[Music] hi and welcome back to freci lessons. co.uk by the end of this video you should be able to describe the reactions that take place during electrolysis of an aquous solution you should then be able to predict the products at the electrodes during electrolysis of aquous solutions and finally if you're are higher tier student you should be able to write half equations for the reactions at the cathode and at the anode in the last video we started looking at electrolysis of aquous solutions and remember that the word aquous means dissolved in water we saw that water molecules split and they produce the hydrogen ion H+ and the hydroxide ion o minus we've got to remember to consider these ions when we look at what happens during electrolysis of an aquous solution in this video we're looking at the electrolysis of sodium chloride solution and I'm showing you that here sodium chloride has got two ions the sodium ion na+ and the chloride ion CL minus we've also got to take into account the ions from the water and here they are we're going to start by looking at the reaction taking place at the cathode which is the negative electrode two ions will be attracted to the cathode these are the sodium ion na+ and the hydrogen ion H+ to work out which ion will react we need to go to the reactivity series and here it is is as we said in the last video hydrogen is produced at the cathode if the metal is more reactive than hydrogen as you can see sodium is more reactive than hydrogen so that means that hydrogen will be produced at the cathode so here's the cathode and we can see hydrogen gases being produced so the next question is what will be produced at the anode two different ions will be attracted to the anode these are the chloride ion CL minus and the hydroxide ion o minus now this brings us to an important rule which you need to learn if the aquous solution contains halide ions such as chloride then the hogen will be produced at the anode so here's the anode and we can see that chlorine gas is being produced that's because this solution contains the chloride ion which is a halide if you are higher student then you need to know the half equations for these reactions here's the reaction at the cathode you can see the hydrogen ion is gaining one electron to form a hydrogen atom that's an example of a reduction reaction now there is a problem here hydrogen atoms immediately pair to form a hydrogen molecule H2 so we need to double this equation to show the formation of H2 I'm showing that here now let's look at the reaction at the anode here it is you can see that the chloride ion is losing one electron to form a chlorine atom now chlorine atom always pair to form a chlorine molecule so we need to double everything to show this and I'm showing you that here we can write this half equation in a slightly different way like this however both of these half equations show the same reaction so don't worry remember you'll find plenty of questions on the electrolysis of aquous Solutions in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe the reactions that take place during electrolysis of an aquous solution you should then be able to predict the product at the electrodes during electrolysis of aquous solutions and finally if you're a higher tier student you should be able to write half equations for the reactions at the cathode and at the anode [Music]