in this video we're going to focus on distinguishing pure substances from mixtures now here's a question for you what exactly is a pure substance and how is it different from a mixture a pure substance has constant composition pure substances can be elements they can be compounds but they always have a definite and constant composition a mixture is basically a combination of multiple pure substances and a mixture can have variable composition so for example let's say if we have the element helium is that a pure substance or is that a mixture helium is a pure substance if you have a single element it will always be a pure substance now what about H2O water is water a pure substance or mixture now water is a compound it's not a Pure Element like helium helium is only made up of one type of atom water is made up of two types of atoms hydrogen and oxygen so therefore water is a compound compounds are made up of two or more more different atoms if you have a single compound it's going to be a pure substance now what about hydrogen gas is that a pure substance or is that a mixture hydrogen gas is a pure substance like helium it's a Pure Element however it's slightly different than helium helium is composed of single individual atoms hydrogen gas is composed of molecules a molecule is basically a substance that has multiple atoms so water is a molecule and hydrogen gas is a molecule the difference though is that water is made up of two different atoms which makes it a compound in addition to being a molecule so you can call it a molecular compound but hydrogen it's only made up of one type of atom which is hydrogen so H2 is a Pure Element and at the same time it's a molecule so pure elements are made of only one type of atom like helium or hydrogen gas those are pure elements molecules are made up of multiple atoms two or more atoms it could be the same type of atom in a case of hydrogen gas or it can be different types of atoms in the case of water so whenever you have multiple atoms in its individual particle it's a molecule now if you have a particle that has different atoms like water it's a compound so I want you to be familiar with those terms so if you have an individual molecule an individual atom a pure element or a single type of compound all of these are pure substances now a mixture is simply a combination of multiple substances so for example if I have a beaker that has hydrogen gas and helium gas I now have a mixture so let's say if I have nitrogen gas combined with oxygen gas that is a mixture I have two pure substances mixed together now what about salt water is salt water a pure substance or is it a mixture salt water is a pure substance I mean I take that back not a pure substance it's a mixture now let's talk about why salt water is composed of water and salt salt is NAC sodium chloride so individually pure salt is a pure substance Water by itself is a pure substance but when you mix these two together when you combine them you now have a mixture so salt water is a mixture now I briefly mentioned this early in the video but pure substances they have a constant composition a mixture can have a variable composition and let me illustrate what is meant by that so I can mix salt with water in different proportions for example I can take 5 G of table salt and mix it with 95 G of water so in this case I have a 5% salt Solution that's 5 G out of a total of 100 gr of solution or I can Mi 10 G of salt with 90 G of water so now I have a 10% saltwater solution so as you can see a mixture it can have a variable composition I can have a 5% salt solution or I can have a 10% salt solution or a 20% salt solution I can control the composition of my mixture now a pure substance the composition is constant you can't do that for example the only thing you can change about a pure substance is the amount of matter you could change the volume or the mass I can put let's say 10 millit of water in this Beaker let's say it's pure water or I could fill it with 20 M of water so I can change the quantity of water in this Beaker but I can't change the composition in both cases it's pure water it's not mixed with anything else so this is 100% pure water and this is 100% pure water so whenever you have a pure substance regardless if you have a little or a lot it's still 100% pure you cannot change the composition the only way to change a composition is to create a mixture now if I add salt it's no longer going to be pure water it could be 95% pure water it could be 90% pure water but once the composition changes you now have a mixture you no longer have a pure substance so remember a pure substance has a constant composition but a mixture has a variable composition now another way that you can disting a pure substance and a mixture is the way in which you can separate them or break them down into their components a mixture you can separate the components of a mixture by means of a physical process the components of a pure substance if you have a compound you can separate it by means of a chemical process so let's take a let's take salt water for example so imagine if you have a beaker and there's water and there's also some salt you have your sodium ions and your chloride ions now if you were to put this salt water on a stove or if you add heat to it what's going to happen eventually when it gets hot enough all of the water molecules are going to boil off and then what's going to happen is you're going to be left with this dry solid residue which is basically table salt sodium chloride so by applying heat you can boil off the water and the solid sodium chloride will remain because it's very difficult to boil off sodium chloride it has a very very high melting and boiling point so you can use a physical process to separate salt from water now it doesn't have to be boiling which you have to heat it to its boiling point to separate water even if you left let's say a puddle of salt water if you left it out in the open in a dry room without raising the temperature water can evaporate on its own perhaps you've placed a pot of water on a table and if your AC is on you'll notice that eventually that small pot of water water is going to evaporate evaporation is the process where something that's volatile like water it can evaporate without the use of heat all you need is a dry room if you want to boil it off you got to add heat and water is going to EV vaporize into a gas AKA steam but to get back to what we're talking about you can separate a mixture by means of a physical process evaporation boiling decantation filtration centrifugation chromatography all of these are physical processes that can be used to break down a mixture into its components now let's talk about a chemical process that can be used to break down a pure substance in the form of a compound a good example is H2O now let's say if we take a beaker you add water and you place two metal electrodes it could be two graphite pieces graphite conducts electricity and let's say you take a 9volt battery and you connect it with a wire across the graphite electrodes what do you think is going to happen now pure water doesn't conduct electricity very well so you may need to add some table salt to it once you add salt to water it conducts electricity a lot better now this is known as electrolysis electrolysis is a chemical process that can break down water into its component elements it can break it down into hydrogen gas and oxygen gas so at one of these electrodes hydrogen gas will evolve from it you'll see these little bubbles uh bubbling up from the solution if not maybe have a dead 9vt battery maybe have to increase the voltage on the other side you'll see another set of bubbles which will be oxygen gas so electrolysis is a chemical process that can break down a compound into its pure elements in the case of water it breaks it down into hydrogen and oxygen so you can use a chemical process to break down a pure substance into simpler elements but you can use the physical process to break down the components of a mix to separate one component from another in the case of salt water if you had heat you can boil off the water and the salt will remain behind that's a physical process now what I'm going to do at this point is I'm going to give you a list of stuff and I want you to classify it as a pure substance or mixture so we're going to go over a lot of of examples carbon dioxide dry ice CO2 is it a pure substance or mixture carbon dioxide is a compound because it's only a single compound it's a pure substance now what about iron metal is iron metal a pure substance or is it a mixture now iron metal is a Pure Element it's a single element so that makes that makes it a pure substance now what about brass b r a SS is brass a pure substance or is it a mixture now brass is not a Pure Element brass is known as an alloy an alloy is something that's composed of many metals in the case of brass it's composed of copper and zinc so brass is actually a solid solution of copper and zinc now what about air is air a pure substance or is it a mixture air is a mixture air is not composed of just one type of compound or element rather it's a mixture of gases air has nitrogen gas it has oxygen gas it has carbon dioxide gas sometimes water vapor and even some Argon gas so air is a mixture of gases it's a homogeneous mixture a homogeneous mixture is a mixture where it has uniform composition a heterogeneous mixture it does not have that uniform composition one side could have a a different composition from Another Side now what about sugar is sugar a pure substance or a mixture sugar is a pure substance it's C6 h126 that's a glucose table sugar is sucrose which is C12 h221 perhaps you've learned that in U biology class but table sugar is a pure substance now sugar water that's a mixture of sugar and water so that's not a pure substance now what about 24 karat gold is that a pure substance or is that a mixture 24 karat gold is pure gold and gold is an element so that's a pure substance now if you have like 14 karat gold that's not a Pure Element that's a mixture it's an alloy like brass 14 karat gold means there's some gold in it but there's also something else you could have silver there could be copper or another metal inside of it so 14 karat gold is a mixture of many metals now what about rubb and alcohol is rub and alcohol a pure substance or is it a mixture rubb and alcohol is a mixture it's composed of isopr alcohol with some water added to it so if you look at a bottle of veral and alcohol it might say it's 70% alcohol that means the other 30% is water so it's not pure alcohol now let me clear the page now what about soda so let's say if you're drinking a bottle of Pepsi or Coca-Cola is soda is it a pure substance or is it a mixture soda is a mixture it contains water it contains sugar it might have some caffeine so that's a mixture now what about milk is milk a pure substance or is it a mixture milk has water it has proteins it has uh fat molecules fatty acids so milk milk is a mixture there's multiple substances in milk now what about silver metal is that a mixture or is that a pure substance silver is a Pure Element which makes it a pure substance now what about something called sterlin Silver is that a pure substance or is that a mixture sterling silver is a mixture it's an alloy it's 92.5% silver and usually about 7.5% copper so it's a solid solution of two metals so anytime you have an alloy it's always going to be a mixture now what about sea waterer is seawater a mixture or is that a pure substance sea water is basically salt water you might have some other elements there too but it's mostly water and sodium chloride with some other stuff so that's a mixture now what about wood soil and wine go ahead and classify these as mixtures or pure substances wood comes from living material like a tree and things that can grow nature are usually composed of carbohydrates proteins nucleic acids so wood is definitely a mixture it doesn't consist of one type of compound or a Pure Element soil is also a mixture soil could have some sand in it silicon dioxide it could have some fertilizers it can have water in the soil it could be a wet soil so soil is a mixture and wine is basically water plus alcohol typically ethanol so wine is also a mixture so keep this in mind a pure substance is usually a single element or single compound a mixture is the combination of multiple pure substances if there's a lot of stuff in it chances are it's a mixture for