# Will the refractive index of a electrolyte change when chemical reaction happens?

Since polarization is the reason of refraction, then anything that changes the structure of molecule, atom, or electron will present as a change of reflection. Thus, to my understanding, chemical reaction of electrolyte will accompanied by a refractive index change. I monitored the refractive index of NaCl solution before and after a 4.5 V voltage was applied. The sensitivity of the refractive index sensor is known as 1100 nm/RIU, which is enough to detect a 10 ppm (10$$^-^5$$) refractive index change. But nothing was detected.

Now I'm not quite sure if the refractive index will be changed due to chemical reaction. Or is the sensor still not sensitive enough? Thanks!

• Choosing NaCl is arguably a poor choice. Electrolysing a dilute solution of it creates an NaOH solution of the same molarity. This would result in very little change of the RF. The electrolysis of something like CuSO4 could be more interesting in that respect because it effectively deposits the Cu ions as Cu metal at the cathode. – Gert May 7 at 21:04
• @Gert: do you get a refractive index change more visible in that case? – Exocytosis May 9 at 12:41
• @Fengfeng; I upvoted your question as I am interested in hearing answers to this one. Unfortunately it doesnt seem to bring a lot of attention. – Exocytosis May 9 at 12:43
• Hi @Exocytosis, sorry for the late reply. I ordered FeCl$_3$ crystal yesterday since we are interested in Ferric and Ferrous ions mostly. It's still not delivered yet. I'll let you know the result later, thanks for your interest. – Fengfeng May 9 at 15:17