SCIENCE PAPER 2 || 2024 GCE || SECTION B FULLY ANSWERED AND WELL EXPLAINED

[00:00:00]Hello everyone, welcome back again to God from Academy. So today we are dealing with 2024 GCE uh science paper two which is chemistry.

[00:00:12]So we'll answer the entire section B and because of that if you haven't subscribed yet ensure that you do so make sure you do what you subscribe. All right so this is the paper I'm sure you are able to see here. This is GCE.

[00:00:30]All right. So section B has nine questions and this is the first question.

[00:00:40]So the first question is saying a box of chemicals in a laboratory has the following symbol attached to it. So they've there is this box in a laboratory then it has this symbol.

[00:00:56]They've attached this what this symbol to the box. Then question A is saying describe the nature of chemicals in the box related to the symbol. So just by looking at the symbol what could be the what the nature of the chemicals inside the box. So if you see here this looks like the flames of fire right it looks like fire. So for this to be like this it means the the what the the chemicals must be flammable. They must be flammable. And by flammable I means I mean I mean they they catch fire easily.

[00:01:36]So in this case for question one we can say so this is our what? This is our our B1. We can note it down here as our B1.

[00:01:51]So this is our A1. We are going to say uh the chemicals are what are flammable.

[00:02:01]The chemicals are flammable.

[00:02:10]They are flammable.

[00:02:15]Yeah. So this is our first answer. Then the second question is saying write a laboratory rule that is observed when handling chemicals in this box.

[00:02:28]Since these chemicals are flammable, what rule must you observe when you are handling these chemicals in in in a laboratory? So since they are flammable, it means you should keep them away from the what? From the uh from the from fire.

[00:02:49]So you simply say keep the chemicals away from fire or you can say keep fire away from the what from these chemicals. So this is the rule which must be observed. Then B is saying when a bottle of ammonia is opened within a few minutes its smell spreads throughout the laboratory. Name the process responsible for the evenly spreading of the smell of ammonia solution. So they open the bottle of ammonia and within few minutes it spreads throughout the laboratory.

[00:03:42]Everyone in the laboratory can smell it just after a few minutes. So name the process responsible for this.

[00:03:51]Of course when just when you just hear particles the the movement of particles you need to know that that is diffusion.

[00:03:58]So our B1 the process responsible for that is what? Diffusion.

[00:04:07]Diffusion.

[00:04:09]That is it. Then for this one describe the process responsible for the even spreading of the smell of ammonia solution. So they want us now to describe this process which is diffusion. So you understand that diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. So now relating it to this what are we going to say? we will say u the particles of ammonia move randomly. So this is what you will say. This is B1. Now we are dealing with B2. So you will say the particles of ammonia moves randomly.

[00:05:06]So they move randomly from a region from a region of higher concentration to a region of lower concentration.

[00:05:30]So this is diffusion of lower concentration.

[00:05:40]So that is diffusion. So this is what will h happen here. These particles of ammonia moves from I mean moves randomly from a region of higher concentration where they are more concentrated to a region where they are less concentrated.

[00:05:58]So then you say until they are evenly distributed.

[00:06:16]So this is the process.

[00:06:19]Then the last question says relate the evidence which the process named in B1 provides to the kinetic theory of matter. They want us to relate the evidence that this process does what?

[00:06:34]Provides to the kinetic theory of matter. So you need to understand this.

[00:06:38]This is very important.

[00:06:40]The kinetic theory of matter states that uh all everything or all objects are made up of what? particles and these particles are in constant random motion.

[00:06:53]In short, particles never rest. They are in constant what? Random motion.

[00:07:00]So they want us to relate this with with this same theory.

[00:07:07]So this is our what our B3.

[00:07:11]So what are we going to say here?

[00:07:16]So you're going to explain to say because these particles are are are spreading right? Yeah they are moving.

[00:07:25]So you will say this spreading of particles, the spreading of particles shows or proves that. So this spreading of particles proves the kinetic theory of matter in such a way that it proves that indeed particles are in constant constant random motion.

[00:08:07]Okay.

[00:08:09]Only when particles are in constant random motion can they evenly distribute can they evenly get distributed in the entire laboratory room. So that just proves this for the particles to be uh to to to fill the entire space it means they in constant what random motion. So this is what this means.

[00:08:34]Then the second question. So the second question is here it is saying the diagram I mean the following diagram shows a piece of apparatus used in the laboratory. So we have this piece of apparatus used in the what in the laboratory [snorts] and it is saying name the piece of apparatus shown in the diagram. What is this? So when you just see it like this stopper a tap then it's like this just know that this is a separating funnel. So this is our this is our B2.

[00:09:11]So B2 then we have question one. So this is a separating F.

[00:09:22]Okay, separating F. That's the the diagram here. Then it says identify one property of a mixture separated by the piece of apparatus named in A. So you understand that this is what this is separation techniques and this one is used to separate imissible liquids.

[00:09:48]By imissible liquids I mean those liquids that are not soluble in each other those that cannot mix completely are the ones that we use uh that are separated by these operators. So for B2 one property of the of the mixture separated you will say the liquids or mixture since they've used mixture in the question are imissible or must be emissible.

[00:10:28]Imissible. This simply means they should be insoluble in each other or they should not mix completely. So this is the property you must know this. So this is imissible. Missible is the opposite of this. Those liquids that can mix completely.

[00:10:46]Then it says suggest the names of two liquids that can be separated by the piece of operator shown in the diagram.

[00:10:53]So now give examples of these same imissible liquids. Well, this is a a very common question. So, cooking oil and and water, cooking oil and H2O water, these two are immissible. They don't mix completely.

[00:11:18]So C suggest two precautions that need to be taken to separate the mixture in B two. So two precautions. The first one before opening the tap you should remove the stopper. That is very important. Remove the stopper before opening the what the tap. Then open the tap slowly and gently and close it immediately as soon as immediately as soon as uh immediately as the the the liquid at the bottom here moves out. Okay? You shouldn't wait until the the one on top also starts moving out. The moment you just see that the the one at the bottom is finished, you close it as quickly as possible.

[00:12:11]So that's another what another precaution. So what do you say here?

[00:12:17]Well, here this is our our C. So first one should be I said you should remove the stopper.

[00:12:31]Remove the stopper before opening the tap.

[00:12:43]Then number two, open the tab slowly and close it.

[00:13:00]As soon as the bottom liquid or the liquid at the bottom moves out.

[00:13:20]Okay. So these are the two rules. These are very important. All right. This is it for question B2. We go to the next.

[00:13:29]So this is the question. So question three is saying the following diagram shows the electronic configuration of the ion of an element M. So this is the electron configuration of an ion. Don't forget that an ion is a charged particle. Okay? So this is charged. By that I mean it has either lost electrons or it has gained. That's that's an ion.

[00:13:55]So they are saying draw the atomic structure and write the electronic configuration of the neutral atom of M.

[00:14:02]If this is the what? If this is the uh the the atomic configuration or the electronic configuration of this ion.

[00:14:14]What about the neutral one? So they want us to draw but before it uh it it was charged when it was still neutral how was it structure that's the one they want us to do what to draw.

[00:14:28]So for that one what you need to know very important you need to understand that when you see a positive here it means it has lost electrons. When it gains electrons we represent it by a negative a minus. So this is positive2 or 2 plus it means it has lost two electrons meaning before it had two more electrons in the outer shell but this is showing that it lost them.

[00:15:00]So this is simple if you want to draw the original well all these will be included and also will include these two before it lost the two electrons. So the two will be in the outer shell as simple as that.

[00:15:18]So one thing that you need to understand also you need to count the number of electrons.

[00:15:26]So here we have two 1 2 then in the second we have eight plus this two we have 10 and in the third shell we also have eight if you count here. So 10 + 8 is 18. So here we have 18 plus the two it lost meaning the total is 20 electrons. 20 electrons is equal to 20 protons because the number is same is equal. So if it has 20 protons it means the atomic number is what is 20 because the atomic number is the number of protons.

[00:16:01]So since it has the atomic number of 20 we can write this element they saying it is m. So we can say m M the electronic configuration since the atomic number is 20 here actually the periodic table is always given in the exam paper. So this shows element M. You can come to your periodic table here and just find where element M is the one with 20 at the bottom here.

[00:16:39]This is the 20 here if you can see. So this is Gausam with a 40 on top. So our 20 here with a 40 on top. It's gausium. So for this 20 to write it here. The first shell has two always. The second shell has eight. Third shell as 8. So this is 2 + 8 10 + 8 18. Then this has 20. So we are remaining with a two. So this is the original configuration but it lost the two. Then they draw that diagram. Okay.

[00:17:19]So this is how it was at first before it lost these two. This is Kam. So for us to draw the original we will still follow this and this together. So what are we going to say? We will draw this the first one. It had two electrons these two. So the first one. So inside we say this is our calcium.

[00:17:42]Then it has two electrons for the first shell. The second shell we need to use a pencil.

[00:17:52]Yeah. In the exams. So the second one had I mean has eight here. So we draw eight.

[00:18:02]So 2 4 6 8. Third one also eight. This one. So even this one will have eight.

[00:18:15]Then the last one only two.

[00:18:20]So this is the last one. So this is how it was. So if you see this is just same as this. Then these two is the one now I've shown here these two electrons. So that's it. So this is the atomic structure and this is the electronic configuration.

[00:18:42]So the next question says find the name group and period of the element M. Well you you can easily identify it. So our the 20 is the atomic number. The number at the bottom there, this one, not this one. This is the mass number. But this is the atomic number. So is here the caus. That's the one we use to identify the element. So this is in group what?

[00:19:09]It's in group two. And the name is Kawam, right? So here on the question, the name is Kawam. The group is group two. What about the period? So we'll start with So this is our A two name this is caus then group is group two then period.

[00:19:45]So period this is causam right the period is these horizontal ones. So the groups are vertical group one group two group 3 4 5 6 7 and group.

[00:20:00]These are periods. Period 1, period 2, period 3, period 4. So kosam is in period 4.

[00:20:08]So period 4.

[00:20:14]Then the question is saying compare the reactivity the reactivity of an atom of M and an ion of M. The reactivity between the atom and the ion. Now you need to understand that when they say the atom this is the atom it has 2 88 8 and two in the outermost shell. When they say the ion in the outermost shell it has how many? Eight.

[00:20:40]So the concept is for it to be reactive unless it is not stable. And by being uh by not being stable I mean if in the outermost shell for the first one the first shell only needs two electrons but the second shell the third the fourth all these needs eight electrons. I hope you understand that that concept. They need eight electrons to be stable. So if they have any number apart from eight it means they are not stable and they will be reactive so that they can be stable.

[00:21:16]So this atom has two so it's it's not stable meaning it is reactive. It needs to react by losing these two electrons.

[00:21:26]Then it will become stable.

[00:21:29]But for this one it has already lost these electrons. Meaning this one is what? This one is already stable.

[00:21:37]So they want us to compare the two. So you will simply say this is our question.

[00:21:46]So you you will say this is B.

[00:21:50]An atom of M is reactive and needs to lose to lose two electrons to be stable.

[00:22:19]Wow.

[00:22:22]An ion of M is unreactive because it is stable.

[00:22:40]It is already stable because it has already lost electrons. So this is it for this one. Then B4 salts are substances that have many methods of preparation. Okay. So this is preparation of salts. Then a ion 2 chloride can be prepared by reacting substance X and dilute hydrochloric acid which reactant should be in excess. So when you when you come to acid bases and salts specifically preparation of salts whenever you are re reacting an acid and a solid the concept is a solid should always be in excess that is a must so that the acid can so that the entire acid can be used up.

[00:23:32]So that is the reason so always the solid is in what is in excess. So when they say which reactant should be in excess. Of course since we are reacting solid to chloride I mean we are preparing solid I mean we are we are preparing ion to chloride by reacting X and hydrochloric acid. So we are reacting X and hydrochloric acid.

[00:23:58]So X is a solid and what you need to understand you you need to identify this X. How for us to prepare ion to chloride?

[00:24:11]It means the solid has to be what? Ion. When we react ion plus hydrochloric acid we are going to produce ion to chloride. So when we react ion 2. Okay. So ion 2 must be in excess or substance X has to be in what? In excess. So that is the answer for that question. Substance X should be in excess because the acid should not be in excess always. Always. That's what I'm saying. So here we tell them this is our B4.

[00:24:52]This is A. So you are going to tell them which one is going to be in excess. You simply say substance X because the solid should always be in excess. So here they are asking why should the name reactant in A1 be in excess? Because this is the solid. Okay since it's reacting with an acid. So the reason this should be in excess because solids should always be in what? in excess and to ensure that the acid is used up. So you say so that the acid can be used up as simple as that or to ensure that the entire acid or the whole acid reacts.

[00:25:49]That's it for that one. Then B suggest a suitable reactant as substance X. So now they want us to suggest this suitable substance. So we need to identify it. It is reacting with hydrochloric acid to form ion chloride.

[00:26:10]So since it is forming ion the substance should be ion 2. Okay. When this ion reacts with hydrochloric acid, it will be it will give us ion to chloride. So the term the name chloride is coming from hydrochloric acid. Yeah. The last name of the salt is taken from the acid.

[00:26:32]If it was sulfuric acid, it would have been ion to sulfate. But since it is hydrochloric acid, it has to be ion to chloride from hydrochloric. So that's the concept. So this the suitable has to be ion. Ion plus hydrochloric acid it's giving us this. So can come here.

[00:26:56]So we write it here. This is our B one.

[00:27:01]So we say ion simply ion which is Fe.

[00:27:11]Then the next question is saying write a balanced chemical equation for the reaction between substance X suggested in B1 and dilute hydrochloric acid. So this one B a balanced chemical equation between this and hydrochloric acid. So this is ion this is the symbol right? So this is the symbol. So we will say ion it is a metal so it is in solid state is reacting with what? Hydrochloric acid.

[00:27:42]This is hydrochloric acid. Okay. So you need to know this because they are not given. So hydrochloric acid it is an acid. Acids are in aquas state to give. They are saying it is producing what? We are preparing ion 2 chloride.

[00:28:03]So it's giving ion 2 chloride. So ion 2 chloride is like this.

[00:28:13]So it has a two here.

[00:28:17]Why does it have a two here? We get back to how to write chemical compounds.

[00:28:23]There's that topic a very short topic in chemistry. So you write ion just a recap like this and chlorine like this. Then what is the valance number for this ion?

[00:28:38]So when you see that they are saying ion two in these brackets it means the the valance number is what is two because ion is able to change the valance number. It can be two three. Yeah because those are what are transition metals just like copper. We have copper one copper 2. So depending on the context so this is two but this these other elements have fixed valance numbers. So like chlorine is always one group seven. So you simply exchange the valences.

[00:29:12]So Fe will be like this. This valance number is going to come here. Then chlorine is going to be like this. This valance number will come down here.

[00:29:23]Okay. So one we don't write. So it will be like this and this is ion 2 chloride.

[00:29:32]So that's the one I wrote here. Then you need to understand that when you are reacting a metal and an acid. This is very important metal plus acid is always a salt and hydrogen H2 which is a gas. So this is in aquas.

[00:29:53]So we always produce hydrogen. Sometimes they will put it X and ask you to identify or put a letter any letter.

[00:30:01]This is very important. So they need they want us to balance it up. So here we have one ion.

[00:30:09]Even here we have one ion. Here we have one hydrogen. Look here we have two. So we need to add the two here. So here we have two hydrogens. Even here two hydrogens here. So this two has affected the chlorine. The chlorine is has now become what? Two. What about here? It is two. So this is balanced.

[00:30:35]All right. We got the next question.

[00:30:36]Question five. So this was the question we are answering. This is five. Now it is saying 10.5. So this is more concept and pay attention for this one.

[00:30:50]5 point I mean 10.5 grams of sodium hydroxide was reacted with dilute sulfuric acid according to the equation. So we have sodium hydroxide with the mass of 10.5 it reacts with sulfuric acid to form this sodium sulfate sodium sulfate and water balance the given equation. This is the first question. So let's write it down here. We have sodium hydroxide in aquas reacting with sulfuric acid to form sodium.

[00:31:48]sulfate plus H2O water. So they want us to balance this equation. By balancing this is very important. The number of moles here should be equal to the number of moles even this side. So like we did in the previous question, how are we going to balance this equation? So for us to balance this equation what we need to do we need to count the number of the first element on the first what on the first side on the left side so we'll start with sodium we'll say how many sodium atoms do we have here we have one there's nothing here there's nothing here so it is one about here we have a two here this two is with this. So we have two here we have one.

[00:32:48]So we need to balance right here.

[00:32:51]So since here it's a two we will add a two here. So these two we have two sodiums. Even here we have two sodiums.

[00:32:58]So sodium is balanced. Now we go to oxygen. So oxygen these two affects everything. So oxygen now also becomes two because of this here. So we have two oxygen plus this one three.

[00:33:17]No no no we have O4. So these are four oxygen here. Yeah. Four oxygen plus these two. We have six on the left side.

[00:33:27]On the right side we have four here.

[00:33:29]Here we have one oxygen.

[00:33:32]So we need to add a two here.

[00:33:36]So that these two affects this oxygen and oxygen becomes 4 + 2. So it becomes six even this side. What about hydrogen?

[00:33:45]It's two here.

[00:33:47]Two here plus this two because here we have hydrogen also and it is being affected by this two. So two plus this two four even this side two times this two is four. So hydrogen is four. Sulfur is one here. Even here it's one. So this is how we balance. This is very important. If you fail to balance, you'll get the calculations wrong for the following questions. So this is it.

[00:34:17]Then B1 use the balanced chemical equation.

[00:34:23]See, so it needs to be balanced to calculate the mass of sodium sulfate formed. So they want us to find what?

[00:34:30]The mass of sodium sulfate. This is sodium sulfate. the mass of this but we need to use a balanced one. So how do you go about it in the question? This is very important to understand and more concept they will always give you something to use to when whenever they ask you to calculate anything they ensure that they provide something somewhere somehow. Okay, that is very important to understand. You cannot calculate whatever they ask you without giving you anything. So you need to focus on what you are given because that's what you use. In this case just in the instructions they've said 10.5 g of what? Sodium hydroxide was reacted.

[00:35:20]So we've been given mass because grams the SI units of mass.

[00:35:27]So we've been given the mass of what?

[00:35:29]sodium hydroxide.

[00:35:31]So this is very important. So you will come to your equation. Where is sodium hydroxide? This is sodium hydroxide. So we've been given the mass of this 10.5 g. So when you start calculating this is what you do. You get what you are asked.

[00:35:48]We are asked to find the mass of this using the mass of this because they've given us this mass and they asking us to find the mass of this.

[00:35:58]This is what we call mass to mass calculations. Why mass to mass? Because we are using the mass to calculate the mass.

[00:36:08]I hope you get the concept. We using this mass the mass of sodium hydroxide to calculate the mass of what? Sodium sulfate. So this is mass to mass. There is mass to mo and to mass and more to mo. More to mo. They'll give you moles and ask you to calculate moles. More to mass. They give you moles. They ask you to calculate mass. So there are those conversions that you need to know there.

[00:36:29]So this is mask to mask. For this one you can answer it in two ways but the simplest one you get the one you are asked. So this is the one they want sodium sulfate versus the one you are given now which is sodium. So you get the balanced chemical equation. It has a two here.

[00:36:57]Okay. So this is what we are dealing with. So for us to find the mass of this because we are looking for this the mass of this sodium sulfate.

[00:37:08]What we are going to do for mass to mass you get the mass of this and the mass of this. You write them down as a ratio. So for mar mass of this how do you calculate the mar mass? The mar mass you calculate it like this.

[00:37:25]So you get the first element the last here.

[00:37:30]Then this is oxygen. What is the mass number of oxygen? You just get to your periodic table? It is six here. 16 rather. So it is 16 multiplied by how many atoms do we have here? Four. Then what about sulfur?

[00:37:51]sulfur again you come here you find where sulfur is so sulfur is here it has 32 so you say 32 multiplied by how many atoms of sulfur here only one then this is sodium sodium has 23 the mass number 23 3 * how many sodiums do we have? Two. So now you say that is 16 * what * 4. You have a calculator. So then this will give us 32.

[00:38:36]This will give us 46.

[00:38:44]Then you you now do what? You add. So we have 64 + 32 + 46 it's giving us 142 g per mole.

[00:39:00]These are the SI units. So this is what this is the molar mass of sodium hydroxide. This is very important.

[00:39:07]Sometimes they will ask you just to calculate this. Very important. So here you write it 142 as the what the mar mass. Then you find the mar mass of this also. So this is sodium hydroxide oxygen is so it's balanced like this. If you want you can find this then you multiply by two at the end or you go one by one.

[00:39:35]So we take it as hydrogen the mass number you come to your periodic table.

[00:39:40]this hydrogen it's one multiplied by how many atoms of hydrogen we have here. So we have two then we have oxygen it's 16 * 2 sodium sodium is what?

[00:40:00]Sodium is what did I write here? Yeah this is sodium hydroxide. Sodium is 23 multiplied by 2 also. So this is 2, this is 32, this is 46.

[00:40:15]So again we'll find the total. So that is 4 + 46.

[00:40:23]It's giving us 80 g per mole. So this here sodium as 80 80 what am I writing? This is 80 g per mole. Yeah, just like this. So when you write the mar mass of this, even the mar mass of this, what you do next now is you do what? You now get the mass that you are given. So you get back to your question. The question is clear. 10.5 g of sodium hydroxide. So where is sodium hydroxide? Now you put your what? Your mass here.

[00:41:02]No, this is sodium sulfate. Sodium hydroxide is here. 10.5 g. Then we are looking for this mass sodium sulfate. Then we cross multiply here x by 8 to give us 8 x being equal. This is 142 * 10.5.

[00:41:30]It's giving us,491 over 8 80 / 80. So x is equal to 18 18.6 4 g. Therefore you say we have mass is equal to 18.6 6 g.

[00:42:01]64.

[00:42:02]Yeah. 64. So 6 4 g of what? Of this sodium sulfate.

[00:42:14]This is how you write it at the end. So this is how we find the mass for this question.

[00:42:20]All right, we go to the next question.

[00:42:26]So this is the next it is saying an element A is in group one of the periodic table. Another element N is in group uh seven. So this is periodic table. A is saying write one property of the compound formed when element A and N react. This you have to know because this question does not even need the the periodic table. Question A.

[00:42:54]They just want you to name one property formed between a compound that will be formed when A reacts with N. So when group one reacts with group what? Seven.

[00:43:05]Because A is in one, N is in seven. What are the properties?

[00:43:11]Well, you need to consider the compound.

[00:43:14]What type of compound is formed? What type of compound? So A being in group one it means it is a metal an alkal metal right? Yeah. Then N being in group seven it means it is a nonmetal. So a reaction between a metal and a nonmetal will give us the ionic compound because the bonding will be ionic bonding right between a metal and a nonmetal. So you get now the property of what ionic compound. I hope you get that one. So our base B6 for A it's going to be the property of an ionic compound. So ionic compounds number one have high melting and boiling point.

[00:44:18]So this is very important but they just want one. So this is enough. Second question is saying what type of bonding exists in the compound formed when the two elements react. So I'm from saying it to say the bonding is ionic bonding.

[00:44:40]Ionic bonding is formed between a metal and a nonmetal. Then we have coalent bonding. Coalent bonding is between a nonmetal and a nonmetal. That's the difference. Then we have metallic bonding which is between I mean which is in metals only. So those are the three types very important.

[00:45:00]Then the next how does the reactivity of elements in group one differ from that of elements in group seven. The reactivity this is very important this question usually comes. So the reactivity of group one increases down downwards.

[00:45:21]This is group one. The more you go downwards, the more metals become reactive. Okay? So this sodium is more reactive than this.

[00:45:32]This is more reactive than this. This is more reactive than this. The most reactive that is also asked. It's this one. So the least reactive is this one.

[00:45:42]So in group one the more we go down downwards the more the reactivity increases which is opposite to group seven. In group seven the more we go downwards the more the reactivity decreases.

[00:45:56]So you say in group one the reactivity increases downwards.

[00:46:18]Why in Group seven, it decreases downwards. As simple as that.

[00:46:41]So this is it for this question. We go to the next.

[00:46:47]So this is the next question.

[00:46:51]So it is saying metallic bonding occurs for the for most of the physical properties of metals. Yeah. So this is bonding metallic bonding.

[00:47:01]So it occurs for the most uh for for most of the physical properties of metals. A with reference to metallic bonding. Explain why most metals have high melting points. Why metals have high melting points? referring to um chemical bonding I mean metallic bonding.

[00:47:23]So for metallic bonding one thing that you need to understand is it occurs in metals. So the reason metals have high melting point is you tell them now this is B7.

[00:47:38]So this this was the one I was talking about not I think I was saying chemical bonding it's actually metallic bonding.

[00:47:45]So in metallic bonding this is our a in metallic bonding.

[00:47:57]So in metallic bonding positive ions of metals are surrounded by a sea of deoized electrons.

[00:48:26]Deoized or mobile or free electrons whatever is but this is the chemical term so this is preferred. So deoized electrons So now the electrostatic forces of attraction between the positive Ions and electrons are very strong.

[00:49:27]Therefore to break this you need a high melting point melting point.

[00:49:48]Now you conclude thus metals have high melting points.

[00:50:02]So you've seen the way I've explained this question is usually asked why metals have high melting points relating it to metallic bonding. This is understood well when you look at the structure. So I think that's the next question.

[00:50:17]The metals have two charges. We have positive ions and electrons. These are opposite. Okay, are oppositely charged. So now these electrons are called deoized because they are free to move. Deoized electrons are electrons which are free or which are mobile. That's one and the same.

[00:50:41]So these attract each other because the ions are positive the electrons are negative. So they attract each other and the forces between them which are called electrostatic forces of attraction are what are very strong. So breaking them requires a very high melting points and that is the reason why metals have high melting point. I hope you you understand that concept. So that's it.

[00:51:09]It has two marks. Then draw a diagram to show metallic bonding in zinc metal in zinc. So this is what now I was explaining.

[00:51:20]This is the illustration.

[00:51:22]All right. So for zinc we use zinc. This is zinc.

[00:51:32]Okay.

[00:51:33]So this is zinc. We make it like this.

[00:51:38]Then even here zinc positive2.

[00:51:46]Even here we have zinc.

[00:51:50]Even here we have zinc.

[00:51:54]And here we have zinc.

[00:51:57]Then here we have the deoized electrons.

[00:52:04]So this is it. When you look at this, these are positive ions. The one the ones I'm talking about here. Then these are electrons. So these two charges attract each other. And the forces between them are so strong such that to break them, you need a high temperature, very high temperature. So that's the reason metals have what? High melting points. So this is it for for the last question here.

[00:52:34]No for B we have question C. So let's look at C.

[00:52:40]So this is the question for C. It is saying Elena carried out the following experiments. So in experiment one, 5 g of powdered zinc and in experiment two, five of granules of zinc were each reacted with equal volumes of dilute hydrochloric acid both of the same concentration for 15 seconds. The reactions were not yet completed at 15 seconds. So let's understand the question here. This learner carried out two experiments. In the first he had 5 g of what? Of powdered zinc. In the second he has 5 g of granules of zinc. So the first experiment zinc is in powdered form. The second one these are granu.

[00:53:39]These they are more like uh more like the bars. They are big. Okay.

[00:53:45]They are big particles or big pieces of zinc. But these ones here are in powdered form. So that's the difference. That is very important. These ones are in powdered form. These ones are in big bigger pieces. Then he reacted with the same uh volume for the same time. So the reactions were not yet completed. Now the question is asking in which experiment was a large volume of hydrogen produced. Give a reason for your answer. So in this case it was experiment one. So we give the reason. So we say one we say experiment experiment one.

[00:54:38]So experiment one this is because so this is a mark now the explanation is also a mark because it has two marks.

[00:54:53]So experiment one contains powdered zinc. So this is because powdered zinc has Okay, it's not clear here. Yeah, now it becomes clear. So this is because powdered zinc has a higher surface area than zinc granules.

[00:55:36]So this one has a higher surface area because the size is the size is smaller than this one. So the smaller the size the higher the surface area and the higher the surface area the higher the reaction. So this will have will produce more more gas. All right that's it for this one. Then the last question for this question uh what would be the effect of reducing the temperature of the acid in the reaction. So they just want the effect one mark. So temperature is directly proportional to the rate of chemical reaction. The higher the temperature, the more the reaction. The lower the temperature, the less the what the reaction. So the effect would be You will say the reaction will be slower because particles will have less kinetic energy.

[00:56:55]So particles are going to have less kinetic energy. So they the the the the rate of collision will be lower. They will they will be colliding um not as much as they could collide when the temperature is high. So collision will be less. So this is it for this question. Now we go to the next question. So this was question seven.

[00:57:18]Now we go to question eight.

[00:57:22]So it is saying the following diagram shows the laboratory preparation of a gas and its collection. So we are preparing a gas in the laboratory then with its what collection.

[00:57:34]So this is gas X here dilute hydrochloric acid. Then yeah these are granules of metal Y. So just by looking at this you even understand because I explained this concept earlier this is an acid reacting with what a metal the reaction where is that reaction that we there was that question that we dealt with um I can't find it all right so it was like we we had uh we were dealing with a certain Yeah it's this question the same paper question before we we were dealing with what ion reacting with what reacting with hydrochloric acid. Same question actually they just changed it now they bring it in the diagram form. So this you understand that substance X which was ion was reacting with a dilute hydrochloric acid to form what to form ion 2 chloride and hydrogen because when we are writing the the equation I said the gas that is produced whenever a metal reacts with an acid is hydrogen.

[00:58:57]So that is very important under metals preparation.

[00:59:03]So identify one error in the setup in the diagram shown the error. So the error is here. There is no tap here. How can you put it like this? Hydrochloric acid here has to be controlled. The flow has to be controlled by the tap here.

[00:59:21]When you open it, it comes it falls down. When you close it stops but there's no tap here. So the top is what is missing. So this is our B 8.

[00:59:35]The tap is missing to control the flow of hydrochloric acid.

[00:59:58]All right. Then identify gas X this one. So the same one gas X is what is hydrogen.

[01:00:18]Yeah. Gas gas X is hydrogen. Then B predict what will be observed if metal Y is replaced with copper. Suppose this metal Y is replaced with copper. What would be observed? Well, the reaction will stop.

[01:00:37]Gas X will be will will not be getting produced anymore.

[01:00:44]So you will say this is for B.

[01:00:48]the reaction will stop and gas X which is hydrogen will stop being produced.

[01:01:18]Why?

[01:01:19]So the reason is simple. Copper is unreactive.

[01:01:25]This copper is one of the unreactive metals.

[01:01:29]Because of that when you put it here, you replace this metal with copper. It's unreactive. So it will not it will not be reacting with this. It doesn't react with hydro hydrochloric acid. So the reaction will stop and because the reaction will stop even the gas will will no longer be produced. Then the last question with reference to air pollution compare the use of ethanol and diesel fuels. So referring to air pollution they want us to compare the use of ethanol and diesel fuels.

[01:02:06]So the first thing for C.

[01:02:10]The first thing Ethernet is a clean fuel.

[01:02:26]While diesel fuels produce pollutants or pollutes the environment pollutants such as carbon monoxide.

[01:02:55]even sulfur dioxide. So this is the main difference. Okay. So ethanol is what is a clean fuel while these diesel fuels produce what? They produce pollutants.

[01:03:13]So if you want here you can say ethano is friendly to the environment while this one is not friendly. Then the second one because it has two marks.

[01:03:21]Ethan is renewable while diesel fuels are non renewable.

[01:03:46]So this is the difference. All right, let's go to the last question now.

[01:03:54]So this is the last question. Organic chemistry. So it is saying the following table shows some of the fractions of hydrocarbons obtained from fraction distillation of crude oil. So we have fractions here A, B, C, D. Then the boiling range you have 22 ski all the way to 300 to three.

[01:04:20]So first thing you need to understand these are fractions of what?

[01:04:23]Hydrocarbons. This question gets asked also define the term hydrocarbons. So these are compounds containing the elements hydrogen and carbon only. Okay.

[01:04:36]So that's it. Then a which fraction contains the longest chain then give a reason for answer. So by looking at these fractions and the boiling range which one contains the longest chain. So we need to understand that the longest chain is directly linked to the boiling point. The higher the boiling point or the higher the boiling range, the higher the what? The longer I mean the longer the chain. So meaning the fraction is D with the higher with the longest chain because it has uh the what the longest chain I mean it has the the higher boiling range from 200 to 3K.

[01:05:20]Since it has a higher boiling range from 200 to 3K it means it has the what the longest chain. So here what are we going to say? We will say this is our B9 for A.

[01:05:37]We will say fraction D.

[01:05:44]Then this is because it has the highest boiling range which is we've been given here 200 to three. So because it has the highest boiling range and the higher.

[01:06:19]Okay, you can you can say and this means it has the highest I mean the longest the longest chain the carbon chain. So that's it for that one.

[01:06:45]Then they are saying B decan this one C10 H22 can be cracked to produce hexane C6 H14 and one other hydrocarbon T. So this is cracking. They break this down to produce this and T. So T they've not told us. Then they saying deduce the chemical formula of T one mark. So this is simple what you need to do you get dec then they've written. So this is our B C10 H22. This is decay.

[01:07:30]You can even write the equation. This decay is being broken down. This is cracking. So cracking they use heat and they also use um the re the the what the activators. Yeah.

[01:07:49]So when this one gets broken down they're telling us that it is producing hexen C6 H14 and substance T. So we need to know T and they want us to find the chemical formula. So this is simple. What you do?

[01:08:09]You just subtract. How many carbons are here? We have 10. This one is getting six. So we are remaining with 10 - 6 which is four carbons. Okay. What about the hydrogens? When we subtract 14 from 22, what are we going to get? So you say 22 - 14? we are getting eight hydrogens. So that when we add 6 + 4 gives us 10. 14 + 8 gives us 22. So this is the other compound T which is being produced. So for B we are going to write as C4 H8. So this is the compound produced. They just want the chemical formula.

[01:09:00]Then B is saying draw the display structural formula of T. So here they wanted the chemical formula now the structural formula.

[01:09:09]So for two structural formula. So the structure now how do you draw it? Well you need to understand is this an alkan or an alken that is very important because the the drawing the drawings are different for alkanes and alenes. If you miss there you get everything wrong. So you need to understand here you need to get back to the general formula. So the general formula for our ales our can then also these are very important they also ask to write the general formulas. So for our it's CN H2N + 2. This is their general formula.

[01:10:03]Then for alkenes, it's CN H2N. It doesn't have a plus two. I hope you get the difference. So for you to to know this whether it's it's in on it's under the alkanes or the alkenes you get the number of carbons here. How many? Four. And you substitute in the N you see how it will give you. So for this one it's giving us when we get C I mean the N here as four we'll replace four here. So it's giving us so this one is giving us C4 where there will replace with four. Here we have H 2 where there is N we replace 4 + 2. So this is going to give us C4 H this is 2 * what * 4 8 + 2 that is 10.

[01:11:03]So for our I mean for our when N is equal to 4 it should give us C4 H10.

[01:11:12]Okay. Now let's come to the our when N is equal to 4 this is going to give us C4 then it will be H to N. Where is N? I now we put four. So this will give us C4 H 2 * 4 is 8. So for alen it's giving us this. So you see the difference. So it means this substance this hydrocarbon is in is under what the alken because the number of hydrogen hydrogens is twice the number of what the carbons that is very important to understand.

[01:11:55]Here it's four. This is eight. So this is double this. It's twice. But for this one it's more than half. It's more than double because it's 10. So since this is giving is leading us to alen it means this is from alins and alken number four is butine. Yeah is butine. So this is butine. So when you are drawing this the structural formula you start with the carbons. How many carbons do you have?

[01:12:26]Four. You write them like this.

[01:12:29]four of them for alen the reason I said you need to understand because ales have a double bond here don't have so that's the difference so they have a double bond here then the rest are like this so we have eight what eight hydrogens >> [snorts] >> So this one doesn't have here.

[01:13:09]Yeah, this is the correct one. So without this here made a mistake because the number of hydrogens's are eight and each needs four. Each carbon needs four.

[01:13:21]So this one has 1 2 3 four. This one has 1 2 3 4. This one has 1 2 3 4. Even this one 1 2 3 4. So two 3 4 5 6 7 8. So this is the structure without this.

[01:13:38]So this is it for this one. Then the last one, would you expect hydrocarbon T to undergo polymerization?

[01:13:48]Explain your answer. So would you expect this to undergo polymerization?

[01:13:56]The answer is yes. One mark. Then explain because it is an aline and all alins undergo undergo polymerization.

[01:14:32]because of their So because of their double bond, their double carbon to carbon bond. So this was the last question. Hope you've gotten the concepts. Don't forget to do what? To subscribe.