[dagarshali]

Hi, I am new to this forum and basically a Mechanical Engineer. I am trying to get quantitative data for mixing in microchannel. The way I do this is by using a 0.33mol/L solution of phenolphthalein in ethanol and 0.31mol/l of NaOH in ethanol. I pass these two streams separately into the mixer and take images of the color change caused. I am have two problems here..

The paper which describes this technique uses 0.33mol/L solution of phenolphthalein in 99.99% pure ethanol. I am using denatured alcohol. The problem is when I pass this liquid thru small  microchannel, the phenolphthalein comes out of the solution. what can I do to overcome this?

Also, I use a tiny bit of water to dissolve NaOH pellets and then add alcohol. The solution is very clear when I mix alcohol. But, if I let that sit for some time, the solution turn like lemon juice (pale ash color) and i see some suspension as well.

Can you please help me solve this issue.

Thanks a bunch in advance

Vishwa

[Arkcon]

You're probably having some difficulties because of the nature of microchannels, which I'm not well versed in.  However:

1). That is more alcohol in the phenolphthalein than is needed, 30-50% alcohol in water is adequate to dissolve a tiny amount of phenolphthalein.

2).  I don't see why you're using alcohol to dissolve NaOH, your microchanel application may need it, but you should expect solubility problems

3).  Outside of the microchannel, I don't mix more than a few drops (approx < 1 ml) of phenolphthalein per 100 mL of solution to be titrated, so you may want to dilute the phenolphthalein even further.

You need less alcohol and phenolphthalein in your system, dependent on your needs, surface tension, and your ability to detect a color change in a very small volume.