in this video we will be looking at topic four of GCSE chemistry and that is chemical changes here are some of the subtopics we'll be looking at throughout this video and as always these pages will be available to buy on my Etsy in the description thank you very much for watching and I hope you enjoy first of all we have the pH scale the pH of a substance is measured using Universal indicator or a pH probe and meter the universal indicator will turn one of the colors on the scale below as you can see in the middle of the screen and a pH meter will return a number from 0 to 14 anything on the red hand side or left of the number seven the neutral color is an acid and anything between 8 and 14 is classed as an Alkali examples of different acids include battery acid lemon juice and acid rain and examples of alkaly include bleach soap powder and washing up Liquid I would definitely recommend remembering at least three examples of each of those and if you do think of any others please let me know down below and the only real example of a neutral substance is pure water that's all you really need to remember next we have acids and bases an acid is simply as we said before a solution with a ph7 or lower but the new fact about acids that is really important is acids form H+ ions in water so they dissolve and form H+ ions bases are any substance that will form a salt when reacted with an acid it's a very common mistake that people think that an Alkali and a base is exactly the same thing as we can see on the second bullet point an Alkali is a form of a base with ph more than seven alkalis instead of H+ ions like acids they form oh minus ions in water it is also important that you are aware what causes a strong or weak acid or Alkali as you can see written down below a strong acid or alkal ionizes completely in water and this means it releases lots of those H+ FR an acid or o minus for an Alkali ions there are quite a few reactions that are important to remember that you could be asked to kind of fill in the blanks or that kind of thing within your exam so up the top I've put the two that are the most different so water plus a metal makes metal hydroxide and hydrogen and if you think about it water is just two hydrogens and an oxygen so if you take metal and react it with those two things metal hydroxide is just going to be the metal plus an oxygen and a hydrogen which leaves you with a hydrogen so if you understand a bit about the atomic like makeup behind water or these compounds it can make these reactions a lot easier to remember the other one on the right hand side is an acid and a metal make salt and hydrogen and it's a very similar thing so an acid could be an example such as nitric acid and ion so the salt comes from the ion and the nitric acid forming ion nitrate and acids have hydrogen in it as we found before when it's dissolved in water so that is why the extra hydrogen is on the end there the other four reactions you have to remember are forms of neutralization reaction neutralization reactions are simply when you have an acid so a low PH reacting with a high pH like an Alkali or a base and they kind of neutralize each other so the four we have is acid plus base makes a salt and water acid plus metal oxide makes salt and water acid plus metal hydroxide makes salt and water and then acid plus metal carbonate Mak salt water and carbon dioxide so again a lot of those are fairly similar very important to remember that metal oxide metal hydroxide and metal carbonates are rule bases which is why they are classed as neutralization reactions and something key to Remember at the bottom about different acids and what salts they create so sulfuric acid creates sulfates nitric acid creates nitrates and hydrochloric acid creates chlorides so as I said before if you had something like aluminium reacting with sulfuric acid it would create Al aluminium sulfate or if you had copper reacting with hydrochloric acid that would create copper chloride so it's just simply the metal and the salt next we have the reactivity series now this is something I believe you are given in the exams however I would also recommend remembering a good chunk of it so you can see a lot of the top elements on this list are group one elements and they are typically known as being very reactive and as you go down the list you get some more copper silver and gold they're like the transition metals in the middle of the periodic table so sometimes it is a bit of Common Sense and you can kind of remember which ones are going to be higher than others when it comes to those exam questions but effectively the reactivity series lists in order how reactive different metals are in comparison to each other the reactivity is determined by how easily they lose electrons so again potassium sodium lithium all in group one they will lose that one electron very easily carbon and hydrogen you'll notice are on the list and they're in red now they are not Metals obviously they're non-metals the reason they're included is because it gives us an idea of if we have to extract that metal from its natural form so from like an or for example then if it's more reactive than carbon there's certain methods we can use to extract it and if it's less reactive than carbon there's other methods and the same kind of thing happens with hydrogen next we have Redux reaction this is just a reaction where electrons are transferred now there are two more key words we're going to learn about in this page and that is oxidation and reduction reduction and oxidation is where the name Redux gets its name from CU reduction and oxidation makes Redux if you shorten it and something very important to remember is oxidation is loss and reduction is gained and that is remembered with the pneumonic oil rig what that actually means what it's losing and gaining is just the electrons so as you can see in the little purple box a loss of electrons is called oxidation and the gain of electrons is reduction again could just simply be a definition that you need to understand and be able to recite an example of what I've got here is a type of Redux reaction called a displacement reaction and this Works hand in hand with the reactivity Series so Fe iron plus C so4 so that is copper sulfate reacts to make ion sulfate feo4 and CU now all you can see here is the ion is more reactive than the copper so basically what happens is the iron displaces the copper and binds with the sulfate finally we have electrolysis effectively all that happens is you've got your purple liquid in this case which is called an electrolyte and that is usually a compound of metal and a non-metal so in this case I've got aluminium and bromine you've got a DC so a direct current power supply at the top and that is supplying electrons to both of the electrodes so the positive and negative the anode and the cathode that are dipped into the electrolyte now all this does is when the metal and the non-metal ions are in that electrolyte the positive metal ions are attracted towards the cathode because they are positively charged and the negatively charged non-metal ions are attracted to the anode the positive electrode at each of the cathode and the anode the electrons are either stripped from the ion or electrons are given to the ion to neutralize them both and then once this happens the metal ions will sink and form a molten metal layer at the bottom and the non-metals float up to the surface often as a gas and Escape through that way and this is just explained in a more concise summary at the Bott bot of the page that sums up the end of topic four chemical changes and the next topic we're going to be looking at is energy changes thank you very much for watching I hope this helped and please like And subscribe if you found this useful