2026 GCE Science Paper 2 Predicted Mole Concept Exam Questions

[00:00:04]As you go and like your exam, you need to know these questions and this topic cuz you're going to find this topic in the exam.

[00:00:14]Uh it's compulsory.

[00:00:17]Section A and Section B.

[00:00:19]So, what you need to understand is that the question was saying it's under uh mole concept.

[00:00:28]It was saying excess of zinc metal was it added the to 200 cm cubic of 2 m or 2 2 mole hydrochloric and this is volume. of This is the concentration of hydrochloric acid and this is the volume of hydrochloric acid.

[00:00:57]So, uh that's what you need to know.

[00:01:02]And the question was saying write a balanced chemical equation for the reaction. So, this is the question they like most in GC.

[00:01:10]So, the moment you understand zinc when it reacts with hydrochloric acid, we are going to write the zinc here.

[00:01:18]You are going to write the Zn. The symbol of zinc is Zn.

[00:01:25]It reacts with uh reacts with hydrochloric acid.

[00:01:28]It will produce Oh, hydrochloric acid This is the symbol of hydrochloric acid.

[00:01:33]HCl.

[00:01:35]It will produce the zinc will replace the H because zinc is more reactive than uh uh hydrogen. So, it will replace hydrogen.

[00:01:50]Then they it is going to produce zinc chloride. It will go with a nonmetal and the hydrogen will remain alone.

[00:02:00]You know, hydrogen when it's alone it'll it's it's always have two because you see it's diatomic.

[00:02:07]So, the the this one you're I'm going to say for it to be balanced here you have to put two.

[00:02:18]Two, that means here uh the this is the chemical formula for zinc chloride because why we are putting two? Because we are exchanging the valence. Zinc has got two valence, then this one has got one valence. No wonder we have got this chemical uh chemical formula.

[00:02:37]So, now we have write a chemical equation. But if they say this even state symbols you could have put, but they just say write the balanced chemical equation.

[00:02:47]So, now the next question is saying calculate the number of moles of hydrogen gas produced in the reaction. So, this this where some of the learners don't understand. So, for you to find the number of moles you have to first find the number of moles of hydrochloric acid because they are they have given you just the volume of hydrochloric acid and also concentration. So, you have to convert this um this concentration or this three volume into decimeter cubic. You divide by 100. You say you divide by 100.

[00:03:30]When you divide by or you divide by 1,000. When you divide by 1,000 it's going to give you um 0.2 decimeter decimeter cubic. That means you have converted it in in in in in in the volume where it's supposed to be put. Then you're going to say for you to find number of moles, you're going to say more number of moles equals to you can say concentration multiplied by volume we need decimeter cubed.

[00:04:04]So, now So, for us to find the to find the what?

[00:04:12]The the number of moles, you say concentration concentration was two here. You're going to say two multiplied by multiplied by uh concentration which was two here. So, it's supposed to be two multiplied by the volume which is 0.2. It's going to give us a 0.4 mole.

[00:04:47]That means hydrogen has got to 0.4 mole.

[00:04:50]So, for you to find the um the number of moles of hydrogen you're going to say you have to get the ratio. In front of hydrogen, there's nothing.

[00:05:02]In front of hydrochloric acid, there's two. So, the ratio is two. Then here to hydrogen, if there's nothing that means it's one. So, the ratio will be two to one.

[00:05:14]So, you have to put it down where there is you can say where there is the This one is for uh hydrochloric acid. So, you put it small.

[00:05:26]The number of moles of hydrochloric acid is 0.4. You say 0.4 to the number of moles of hydrogen. We don't know, you put X. You cross multiply.

[00:05:37]Two times this one it will be 2x.

[00:05:42]Two 0.4 times one is going to give us 0.4.

[00:05:47]So, you divide both sides by two, divide both sides by two. X is close to 0.2 mol.

[00:05:56]So, the number of moles uh of hydrogen gas produced is 0.2 mol.

[00:06:02]That's the number of hydrogen gas produced.

[00:06:05]So, now the last question was saying volume uh calculate the volume of a gas produced at the uh room temperature. You uh this is simple. You are going to say just see volume is close to at room temp uh temperature say moles multiplied by 24.

[00:06:32]So, moles that we found it was uh 0.2 of hydrogen multiplied by 24.

[00:06:40]You you must always put multiplied by 24. You're going to say the answer it will be 40 it will be 4.8 dm cubed.

[00:06:48]So, that's the answer. Thank you very much for watching my video. Don't forget to subscribe for more uh exam preparation with the Uza graduate teacher where learning never stops.