In this video we make sodium hydroxide ( lye ) from table salt through electrolysis using a divided cell! _____________ More detailed explanation why divided cell is necessary: Following reactions are happening: At the anode 2Cl− → Cl2 + 2e− At the cathode 2H2O + 2e− → H2 + 2OH− The ion-permeable ion exchange membrane at the center of the cell allows the sodium ions (Na+) to pass to the second chamber where they react with the hydroxide ions to produce sodium hydroxide (NaOH). The overall reaction for the electrolysis is thus: 2NaCl + 2H2O → Cl2 + H2 + 2NaOH A membrane cell (cotton ball in this case) is used to prevent the reaction between the chlorine and hydroxide ions. If this reaction were to occur the chlorine would be disproportionated to form chloride and hypochlorite ions: Cl2 + 2OH− → Cl− + ClO− + H2O That's why you can't do this electrolysis in one cell! Extra justifications: -The formed OH-ions in the NaOH cell want to migrate because of entropy. The cotton wool creates a resistance which is bigger as the plausible entropydifference that could happend. Therefore the OH-ions will stay in one cell -The Na+ ions formed in the other cell don't migrate because of entropy but because of the current. If you use a high current they wil pass the cotton ball. So we created a pseudo semi-permeable membrame ________________ Script: Hi everyone , In this video I will show you how to make sodium hydroxide. The only things we will need is regular table salt (sodium chloride) , an electrolysis cell which we will make right now and a few 9V batteries. We will start by making the cell. We will make a divided cell. You can’t make sodium hydroxide in a pure form in one cell. If you want to know why that isn’t possible and why it is possible in a divided cell please check the description box for further explanation We begin by making a small cotton ball from make-up pads. This cotton ball is inserted in a piece of flexible pvc tubing. As cells I will use two small plastic bottles in which I made a hole, here I will insert the pvc tubing to connect both cells. So the electrolysis cell is almost finished we just have to add the electrodes, they have to be inert so we will use carbon. The electrodes are easily obtained from pencils. All we have to do is secure the them to both cells and as you can see I also secured the pvc tubing with superglue. Now we will prepare a saturated solution of sodium chloride. The electrodes are connected to the power supply using two copper wires. To one cell we will add water and to the other cell we will add the concentrated sodium chloride solution. Ideally this should be done at the same or first the water quickly followed by the sodium chloride solution. It’s important to connect the negative pole to the water cell and the positive pole to the sodium chloride cell. Sodium hydroxide will start forming in the watercell without contaminations of sodium chloride. The sodium chloride cell stays in the sodium chloride cell. Due the resistance of the cotton ball we have to use a high a current. I am using 2x 9V batteries but that’s the absolute minimum , 4 should be ideal. You can buy 10 9v batteries for about 10 bucks on amazon. After several days of electrolysis we will do a pH test on both cells. If everything went right the pH of our sodium chloride cell should be around 7 and the pH of our sodium hydroxide cell should be 13 to 14. As you can see this is the case and our electrolysis was successful. Now we have to collect the sodium hydroxide solutions without contaminating it with the sodium chloride solution from the other cell. So there you have it, your concentrated NaOH solution! NaOH can be obtained in powder form by boiling the solution. But be aware that this is dangerous and can’t be done in glassware because hot caustic soda will corrode glass. For more information about this divided cell please check the description box! If you enjoyed the video please like and comment I really appreciate it! Thanks for watching

• published: 07 Aug 2015
• views: 14332