[docteurdeno]

Hello all,
I would like to conduct an experiment to determine the salinity of different water bodies using beer's law for my lab report. I have some questions about the experiment, and I would appreciate it if you could answer them. I apologize if my "experiment" sounds like a disaster, but that's why I have questions about it.

First of all, does my experiment even have a point? You can measure the concentration of unknown solutions using beer's law, but as this is an actual experiment, I will already know what I'll be working with. My independent variable would be the concentration of salt, and my dependent variable would be absorbance, but does it really make sense to calculate the salinity of a solution after measuring its absorbance, when I already know what the concentration of it is beforehand? I'm conflicted on this.

Secondly, if my experiment does have a point at all, which dye would be the most suitable for my experiment? As far as I'm aware, spectrophotometers require some kind of color when working with visible light. A dye that gets more opaque as the solution is concentrated more would be really helpful for this experiment. Also, do I need a dye at all?

Also, to piggyback off the second question, how would the dye affect the beer's law calculations? The absorbance is most likely dependent on the type of dye, and my calculations wouldn't yield me the concentration of salt in the substance when a dye is present.

Finally, which wavelengths would I need to work with?

Any and all feedback is appreciated, thank you for everyone who spared their time to respond to me.

[Corribus]

Well, you didn't really explain what your experiment is, so it's hard to judge it. But generally you need to connect what you are actually measuring to what you want to know. In this case, you need to be able to link (in some kind of mathematical way, but strict proportionality is best) the absorbance (what you're actually measuring) to the salinity (what you're interested in knowing). If you can't do that, then you can't use the technique. So, here, either your salt (whatever it is) needs to do the absorbing of light, and the absorbance needs to scale somehow with the concentration, or the salt needs to influence the absorbing of light of something else (a dye, as you put it).

Whether or not it is a good method, or whether Beer's Law can even be used, is a different matter entirely. You're not there yet.