How to solve ATP Exam OL/IGCSE as a student | Model Paper Solving Technique 0620_s25_qp_63

Added: 2026-05-12

[00:00:02]Hey everybody, we're live and in studio.

[00:00:04]My name is Surman Khan and tomorrow is your ATP paper. I'm going over two more papers today to quickly give you guys an idea. Okay, this is how you need to think in tomorrow's exam. If you don't know how to think in tomorrow's exam, that's going to cause a big problem for you. So, please follow my lead when I start solving questions. Right. Question one says, fermentation is a process in which yeast is converted to acqueous yeast is used to convert acqueous glucose to ethanol. You already know all of this. C6 H1206 is glucose and you add yeast to it. A temperature of 25 to 35° and what happens? Ethanol forms. C2 H5O plus carbon dioxide forms. Right? And now also one more thing to keep in mind.

[00:00:50]The moment you recall this equation in your brain, you're like, aa, I need a temperature of 25 to 35°C. That means I need to have a constant temperature between this range. And so what should I use? I should use something known as a water bath because I need to keep the temperature constant. This is what should come in your brain, right? Yes, absence of O2, all of these conditions apply. But now he's saying, okay, he fermentation takes place at a temperature between 25 to 35°C. So he needs a water bath. He needs to use it.

[00:01:19]and see he's using it. Now a lot of students confuse this. They either water bath is required because obviously um obviously there's water present inside here and he needs to maintain a temperature of 25 to 35°C. But normally sometimes you also see an apparatus that is very elongated. This type of apparatus is called a trough. The name of the apparatus is a trough. T R O U G H. You know this big elongated beaker.

[00:01:46]It's not a beaker. It's called a trough.

[00:01:47]Right? It can also have water in it.

[00:01:49]He's just saying this is water bath. The apparatus right here is called a beaker.

[00:01:53]By the way, this is a beaker that the examiner has shown you, but he's called it a water bath. What is a a conical flask? What is this guy right here? This is called a gas syringe. What is the tube that's shown? This is called a This is called a delivery tube.

[00:02:12]What is this thing right here? This guy This guy is called a stopper or a bung.

[00:02:16]What would it do? It prevents the gas from escaping. It prevents the carbon dioxide from escaping. So carbon dioxide escape prevent, right? All of these things need to come into your brains.

[00:02:26]Now what is A? A is a conical flask. B is what? B is gas syringe. We already talked about it. Now what he's saying is why is a water bath use? Huh? By this should these are all suggest means that I've given you enough information to use your brain and tell me why to keep the temperature constant. Absolutely. to keep the temperature of this flask constant. Yes. So to keep the temperature of the flask constant between what?

[00:02:56]Between what range constant at at what whatever temperature you use at 27° C at 30° at 35°C whatever temperature you use it doesn't matter.

[00:03:12]No, no, no. You you can't say it keeps the temperature of the water constant from 25°C to 35. No, you have to select one temperature.

[00:03:21]Wouldn't the gas produce crack the No, it wouldn't crack anything because the gas that's been produced, it'll go through the delivery tube and be collected right here in the gas syringe.

[00:03:29]The gas syringe piston would move outwards.

[00:03:33]Yeah, ethanol is being produced which is highly volatile and flammable. So, you need to keep in mind don't directly heat it, right? You don't want to increase or decrease the temperature. You want to make the temperature constant. You want to keep the temperature constant. Right?

[00:03:47]Now, one more thing to keep in mind is the fact that ethanol that's been produced here, it's acqueous. We already know this idea from organic chemistry. It's about 15% concentrated, isn't it? Ethanol is very very dilute here. Its concentration is roughly about 15% out of 100. So, what do you do? The the rest is water. The rest of 85% is just water. How do you separate ethanol from water? you perform something known as fractional distillation because ethanol and water has different boiling points and based on this idea they can be separated through the idea of fractional distillation. Ethanol boils first. So ethanol vapors will go up it they'll fractionally distill. You'll collect them and then the temperature will increase go to 100 and then you can collect water. But we couldn't care less, right? So you can get more concentrated ethanol by performing fractional distillation. Yes, ethanol has in fact a lower boiling point than water. Therefore, it boils first and is collected first. He says the student measures the temp the volume of gas that and collected at every 10 minutes for 90 minutes. So, how many how many uh recordings does he take? If he's saying 90 minutes in total and after every 10 minutes he records it, what happens? You get nine readings, don't you? You get nine readings, right?

[00:05:01]And that's the nine readings as you see.

[00:05:03]1 2 3 4 5 6 7 8 9. He started at times equal to zero. there was zero volume um obtained. Now is the reaction over? Does this graph tell you that the reaction is over? No, because I don't know that the line is not getting horizontal, is it?

[00:05:18]The line is not getting horizontal. It's it keeps on increasing, increasing, increasing. The curve is still increasing. The volume of the gas is still increasing. It hasn't become constant, has it? The volume of gas hasn't become constant. So, I don't know whether the reaction is over or not.

[00:05:33]It's not over. It's not complete at all because if it were complete then the volume of gas would no longer be changing. So since he's saying why why is it not complete after 90 minutes since the volume of gas is still increasing not constant.

[00:05:54]Therefore therefore what? Therefore you understand it's not complete since the volume of gas is still increasing. It's not constant decreasing since done. Next um now what he has done is he is he's bubbling the gas through lime water. Why would he be doing that? See he's he's also testing your fermentation knowledge but even even you know even then he's giving you the equation here because ATP is not going to test a lot of your theoretical knowledge. He's telling you the equation which is carbon dioxide gas is being produced. You can say that the graph hasn't become horizontal. Yes, you can say whatever. So what do you what do you write here? You say aa because you already know that the gas is carbon dioxide. That's the test for carbon dioxide. You bubble it through lime water and lime water turns milky. So he says what happens to the appearance of the lime water? It turns milky. These are very easy questions by the way. You can easily score full marks in ATP.

[00:06:51]literally you know state one observation the student would make to show that the fermentation is complete. Well um until and unless the bubbling stops because you know carbon dioxide is being evolved inside a solution. Whenever a gas is bubbled in a solution it's forming in a solution you'd see bubbles here. You'd see effervesence here and especially when carbon dioxide starts to form you write the word effervesence right. So because there's going to be effervesence there's going to be bubbling there's going to be fizzing. You wouldn't see fizzing anymore once the reaction is over. Right? If the reaction is not over, carbon dioxide is going to be made and obviously it'll it'll go on and on and on and on and on and on and on and on and on until carbon dioxide stops evolving and that will be an indication the reaction is over. So you say effervescence or bubbling since the temperature is pretty low. Ephervesence is a rapid evolution of bubbles. By the way, those who do not know what effervescence is, effervescence is a rapid evolution of bubbles like right now since the temperature is too low, it's like about 25° C or 35° C, you realize rather than fervesence, you'll probably observe bubbling or um you know fizzing, but the better word would probably be bubbling. Either or it's going to be correct. If you write fervesence, it's going to still be correct, marked correct. If you write bubbling, it's going to be correct.

[00:08:10]Well, normally it's since the temperature is too low, favesence is a rapid evolution of bubbles. And so if the temperature is too low, the bubbles would not evolve so rapidly. So you just say, hey, you would see no more bubbling or fizzing is seen. I don't know what the marking scheme might say, fizzing, bubbling, all would be correct. State the method the student would use to obtain ethanol from the fermentation mixture. What should you do? Fractional distillation. You already know that fraction distillation right next now in the exam if I were you I would skip this longass question I'd skip to see it's such a long question I come back towards it at towards the end cuz I can finish the entire it's a 1 hour paper right so I can finish the entire paper in about 25 minutes I can literally do that and then I have so much time always do question twos at the end especially when you are supposed to make graphs cuz it takes a lot of time to make graphs, right? It it and you might not even know and you might, you know, fumble on the time. You might fumble. So that's why the better thing to do is have a good night's sleep after this uh session. And how much time should you spend on question four? Roughly 5 6 minutes. It wouldn't take so long, Ryan. Just the writing takes long. Thought processing.

[00:09:34]The entire ATP paper can be done within 25 minutes. within 25 minutes in excluding question two. Question two 35 minutes.

[00:09:47]Please remind me sir, you will also teach oxidizing reducing agents. You said you could sure remind me towards the end. Aa solid L is hydrated. Hydrated means water of crystallization. Aluminum ions or chloride ions. Test for aluminum ions is what? NaOH or aquas ammonia it should directly come in your brain huh NaOH it gives you a white PP it's written at the back of the paper and it is soluble but with excess with aquis ammonia it gives you a white PPT and it is insoluble right this guy is a monafik it becomes insoluble and you can see it at the back of the paper and chloride you you add dilute nitric acid and it's effectively the silver ion so you add silver nitrate and so silver ions react with chloride ions and give you what gives you AgCl which is a white PPT. Now he's saying to the first portion of L the student adds sodium side dropise you see a white PPT which what is observation in excess don't write PPT in the exam please write precipitate completely don't write PPT in the exam I beg of you write precipitate right it wouldn't take so long and what will happen in excess you write the complete observation so since there are no transition metal ions right so I'll say hey it dissolves the solid or the PBT dissolves to give a puri puri bath dissolves to give a yes thank you Shyan to give a colorless solution it was white PTS when they dissolve they give you colorless solution until and unless there are some other transition metal ions present but there aren't any transition metal ions present can we write soluble in excess a you could write whatever you want kiddo but this is what you should write properly right soluble in excess he's already given you observation in excess you write soluble in excess he's already think what happens in excess you think it's soluble in excess you Just even write soluble then but it's better to write the complete idea. Don't just say soluble back of the paper.

[00:11:48]Add aquas ammonia again you see a white pity insoluble. The white p insoluble it remains. The observation is that the white pt remains right. The white PPT remains inolub remains bracket basically insoluble to the third portion he adds dilute nitric acid followed by silver nitrate.

[00:12:17]So silver ions are a test for chloride ions. Egcl forms you see a white ppt.

[00:12:22]Next then he say to the third one add dilute and berium ions. Berium ions are a test for sulfate ions. There are no sulfate ions. So you say no change here.

[00:12:30]No change or bracket. No visible examiner visible. So no visible change.

[00:12:37]Bracket visible. No PPT is observed or incorrect but no visible change.

[00:12:44]Observation means what can you see with your eyes? You don't say what you don't see with your eyes. No PPT is observed like you're telling the examiner I'm not seeing this. He's saying what do you see? You say I see nothing. I see no change. That's what you see. Don't tell the examiner what you don't see. He's not asking you or what don't you see.

[00:13:01]He's saying what is the observation? The observation what you see with your naked Gangar eyes.

[00:13:08]Said I'm not getting all these reactions. What should I do? Hussein, you should go on to my YouTube and watch question three marathon. Why haven't you watched the ATP recordings? Go on to the YouTube channel and watch question three. How is there no change? Cuz we've done um I think a billion questions now.

[00:13:23]Berium ions are a test for sulfate ions.

[00:13:26]There are no sulfate ions present. You have chloride ions.

[00:13:31]Go over 2023 recordings. Susan, if if this this is only for those students who are enjoying the class, right? This is only for those students who are enjoying the class who are already done with everything. Not for those students who are sitting here solve. I'm teaching students how to solve the paper. If you don't know the core content behind it then there's no point in knowing okay how to solve the paper go fix your concepts you still have time go watch question three if you find these questions difficult they are present on the portal go and even on YouTube light green color is observed solid m light green color is berium ions berium 2 plus ions then next no visible change now why is there no visible change he's saying he divides this guy and he says he adds aquis sodium hydroxide and aqua sodium hydroxide he sees no visible change it's The berium ions that are present, they are soluble. That's what it means. It has never been tested, but you could infer this from this. The berium ions are soluble. Don't say they there's no cation. There is a cation. You saw this berium right here. But that means that berium hydroxide is soluble. That's why you see no visible change. Right?

[00:14:44]Right?

[00:14:47]Then he says to the second portion, add aluminum foil, sodium hydroxide and test for any gas. What is this a test for?

[00:14:54]Especially when aluminum foil is involved, you test. This is a test for nitrate ions. We've done it a billion times. And so affervesence is seen and damn red paper is turned blue. You know that nitrate ions give you ammonia. So if you see a fervance, that's going to be because of ammonia. Damn red lm paper turns blue. The gas is ammonia. But this is an indication you have nitrate ions.

[00:15:14]You have nitrate ions, berium ions. The salt is berium nitrate. Now he says he adds dilute sulfuric acid and he sees a white PP. Why? The sulfuric acid has the hydrogen ions and the sulfate ions. And you know sulfate ions react with berium ions to give you what? Berium sulfate.

[00:15:29]That's why you see a white PPT. It's very basic. Again confirms the berium 2 plus ions. So what is solid? M is berium nitrate, right? because there is nitrate ion and there's banium ions and it says identify the gas given off in test three that's ammonia done this is how you do these questions s ba being soluble part I didn't understand fata I'm just saying if you added sodium hydroxide to it and he's saying there's no visible change berium berium ions when they came into contact with the hydroxide ions it formed berium hydroxide and the reason Why you saw no visible change was because no solid formed. And why would no solid form? It'll be because berium berium hydroxide would have been soluble. That's the idea. Fatma you can write the name instead too.

[00:16:22]Done. That's all. Then next question. He says lead 2 chloride PBCL2 is an insoluble salt. Please do question two towards the end. This is my recommendation.

[00:16:31]He's saying this guy is an insoluble salt. Um solid lead 2 chloride can be made. It's a basic salt preparation question. Nothing else. He's saying it can be made by reacting sodium chloride and aquis lead nitrate. Describe how you can make dry samples of this. You are he's even given you the entire equation for it. God damn. You just need to perform filtration and all but obviously you have to identify all the steps along the way. Right? So what do you say? You say yeah you add sodium chlor you take sodium chloride. You take berium you take lead 2 nitrate. You add them both to water. See he's given you half of the tips in this particular equation.

[00:17:09]Literally this is how you prepare an insoluble salt. Now so you take sodium chloride the the salt that he's given you the equation that he's given you you should use it right. This is a precipitation reaction. So what do you do? You say yeah add sodium chloride add NaCCl aquas to Pb NO3 twice aquas. What do you do?

[00:17:32]You mix it. You stir it and mix it and shake it. Mix it. What happens? Slash shake it. Whatever you write for look here.

[00:17:47]Oh my god.

[00:17:56]You can't mess this up. Please don't. No need to use bat bur but simple simple.

[00:18:02]You have sodium ions, you have chloride ions, you have lead two plus ions and you have nitrate ions. You know when you mix them together all the ions will come into contact with each other one by one.

[00:18:12]But the moment lead ions come into contact with chloride ions it'll form lead chloride which is he's saying it's an insoluble salt. So it's insoluble.

[00:18:21]It's a precipitate. Once the precipitate forms what do you do? This is a precipitate. Then you perform filtration. This guy is going to be obtained as a residue because it's insoluble. And you will obtain this guy as the filtrate. NO3. And then what do you do with this guy? You pour distilled water through it so that you can easy wash it with distilled water. And then you dry it by gently tapping it between two filter paper. That's all literally marks. So you stir it, mix it, shake it then solid forms.

[00:18:54]Solid forms of lead chloride inside the beaker right to a beaker shake it mix it with with a glass rod, right? Solid forms inside the beaker, right? Then filter the mixture.

[00:19:36]You can even draw the diagram for them.

[00:19:38]Has he asked about the diagram? No. But you can even draw this diagram for him.

[00:19:43]And filter the mixture. Then what happens? Pbl2 solid is obtained as residue.

[00:19:54]Then what happens? Wash with distilled water. Wash with distilled water. And how do you wash with distilled water? Be very careful in such easy question. Wash with dist. How do you do that? By pouring distilled water through the there's no need for cold in this case.

[00:20:16]It's already insoluble. By pouring distilled water through the filter funnel.

[00:20:24]Right? Then what happens residue trap?

[00:20:28]Then you pour distilled water right here. Distilled water.

[00:20:32]If you want to heat, you can heat. No need to heat by the way. Press by. Then what happens? Then you washed it. Now dry it by gently tapping between by gently dry lead chloride.

[00:20:48]tapping between two filter papers description cuz examiner always loves description. How do I say add water in excess to ensure that the solid dissolves completely he's already done that portion for you Ryan? Sorry, Isel look he's already done that for you.

[00:21:08]NaCCl is in accur state. This guy is inac state right? So add NaCCl or you could have said add excess water to NaCCl solid. Add excess water to PBN P dead nitrate solid. You know you could have done that is if you wanted to be even more majestic about this answer.

[00:21:26]You could have molded this however you liked. You could have said yes. Add excess water to NaCCl solid. Add excess water to PBNO2 solid in uh PBNO3 hold twice solid um until and unless all the solid dissolves. Stir it. Mix it. then two separate beers then mix the two solutions together. You could have done all of this the way I've shown it in the um exams minute in 15 minutes your paper is almost done in 15 minutes. Now you come to question number two because this is just graph you read it. I don't want you guys to be wasting a lot of time. You finish off all the marks. Now you come to this. You have a lot of time on your hands. You don't need to rush here.

[00:22:05]You could use it's not a soluble salt soluble salt. We need to separate lead. We need to get lead chloride. We don't need to get um we don't need to get a soluble salt. Sir will we not heat?

[00:22:22]Will we not heat till the solution?

[00:22:26]We need We need a solid. We need lead chloride. We don't need solid lead chloride. Aa solid lead chloride. Dry sample of lead chloride.

[00:22:38]Sodium chloride.

[00:22:45]Pour it into an evaporating dish or this is pathetic. Somebody saying it's not a hydrated salt. Oh no. Yeah, lead chloride is a insoluble salt. You just obtain it as a residue. Go watch part four of the guest paper. Go watch part four of the theory guest paper onto YouTube. Yeah, for salt preparation.

[00:23:05]I've taught it in part four of the theory paper or part five, I don't remember. Watch it. It's going to be given in the description. If your salt preparation is weak, please leave the class and watch salt preparation. It's so basic. It can be tested in the upcoming exam. What are you guys doing?

[00:23:19]It's may heat till the point of crystallization.

[00:23:23]You have lead chloride. You obtained it as a residue. You needed this. Now you just wash it and dry it. That's all. You don't need NO3, do you?

[00:23:39]You don't have two solids to separate, right? Please, I said, what are you doing?

[00:23:46]Please, I beg you, don't make these silly mistakes. There's still time.

[00:23:52]Heat till saturation is for titration.

[00:23:54]Sadi, no. Um, no comment. Please watch the uh video. Don't attend this class.

[00:24:02]Watch the video. For those who are saying Goluble, a student investigates how the rate of reaction between dilute hydrochloric acid and acquisium thioulfate. We've already done this experiment in our live classes multiple times. You must have seen it in the live classes even you should know.

[00:24:25]This is for you and we've done it a billion times in the ATP. It's the same thing. And please understand when sodium thioulsulfate reacts with when sodium thioulfate reacts with hydrochloric acid it tends to form sulfur as well and sulfur is a yellow solid. This is for your information. You don't need to know this but I've taught it in my live classes and if you did not know this you know it again I've also taught it in the past paper session.

[00:24:50]This guy is a yellow solid. So you could use this idea to your advantage and you could you could look from the top of a colorless solution and put a cross or anything under the beaker, right? And then when the moment these guys start to react with each other, sulfur starts to form, it starts to turn this solution into a cloudy mixture. And the moment it gets cloudy, your eye can no longer see the text written on this piece of paper.

[00:25:17]It's a very basic idea. If a solution was colorless, you were able to see through this. But then if the solution is no longer colorless, why I told you why? Because a yellow solid forms. So because the yellow solid forms, you're not able to see through this. And then you aren't able to see the cross or the printed text. Right? So the quicker the reaction, the quicker you will not be able to see it because the quicker the reaction, the quicker the solid sulfur forms and the quicker your eye will no longer be able to see the printed text.

[00:25:45]That's the idea. But he's saying the student is investigation please aqua sodium thioulfate the rate of reaction. So I taugh taught you which guy will have a higher rate of reaction the one in which the cross disappears or the printed text disappears quickly. Now you're saying the concentration of um as the concentration of aqua sodium thiosulfate decreases. When the concentration of sodium thiosulfate would decrease what would happen what would happen if you decrease the concentration of sodium thiosulfate it'll take longer for the cross to disappear wouldn't it cuz sulfur would form slower.

[00:26:18]So yes you could use this idea in planning questions too. And he says during the reaction the solution slowly becomes cloudy. You know why it becomes cloudy? As the solution becomes cloudy, it becomes more difficult to see through the solution.

[00:26:32]The student does five experiments. Use 50 cm cube measuring cylinder to pour 50 cm cube of aqua sodium thiofate into it's better to use a bureet or use a puppet twice pipet of aqua sodium thiofate into a 100 cm cq beaker. Right?

[00:26:49]So he added aqua sodium thiofate 50 cm cube of this guy. 50 cm cq sodium thiulfate. Now it's saying use a 10 cm cq measuring cylinder to pour 5 cm cq of dilute hydrochloric acid to the beaker containing sodium thiofate. So I'm adding 5 cm cq of HCl.

[00:27:13]Now see immediately start the stopwatch and stir the contents of the beaker so that they mix together and so that this because why do you start the stopwatch?

[00:27:21]Because HCl will now start to react with sodium the sulfate and you're now going to see it from the top for the cross of the printed text to disappear. Why would it disappear? It's not magic. It's not going to disappear because there's abracadabra going on. This solid forms in a colorless solution. So the moment a solid forms, you're not able to see through that opaque solid. Right? And that's what he has even said. He's even those who have not performed this experiment, he's told them, okay, this guy becomes cloudy slowly. It's because s of sulfur being formed. I told you that. But you don't need to know it. Now he's saying, "Stand the beaker on a printed sheet and look down from above the beaker as shown in figure 2.1." And we've already discussed it. When the text on the printed sheet is not visible, stop the stopwatch and record the time to the nearest whole number of seconds. So no points, whole numbers.

[00:28:08]Empty the contents of the beaker and rinse the beaker with distilled water.

[00:28:12]Then he says, "Repeat experiment one using 40 cm cq of thioulfate instead of 50 and use use the 50 cmq measuring cylinder to add 10 cm cq of distilled water before adding dilute hydrochloric acid." Why is he doing this? See, in every case, look at him. He used 40 cm cube of aqua sodium thio. But now he's using 10 cm cube of distilled water.

[00:28:36]What does what is the sum of these two?

[00:28:37]It's 50 cm cube. Again 30 cmq of aqua sodium thulfate and 20 cmq of distilled water. What's the sum? What's the sum?

[00:28:47]The sum is 15. 25 + 25 the sum is 50. 20 20 + 30 the sum is 50. Why? Hm. Why? I don't know whether it's going to be tested. But why?

[00:28:59]I don't know whether the exam maybe he asks it later on in the future. Who knows? Why do you think that might be the case?

[00:29:07]To keep the volume constant. Why? Why does he want to keep the volume constant? That's my question. Why does he want to keep the volume constant?

[00:29:15]It's because he wants to figure out he wants to figure out what he wants to figure out how the rate of reaction changes between dilute hydrochloric acid and sodium thioulfate as the concentration of acu sodium thio sulfate decreases.

[00:29:31]Right? This guy's concentration is being decreased, not this guys. If you use different volume of liquid, let's suppose it becomes 70 cm cube of liquid in the next experiment and then you add hydrochloric acid to it. Hydrochloric acid would get diluted, wouldn't it? So the concentration of hydrochloric acid must remain the same. That's why he's making sure her experiment the total volume added of sodium the sulfate or the distilled water the sum of these two is 50 because for the first experiment he used 50 cm cq of solution right solution also contains water so if he uses something more than 50 cm cq the problem is not k the volume should be constant why should the volume be constant it should be constant because if you use hydrochloro if you if I'm going to add hydrochloric acid to this its concentration is going to with respect to 50 cmq now 50 cmq will get diluted so if I add something if I if I make this total more than 50 let's suppose I make it 70 the results are not going to be comparable anymore why because the moment I add hydrochloric acid to it it's hydrochloric acid concentration is also going to get more diluted so to ensure hydrochloric acid concentration is the same for experiment one dilute experiment one because The volume remains the same. The total volume remains the same. That's the reason hydrochloric acid concentration sodium volume right. Yes, Iration but obviously the moment you add the acid is concentration to solution the acid gets more diluted it's present HCl particles will now be present in 50 cm of this guy. But if you change this from 50 cm to maybe 80 then hydrochloric acid. Make sense? That's what we know.

[00:31:59]Acid concentration.

[00:32:07]That's why he's keeping the overall volume the same. Okay.

[00:32:11]>> Thank you.

[00:32:12]>> No problem.

[00:32:14]Moving on. So that's what happens. I I'm pretty sure it may not be tested. It's okay if it's not tested.

[00:32:22]Act with sodium thio in experiment 2 3 4 5 how much is being added? In experiment two, it's 40, then it's 30, then 25, then 20.

[00:32:32]40, then 40, then 30, then 25, then 20 volume of distilled water. See 40 + 10 50 + 20. I don't even have to look above. Plus 25 + 30 that's given in the top as well. At the top, it must be same. Then what happens? dilute hydrochloric acid in every case he's adding 5 cmq he repeats the entire experiment 5 cmq of hydrochloric acid is added 5 cmq and he's not mentioned anything about this which means he's going to still add 5 cmq it doesn't change so hydrochloric acid added is the same 555 and then you have to look at the stop clock please this is the second clock and the inner clock is the minute's clock please don't confuse so minute is at zero second clock is at 30 so it's 30 seconds again. Minute clock is at 0 secondond clock is at 35 36 37 then this guy no DP here whenever you use a digital stop clock there's no DP whole number he's also even told it to you above whole number 55 55 this guy 45 46 47 48 8 49 then this guy is 60 say a come so this is 59 and the next guy g it's 73 see the total volume is being is kept constant why is it 73 is because 1 minute h the 1 minute is 60 seconds plus this is what 5 seconds 10 seconds 11 12 13 so 60 + 13 seconds is 73 that's how we got 73 so you have to write it in seconds. Why not minutes? Because it says in seconds. Now my question to you is which guy has the slowest rate of reaction just by looking at this this idea. Which guy has the slowest rate of reaction?

[00:34:37]Sir, when do we mention quantities added in question four? Always, not the first one. It's because it says time taken for the text to not be visible.

[00:35:00]It's going to be the fifth reaction.

[00:35:01]Why?

[00:35:11]Why?

[00:35:13]Tell me why. Because it takes the longest to disappear.

[00:35:18]longest to disappear. The printed text.

[00:35:25]So the printed printed text takes the longest to disappear. Then plot highest time reach is about 30 73 right?

[00:35:41]You can say if this is 20 you can also start from 20 doesn't matter. You say this is 20, this is 40, this is 60 and this is 80. You could have done that even it's okay 75% of the graph cover 20 40 60 80 you could start from 20 30 40 50 and this would be 100 then now each block represents how much uh seconds each block in order to figure that out you No. Okay. The difference between these two guys is 20 and 20 is the difference for 10 blocks. Yeah. B 10 to 10 boxes represent 20 difference to a difference. Yeah. A box difference represent X cross 20 that's two. So each box represents two. Similarly here 10 boxes represents five difference. Please 10 21 20.5 21 but five difference the difference of these two is five and it represents 10 boxes. So one box represents how much difference x cross multiply what do you get 5 / 10 which is.5 now he's saying volume of aqua sodium thioulfate added volume of sodium thulfate added is now 50 40 30 so you start from 50 40 30 then 25 may it took 30 seconds so at 50 it took how many seconds 20 30 right here then Next at 40 it took 37 seconds. 40 it takes uh 30 31 sorry 30 32 34 36 37 in between. Then at 30 it takes 49 seconds. At 30 it takes 50 49. Then at 25 it takes 59 seconds. At 25 it takes This is 50.

[00:37:55]Sorry this is uh 50 52 54 this 60 to 60 say a come 59 seconds then at uh 20 seconds it takes 70 20 cm cq it takes 73 seconds.

[00:38:09]So at 20 takes 60 70 is in the middle right here 60 or 80 middle 70 72 73 is going to be in between. So 70 72 best line best. It's a curve. Please. So line of best fit can also be a curve. Keep this in mind. Always follow the trend.

[00:38:52]must examiner allows half Right.

[00:39:29]H then equal number of points above and below it equarian standard deviation the relative rate of reaction the rate of reaction in experiment one do not do not give units time in experiment What is the time taken for it to disappear? It's 30. 1 / 30 1 / 30 is what significant figures 0.0 333 0.033 033 reaction rate of which experiment's rate of reaction is the greatest the one in which it disappeared the state bus experiment one or reason because the the printed sheet disappeared the text on the printed sheet disappeared the quickest four three four round how can three be rounded up you could say 0.33 Plus three round up truncate round down in experiment the total volume of acu sodiumfate and distilled water is constant must be constant. Create the distilled water needed 35 cm 30 experiment.

[00:41:21]Experiment two is the easiest.

[00:41:37]Right. Soal 13 cm right for this one.

[00:42:14]Total 50.

[00:42:22]Right.

[00:42:30]Let's suppose one of the reason is to not to ensure Okay, if you add more than 50, what will happen is the depth of the solution changes. Depth of the solution, right?

[00:42:56]Let's suppose height hydrochloric acid. The other reason is it can be the reason paper from your eye also increases.

[00:43:57]Basic solution depth.

[00:44:31]Do not change it.

[00:44:40]Distance.

[00:44:55]So that's the idea.

[00:45:00]Deduce the time taken for the text to not be visible when the volume of 30 when the volume of sodium was used uh was 37 cm. Show clearly how you work the answer.

[00:45:16]37 cm 35 35 and 35.5 36 36.5 37 show clearly your answer right construction lines or please please make sure construction lines you draw it with a ruler construction lines so this is what this is 30 32 34 36 38 38 seconds.

[00:45:52]Explain why the total volume of acqueous sodium thiofate and distilled water is kept constant. Total volume constant.

[00:46:01]Do not change the depth.

[00:46:04]Not change the depth of the solution.

[00:46:13]Yeah. Or or yeah so that it is the same for all experiment to ensure it is same for all exper oh for all experiments dilute hydrochloric acid concentration right to make the results comparable these generic answers are not going to help you out guys generic answers explanations results comparable and to make and thus ensuring comparable results.

[00:46:50]Thus ensuring comparable to make the results comparable invert the question. This is a trick Einstein used to use. He used to say invert the question. Invert comparable result.

[00:47:21]But I knew right acid concentration. So to ensure to ensure acid concentration due to dilute HCL key concentration that remains constant for all experiment and for all experiment thus ensuring that the results are comparable statewide measuring cylinder uh measuring the volume of hydrochloric acid with a boret instead of a measuring cylinder. A borete accurate boret is more accurate. It has a higher resolution.

[00:48:15]Why is boret more accurate?

[00:48:24]Why is more accurate? Because it measures still 2dp or has a higher resolution.

[00:48:34]Why or state? Please keep this in mind.

[00:48:37]Explain why is it not possible to use volumetric paper to measure the volume of aqua sodium.

[00:48:57]So since the volume of sodium thio sulfate is changing pipet cannot be used or changing.

[00:49:16]Why? Because pipet because pippet measures a fixed volume bus.

[00:49:34]How does keeping the total volume constant keep the hydrochloric acid concentration constant cmq hydrochloric acid total 55 cm cm of hydrochloric acid cm cmq of hydrochloric acid cmq to solution total solution is now 85 cmq 85 let's suppose hydrochloric acid 1 mole 1 over 85 /,000 1 over 50 / 55 /,000 solution.

[00:50:30]Hm.

[00:50:33]Explain why is it important to not change the size of the beaker to a larger beaker. Larger beaker larger beaker because the depth would change.

[00:50:44]Obviously surface area would affect the rate of reaction.

[00:50:48]That's also correct. You could have said surface area rate of reaction changes.

[00:50:56]So depth changes.

[00:51:04]Therefore, um it's going to have because it'll have different depths. Depth would change. Therefore, increase rate of reaction changes visibility.

[00:51:26]also depends on depth, right? So results will not be comparable.

[00:51:44]Will not be comparable.

[00:51:56]Done.

[00:51:58]Next paper. Let me restart the recording. Next paper. I'm restarting the recording, guys. Break. Pment.

[00:52:04]Break. I'm restarting the recording.

[00:52:06]Join again, guys. Join again.