in today's video we're going to take a look at redox reactions which are reactions in which oxidation and reduction both take place at the same time and to do this we'll cover displacement reactions ionic equations and half equations we saw in a previous video that one meaning of oxidation is the gaining of oxygen and that reduction is the loss of oxygen for example if aluminum reacts with oxygen to form aluminum oxide we can say it's been oxidized whereas if we take away that oxygen then it's been reduced the terms oxidation and reduction can also refer to the loss and gain of electrons though and instead of just remembering which is which most people use the mnemonic oil rig which stands for oxidation is loss reduction is gain and this refers to electrons so if we had a magnesium atom and it loses two electrons to become a two plus ion then has been oxidized and if it gained those two electrons back then it would have been reduced most of the time though these oxidation and reduction reactions don't happen by themselves instead they both take place at the same time because if one substance loses electrons then another substance has to gain them and because both happen together we call them a redox reactions which just means reduction oxidation reactions for example if we react some magnesium with a dilute acid which we can represent as h plus because that's the important part of an acid then the Magnesium atoms will lose two electrons and be oxidized forming magnesium two plus ions meanwhile the hydrogen ions will gain those electrons and so be reduced to neutral hydrogen atoms in the form of hydrogen gas another place we see redox reactions is in displacement reactions which involve a more reactive metal displacing a less reactive one for example if we look at our reactivity series we can see that calcium is more reactive than iron so if we added some calcium to a solution of iron sulfate then the calcium would displace the iron to form calcium sulfate while the iron would precipitate out as a solid for reactions like this is sometimes useful to write them as ionic equations in which we only showed the particles that actually take place in the reaction and change in some way for example if we showed everything here as ions we can see that these sulfate ions stay as so4 to minus ions they don't actually change or take place in the reaction by exchanging electrons because of this we call them spectator ions and get rid of them from our equation and what we have left is the ionic equation we can actually break this down even further though by writing individual half equations which show the gain and loss of electrons for each of the elements involved to do this we first copy the ionic equation but only for one particular element so for calcium we would write that a neutral calcium atom goes to form a calcium two plus ion next we need to add our electrons to make the charges balance as the calcium atom loses two electrons we can think of the calcium ion as one product and the two electrons as another product so we put plus two electrons on the right hand side then for iron we show the Iron II plus ion going to form an iron atom and then again think about our electrons this time the iron ion gains two electrons so we place the two electrons on the left because they have to combine with the iron ion whenever you do these half equations just check that the overall charge on each side balances for example in our iron half equation we can see that on the left we have a two plus charge and two one minus charges which add together to make zero and on the right everything is neutral so also zero if you ever find that the overall charges on each side aren't the same then you've probably put your electrons on the wrong side anyway that's all for this video so if you enjoyed it then please do tell your friends about us and we'll see you next time