hello this is the chapter on acids bases and salts um so let's first of all take a look at the definition remember that if he asks you to define acid or base acid is proton donor base is proton etc that's the definition now what does that mean it means that when you have an acid and it reacts in a reaction it donates or it gives h plus ions so when we talk about a proton we're not talking about the what we call subatomic particle the particle inside the atom we are talking about an h plus ion why do we refer to it as a proton do you understand that hydrogen atom is something that has one proton one electron nothing else so if it forms h plus ions what did it do it lost that outermost electron so it's actually an atom that has just one proton in its nucleus and that is why we refer to it as a proton so when we ask what is the species that has been donated by the acid the species is h plus iron so acid is a proton donor when we dissolve an acid in water it uh ionizes or breaks up to form h plus ions a base is a proton acceptor so when it reacts it takes the h plus ions from the acid and that is because when you dissolve a base in water it forms hydroxide ions and the hydroxide ions when they accept the h plus they form water so a reaction between an acid and a base would result in the formation of water okay so acid is a proton donor and we understand that proton is what proton is h plus iron a base is a proton acceptor now how do i know if something is an acid or a base that is from the formula the acid will always have an h at the beginning or at the end if it's organic but let's just stick to um the h at the beginning the base will always have an oxygen or a hydroxide ion at the end of so an acid is h something a base is something o h or something o okay so what is an alkali an alkali is a base that dissolves in water so if i have a base some of them dissolve in water and some of them don't if the base dissolves in water it is called an alkali so for example you should know that sodium hydroxide is a typical alkali because sodium hydroxide is a base and it dissolves in water now when we react an acid with a base what forms is called a salt so salts are ionic substances that are produced from the reaction of acid with base you could have two different types of acid the acid could be concentrated or could be dilute this is when i add a small amount of water or a lot of water so if something is concentrated that just means that it has only a small amount of water added to it when something is dilute that means it has a lot of water added to it and that could apply to an acid or it could apply to a base so i could have concentrated base or dilute base and it is the same idea if i have a base and i put a little bit of water on it it's concentrated if i add a lot of water it is dilute okay okay there are two types of acids and two types of bases so an acid is either a strong acid or a weak acid a strong acid is one that will for a break up to form a lot of h plus one so if i have hcl hcl is an acid when i dissolve it in water it ionizes ionizes means it breaks up into h plus and c l minus now because hydrochloric acid is a strong acid all the molecules of hcl in the solution will break up to form h plus and cl minus this is a characteristic of the acid so an acid like hydrochloric acid is a strong acid and that means that it ionizes completely in solution to give lots of h plus ions other types of acids are weak a weak acid will only ionize partially what does that mean ch3cooh is ethanolic acid we will be talking about it a lot more when we talk about organic acids for now just know that ethanoic acid is ch3cooh when i dissolve it in water only some of the ethanoic acid molecules will break up to form h plus ions so we say it ionizes partially to form a small amount of h plus ions and that is definition of a weak acid so the acid is either strong or weak hydrochloric is strong sulfuric is strong nitric is strong things that are weak are like ethanoic or citric acid i'll talk about ph in a minute so let's just ignore the ph for now now a base also may either be strong or weak we said how do i know if something is a base if it ends with for example hydroxide also something hydroxide would be a base now sodium hydroxide is a strong base and with the same idea that that means that when i dissolve the sodium hydroxide in water all the molecules will break up will ionize to form lots of o h minus ions but there are some bases that are weak a weak base means it will ionize partially so if i have ammonia molecules and i dissolve it in water only some of the ammonia molecules will ionize to give just a small amount of oh h minus ions so for now know that sodium things like sodium hydroxide potassium hydroxide calcium oxide things like that are strong bays ammonia is the only weak base that we deal with in this cellus okay what does that mean or how can we distinguish between these different types um they have um scientists i mean um have chosen a scale to determine or to given to the acids and bases in order to indicate whether an acid is strong or weak or a base is strong or weak now this ph scale are numbers from 1 to 14 and sometimes we have 0 to 14. and we say if something is a strong acid i'm going to give it numbers 1 and 2 and 3. so if we say suggests a ph for hydrochloric acid you can either say one or two or three this is whether it is concentrated or dilute so if we say dilute don't give it anything more than three it is still three uh ph of sulfuric acid is either one or two or three ph of nitric acid is either one or two or three this is because all of these are strong acids but if i say suggest the ph of lemon juice or ethanoic acid or vinegar we just said that ethanoic acid is an example of a weak acid do you remember the definition of weak acid weak acid means it will dissolve in water ionize partially so only some of the molecules will ionize to give h-plus ions now if he's asked to suggest the ph of any of these i would say four or five or six not more not less so ethanoic acid should not have ph2 for example because it is not a strong acid it's weak acid now if something is not an acid and not a base we say it is neutral and we give it a ph of seven so what are the things that are neutral that we deal with water is neutral salt like sodium chloride is neutral so we give it a ph of seven now bases some bases are weak and some bases are strong and we said things like sodium hydroxide calcium hydroxide are strong bases so if he says to just the ph of sodium hydroxide you can either say 11 12 13 14 not less than that a weak base like ammonia will have a ph of 8 or 9 or 10. you have to know these things you may be asked to suggest the ph of any of these solutions so let's try a sample question this question says concentrated hydrochloric acid is a strong acid what is meant by strong and what is meant by acid so strong means we said the strong mean contains a low proportion of water or is fully ionized remember that we said if something contains a low proportion of water we don't say it's strong we say it is concentrated so a strong acid is something that is fully ionized when dissolved in water okay we said what's definition of acid we said an acid is a proton donor so my answer is d okay the next one which one of the following ph values could be the ph of aqueous ammonia remember what what did we say about ammonia we said ammonia is a weak base and a weak base will have ph's we said 8 or 9 or 10 so my choice here would be ph 10 okay now if you've gone to the lab at any point and seen solutions of acids and bases you would know that an acid and the base are both colorless solutions so hydrochloric acid is a colonist solution sodium hydroxide is a colorless solution if i have in one beaker i have acid and in another beaker i have base how can i distinguish which beaker is which i can add a little bit of indicator so an indicator is a substance that has different colors in acids and bases so if i have something i put it in acid it gives a color i put it in base it gives a different color then that thing can act as an indicator so what indicators do we talk about we have four indicators in our syllabus we have litmus paper universal indicator paper phenolphthalein and methyl orange so let's take a look at this litmus paper litmus paper is used to determine whether something is an acid or a base it doesn't tell you whether it is strong or weak it just says whether it's an acid or a base it doesn't tell you what is the ph of the solution so here i have two beakers they are both colorless solutions there is no way for me to determine by looking at them but which one is an acid and which one is a base but if i put litmus paper and if you've seen litmus paper it's a paper like this some of it is blue and some of it is red so i have what we call blue litmus paper and we have red litmus paper now if i want to determine if something is an acid and i put the blue it will turn to red now if i put the red it remains red so litmus paper is red in acids so if it was originally the red one it would remain red if it originally it was the blue one it will turn to red okay what if i put litmus paper in base litmus paper in base turns blue so if it was originally blue it would remain blue if it was originally red it will turn to blue so litmus paper in acid is red in base it is okay so that tells me whether this is an acid or a base but it will not tell me whether it is a strong acid weak acid strong base weak base if i want to know exactly what type of acid or what type of base i use what we call a universal indicator paper the universal indicator paper is actually originally it's yellow but when i put it into the different solutions it will take one of these colors so if i put it in sulfuric acid for example it will be red if i put it in lemon juice or ethanolic acid something that's a weak acid it will be yellow or orange if i put it in water it will be green if i put it in ammonia which is a weak base it will have shades of blue up to the strong base which is blue so remember that universal indicator paper in strong acid and in strong base it gives almost the same colors as litmus so in strong acid it's red and strong base it's blue you have to remember that if i put it in something neutral it gives what color neutral is ph 7 like water so it gives green if i put it in weak acid it gives yellow or orange and you're not required to know all of the shades of blue for the weak and strong bases okay so red and strong acid blue and strong base you could call it purple if you like but it's actually we call it blue in strong base green in neutral yellow or orange in a weak acid okay now the other two indicators are liquids so i have phenothelene and methyl orange and this is what we use in something we're going to be talking about which is titration now each of these has different colors in acid or base or neutral and you have to remember the colors so if i put phenophthalene in a base like sodium hydroxide for example it will give that color which we call pink in neutral or in acid phenophthalene is colorless so you have to remember that phenolphthalein in a base is pink in neutral or acid it is colorless now what about methyl orange methyl orange is red in acid yellow in a base and when the solution is neutral this is called methyl orange so it is orange remember that it's called methyl orange because it is orange in neutral but in base it is yellow in acid it is red you have to remember these colors so let's try this four different solutions are tested with universal indicator which solutions are acidic now we said if something is an acid it will be what color in universal indicator it will either be red or yellow or orange these are the colors that we had in universal indicator paper so the ones that are acidic here are the ones that are red and orange so that is the x and z okay okay let's talk about reactions of acids and bases and the first reaction that we have is called neutralization reaction neutralization reaction is a reaction between acid and base and this gives salt plus water so if i have something like acid like what like hcl for example hydrochloric acid a base like sodium hydroxide now what would be the ph of the acid we said hcl is a strong acid so its ph is either one or two or three sodium hydroxide is a strong base so its ph is 11 12 13 14 any one of that and when they react together what do they give they will give sodium chloride plus water that's my salt so the sodium chloride is actually what we call salt sodium chloride is the salt that we add to our food but it is we call it salt but actually it's only one type of salt so anything that is formed from acid and base is called a salt so what is the ph of the salt it's seven what is the ph of the water it's seven that means i have changed uh solutions that were originally acidic and basic into neutral solutions so we call that neutralization reaction okay what about acid plus metal now if i react acid with a metal what comes out is still called the salt but this is a salt plus hydrogen gas so if i have zinc with hydrochloric acid for example zinc when it reacts with hydrochloric acid it forms zinc chloride zinc chloride and i'm left with what i'm left with hydrogen so remember acid plus base gives salt plus water acid plus methyl gives salts plus hydrogen okay what about acid plus carbonate acid plus anything carbonate would give a salt plus carbon dioxide and water so for example if i have hydrochloric acid with calcium carbonate hydrochloric acid with calcium carbonate should give something plus common carbon dioxide plus what so what is that something that is left it's calcium chloride okay okay base the only reaction that we're going to talk about is the base with ammonium salts so a base with an ammonium salt you should know will give ammonia gas and when we talk about there's a reaction that we will talk about later when we talk about tests for ammonium if i want to know if something is an ammonium salt i can add a base like sodium hydroxide for example and it this gives ammonia gas you don't worry about this uh reaction it just gives the salt plus ammonia plus water okay okay the other reaction is if i have ammonia we said ammonia is the only weak base that we have we're talking about anyway so ammonia plus acid what happens what for what is formed is called ammonium salt we know that ammonia is a base and we just said that base plus acid should give salt plus water but ammonia is the only base that we are talking about that doesn't have o h we said a base is either something that ends with o or with o h but ammonia doesn't have any oxygen in it so there is no way i'm going to get water from this reaction so ammonia plus acid actually gives just salt remember ammonia plus for example hydrochloric acid will give ammonium chloride ammonia plus nitric acid will give ammonium nitrate ammonia plus sulfuric acid will give ammonium sulfate and so on ammonia plus phosphoric acid will give ammonium phosphate and of course we check the variances of each of them okay okay let's try this sample question which property is shown by the alkali sodium hydroxide so we said what what is meant by alkali again we said an alkali is a base that dissolves in water so sodium hydroxide is a base so which of these would be correct it has a ph less than seven what did we say about the base now a base will have ph more than seven okay it produces a gas when it is warmed with ammonium chloride yes sodium hydroxide is a base and we said base plus ammonium will give ammonia gas so this is actually my correct answer let's check the rest it turns blue litmus to red no this is a base a base will turn the red to blue not the other way around okay it turns universal indicator green no this is a base so it should turn universal indicator blue green is for neutral okay so let's try this question with five marks describe the reactions of hydrochloric acid with calcium oxide magnesium a named indicator of your choice so you're supposed to explain what will happen if you react hydrochloric acid with calcium oxide and hydrochloric acid with magnesium and if you put a certain indicator in the hydrochloric acid so you should react you realize that reaction of hydrochloric acid with calcium oxide this is a reaction of acid with base so this is a neutralization reaction and this forms calcium chloride and what now if i put hydrochloric acid with magnesium what is formed magnesium chloride and hydrogen gas so i will see bubbles of hydrogen gas remember that any reaction that gives out a gas if he says what is observed or what do you see you see bubbles of gas now if i put hydrochloric acid which which indicator did we choose here which was phenolphthalein if i put hcl that's an acid with phenolphthalein it forms what color colorless solution what if i had chosen methyl orange do you remember the color of methyl orange in acid what was the color of methyl orange in acid remember methyl orange is red in acid okay okay so let's try this question three chemicals were each dissolved in water the table shows some of the reactions of these solutions so let's look at p what what did he say about p with carbonate it gives off a gas so p is an acid or base p we said what is the substance that will react with carbonates to give out a gas it's acid so p must be an acid so acid means its ph could be 2 or 7 or 13 acid means it must be 2 so my answers should be a or b okay so remember an acid with a carbonate gives carbon dioxide gas with ammonium an acid will not react with ammonium which one reacts with ammonium ammonium we said reacts with a base to give ammonia gas okay so we've decided that p is an acid now what about q q when i put it on carbonate no reaction that means it is not an acid but when i put it on ammonium something a gas evolved so q must be a base because a base reacts with ammonium to give ammonia gas so q is a base so base is which ph 7 or 13 we've already decided that it's a orb so i want a base so a base is ph 13 so my answer must be b let's check r r no reaction with carbonate so it's not an acid no reaction with ammonium so it's not a base so it is something neutral so that is correct my answer is be okay so what is a base do you remember the definition of a base a base is proton acceptor that is what you're supposed to write right the balanced equation for the reaction between ammonia and sulfuric acid you remember how to write equations remember that all chapters from now on will be dealing with equations so the chapter on equations is actually a basic chapter that you have to know for sure so that we can answer questions in any other chapter so ammonia and sulfuric acid ammonia you remember how do we write ammonia ammonia is nh3 sulfuric acid is h2so4 and we said when we have ammonia with an acid it gives ammonium something so ammonia with sulfuric will give ammonium sulfate remember valency of sulfate is two and then to balance i need two in front of the ammonia okay so just the chemical equation for the reaction between sodium hydroxide and carbon dioxide now sodium hydroxide is a base and we said a base when it reacts with something that thing must be acidic and actually that is correct carbon dioxide is an acid so when it reacts with it it will form sodium carbonate plus water and then you balance okay okay let's try this one which reaction is a neutralization reaction remember we said what do we mean by neutralization reaction neutralization reaction means acid plus base so which of these is a neutralization reaction silver nitrate is that an acid base or salt now if it's an acid it should start with h if it's a base it should end with o h or o this is a salt so a is not a neutralization reaction what about b b is calcium carbonate breaking up this is called a decomposition reaction not a neutralization reaction c sodium is not an acid or a base so it's not c d i have sodium hydroxide and that is a base we said sodium hydroxide or any hydroxide is a base plus sulfuric acid so that gives salts and water so that is what we call a neutralization reaction okay okay which one of the following ph values is the ph of an aqueous solution of sodium hydroxide remember that we said sodium hydroxide is something that has a ph of 11 12 13 14 so my choice would be ph 13. okay he says the mixture of sodium hydroxide and ammonium sulfate is warm gently what is the name of the gas produced remember we said base plus ammonium will give ammonia gas complete the following equation to show that hydrazine acts as a base so hydrazine is something we haven't studied but it is something that is similar to ammonia n2h4 plus water now if i react it with water then it will form ammonium it's just like ammonium hydroxide if i say ammonia in water is ammonium hydroxide so hydrazine in water will be this n2h5 plus and oh minus okay write a chemical equation for the reaction between magnesium carbonate and dilute nitric acid remember that we said any carbonate with acid should give what a salt plus carbon dioxide plus water so magnesium carbonate remember valencia magnesium is two and valencia of carbonate is two plus nitric acid is hno3 so this gives magnesium nitrate and magnesium is a valency two so i have to put two under the nitrate nitrate is vanessa one so i don't put anything under the magnesium and we said carbonate plus acid will give carbon dioxide plus water now please remember that you never leave an equation without balancing it so this needs to be balanced so i put two in front of the nitric acid okay no reaction should be left without balance okay so i said that something that has o or o h should be a base something that has uh [Music] h at the beginning is an acid but actually that is not completely true so oxides or hydroxides so we're talking about oxides now some oxides are actually acidic some oxides are basic some oxides are amphoteric some oxides are neutral now what does that mean if i say that something is acidic that means it will react with a base if i say that something is basic then it reacts with an acid now if something is an amphoteric if we say something is amphoteric the word aphoteric means it can react with both acid and base okay if something is neutral then it does not react with acid or base following so an acid reacts to the base a base reacts with an acid amphoteric can react with any of them and neutral does not react with any of them now which oxides are acidic basic of photonic neutral remember that oxides of most non-metals non-metals are where in the periodic table non-metals are on the right side of the periodic table so oxides of most non-metals are acidic carbon dioxide nitrogen dioxide sulfur dioxide sulfur trioxide silicon dioxide all of these are acidic acidic means first of all if they are dissolved in if they dissolve in water they form acid and they will react with a base now so oxides of most non-metals are acidic but there are some exceptions some oxides of non-metals are neutral can you see where neutral is which ones are neutral carbon monoxide is neutral so carbon dioxide is acidic but carbon monoxide is neutral neutral means doesn't react with acid doesn't react with base nitrogen dioxide is acidic but nitrogen monoxide is neutral so no is neutron neutral means doesn't react with acid or base of course the oxide of hydrogen is neutral because oxidative hydrogen is what we call water and that is neutral okay so oxides of most non-metals are acidic except carbon monoxide nitrogen monoxide h2o these are neutral okay what about the basic which ones are basic oxides of most metals are basic so calcium oxide copper oxide magnesium oxide sodium oxide all of these are basic basic means if they dissolve in water they will form hydroxide ions but there are some exceptions some are not basic they are emphatic so which ones are amphoteric you are supposed to know these examples oxide of zinc oxide of aluminium oxide of lead these are amphoteric these are the examples we are required to know zinc oxide aluminium oxide lead oxide or amphoteric alpha etheric means they will react with acid and they will react with base okay so magnesium oxide is basic if i dissolve it in water it forms magnesium hydroxide carbon dioxide is acidic if i put it in water it forms an acid and you should know that when you dissolve carbon dioxide in water the acid formed is carbonic acid sulfur dioxide in water this forms sulfurous acid sulfur trioxide plus water forms sulfuric acid eye paint function sulfur dioxide and sulfur trioxide are both acidic but sulfur dioxide will dissolve in water to form which acid sulfuros h2so3 while sulfur trioxide will dissolve in water to form sulfuric acid h2so4 okay so let's try this the oxide of element x forms a solution with ph4 so oxide of x i dissolve it in water it forms ph4 is ph4 acid obese acid so oxide of x is acidic so x must be a metal or a non-metal which one did we say the oxides are acidic we said oxides of non-metals are acidic so x must be a non-metal now oxide of element y forms a solution that turns universal indicator blue and that means that y is the oxide of y is a base when it turns universal indicator blue it's away so the oxide of y is a base and we said oxides of what are basic metal or non-metal metal so my answer is c which oxide is amphoteric remember we said which oxides are amphoteric the examples that we had were aluminium zinc length aluminium zinc lead so aluminium oxide is amphoteric what about the others let's see the others what is calcium oxide this is oxide of a metal and we said oxides of a metal are basic carbon monoxide what did we say about carbon monoxide is it acidic basic amphoteric or neutral carbon monoxide is neutral what about sodium oxide sodium oxide is an oxide of a metal outside of a metal if it's not amphoteric then it is a base so sodium oxide is at least okay which statement describes the chemical property of aluminium oxide okay what is aluminium oxide again aluminium oxide is what acidic basic neutral hypothetic aluminium oxide is amphoteric you should remember we said which ones are amphoteric oxides of aluminium zinc length so aluminium oxide is amphoteric what did we say about amphoteric it means what it reacts with what you should remember that amphoteric means it reacts with both acid and base okay methyl orange turns red in the solution formed when substance r reacts with water again are in water from the solution that turns methyl orange red when does missile orange turn red in in what in a basic solution right missile orange is red in uh sorry in an acidic solution methyl orange turns red in an acidic solution so which of these is acidic calcium oxide potassium oxide sodium oxide sulfur dioxide yes sulfur dioxide is acidic so it is d okay okay how do we prepare salts the method used depends on the type of salt and its solubility we're going to say that there are three types of methods or three methods to prepare salts and the method that we're going to choose depends on whether the salt i'm using is soluble or not soluble and what i'm starting with is soluble or not solid so before we decide we have to remember which substances are soluble and which substances are not solved so you have to remember that all nitrates are soluble compounds of sodium potassium and ammonium are soluble so sodium something sodium salts potassium salt ammonium salt these are sold all acids are soluble barium chloride magnesium chloride calcium chloride these are solid copper sulfate is something that we use a lot in the syllabus and you should know that it is soluble okay most carbonates are insoluble so barium carbonate calcium carbonate or insulin silver halide silver chloride silver bromide silver iodide all of these are not soluble in water so they form a precipitate when they're formed in reaction lead chloride lead bromide lead iodide all of these are not soluble barium sulfate we're going to be talking about it is not soluble copper oxide is not soluble you should actually know that copper oxide is a black solid and of course all metals do not dissolve in water so this is basic you need to know so to prepare a salt we need to decide are we going to use a method called titration or a method called neutralization or a method called precipitation so when do we decide on each of these we choose titration f we're trying to prepare something soluble and we're starting from soluble reactants so everything we're talking about is soluble then we're going to choose titration and we'll talk about what does that mean if we're trying to make something that is soluble but what i'm starting with is not soluble then i'm going to choose a method called neutralization remember this is the name of the method not the name of the reaction we talked about neutralization reaction is a reaction between acid and base well here this is the method the name of the method okay precipitation precipitation is a reaction in which what is formed is not soluble so when what is formed is not soluble it comes down and it's called a precipitate so this is called precipitation reaction so let's talk about each of these now what if i'm trying to prepare sodium chloride crystals okay so the first thing i asked myself is sodium chloride soluble or not we said that compounds of sodium so salt of sodium are soluble so sodium chloride sodium anything is soluble okay then the next question i'm going to ask myself which acid in which base should i use to make sodium chloride so i need sodium something so i need sodium hydroxide and i need something chloride so hydrochloric acid now are they soluble or not we said sodium anything is soluble so sodium hydroxide is soluble all acids are soluble so hcl is soluble so all of these are soluble soluble and the method which use is titration so basically if i put sodium hydroxide base so on hydrochloric acid in a beaker i should end up with sodium chloride and water but the problem is how much sodium hydroxide should i add to how much hcl in order not to have any of them excess i don't want to add too much the word excess means too much or more than needed so i don't want to add too much sodium hydroxide because if i add too much sodium hydroxide i will end up with sodium chloride plus the extra sodium hydroxide i don't want to add too much acid because i will then end up with sodium chloride plus extra hydrochloric acid which i am not going to be able to uh separate so the problem for the first problem we meet is how much should i add in order to know how much i should add i do what we call titration in titration i use two main things i use a buret and the buret remember is the one that has graduations with the tap and i need a pipette do you remember what a pipette looks like it's a smaller apparatus and it is used to measure a certain volume of solution or liquid accurately so for example pipette is used to measure for example exactly 25 centimeter cubed you cannot use it to measure anything else okay so what are we going to do first of all we're going to fill the burat with the acid you could put acid or base but usually we put acid in the burat and base in the conical flask so the first thing we're going to do is fill a buret with the acid and then i want to put a specific amount of sodium hydroxide solution into the flask so i put that using a pipette so we put 25 centimeter cubic sodium hydroxide solution in a flask using a pipette and we have acid in the buret or we fill the buret with acid and our next problem is that all of these solutions are colorless how will i know if i have added enough so i need to add indicator so for example i could add three drops of phenophthalene to the flask so now in my conical flask i have 25 centimeter cube of sodium hydroxide which i put with the pipette and three drops of an indicator this indicator could either be phenolphthalein or methyl orange you cannot use universal indicator you cannot use litmus you have to use phenolphthalein okay and remember that when i put fin of saline on sodium hydroxide which is a base phenolphthalein in a base we'll have what color pink so the solution turns pink now i'm going to add dilute hydrochloric acid from the buret drop by drop gradually until what until i want the solution in the flask to become neutral what is the color of phenolphthalein when it is neutral it's colorless so i add dilute hydrochloric acid gradually from a buret until the solution in the flask turns colorless now i note the amount of acid used how much did i need for example i needed 20 something here i needed 27 centimeter cubed for example so now i know that if i put 25 centimeter cube of sodium hydroxide i will need 27 centimeter cubed of the acid now i'm going to throw away this flask because it has indicator in it i don't want a solution that has indicator in it and i'm going to repeat the reaction by adding the required amount of acid so now i know that i need 27 so i'm just going to put 27 on the 25 centimeter cube of sodium hydroxide without using indicator so in that case now i know that i have in my flask a solution of sodium chloride in water how do i get pure dry crystals from that i heat the solution to point of crystallization cool this will form crystals then i need to filter the crystals from the solution wash the residue or wash the crystals with a few drops of distilled water and dry between filter papers remember that in any of our experiments when we want to dry the crystals we dry them between filter papers we do not put them for example in an oven or things like that to avoid breaking up of the crystals okay okay so this is how we do the titration we had the flask and we added until the uh pink color just disappears or forms a colorless solution so let's try this question aqueous ammonium phosphate can be made in the laboratory by reacting aqueous ammonia with aqueous phosphoric acid again i'm going to remind you that the word aqueous means dissolved in water okay okay so the first question here says state the name of the piece of apparatus labeled a what is the name of a again we said a is something that has graduations and at top a is called buret suggest the ph of phosphoric acid well let's think phosphoric acid is what you should remember that phosphoric acid is a strong acid a strong acid means its ph could be one or two or three so choose any of them so let's say ph2 it cannot be more than that describe how the ph of the mixture in the flask changes as the acid is added remember what would be the ph of the ammonia originally in the flask ammonia has a ph of what we said ammonia is a weak base so it should have a ph of 8 or 9 or 10. now when i add acid what is the ph of the acid the ph of the acid is 2 and i'm trying to add it until it becomes neutral so actually the ph in the flask should change from either eight or nine or ten and it should go down to about ph seven because i need to be neutral so the ph is decreasing okay okay this is a kind of experiment which we have at the end of paper six and this is usually a question with about six marks five marks seven marks sometimes okay oven cleaners contain an aqueous solution of sodium hydroxide so he's telling me that oven cleaners are solutions of sodium hydroxide okay plan an investigation to show which of the two different oven cleaners contains the more concentrated solution of sodium hydroxide so basically you're given two solutions of sodium hydroxide and you want to know which of them is more concentrated so he's not telling you to prepare a salt here but he's just telling you to find out which of the sodium hydroxide solutions is more concentrated well let's think if i do titration with an acid the one that is more concentrated is the one that will do it is the one that will need more acid to be neutralized right if i'm adding an acid to a base if i have a concentrated base then i will need more acid if i have a less concentrated base i would need less acid so basically you're describing titration so what are we going to do we have sodium hydroxide solutions two different sodium hydroxide solutions so we're going to use the first one for example do titration and then the second one do the titration and determine which of them needs more acid right so how do we explain that so how do we do titration we said we put 25 centimeter cubed of the first sodium hydroxide solution into a flask using a pipette add three drops phenolphthalein the solution turns pink so we're doing a typical titration okay and dilute hydrochloric acid from a buret until the pink color disappears note the volume of acid used and then we're going to repeat the same thing using 25 centimeter cubed of the other alkali solution the one that uses more acid is more concentrated do you understand how to explain this first of all when we explain these experiments we need to explain them in detail um mention all the apparatus um mention what is the same what are we keeping the same for example here uh in order to compare between the two oven cleaners i have to use same volume of the two of them cleaners so i'm going to use 25 of the first one and 25 of the second one and everything else is the same and the only difference is how much acid they will use okay okay we can use titration for something else so if we have solution a and solution b so i have a certain volume of uh sorry a certain solution of hcl in the buret and i have two solutions so this is what we were just doing i'm using titration to determine which solution is more concentrated so if i have the acid in the buret and then i add some acid for solution a to neutralize solution a i need another acid another volume of the acid to neutralize solution b and we said which of these is more concentrated well the one that will use more acid is more concentrated so a is more concentrated okay but in another kind of experiment he could put two different acids in the buret and the solution in the flask is the same so if i put two different acids once i do it with acid and the burat and once i do it with acid being the birat and i'm using it to neutralize the same solution of sodium hydroxide the same solution of sodium hydroxide so um if i do the titration with acid a and i need a lot of acid a does that tell me that a is concentrated or dilute if i need a lot of something that means it's not really concentrated that means it's dilute if i need less of acid b i needed only a very small amount of b to neutralize the base that means that b is more concentrated so sorry um yes b is more concentrated okay or a is less concentrated do we understand the idea so if the ones in the flask are the same then if i need more of the acid in the buret then it is not as concentrated as the other one but if i have different solutions in the flask then solutions different solutions in the flask and the solution in the flask requires a lot of the acid much more than the other one than the one that requires more of the acid is the more concentrated am i confusing you completely think about it it's it's reasonable okay okay the other method is neutralization and neutralization we said we use this method that i'm going to describe if we're starting with something that's not soluble so for example i want to make copper sulfate you should know that copper sulfate is soluble but how can i make copper sulfate i can make it from acid plus base now which acid and which base should i use i need copper sulfate so i need sulfuric acid if he was telling me to prepare copper chloride then i can start with hydrochloric acid if he's saying copper i don't know phosphates then i will start with phosphoric acid do you understand the idea so i'm trying to make copper sulfate so i need sulfuric plus what i want you to remember that i can either make a base with an acid or a metal with an acid but remember that copper metal does not react with acid so we said metals with acid would give salt plus hydrogen but metals that are more reactive than hydrogen so i will tell you for now that copper alone will not react with acid so i have to use copper oxide copper oxide is a solid so i cannot do titration so i need a different method so the method that we use is neutralization how do i do neutralization i get sulfuric acid in a beaker and i start adding copper oxide which is a solid of course when you are adding a solid to a solution you use a spatula do you understand the meaning of spatula it looks like a spoon it's not a spoon it's a spatula so we add copper oxide to the solution in the beaker until what now when i'm adding the copper oxide to the sulfuric acid it will form copper sulfate and you should know that copper sulfate is soluble that means the copper oxide will dissolve to form copper sulfate now i add a little bit more of copper oxide it will dissolve i add a little bit more of copper oxide until what until all the acid has been used up so once all the acid has reacted and i add some more copper oxide there is nothing for it to react with so the extra copper oxide will remain in the beaker so we call that excess copper oxide because this is more than we needed okay so we add basically copper oxide um to the sulfuric acid in the beaker until what how do i know if the reaction has finished until excess solid remains in the beaker now what should i do next now i know that my solution has the copper sulfate and water and i have excess solid at the bottom of the beaker so i need to filter the solution when i filter the solution what is in the filter paper the one in the filter paper is the excess copper oxide that i don't really need and what i need is my copper sulfate solution right so the copper sulfate solution i need to take it and make crystals from it how do i make crystals heat the filtrate to point of crystallization cool filter the crystals if you once it's pure and dry i should say wash with a few drops of distilled water and dry between filter papers okay so we add the solid copper oxide until using the spatula 25 centimeter cube of sulfuric acid in the beaker until excess solid remains in the beak filter to remove the excess solids why are we filtering to remove the excess solid now we take the solution and we heat to point of crystallization uh cool filter the crystals so this method is called neutralization okay okay let's try this question assault is made by adding an excess of an insoluble metal oxide to an acid how is the excess metal oxide removed from the mixture how did we remove the excess solid by filtration right okay another method is titration sorry i'm sorry precipitation precipitation is a method in which you are trying to prepare something that does not dissolve so you're trying to prepare an insoluble salt and that means when you put two soluble solutions on each other they will form what we call a precipitate do you understand the difference between precipitate and excess in the previous reaction we had excess solid so let's go back to here we had the copper oxide here i added it until it was excess so the solid in the beaker there is it is called excess because it is just extra solid that i added but here when i put two solutions and they form a solid that solid is called a precipitate okay so i'm trying to make what i'm trying to make silver chloride now the question is what am i going to use to make silver chloride i need silver something and something chloride okay silver something has to be soluble i need to start with something that's soluble so silver what is soluble you should remember that all nitrates are soluble so silver nitrate is an aqueous solution okay i want something chloride we said anything any compound of sodium potassium ammonium is uh soluble or acid so actually you could put sodium chloride or you could put any of the other substances that are soluble now i put the two solutions on each other when i put the two solutions on each other i get a precipitate so the silver chloride forms as a white solid at the bottom of the container the bottom of the flask this is called a white precipitate now what do i want i want this white precipitate so i filter it and the residue in the filter paper that is what i want that is the silver chloride i'm trying to make so i just wash this i don't do any crystallization here because i don't want the filtrate the filtrate is sodium nitrate solution i don't want sodium nitrate i want uh the silver chloride which is the white solid that remains in the filter paper so i just wash the residue with a few drops of distilled water and dry between filter papers are we following okay so let's try this question which two processes are involved in the preparation of magnesium sulfate from dilute sulfuric acid and excess magnesium oxide okay which method is this the first question i ask myself which method is this i'm trying to make magnesium sulfate and i'm starting with magnesium oxide and he's telling me i'm going to use excess magnesium oxide is a solid that means i'm using the method called neutralization so neutralization and then after that what should i do i should do filtration okay so it's talking about the neutralization process which method is used to make the salt copper sulfate how did we make copies of faith we made copper sulfate from acid and what i can use can i use alkali to make copies of it we said copies of it we're going to use what to make up or something we said first of all i need sulfuric acid so i will need need the dilute acid we said sulfuric acid plus what um in the experiment i explained we used copper oxide we said i cannot use only copper because copper does not react with acid so i cannot say dilute acid plus metal so c is wrong and we're not talking about a non-metal oxide we're talking about copper oxide so that would be a metal oxide not a non-metal so d is wrong so i have to choose between a and b so i'm reacting copper what i can either use copper oxide or actually i can use copper carbonate to react okay so copper carbonate or copper oxide plus acid will give copper sulfate okay so let's try this question the diagram shows the steps in preparation of assault which salt is prepared by this method okay well let's take a look at which method is he doing he's crushing something and then he's adding it to something in a beaker and then his filtering and taking the filtrate so which method is this it's definitely not titration titration would use a burette and the flask and so things like that and now is it neutralization or precipitation remember that in neutralization i take the filtrate in precipitation i take the residue that is in the funnel so this is obviously a neutralization reaction now the question is which of these salts can be prepared by neutralization reaction well let's look at them barium sulphate what is barium sulfate soluble or not soluble barium sulfate is not soluble so and we said to prepare a soul that is not soluble i use precipitation so this is not neutralized now to make copper sulfate yes we said we make copper sulfate from copper oxide which is a solid added to sulfuric acid and then we filter and we take the filtrate so yes this method would be used to make upper sulfate what about the others potassium sulfate sodium sulfate no potassium sulfate and sodium sulfate are both soluble remember we said potassium salts are soluble sodium salt is soluble so to prepare something that's soluble i usually use and potassium i will start with anything also that's soluble so this will be done by titration okay okay we're at the end of this and i would like you to study this chapter and try the questions so that we can discuss them in the next video okay thank you