to find it.
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