hello this is Dr Henna aseel and we're talking about preparation of souls so this is the second part of the chapter on acids and bases in IGCSE chemistry syllabus so in order to determine which method to use for preparation of souls we need to determine whether the salt we're trying to prepare is soluble or insoluble and the reactants or the reagents that we're going to use are soluble or insoluble so first of all we need to know which substances dissolving water so their state symbol would be aqueous or things that do not dissolve in water so their state symbol is solid or s okay so which substances dissolve in water you should know all nitrates are soluble in water so all nitrates are aqueous all sodium salts potassium salts ammonium salts so sodium anything potassium anything ammonium anything would dissolve in water all acids are soluble in what things that we use a lot in our syllabus like barium chloride magnesium chloride calcium chloride these are all soluble copper sulfate you should know is follow now which things are insoluble insoluble means they don't dissolve in water that means if they are produced in a reaction they are formed as a precipitate so the word precipitate means a solid that is formed from reaction of two solutions so these would be precipitates or they would not dissolve in water or their state symbol is s so which of these barium carbonate calcium carbonate silver chloride silver bromide silver iodide lead chloride lead bromide lead iodide things like barium sulfate calcium sulphate lead sulfate copper oxide you should know is a black solid all metals are insult now we have three methods of preparing salts we have a method called titration a method called neutralization and a method called precipitation so when do we use any of these we use titration if I'm trying to prepare something that is soluble from soluble reactants so everything I am using in the reaction is soluble and I'm trying to prepare resolvable salt then we are going to explain something called titration but if I'm trying to make a soluble Zone but one of my reactants is insoluble so I'm trying to make it from something that is infallible then I use a method called neutralization if I'm trying to prepare an insoluble salt then we will explain a method called precipitation so let's take a look at this so first of all what is titration titration is used if all my reactants and products are all solid so for example if I want to prepare if he says prepare sodium chloride crystals the first thing I need to know is what do I react to form sodium chloride usually these things are either acids or bases or reaction of acids and bases so which acid do I need to make sodium chloride I need the acid that has chlorine so I'm going to use hydrochloric acid which base should I use to prepare sodium chloride well I need the base that has sodium you know that bases are usually oxides or hydroxides so sodium hydroxide with hydrochloric acid should give me a solution of sodium chloride the question is how much should I add from the acid to the base in order to end up with a neutral solution I don't want to add too much acid and I don't want to add too much base so I go through a process called titration in which we use a puret a flask and a pipette so what we're going to do is we're going to fill a burat with acid and then put a specific amount of sodium hydroxide into the flask using the pipette so the first thing I'm going to explain to him and you need to explain in this way one by one in the correct order I want to place 25.0 centimeter cubed of sodium hydroxide 25.0 means exactly 25 centimeter due to sodium hydroxide in a flask using a pipette then we need an indicator because both of these Solutions are colorless so I need to see a color change so we're going to add three drops of an indicator now which indicator can we use we can use either methyl orange or thymolfeline so in this case I'm saying add three drops methyl orange if you add methyl orange to a solution of sodium hydroxide the solution turns yellow then I'm going to tell him add dilute HCL from a buret until the yellow color turns to Orange and node the amount of acid used so now I know how much acid I should add to 25 centimeter cubed of sodium hydroxide what I'm going to do is I'm going to repeat by adding the required amount of acid to 25 centimeter Cube the sodium hydroxide without using an indicator heat the solution to point of crystallization so I'm going to explain to him how to do crystallization please note when we are trying to do crystallization heat the solution to point of crystallization cool to form crystals filter the crystals wash with a few drops of distilled water and dry between filter papers this is if he's telling me to prepare pure dry crystals of sodium so this is the method of Thai Trish you should know that when we do a titration the flask should be placed on a white tile or a white paper if he says why this is of course to see the color change clearly I want to see exactly when the yellow turns to Orange the flask should be swirled while adding the solution from the buret why in order to mix the content so these are things precautions that you should take while doing titration also when reading a burat the eyes should be on the same level as the meniscus so he says a precaution the eyes should be on the same level as the meniscus remember the meniscus is that Round Top of the liquid and we're supposed to read the bottom of the meniscus so for example this one is 24.2 for example so this is the bottom of the minute also in any titration experiment we sometimes need to repeat the titration or to do another titration with another solution so to perform more than one titration the burat should be first rinsed with water to remove traces of the previous solution then we rinse it again with the solution to be used in order to remove the water because if I keep water in the buret that will change the concentration of the solution please note all of these we usually have these questions in uh paper six so for example here he's saying aqueous ammonium phosphate can be made in the laboratory by reacting aqueous ammonia with aqueous phosphoric acid what is the name of this piece of apparatus a of course you should know a is something that has a tap and graduations this is called a buret remember if it has a cup but no graduations it is referred to as a dropping funnel not a bureau so just the pH value of phosphoric acid we said before that phosphoric acid is a strong acid so I can say pH 1 or PH2 or pH three describe how the pH of the mixture in the flask changes as the acid is added of course the flask has aqueous ammonia so do you remember what the pH of aqueous ammonia was aqueous ammonia is around pH 8 or ph9 but as I add acid which has PH2 what will happen to the pH in the solution it will start to decrease until it reaches the neutral pH of Step this is a typical question he says oven cleaners contain an aqueous solution of sodium Hydrox plan an investigation to show which of two different oven cleaners contains the most concentrated solution of sodium hydroxide so we have two solutions two different solutions of sodium hydroxide and I want to know which of them is more concentrated you are provided with common laboratory apparatus and chemicals so of course if I have two sodium hydroxide Solutions and I want to know which one is more concentrated what I do is I do titration of the first solution find out how much of the acid it will need to neutralize repeat it again with the other solution and the one that what the one that uses more acid is more concentrated so how do I explain that put 25 centimeter cubed of the first sodium hydroxide solution into a flask using a pipette add three drops in this case I'm saying thymolfeline I want you to remember the time of saline is a new addition to the syllabus of 2023 now if I add thymol saline 2 sodium hydroxide dissolution turns blue then I add the dilute acid from a buret and be specific Which acid you're using so in this case I'm using dilute HCL from a buret until the blue color disappears remember the simultane in neutral and acid this is color know the volume of acid used so now I know this specific sample of sodium hydroxide we'll need how much acid now I'm going to repeat using 25 centimeter cubed of the other Alkali solution the one that uses more acid is more concentric so if we have two solutions A and B and I want to know which one is more concentrated I do a titration with the same acid the one that uses more acid is more concentrate but sometimes he has in the buret two different acids A and B and he wants to know which one is more concentrated in this case I have the same solution of sodium hydroxide in the flask now the first sodium hydroxide used about what 28 centimeter cubed of acid a but for the uh second acid I needed only less of it to neutralize my sodium hydroxide remember that the one that I need less of is more concentrate so mole of acid a was needed that means acid a is less concentrated than acid B so in this case the one that is more concentrated I will need only a small amount of it so in this case b is more concentrated another method of preparing Souls is neutralization so in neutralization I am starting with something that's insoluble for example I want to prepare couples of it crystals now what am I going to use to prepare copper sulfate where copper sulfate I need first of all Which acid I need sulfuric acid and then what am I going to react with the acid remember that acids can react with bases or metals or carbonates so in this case I can say sulfuric acid plus copper oxide which is a base or copper carbonate carbonate will react with acids but remember that I cannot say sulfuric acid plus copper mat copper metal does not react with acids please remember copper is less reactive than hydrogen copper metal does not react with sulfuric acid but if I were trying to make for example zinc sulfate I can say zinc plus the three gas if I'm trying to make magnesium sulfate I can say magnesium plus sulfuric acid but I cannot seek up so okay so we're going to use copper oxide with sulfuric acid now of course copper sulfide copper oxide is something that does not dissolve in water so I cannot do titration I have to do it in a different map I get a beaker I add a certain amount of sulfuric acid so let's say uh 25 centimeter Cube dustulfuric acid and I add solid copper oxide using as Patrick now as I add the copper oxide the copper oxide won't react with sulfuric acid it will dissolve to form caprisulphate solution which is blue but as I add more and more of the copper oxide at some point all the sulfuric acid has reacted no more sulfuric acid to react so the excess solid remains in the beak so how do I know if the reaction has finished if excess solid remains in the beaker now what do I want I want the solution so I can get rid of that unreacted copper oxide by filtration so in that case my residue is something I don't want it is the excess copper oxide I added and the filtrate is my copper sulfate solution so once I take the filtrate I can heat the filtrate to point of crystallization cool filter the crystals now if he says he wants pure dry crystals I can say wash with a few drops of distilled water and dry between filter papers this question says assault is made by adding an excess of insoluble metal oxide to us how is the excess metal oxide removed from the mixture how did we remove the excess copper oxide when we put the copper oxide until it was excess I removed it by filtration my answer is d the other method is precipitation for precipitation what I'm trying to prepare is insult so for example we said silver chloride is insoluble now to make silver chloride I have to start with two things that are solved so I need silver something that is soluble and we said all nitrates are soluble so I can use silver nitrate and I want something chloride that is soluble so sodium chloride we said all sodium salts are soluble and in this case all I do is I add the silver nitrate solution to sodium chloride solution the silver chloride forms as a white precipitate remember we said the precipitate is a solid that is formed from reaction of two solutions now I can filter and in this case what I want is the residue so now the silver chloride precipitate is residue wash the residue with a few drops of distilled water and dry it between filter papers so this question says which two processes are involved in the preparation of magnesium sulfate from dilute sulfuric acid and the excess magnesium oxide remember excess magnesium oxide means we're talking about which method we're talking about the neutralization method so how did we do that we did neutralization and filtration because magnesium oxide is insult which method is used to make the salt copper sulfate so to make copper sulfate can I react dilute acid plus Alkali remember an Alkali is a base that dissolves in water how did we make copper sulfate we made copper sulfate from sulfuric acid plus copper oxide copper oxide does not dissolve in water so it is not an alkaline so a is wrong dilute acid plus carbonate yes we said we can do sulfuric acid plus copper carbonate can we use dilute acid plus metal remember we said I cannot say dilute acid plus copper metal because copper metal will not react in acid dilute acid plus non-metal oxide well I need the metal oxide not a non-methyl oxide so out of these choices I can use carbonate plus acid the diagram shows the steps in preparation of a salt so first he's crushing in Step One is Heating in step two he is filtering in step three and his crystallizing in step four so which salt is prepared by this method so which method is this is this titration or neutralization or precipitation obviously this is a neutralization method in which he added in step two he added excess of one of the reactants so which of these do we prepare using neutralization of course it is copper so Faith remember that a barium sulphate is insulin so if I were trying to make barium sulfate I would use precipitation potassium sulfate is soluble and it will be from soluble things so it will be titration sodium sulfate also titration so the only one that I can prepare using neutralization out of these choices is copper sulfate okay that's the end of this uh please study all of this and I hope um it was useful to you thank you for listening