COMBINED SCIENCE REVISION ON ACIDS ,BASES AND SALTS

[00:00:00]So, to cha, to change the question and answer session on chemistry.

[00:00:07]The reason why I'm going back to the second topic after after separation.

[00:00:17]Any of you got your media exams around the corner now.

[00:00:21]So, I must revise with you.

[00:00:25]Our questions are targeted at our and also which are about silver.

[00:00:31]Langa [clears throat] la sippo. That's how we learn.

[00:00:35]That's how we hope and that's it.

[00:00:39]So, this was a test >> [clears throat] >> for the online class, but we're going to do it as question and answer session and I'm going to give you your own test maybe tomorrow after some sessions.

[00:00:53]Some light sessions.

[00:00:56]So, let us go straight to the first question.

[00:01:01]Those who are watching online, I'm sure there is a number here.

[00:01:08]>> [clears throat] >> If you want to join our online lessons, you can contact me on that number shown on your screen so that you can join our online lessons as soon as possible and you'll be part of what we are doing.

[00:01:25]All right, let us go to the first question.

[00:01:29]The first question ladies says, "Calculate the number of moles in 22 g of carbon dioxide."

[00:01:40]So, on your notebook, I want you to write that topic is it is you write number of moles. This is where the question is coming from. The question is going to ask you about how to calculate the number of moles.

[00:01:57]So, you write that to We write that question as it is. Then, after that, you write solutions.

[00:02:05]There is something written inside the bracket just below the question.

[00:02:11]Can you read that one for me, Sean?

[00:02:16]There is something written below the question, the first question.

[00:02:21]>> Show all your workings.

[00:02:23]>> Show all your working.

[00:02:27]As you are going to provide the solution, you must show all your working.

[00:02:41]All right.

[00:02:43]So, this is question number one.

[00:02:46]But, number one thing that you must do if you are dealing with chemistry calculations, you want to find number of moles. First thing, write the formula.

[00:02:58]If you don't know the formula, don't write it.

[00:03:02]It's as simple as that.

[00:03:04]If you don't know the formula, don't write it. But, if you know, write it.

[00:03:08]So, number of moles, you can just write moles is equal to >> [snorts] >> M over Mr. M over [laughter] what?

[00:03:25]>> Mr. >> Mr. Moles is equal to M over Mr. Right. This M here, it is simply means the mass in question.

[00:03:42]What is the mass in question?

[00:03:47]Huh?

[00:03:48]20 g, right? Yes.

[00:03:51]It means the mass in what?

[00:03:55]In question.

[00:03:58]What about MR are they?

[00:04:00]It represents molecular Relative molecular what? Mass.

[00:04:06]Relative molecular mass is for the carbon dioxide.

[00:04:16]Because they said, "Find the number of moles in 22 g of carbon dioxide represented by CO2."

[00:04:27]So, you must first of all find the molecular mass of what?

[00:04:34]Molecular mass of what?

[00:04:37]Carbon dioxide. So, let us do that.

[00:04:39]So, we have carbon dioxide, which is CO2. Let us find the molecular mass.

[00:04:45]For us to get the molecular mass of CO2, we are going to say, "The mass number of C, which is carbon." C represents what?

[00:04:55]Carbon. The mass number of C from the periodic table is what?

[00:05:01]It's 12, right? Times number of carbon atoms present. You know what I'm going to say now, times one. Then you say plus mass number of O. It's oxygen, right?

[00:05:13]16 times number of oxygen atoms.

[00:05:17]Two. Then we're going to get 12 plus 16.

[00:05:21]Then we're going to get our final answer is what? 18.

[00:05:24]Oh, it's plus 32, sorry.

[00:05:27]It's plus [clears throat] 32. Then this one plus this one we're going to get 44.

[00:05:32]This is the MR, the molecular mass, right? After that, we are going to say what is our M 22 g over less go 44, right?

[00:05:53]So, we're going to get what? This one into this one. What are we looking for?

[00:05:57]We're looking for number of what? Number of moles. So, we're going to say this one to this one is 0, comma 0,1 0,1 Is this one not the half of this?

[00:06:11]>> It is.

[00:06:12]>> Huh?

[00:06:13]Hey, 22 [clears throat] is the half of what?

[00:06:17]44. So, the answer is 0,5 what?

[00:06:20]Moles.

[00:06:22]Then you get two marks there.

[00:06:26]>> [snorts] >> Let me talk now talk to my online family.

[00:06:33]So, from the question you can actually see that the mass in question is 22 g.

[00:06:39]So, we're going to say 22 all over the MR. The MR represents the molecular mass of carbon dioxide. The molecular mass we are given CO2.

[00:06:54]So, molecular mass tinengadichite.

[00:06:57]Mass of carbon, C.

[00:07:00]From the periodic table, it's 12 times my atom a carbon in code one each.

[00:07:06]Plus mass of oxygen.

[00:07:09]From the periodic table, mass of oxygen is 16. If you go and check your periodic table, times the number of oxygen atoms that are there, we have two.

[00:07:21]So, that's two. So, we're going to have what? 12 * 1 we're going to get 12. Plus 16 * 2 we're going to get 32. Then we're going to have 44. This is the relative molecular mass. So, can I calculate the number of moles?

[00:07:39]Number of moles is got mass in question, which is 22 grams in this case over molecular mass 100 44. So this one into this one or let me just say work it out this way. 22 into 22 get one over 22 into 44 we get two. So 1 over 2 is the same as 0,5. So my answer is 0,5 moles.

[00:08:06]0,5 moles All right, portion of the mass of the air.

[00:08:30]>> [laughter] >> Mhm.

[00:08:36]All right, so somebody can ask a Enjoy Huh?

[00:08:51]Chigava What was my final calculation?

[00:09:22]Mhm.

[00:09:22]>> [clears throat] >> Huh?

[00:09:26]I was just illustrating with what you I don't know what you know what you what are we talking about.

[00:09:33]Next question answer calculate the relative molecular mass of calcium carbonate.

[00:09:42]Calcium carbonate. The formula for calcium carbonate is CaCO3.

[00:09:47]CaCO3.

[00:09:50]Calcium carbonate, another name you know is the limestone, isn't it?

[00:09:58]So relative molecular mass of calcium carbonate say We have a Ca representing what?

[00:10:15]Calcium, right?

[00:10:17]Then we have what? C to me representing what?

[00:10:20]Carbon. Then the last one we have what?

[00:10:23]O representing what?

[00:10:25]Oxygen. So what you're going to do there to get the relative molecular mass, we are going to say the mass of calcium from the periodic table. It's given there. They are going to give you that.

[00:10:43]40 So that times one to that plus the mass of carbon times the number of atoms of carbon that are there one then plus the mass of oxygen 16 times my atoms of oxygen that are there three So let us continue. We are going to get 40 times one.

[00:11:14]40 plus 12 times one 12 plus 16 times three What?

[00:11:23]48 Yes. 48. Then we are going to get to to add everything there.

[00:11:30]Is it 100?

[00:11:32]or This is the answer.

[00:11:51]Without a unit. Don't put a unit.

[00:12:08]>> [clears throat] >> 42 >> [snorts] [snorts] >> I know the empirical formula.

[00:13:03]>> [snorts] >> Last time but I reverse the paper June 2026 paper two but I don't have section C.

[00:13:12]A tak a define the empirical formula as the simplest ratio of each atom in a substance. This one?

[00:13:29]At the a compound it contains 40% carbon, 6.7 hydrogen, and 53.3% oxygen.

[00:13:39]Determine the empirical formula of the compound.

[00:13:42]Then you get five marks.

[00:13:48]But you know what you have in three, four marks already.

[00:13:52]Three, four marks.

[00:14:02]All right. My atoms that appear among others carbon simplest ratio as two.

[00:14:13]The next one?

[00:14:16]As two. The next one?

[00:14:19]oxygen diesel 40% over mass number of carbon 12 as two. Hydrogen percentage given over mass number of hydrogen one as two.

[00:14:48]Percentage of oxygen over mass number of oxygen Can you use what you're going to get here is the number of moles.

[00:15:04]All right.

[00:15:06]Relative molecular mass here carbon is 12. Yeah, hydrogen is one, oxygen is 16.

[00:15:13]You are going to need this information.

[00:15:18]All right. So, what I'm going to do now is to make calculations 12 into this and 12 into this one doing your answer is two, one into this one you know 6,7 is to 16 into 53,43 What do you get there?

[00:15:43]>> [snorts] >> 3,33 Victor 3,33 Right, what about the number of moles on oxygen?

[00:16:10]3,3 3 1,2 All right.

[00:16:21]Wait, I said these are moles. We are trying to check our empirical formula.

[00:16:27]number of moles and then Then I should have I want you to write this statement and I will write it down.

[00:16:39]Divide each atom by the smallest.

[00:17:00]Divide each atom by the smallest.

[00:17:06]3,33 is to 6,7 is to 3,33.

[00:17:15]What is the smallest there?

[00:17:18]It is 3,33. by 3, you ain't going to 3,3 up equal to one decimal place in in the upper hydrogen.

[00:17:26]I did it.

[00:17:27]So, I got to do 3,3 over 3,3.

[00:17:32]I don't know what you are about to show me in the chair.

[00:17:34]One is to panotera two. Exactly two.

[00:17:41]I two is two panotera one. So, I got to write the ratio here in which the carbon to number in the one ish. This one.

[00:17:54]Then turn up a hydrogen to the manga now.

[00:17:57]So, I got to do the H 2 copper oxygen to the one.

[00:18:05]So, I got to negate a C H 2 O.

[00:18:17]>> [snorts] >> I'm sure we're done. Let's go to the next question.

[00:19:00]Calculate the number of atoms present in 0,5 moles of aluminum.

[00:19:11]>> [snorts] [clears throat] >> All right, you know what I formulate number of atoms is equal to moles times Avogadro's constant.

[00:19:36]constant.

[00:19:58]Did you get what I said?

[00:20:04]No formula actually.

[00:20:06]Can I tell you the number of atoms present in 0.5 moles of aluminium?

[00:20:14]My moles are what I gave you times times the Avogadro's constant.

[00:20:24]>> [snorts] >> 6.02 times 10 to the power 23.

[00:20:35]So again, we are going to say what is the number of moles given in the question?

[00:20:42]0.5 times what is our Avogadro's constant?

[00:20:49]6.02 times 10 to the power 23.

[00:20:55]What are we going to do? This is a calculator version paper.

[00:21:01]You are going to multiply these two, aren't you?

[00:21:03]0.5 times 6.02 Let us multiply. Tell me what you get.

[00:21:13]We are going to get 3, 01. So, again, to get 3,01 is going to be times 10 to the power what?

[00:21:24]23 Then you write in front atoms.

[00:21:29]This is the answer.

[00:21:35]This is the answer.

[00:21:36]So, it's going to be 3,01 * 10 to the power Huh?

[00:21:43]10 to the power 23. [clears throat] >> [snorts] >> All right.

[00:22:04]Next.

[00:22:07]4 g of sodium hydroxide Yeah.

[00:22:20]Every time we wake up a banana in body.

[00:22:26]4 g of sodium hydroxide NaOH is it dissolved >> [snorts] >> in water to make 500 cubic centimeters of solution.

[00:22:50]Now, calculate the concentration of the solution in mole per decimeter cubed. This is the condition, right?

[00:23:02]What do we need? The answer you are going to find out there in mole per decimeter >> This is the condition, right? [snorts] per decimeter cubed.

[00:23:20]>> [snorts] >> All right. Most of you have a new question, but now listen.

[00:23:28]Concentration This is the formula.

[00:23:37]Write it down. Concentration [clears throat] is equal to number of what?

[00:23:46]moles over what?

[00:23:52]volume in decimeter cubed, right?

[00:24:06]Do we have number of moles? That's the question.

[00:24:10]Do we have number of moles? We don't have.

[00:24:14]So, the title say moles.

[00:24:26]So, we have what to consider Consider number of moles being equal to Consider number of moles being Number of moles that it gives you and the mass in question Huh?

[00:24:51]Huh?

[00:24:53]Mass in question Ah, man.

[00:24:58]Let's stop here. over Right, molecular mass of sodium hydroxide.

[00:25:05]Huh?

[00:25:07]>> Sodium hydroxide.

[00:25:09]>> Yeah, sodium hydroxide here.

[00:25:15]What's that?

[00:25:19]Do you know concentration in the number of moles? I did.

[00:25:23]But I have my moles here.

[00:25:26]How much time?

[00:25:31]I don't know my sodium E. Is that number of moles is equal to what?

[00:25:37]30 moles, I did. Is equal to mass in question over G.

[00:25:41]Molecular mass, I did.

[00:25:43]So I got to go to check out molecular mass of your sodium hydroxide. Don't worry about it. Mass in question, which is 4 g, I did.

[00:25:50]Over G molecular mass. So the molecular mass of your NA OH. That two minutes I say. To put mass here Your sodium is she 23.

[00:26:05]Together times one number 23, I did. So I got to put that in plus mass of oxygen.

[00:26:11]16 plus mass of hydrogen.

[00:26:14]One, I did.

[00:26:18]Huh?

[00:26:19]40 so I got to put over here.

[00:26:21]Over 40. This one.

[00:26:23]So I got this one into this one to know what I got 0, what is it?

[00:26:29]0, what is it?

[00:26:30]0, 1 mole.

[00:26:36]The concentration to have number of what? Moles. Just check it, G. Volume that I got to put here is not in decimeter cubed. You know what I mean? I got to put in decimeter what? Cubed. How do you do it?

[00:26:52]Volume E convert it I didn't get This one and this one Is it five?

[00:27:05]0.5 decimeter cubed Right, after is also back to what the question is saying Calculate the what?

[00:27:14]The concentration.

[00:27:17]Concentration now what is C now? Is equal to moles 0.1 I didn't 0.1 moles over volume 0.5 decimeter cubed Right, we are going to get what? This one and this one, please use your calculator.

[00:27:37]I'm not chat GPT.

[00:27:39]So >> [laughter] >> And then I tell you don't tell me the answer.

[00:27:49]>> [snorts] >> All right. That's it.

[00:28:03]Just correct that.

[00:28:06]>> [snorts] >> Right, tell me the answer.

[00:28:19]0.1 0.2 So guys, 0.2 more per G decimeter cubed >> [snorts]