How to Make A Bromophenol Blue Solution (pH Indicator)
In this video, I make a bromophenol blue indicator solution using two simple ingredients: bromophenol blue powder and methanol.
WARNING: Methanol is highly toxic and flammable, so be careful when working with it. Alternatively, you could use 95% ethanol for this experiment.
All you need to do to make a bromophenol blue solution is dissolve 0.1 g of bromophenol blue powder in 100 mL of methanol, and stir for a few minutes.
Bromophenol blue is a type of pH indicator, which means it changes color when the pH of a solution changes. In methanol, BB is a reddish-green color. However, when you add a few drops to a solution, it will change to either blue or yellow, depending on the pH:
pH less than 3 = yellow
pH greater than 4.6 = blue
Because of its pH range, BB is great for distinguishing between dilute and concentrated acids. Conc acids with pH below 3 will be yellow, but dilute acids with pH above 4.6 will be blue. This is discussed at 2:14 in the video.
However, it is not a great indicator if you have to distinguish between acidic and basic solutions, because ALL pH values above 4.6 will be blue. I demonstrate this at by adding a few drops of BB to a dilute acid (pH 5), water (pH 7), a dilute base (pH 11), and a concentrated base (pH 14), and they all turn the same shade of blue*.
*The concentrated base is a significantly darker blue than the other three, and this has to do with BB's acid/base equilibrium. I don't have room to explain this fully in the description, but if you are curious send me a private message through youtube, or email me (you will se my email listed below).
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LIQUID CHLORINE Reacting with Metals Trailer! The full liquid chlorine video will be out on Friday, February 5.
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