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I conducted an experiment on electrolysis of concentrated solution of NaCl. Hoffman Electrolysis Apparatus was used for this experiment. I observed a formation of gas bubbles on both anode and cathode. It was expected to obtain hydrogen gas on negative electrode (cathode) and chlorine gas on positive electrode (anode). I also hoped to test these gases: (1) as hydrogen should ‘pop’ with a lighted splint, and chlorine should bleach damp litmus paper. I was unable to demonstrate these tests for gases, as I suppose there was not enough gas formed for test to go efficiently. I wonder, if someone knows what apparatus is better for this goal. I used 9V battery for this electrolysis experiment. Even though I had no direct proof of hydrogen formation, solution near anode smelled as a chlorine gas, and smell was very strong. I am not sure why wet blue litmus paper didn't get bleached by this chlorine. Blue litmus paper got bleached very fast in another experiment (not related to electrolysis) where chlorine was released, within 30 sec of exposure. The most interesting part of experiment was formation of brownish chemical species on anode. At times, I didn't see any chlorine bubbles at all, but I could see formation of this brown chemical species. At first, I thought it is an iodine. I tested it with starch and found, that it was not iodine. Today I tested it with alkene and alkane, and I found it was a bromine (decoloration of bromine water was observed with alkene, but not alkane). Yes, I know, that brine is main source of bromine, but is there any way I can buy NaCl without bromine, just for demonstration purposes?

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  • $\begingroup$ What materials are you using for the electrode? $\endgroup$ – sadljkfhalskdjfh Mar 27 '16 at 2:23
  • $\begingroup$ Platinum electrodes, apparatus is this one: amazon.com/gp/product/B005QDUSMQ/ref=s9_dcbhz_bw_g328_i3_sh No matter, how platinum they are, they are eaten in a course of this electrolysis chemical reaction, and I am not sure, if a real platinum thing would corrode that fast. I'd rather imagine, it would not corrode that fast (I did experiment 5 times, and before that this set was new), but I have no prior experience with that to be sure about it. $\endgroup$ – Sleepy Hollow Mar 27 '16 at 4:05
  • $\begingroup$ Platinum is quite inert; it is unlikely that such electrodes would corrode if they were pure. (You can try carbon or graphite.) I think your estimates for what gases are produced are correct; collect gases inside an inverted test tube filled with electrolyte. The upside-down test tube should be in a bath of electrolyte. Then, you can use the gases. Note that your chlorine might be mixed with oxygen in some cases. $\endgroup$ – sadljkfhalskdjfh Mar 27 '16 at 10:42
  • $\begingroup$ I don't mind to change set up of apparatus, in fact I ordered two more different pieces of equipment for that and I plan to try them next week, upon delivery. One of this pieces of equipment is with carbon electrodes actually: amazon.com/Electrolysis-Apparatus-Contained-Water-Device/dp/… * $\endgroup$ – Sleepy Hollow Mar 27 '16 at 14:03
  • $\begingroup$ Another one would allow test tubes to be immersed in electrolyte: amazon.com/gp/product/B00FGDR6US/… So I will be able to test both your advices soon. Thank you! $\endgroup$ – Sleepy Hollow Mar 27 '16 at 14:05

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