WAEC 2026 CHEMISTRY TITRATION QUESTIONS AND ANSWER

追加: 2026-05-10

[00:00:00]Hello my lovely viewers.

[00:00:02]In today's video, we want to look at predicted 2026 Y 8 chemistry practical part one. That is question one, titration. Predicted question on titration. What What you should be expecting on your chemistry practical exams, question number one. That is to That is to say that titration The question that you'll be expecting on your titration, that is what we are going to tackle today. Almost 95% accuracy. 95%.

[00:00:38]So, just go there and study this question that I'm going to about giving you now. Now, what is the question?

[00:00:44]Now, it is mainly for people who are preparing for Y 8, for teachers, for students preparing for West African Senior School Certificate Examination called WAEC.

[00:00:56]Now, the question goes, A is a solution of 3.9 g tetraoxosulphate VI acid in 400 cm cubed.

[00:01:09]B is a solution containing 4.0 g per dm cubed of sodium hydroxide.

[00:01:18]We are now asked to titrate A against 20 or 25 cm cubed portion of B. That is what? The volume of what? Base.

[00:01:31]Using what? A methyl orange as what? As indicator.

[00:01:35]We are now asked to repeat the titration three more times and record our results.

[00:01:42]Now, from the information, we are now asked to calculate the average volume of acid, the concentration of solution B in moles per dm cubed.

[00:01:54]Remember, the concentration of our solution B has already been given in what? In grams per dmq. Now, we are not asked to calculate what? In moles per dmq.

[00:02:05]There are two types of concentration.

[00:02:07]Concentration in mass per dmq, concentration in what? In moles per dmq.

[00:02:11]Concentration in mass per dmq, it is called uh mass concentration. While concentration in moles per dmq, it is called molar concentration. Take note of that.

[00:02:22]Second one, calculate the concentration of A in moles per dmq.

[00:02:27]Here, we are given in grams per cmq, which we need to convert it into what?

[00:02:32]Into grams per what? Per dmq. The next one is concentration of what? Of the pure acid in grams per dmq. We are asked to calculate what? The concentration of A in grams per dmq. The next one we are going to This question is very fascinating.

[00:02:50]Percentage of purity.

[00:02:52]This question is what you should be expecting because the in the paper, in the what they gave you to use and neutralize, it's a percentage of purity.

[00:03:04]There is a purity of acid is given as what? 98%. That is why you you should be expecting this particular question. Now, percentage of purity and impurity in what? Solution what? A and of course, this is our equation.

[00:03:22]Now, what we are going to do is that to answer this question, for us to be able to calculate the average volume of acid, we are going to prepare our table.

[00:03:30]After preparing our table, we'll now use it and answer this question.

[00:03:36]So, stay tuned. If you have Instagram or TikTok, a complete video of how to solve all these parameter is already uploaded on Oje Mike YouTube channel. Look at there, Oje Mike TV.

[00:03:51]Oje Mike TV. just go there, search for titration 2026 chemistry practical.

[00:03:59]The video will pop out and you'll see how we calculate all these burette reading.

[00:04:06]Under burette reading we have our rough we have rough tighter we have first tighter we have second tighter we have third tighter.

[00:04:34]All of them are what in cm cubes. Now, after that we have final final reading we have initial reading.

[00:04:52]And we have what? Volume of what?

[00:04:54]Volume of acid used.

[00:04:59]This is how your table should be, all right? This is how your table should be.

[00:05:17]Now, your rough here, your rough tighter here of what? Let's look at 13.00.

[00:05:23]When you do your titration, we have already determined how the end point of this 2026 chemistry practical, all right? While you chemistry practical. So, the end point has already been determined. If you're watching for the first time go to Ojay My YouTube channel. Go just go to YouTube, type uh how to determine end point 2026 end point by Ojay My. The video will pop out you see how end point is being determined. So, now here we have what?

[00:05:50]Your initial of the rough is what?

[00:05:52]0.100. To get your volume of acid, minus this one by this one is going to give you 13.100.

[00:05:59]And at the end ideally, if you are doing your titration, you are you are expected that you take the initial initial here will be what? 13.100.

[00:06:09]And at the end when you titrate because this acid, if you look at the volume of that burette is calibrated from 0 to 50.

[00:06:17]Do you get that? So, when you get to 13, that acid is still enough for you to continue. But, if you don't want to do it that way, you can refill your acid and titrate again. Please, that is the method I'm going to use so that it will not confuse you, all right? So, I will say my initial of this the sec- the first titrate is 0.1. And at the end I have 12.40.

[00:06:38]Here, I minus this one give what?

[00:06:40]12.140.

[00:06:43]The next one I have 0.00.

[00:06:46]I have what? 12.40.

[00:06:49]I have 12.140.

[00:06:51]And the third one I have 0.00. I have what? 12.1 12.1 30.

[00:07:00]12.130.

[00:07:02]Now, if you are a teacher if you are a teacher the range of your your values for your students should be either minus one or plus one, minus two or plus two.

[00:07:21]That should be the range of the differences. So, if the end point of your of this one now, if your your first student is using 12.40, the other one can say 12.

[00:07:34]uh 50, 12.56 or 12.30, 12. uh 20.

[00:07:42]Do you understand? That is how to prepare table for your for the board.

[00:07:45]The range of the value should be what?

[00:07:47]-1 and 1. -1 or +1 and -2 or what? +2.

[00:07:53]Is that understood? So, at the end, this is how we are able to generate our table so that we can use and calculate the first one, which is what? The average volume of acid. This is our table. Now, let's go to the first one, which is what? Average volume of acid is equals to What you're going to see is that first, don't use rough. Use first, second, or you can use first and second divided by two, or you can use first, second, third, and divide by what? Divide by three. So, we have first tighter plus second tighter third tighter divided by what? Divided by three.

[00:08:44]At the end, you put the what? cm cubed.

[00:08:47]Please, it is very, very important. cm cubed. You have to bracket and put what?

[00:08:51]The unit. So, first tighter, what is the average? Look at average volume of acid.

[00:08:56]You are using this value.

[00:08:58]All right? We are using the one of first, second, and what? Third. So, we now have what? We have first is what?

[00:09:04]12.

[00:09:06]4 plus 12.4 plus 12.

[00:09:14]4 plus We have is equals to 12.40 plus 12.40 12.40 divided by what? Divided by three.

[00:09:34]Equals to 37.10.

[00:09:38]All right? Divided by what? Divide by three. Equals to what?

[00:09:41]12.

[00:09:44]12.37 cm cubed. This is what you're going to have. So, our volume of acid is what? Is 12.37.

[00:09:55]Volume of acid 12.

[00:09:59]12.137.

[00:10:01]Then, we now go to the first one.

[00:10:04]Calculating what? Concentration of solution B in moles per dm cubed. Just take a look at this table while I clean this one to start calculating these parameters.

[00:10:18]To calculate concentration of B in moles per dm cubed, there are two major formula you can use to calculate concentration of B or A in moles per dm cubed. There are two formula you can use to calculate concentration in moles per dm cubed.

[00:10:33]Number one, but before looking at that, I will say, "Okay, H H 2 SO4 is given as what?

[00:10:44]3.

[00:10:47]3.9 per 400 cm cubed.

[00:10:55]NaOH is given as what? 4 g per what? Per dm cubed.

[00:11:01]This is what is given.

[00:11:07]This is what is given in your question.

[00:11:10]Two formula you can use to calculate concentration in moles per dm cubed.

[00:11:14]Number one, one of the formula is this, molar concentration is equals to mass concentration over what? Molar molar mass.

[00:11:28]The second formula is two, CA VA over C B V B is equals to N A over what? N B. These are the two formula you can use to calculate concentration in moles per dm cubed. I told you that moles per dm moles per dm cubed is called molar concentration. While grams per dm cubed is called mass concentration. So, when you are asked to calculate mass concentration or concentration in grams per dm cubed, look at it is called mass concentration. We are going to make this mass concentration the subject of formula.

[00:12:05]But, in this one now, we are asked to calculate concentration of B in moles per dm cubed, concentration of A in moles per dm cubed. So, which one Which formula can we use to calculate the mole concentration? And remember, you cannot use one formula to calculate the two uh concentration in moles per dm cubed. You use one to calculate either A or B, and use one to calculate the other one. So, in this case now, we are going to use this one.

[00:12:30]Now, using this one is not a choice. You have to determine.

[00:12:34]What do I mean?

[00:12:37]You cannot use this one.

[00:12:39]First, because concentration of B is not given in moles per dm cubed. It's given in what? Grams per dm cubed. If in the question, look at the question here.

[00:12:50]If one of the concentration in is given in moles per dm cubed, you don't use this formula. Go direct and use this formula.

[00:12:58]If any of the concentration, either A or B, is given in moles per dm cubed, and you are asked the other concentration in moles per dm cubed, you go straight to use this formula.

[00:13:10]But, if none of the concentration is given in moles per dm cubed in the question, look at our question here.

[00:13:17]None of the concentration is given in moles per dm cubed. Therefore, we are going to use this one first to get the one of um to get one, and use this one to get the last one. So, we are going to use this formula first to get the one of B in moles per dm cube. We now use this formula to get the one of what? A uh A in moles per dm cube. Is that understood? Now, let's go.

[00:13:37]We say that mass concentration is equals to molar concentration is equals to mass concentration over what? Molar molar mass.

[00:13:58]Which is equals to What is your mass concentration? Remember, we are looking at what? Concentration of B. Look at it here. Concentration of B in moles per dm cube. What is your B? This is our B.

[00:14:09]This is B and this is what? A.

[00:14:14]Do you get that?

[00:14:16]Now, the concentration mass concentration I told you here is always expressed in grams per dm cube. What What is the concentration of our four?

[00:14:23]Divide that. What is the molar mass of this sodium hydroxide? What is the molar mass of sodium hydroxide? Look at N A plus O plus H.

[00:14:35]N A here is what? 23 plus what? O is what? 16 plus Sorry. Yes.

[00:14:41]Plus what? One. Equals to what? 40. So, we have what? 40. At the end is equals to what? At the uh we have what?

[00:14:50]Uh concentration concentration of B in moles per dm cube is equals to what?

[00:15:01]0.10 moles.

[00:15:06]Let's leave it in three decimal place.

[00:15:08]0.100 moles per what? Per dm cube.

[00:15:13]This is our first question. This is I.

[00:15:17]Are you following? It is very very simple. Now, let's go to the second one.

[00:15:21]We say that having used this formula for the first one, we now use we now go ahead and use what? Use this formula.

[00:15:26]So, we are going to use this formula.

[00:15:28]So, we say I I now concentration of A in moles per what? dm³.

[00:15:38]Using this formula, C A V A over what? C B V B is equals to what? N A over what? N B.

[00:15:47]Now, we are going to use we are going to make C A the subject of formula. Making C A the subject of formula, I was C A is equals to what? Cross multiply. This one go up. The one that has three parameters will go up. So, we now have what? C B V B N A over what? Over V A N B.

[00:16:09]Now, C B here is the concentration of your base, which is we have Do you get that? So, now What is our volume of base?

[00:16:20]Volume of base is what? What you use as you have prepared. In the question, they say 20 or 25. So, the one we use the one that is normally used in the laboratory is 25. All right? So, volume of base is what? 25.

[00:16:33]V, look at.

[00:16:35]V B is equals to what? 25. V A is equals to what?

[00:16:40]12.1. Look at the end point. Where is the end point? We have 12.37.

[00:16:46]These are the two parameters.

[00:16:48]Are you following? Now, what is your mole ratio? Mole ratio is acid is to base. Look at what? This one N A is acid. Mole ratio of acid. What Look at the equation. You get mole ratio from the what? From the balanced chemical equation. Now, what is the balanced chemical equation? Look at Nothing is there. So, mole ratio is what? One. What is in front of this sodium hydroxide?

[00:17:09]It's what? Two. So, the mole ratio of acid is what? The mole ratio of base is what? It is two. That is how to get your mole ratio. Are you following? So now, going to that, I will say CA is equals to What is our concentration of base? We have 0.10 multiplied by volume of base. Look at it there. Volume of B, 25.

[00:17:34]Multiplied by Multiplied by What is our mole ratio of acid? Look at it there.

[00:17:40]It's what? One.

[00:17:41]One.

[00:17:42]Divided by What is our volume of acid? What we have in that our table, that is average volume of acid. We have what? We had 12.37.

[00:17:53]12.37.

[00:17:56]Multiplied by What do you have as your mole ratio of base? Look at it there.

[00:17:59]Mole ratio of base, that is sodium hydroxide, I have what? Two.

[00:18:03]So at the end, CA now will now be equals to what? We have 2.5 divided by 24. And CA will now have what? 0.101 101 moles per what? Per dm³ So our CA now, look at concentration of the second question, concentration of acid is what?

[00:18:36]Is this one. Is that understood? So the next question we are going to calculate is what? Concentration of the pure acid and what? Impure acid. Are you following, Susan? Look at the question here.

[00:18:48]A is given in what? Grams per cm³.

[00:18:53]Grams per what? cm³. Then how do we get our grams per dm³? Ordinarily, it is grams per cm³ dm³. Any other time that I am asked to calculate concentration of what? Grams per dm³, you use this formula. Make mass concentration here the subject of the formula. But not when it is given When the question is given in per cm cube.

[00:19:15]Anytime you see per cm cube like this and you are asked to calculate grams per dm cube, it is simple. You see that here we have I I I.

[00:19:27]Concentration of A in grams per dm cube. It is simple.

[00:19:33]What you simply do is that 3.9 divided by what? 400. We have to change it. Multiply by what? 1,000.

[00:19:45]This is how to calculate your concentration in what? In in what? In grams per dm cube. When the question is given in what? In cm cube.

[00:19:54]Don't go and use this formula. Do you understand? So, now at the end now we are have what? If you divide this one, cancel here, cancel here, cancel here, cancel here. So, then at 3.9 * 10 / what? 4. At the end we have what?

[00:20:10]A 9 9.75 grams per what? dm cube. So, our concentration of of A in grams per dm cube is what? 9.75 grams per what? Per dm cube. That is how to calculate. THEN THE NEXT one that is more important to that more important is what? Percentage of what? Purity. This question we have to be very very careful because it is likely that they are going to ask it. You get that? Percentage of what? Purity. How do you get our percentage of what? Purity. Now, let's go. Before getting Remember we are looking at the one of what? The one of A, not B. So, let me write the value of my CA. CA is equals to what? 0.1 1 0.1 moles per what? dm cube. Because I'm going to use this value, all right?

[00:21:07]Also, be able calculate the percentage of purity and impurity.

[00:21:12]What is the formula?

[00:21:14]We say that this one is what? IV.

[00:21:18]Percentage of purity Percentage of purity is given as what?

[00:21:35]is equals to mass concentration of pure acid over mass concentration of impure impure acid multiplied by 100 divided by 1. This is the formula to calculate what?

[00:22:03]Percentage of purity.

[00:22:06]Now, we're going to look at the mass concentration of the pure acid and look at the mass concentration of the what?

[00:22:11]The impure acid and we'll now use it for our problem.

[00:22:16]Did you understand? Did you understand?

[00:22:18]No.

[00:22:20]What is the mass concentration of pure acid?

[00:22:23]The mass concentration of pure acid is the one always given in the question.

[00:22:28]In grams per Remember, I told you that mass concentration is expressed in what?

[00:22:31]Grams per dm cube. So, the one given in the question in grams per dm cube is the mass concentration of the acid.

[00:22:38]Of the pure acid. Now, the one that you you the one of the impure acid is the one that you are not asked to calculate using what? This formula.

[00:22:46]So, here, the mass concentration given here is grams per cm cube, but we'll now change it to what? To dm cube and we have what? 9.1 9.75.

[00:22:57]This is the one of what? Pure acid. How do we get the one of impure acid? You use this formula.

[00:23:04]Do you understand? You make mass concentration here the subject of formula. So, you say what?

[00:23:09]Uh mass concentration of pure of pure acid is equals to what is the value?

[00:23:19]9.1 9.75 grams per what? dmq.

[00:23:26]Mass concentration of impure now of impure acid now is equals to Make mass concentration here the subject of formula.

[00:23:43]You are going to use this formula. So, mass concentration will be what? You cross multiply. Say molar molar con multiplied by what? Molar mass.

[00:23:56]Are you following?

[00:23:57]You cross multiply with what? Molar concentration times what? Molar mass.

[00:24:04]You got it? What is the molar concentration of acid?

[00:24:07]I told you that molar concentration is always expressed in what? Moles per dmq.

[00:24:11]While mass concentration is always expressed in what? Grams per dmq. So, molar concentration of the acid is what?

[00:24:16]Look at it here. Moles per dmq. So, we say that um We say that um concentration of impure acid is equals to Molar concentration 0.101 multiplied by What is the molar mass of the acid? Tetraoxosulphate (VI). What is the molar mass? Of course, is 98.

[00:24:45]How do you get that 98? Look at it now.

[00:24:47]H2 That is um H2 plus what? S plus what?

[00:24:54]4O. Here share is what? Atomic mass hydrogen here one. All right? So, one times this two give us what? Two plus sulfur is what? 32 plus four times four times um 16. Oxygen is 16. It give what? 60 what? 64. At the end I have 98.

[00:25:12]So, multiply by what? 98. So, at the end we now have what?

[00:25:18]9.90 grams per what? dm cube.

[00:25:26]This is the concentration of what? Of the impure. And this is the concentration of what? Of pure. Do you understand? Do you understand? Do you understand? Now, what do we do? Now, subject it into our formula.

[00:25:42]Percentage of purity You say percentage of purity will be equal to what?

[00:25:51]What is the mass concentration of pure acid? 9.

[00:25:54]9.75 divide by by what? 9. what? 9.

[00:26:01]90 multiply by what? 100.

[00:26:07]At the end percentage of what? Percentage purity will give you what? 98%.

[00:26:19]Just multiply this one by this one divide by this one give you what? 98%.

[00:26:25]And that is what is given in the uh purity of the acid.

[00:26:31]What is given in the purity of the acid now is what? See, relative density is 1.84. Now, uh purity of the acid is 98. And this is our 98 that we have.

[00:26:43]You can see that this question calculating the percentage of purity is most likely to come out.

[00:26:50]Now, if you have gotten the percentage of purity, what is the percentage of what? Impurity. Percentage of impurity, you see?

[00:26:59]Uh percentage of impurity is what? 100 minus what? What is the percentage of purity? Minus 90 what? 98.

[00:27:14]Which will give you what? 2%.

[00:27:18]Percentage of impurity is what? 2%. What percentage of purity is what? 98%.

[00:27:25]We have come to the end of our titration calculation. So, this is what you should be expecting in your exam. Especially, most concentration concentration of A in most in class in concentration of B in most and in class in class.

[00:27:44]The question might not be far from it.

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