Waec chemistry 2026 qualitative analysis

Added: 2026-05-12

[00:00:09]Yes, we welcome everyone.

[00:00:11]All right to Imaths. So today I'll be doing the the 2026 WAEC chemistry practical on the qualitative analysis.

[00:00:20]And then we have been asked to provide the respective salts and label C.

[00:00:25]Okay, in equal, you know, mass ratio.

[00:00:28]Starch and lead carbonate in equal mass ratio. All right? Now to proceed in the practical, we have the analysis and the the predicted questions that WAEC would be likely to be asking us in this forthcoming exams. All right. Now here we have the salt sample C. These are the predicted questions.

[00:00:48]Okay, that we would definitely have we would definitely be expecting from WAEC.

[00:00:54]But it may be in different orders, anyway.

[00:00:57]All right. So to begin here, we notice that Now none of the two salts is soluble in water.

[00:01:03]And because of that, we may not be asked to dilute in water.

[00:01:07]Because if we were asked to dilute in water, then we should expect both of them to be residue.

[00:01:13]But in this course here, now it would definitely involve filtration process because we have Now if we engage in this acid HNO3 to begin the dissolution, now we'll observe that lead carbonate becomes soluble while starch becomes insoluble in that acid HNO3. So I suspect that WAEC would be asking us to dissolve salt sample C, all right, in HNO3 first.

[00:01:39]So that tells us from the reaction, okay, if we are asked to dissolve it in HNO3, expect only the lead carbonate to be soluble in the acid while the starch remains insoluble. Is that correct? All right. So if we agree with that, now since this would be soluble while this remains insoluble, then that will now help us to understand, okay, the better experimental procedure as we have drawn on the board here.

[00:02:06]So, having done that, we proceed here, okay, we'll be asked to take a spatula full of specimen C. And of course, you know that specimen C is a combination of the two salts here.

[00:02:17]All right. So, because we have a carbonate ion, CO3 2- ion, to be present in the salt C, then being asked us to dilute in HNO3, we should expect effervescence, and that's what we have here. And so, when we dissolve that C uh in HNO3, we'll have C to dissolve partially. Why? Because starch is observed to be insoluble, while lead carbonate is soluble. And so, the partial dissolution is from the fact that starch is insoluble, while the lead carbonate is soluble. All right, we may use also we can also use the word sparingly soluble. All right, so, now, by reason of this observation, we therefore have this inference, you know, drawn from this observation. Then we therefore observe that, or we conclude rather, since we notice effervescence, and that is nothing but carbon four oxide gas, okay, liberated from this carbonate ion, CO3 2- ion. All right, and that's confirmed.

[00:03:18]All right, that's confirmed. All right, so, we are asked to stir and filter.

[00:03:22]Now, because we know that salt C is not totally soluble. If it was soluble, we would not have been asked to filter. So, filtering the the aqueous, you know, dissolution of that salt, we notice a white residue and a clear filtrate to be formed. And by reason of this observation also, we have this inference to be drawn from it. So, since we have a residue, okay, as we have illustrated here, and the filtrate, all right, to be dis- though the salt we are asked to provide is lead carbonate.

[00:03:53]But here we have the lead nitrate. Why?

[00:03:56]Because we have been asked to dissolve the HNO3 here.

[00:03:59]So which we concluded a 5% and that gave rise to [clears throat] a new filtrate here. So this will be the filtrate that will be you know, that will be drawn in the you know, the reacting vessel.

[00:04:12]All right. And so we have the starch to be the residue.

[00:04:15]The starch represent the residue.

[00:04:18]Okay? And of course we have this to be the filtrate.

[00:04:22]All right. So we also suspect that uh Now having done that, we are asked to be asked to to take the filtrate and divide into three portions as we have predicted here such that we'll be asked to carry test on each of the portion. The first portion, the second portion and the third. And let's see from the first portion. Now the first portion of course we suspect that in the filtrate the ions that we are likely to have there are lead two ions and nitrate ion.

[00:04:52]Meanwhile, we may not be asked to carry any test on nitrate ion.

[00:04:56]Okay? Nitrate we may not be asked to do so. This is only obtained from the first reaction here. Having dissolved the HNO3. All right. So basically on in the test of the filtrate it will specifically be on lead two ion. All right. Now let's see the first test. To test for lead two with sodium hydroxide.

[00:05:15]All right. Now of course when we add sodium hydroxide in drops to uh a salt containing lead.

[00:05:25]So we are expected of course to see a white chalky precipitate is formed. And then among our guests of course we know that these are the likely ions that can form a chalky precipitate or a white chalky precipitate. You know, with the exception of aluminum. Aluminum should also have been guests here but aluminum is rather gelatinous.

[00:05:45]So we may not guess correctly to have put aluminum here. So, that's why we have lead. Either lead forms a chalky precipitate or calcium does or zinc does. So, we're only suspecting either of them. Now, but by putting in excess, we discover that the white precipitate dissolves in excess.

[00:06:02]And so, the fact that the precipitate dissolves in excess tells us that such element is amphoteric.

[00:06:08]And so, from among those guess here, now we'll subtract to eliminate calcium.

[00:06:13]Calcium is not amphoteric. So, we still have the lead and the zinc, you know, brought down here. But, that's not conclusive enough to know which of these two is actually present. So, we went to the second test and second portion.

[00:06:25]Since we have the three portions to be divided into, now we have done the first portion. Now, here comes the second portion. All right? In the second portion, we've been asked to add aqueous ammonia in drops. Now, let's see what happens. Now, aqueous ammonia, when added to a salt of lead two, of course, we'll also notice a white chalky precipitate as we did here.

[00:06:47]Now, so we're still suspecting either the lead or the zinc as the two also may have a white precipitate chalky, okay, with aqueous ammonia. Now, this won't differentiate them also now. We have Now, when we add the aqueous ammonia in excess, in excess, the white precipitate remains insoluble.

[00:07:06]Now, that suspect we have lead two to be present. So, we may go further to the third portion. Then, third portion now gives us the confirmatory test for lead for lead two.

[00:07:17]Now, here, uh for a salt of lead, for a salt of lead, for example, as we have here, lead nitrate.

[00:07:27]Now, to be added with a reagent hydrochloric acid as we are as we are to do so here. Third portion containing the lead, we are to add dilute HCl.

[00:07:38]All right? Now, now let's see this theoretically. We expect to have lead two lead chloride.

[00:07:46]Okay? Which we have this to be a white precipitate.

[00:07:49]All right? Lead chloride and of course we'll have the HNO3, okay? To be formed on the other side. Now, this precipitate, okay?

[00:08:00]Also gives us a white precipitate. So, that's why we have the observation here.

[00:08:04]On adding dilute HCl, we'll expect to have a white precipitate to be formed.

[00:08:09]All right? Now, so here this lead chloride precipitate has um specific specific, you know, attribute. Which we observe that the lead carbon the lead chloride, rather, seems to be soluble in hot water, but insoluble in normal water. And so, that's why Y could also ask us to heat that precipitate.

[00:08:34]Okay? And allow to cool as well to state our observation. So, once we have that question, then it gives us a pointer to the fact that the precipitate is likely to be from the lead chloride.

[00:08:45]Lead chloride precipitate. Okay? So, therefore we said on heating, the white precipitate disappears. Then on cooling, it reappears on cooling. Now, that tells us that lead two is the is the, you know, the element or the cation that is present in that given salt C that we have tested for here. So, lead two is confirmed here. Lead two is confirmed. All right? So, we have done the probable test on the filtrate and we come to the residue. Of course, we know that the residue is nothing but the starch.

[00:09:19]All right? And so, we have a simple test on starch with the test of iodine. So, the residue that we assume to be the starch will maybe asked, rather, okay?

[00:09:28]This is certain, anyway. Residue to be added with iodine solution.

[00:09:33]Now, of course we know that on adding iodine solution to a a solution of starch, we observe a blue black coloration or a dark blue however the expression. A blue black color is formed and that tells us that starch is confirmed. That's a confirmatory test for starch. We may also be asked to add the add little quantity of water to the residue starch and heat on the Bunsen burner. Of course, we know that starch has a specific attribute. It undergoes what we call gelatinization. And that's talking about starch having starch having a a jelly like paste when heated. All right, so if we were asked to do that, so we should expect such observation if we were asked to eat it. Starch will have a jelly like paste is formed and that tells us that starch is present.

[00:10:24]But I suspect that if they would ask us, they would have asked us to they would have asked us prior to this one here because once an element or substance is confirmed, okay, there is no need to carry out any test on that same substance subsequently. Or we may do that. We may we may have been asked before that very time. All right. So, these are the likely questions that we should expect for the chemistry Y chemistry 2026 in the qualitative analysis. So, we'll be having the video in the next the practical class rather in the next video. So, watch out. Thank you.