hello welcome for another great installment of some ap chemistry lectures by mr lambert this is uh the start of unit four chemical reactions um you can see here the book torque problems and the uh the you know these are good just gives the book work problems see please see google classroom for the um outline chapters um we've also posted the bookwork problems up there okay so our first section we're going to just uh just a quick introduction to chemical reactions now a lot of this this is actually um all we really need to talk right right now um a lot of this is a review from from last year or wherever whenever you took honors chemistry so physical and chemical changes physical changes are changes that occur when a substance undergoes a change in its properties but it's still the same substance okay um there's no change in composition there's just a change in the in the properties this could be a phase change it could be um when a mixture forms or separates uh cutting something into smaller pieces crumbling something up changing something if it's a piece of metal we could draw it in wires or flatten it into sheets these are all just physical changes changing its color by like simply painting it or something like that these are these are physical changes a chemical change is a change that occurs when a new substance is produced now we have these four indicators of a chemical change that were discussed in honors chemistry we have a production of energy we have a formation of a gas formation of a precipitate and a color change so um production of energy i should say could be either a use of energy or or a production of energy it should be a change in energy whether it's endothermic or exothermic and sometimes we see this just in heat you know increase or decrease in temperature and sometimes we see it in the form of giving off light or a fire um formation of a gas keep in mind things to look for when you see a formation of or when you see a gas form you might see bubbles coming out of the uh out of the mixture you may see uh or substance um you may see you may see some sort of vapors coming off um something to that extent now keep in mind when when you have a phase change going from a liquid to a gas or a solid to a gas there's a formation of a gas there but we have to think is a new substance being produced and if it is a new substance and it's a chemical change but if it's just a physical change forming a gas well that's just a phase change formation of a precipitate remember with double replacement reactions when you mix two solutions together if it forms a precipitate that is a solid forming from solution that is the definition of a precipitate when a solid forms from solution you can also see this with a single replacement reaction not all single replacement reactions will form a precipitate if they are if they will react sometimes that that substance that a single replacement reaction produces could be a gas or a liquid in the case of something like bromine um so sorry so uh so formation of a precipitate a solid that forms from solution and just keep in mind that not all mixtures of solutions will form a precipitate um which is something that we'll talk about in detail in another unit um color change you're also going to have a color change that occurs with most chemical reactions not always but a color change now just because you see or observe one of these four indicators doesn't mean we always have a chemical change that's not what we're saying here all right because it could very well be a physical change but what you need to use these things for is is another piece of evidence to prove that a as a an observation that you would have to prove to back up your claim that a chemical change would occur okay so the next section we're going to talk about is uh we're going to talk about ionic equations i'm actually probably we'll see how far we get in this video i might actually um um talk about electrolytes and then paul's and then go back and make a video some video about net ionic equations but we'll see so electrolyte is a substance whose aqueous solutions contain ions so you dissolve it and it produces ions okay best example sodium chloride any salt that if as long as it will dissolve will produce an electrolyte um some other covalent compounds when they dissolve will produce ions as well and typically these are these are substances that will produce acids we'll talk about them as well now these electrolytes are going to be able to conduct an electric current okay now this says that there are three types of electrolytes it's actually probably not written correctly um there are three categories uh there's actually two types of electrolytes it's either a strong electrolyte or a weak electrolyte um now strong electrolytes completely break apart into ions whereas weak electrolytes partially break apart into ions and so with a strong electrolyte 100 of the particles that that is there will be ions in the solution with the weak electrolyte some of the particles will be electrolytes some of them will just be the actual molecule still intact with non-electrolytes that is a substance that stays in its molecular form it's dissolved in the water but stays in its molecular form strong electrolytes are going to be salts and strong acids and bases weak electrolytes will be any other acid or base we call these weak acids and weak bases and then non-electrolytes is everything else a lot of organic substances are non-electrolytes sugars alcohols all these things are non-electrolytes okay and we'll categorize them here in a little bit a little bit better all right so when ionic compounds dissolve they're going to produce ions in water so these ionic compounds um when i say salts that's what we mean by ionic compounds all right think about those as being analogous um so each ion in that ionic compound as it's dissolved is going to be surrounded by water molecules like we learned about in the previous unit now these ions the movement of those ions is what is what is conducting that electric current those actual ions and so in order for something to conduct electricity it has to move along some sort of charged particle now typically with electricity electricity we it moves uh through electrons through a movement of electrons but it can move through ions as well electricity that is can move through ions and so that's what makes salt waters uh electrically electrically conductive molecular compounds can ionize into solution sometimes 100 percent sometimes only partially other molecular compounds are not going to ionize in solution and so it's actually a different term that we use here notice notice the use of the word i and i are sorry notice the use of the word let me just make sure notice for ionic compounds notice the use of the word dissociate um you can think about this as the ions when they're dissolving they they are ceasing to associate with one another all right they are dissociating okay they're already ions they're just dissociating but when we come over here when we're talking about molecular compounds that break apart ions we talk about ionize we use the term ionized because molecular compounds are not ions in their molecular form they're molecules so when they dissolve in form ions they have to first ionize before they can actually be in that solution and so it's a the the end result is the same it's just a different uses of the term depending on the substance that we're we're talking about so when we're talking about acids and bases actually technically when we're talking about acids we use the term ionize and if we're talking about bases and salts we would use the term uh dissociate but it's actually not always true now i think about it so um when we're talking about most bases and salts we would use the term dissociate but for a base like nh3 we would actually use the term ionize and we'll have to discuss that later when we talk about acids and bases i'm not going to bring that into the fold now unless it's absolutely necessary later or you can ask me in class um and then you have other molecular compounds that are not going to split apart into ions they are not going to conduct electricity and these are your non-electrolytes these are going to be the non-electrolytes all right so strong um molecular compounds really acids and bases these are going to be either strong or weak we'll go over the list later and then a molecular compounds that do not break apart ions are your non-electrolytes so let's look at this particle diagrams i talked in class about how particle diagrams are really really important piece and so let's talk about what particle diagrams look for um little strong weak and non-electrolytes okay so particle diagrams so over here we have a strong electrolyte in in acl um and we see that in the solution we have positive ions and negative ions broken apart okay and just to just be able to fit more in here i made a little key down here what my positive circles and negative circles were uh but these these n a pluses and these cl one minus and now that i'm looking at i realize that i'm i'm off by one so let's just put another plus right down here because it does need to be even because it's a one to one ratio um so now i think i have five i'm fi wait did i not you know what i had enough all right let's go put a negative right there no i think we're good okay so um so you know you have that implies they're touching so let me get that seed look so you have positive ions and negative ions completely broke apart in the solution surrounded by water molecules over here we have a weak electrolyte a weak electrolyte hf is a weak acid um yeah and in that we have a weak electrolyte and you'll notice that we have some hf particles but then we have some h plus particles and f minus particles okay um and so you're going to have uh both species f minus f minus f minus h plus h i didn't purposefully uh do that i probably should should have put one in the other and put some in the top some of the bottom let me evenly distribute them as best i could hard to do that but but these are acceptable and again i should show that they are separated they are not touching um they really need more a bigger piece of paper right smaller to be able to do this correctly um but you the whole idea is that you have the species that are present you're going to have hf you're going to have h plus and you're also going to have f1 minus all of those species present in the solution whereas over here you only have n a plus and c l minus all right and then we lastly we see over here this is a non-electrolyte all right this is a non-electrolyte and you're only going to see the ca for co2 gas when it's dissolved or should it make it aq because now it's dissolved so you see that you just have the co2 particles you do not have ions here the only species present is co2 okay okay friends so for strong electrolytes when we're looking at uh strong electrolytes um and and showing an equation to represent this what you're going to see here is you're going to see the strong electrolyte written on one side aqueous um and then on the other side you'll have a first of all you'll have a one-sided arrow and then you'll have h plus and aqueous plus cl one minus eight because you have the ions with the aqueous because that's the physical state written after it this is hydrochloric acid ionizes when placed in water um so nacl on the other hand um well actually really same thing you see the na1 plus aqueous plus cl1 minus aqueous when it's dissolved in water this is a this is the way that we would represent it when we're writing ionic equations um so and notice because these are strong electrolytes you're going to have that single forward arrow alright this implies that once the substance is placed in water it exists exclusively as those ions as a as opposed to weak electrolytes now weak electrolytes we're not going to show a one-sided arrow you'll notice here right away there's a double-sided arrow that is implying that you're going to have this species present this species present this species present for this bottom one and then up here you'll have this one this one and this one present all right like i showed you in the particle like diagram for hf this is just two other weak electrolytes um so so yeah so so acetic acid is a weak electrolyte um and so you'll have that double-sided arrow one side you'll have the the the the molecule the molecular compound written as as if it's still a molecule which it is partially and then you also have the ions that it would ionize into um but not a hundred percent okay all right yeah and then lastly we would have a non-electrolyte we really wouldn't change anything here we're going to take this liquid um and you'll place it in water and it'll be dissolved to ch3 aqueous um you could have a situation which is back up here you could have a situation where you took you said all right i got hcl gas and that's the form that you would talk about and you place it in water all right what are you gonna get like if you're stating that i'm taking a gas and i'm placing it in water all right what are you going to sometimes uh you might see all right let's put it in water and then you'll have h plus aqueous and plus a co1 minus aqueous you could have that written for the strong electrolytes but it's important to note for the weak electrolytes you need to have the aqueous here because it's implying that you have this species in the solution as well whereas here you know i've seen it written both ways where what we start with or if you just see this so so what you start with this is what you'd start with hydrogen chloride gas for example or nacl solid all right uh writing this when you see this you need to think this all right when you see a strong electrolyte written the substance aqueous you need to be thinking oh those ions are there that's really what we mean when we write hcl aqueous all right um whereas opposed to if you see a weak electrolyte and it's written aqueous you need to think okay that thing exists the molecule as well as the ions that will ionize it into all right and so you need to be thinking this in your head now here in a minute we're going to use all these when we do um and then non-electrolytes just you know looks the same it's just that you're changing the physical state um here's giving you a few more substances hydrocarbons alcohols and sugars are not electrolytes um so this actually helps you identify the uh strong electrolytes and weak electrolytes um so strong electrolytes are going to be all ionic compounds um none of the ionic compounds will be weak or non-electrolyte okay and then molecular compounds that are strong electrolytes you're going to have strong acids which is table 4.2 in your notes um that's going to be h2so4 you need to memorize these hcl up hcl let me get away from that uh hbr hi 1803 hclo 3 and hclo4 i believe that's right all right seven one two three four five six seven yeah so hydrogen hydrochloric acid um chloric acid and perchloric acid um all right okay so those are your strong acids and now for your weak or sorry enough for your strong bases because they're also going to be strong electrolytes too um and these are all this is given in table 4.2 the list of strong acids as well as the strong bases your strong bases are going to be your group one hydroxides all right group one hydroxides as well as calcium strontium and barium hydroxide um okay if you look on your periodic table calcium strontium and barium hydroxide are the are the heaviest um group two metals um so your group one hydroxides as well as your heaviest group two metals calcium strontium and barium hydroxide okay so this next slide here we would talk to talk about how electrolytes can conduct an electric current but let's talk specifically how what we would see if we were to do this a demonstration of this with a strong electrolyte which is what you see here in the middle you would see a very bright bump because you've got all those ions there and all those particles are able to conduct an electric current with a weak weak electrolyte you're still going to see the bulb light up and i should just back up here we got an electrical source all right and we got the negative in in the water and the positive end in water this is this is completing the circuit to allow the bulb to light up right so when you put these metal plates in the water if the water has some medium for the uh substance to conduct electricity then you will light up the bulb um so that's what we see with a strong electrolyte we see a bright bulb because there's lots of ions there to be able to conduct that electricity now with the weak electrolyte we're still going to see the bulb light up but it won't be as bright because we don't have as many ions there and so you'll see you'll see the bulb light up but it definitely won't be as bright we see acetic acid here which is a a weak acid and i should have gone over that so we have our list of strong acids here and our list of strong bases any other acid or base is going to be a weak base okay so acetic acid is not on the list of a strong acid so it's a weak acid um and that's what we see here acetic acid all right particle level diagram for it a little bit deceiving because it's actually c2h3o21 minus but hey this is your molecules that are present and here's your ions it's just not as many ions to be able to conduct the electric current and then over on the far left we see we have ethanol which is an alcohol does not break apart into ions does not light the blood so this is going to be your non-electrolyte i'm going to stop here i'm going to put all this together in one video and then i'll make a separate one on how to do ionic and net ionic equations