How to Solve Any pH Calculation Question Without Confusion

Indexed: 2026-05-20

[00:00:00]Hello everyone. You're welcome to today's class. And in today's class, we're going to be looking at a very, very important topic. Today, we're going to be looking at pH and pH calculations.

[00:00:13]So, we're going to look at what pH is and then we do some calculations. You'll see in exams on pH. First of all, what is pH? PH is the measure of how acidic or how alkaline a substance is. Now you must have known the meaning of pH. But let me let me let me break down something here. We said pH you measuring how acidic or how alkaline a solution is.

[00:00:50]How acidic or alkaline the solution is.

[00:00:53]Good. I know sometimes you've been using how acidic or how basic a substance is.

[00:00:58]Now, what's the difference between an acidic substance and a sorry an alkaline substance and a basic substance? First of all, any base that can dissolve in water is an alkaline is an alkali.

[00:01:18]So an alkali is a soluble base.

[00:01:27]Please follow me. There are some bases that can dissolve in water. Not all bases can dissolve in water. Do you understand? Those ones that can dissolve in water are called alkali. So alkali are bases that can dissolve in water are soluble.

[00:01:43]Right? Do you understand that? Good. So, pH is the measure of the acidity or alkalineity of a solution. We are talking about solution. Now, solution. So, we can say this solution is acidic. This solution is basic. Do you understand that? Good.

[00:02:05]So, next thing is if you want to know if a solution is acidic or basic, how will you know that?

[00:02:15]How will you know if the solution is acidic or it is basic? Right? If the pH is high, if the pH of the solution is high, and listen, look at how I'm writing the pH here. Small letter P, capital letter H. You understand? Now, if the pH is high, that solution is said to be alkaline or basic.

[00:02:43]If the pH is low that p that solution is said to be acidic.

[00:02:54]Now before we start calculation let's quickly look at the pH so we can explain this very well. Now the pH scale runs from 0 to 7 to 14.

[00:03:12]The pH scale runs from 0 to 7 to 14.

[00:03:16]And with that we said that if the pH is high it is alkaline right if it's low it is acidic.

[00:03:26]Now pH of 7 is said to be neutral is neutral and pH below 7 that is any pH lower than 7 is acidic. The lower the pH, the more the the more acidic it is.

[00:03:46]So here we can have 1 2 3 4 5 6 and 7.

[00:03:53]Right? Now pH of one and pH of six, which one is more acidic? pH of one. The lower the pH, the more acidic it is. So acid strength increases this way.

[00:04:07]Acid strength increases this way. Why?

[00:04:10]Basic strength increases this way.

[00:04:16]Do you understand that? So the lower the lower the pH, the more acidic it is. The higher the pH, the more basic it is.

[00:04:26]This is the pH scale. I hope you understand this. Good. Let's move on to the calculation aspect of it. And maybe you must have been doing small small calculations or you have been doing some calculations under pH but trust me there's something I'm going to point out here that probably you are seeing the first time or maybe it was not clear before but now opening your eyes to see it right now formula for calculating pH to calculate pH this is the formula you have to write please write it down this is the formula you have to use this is a general formula pH is minus log of hydrogen ion concentration.

[00:05:11]Please let's examine this formula very well and please some of the exams you be writing there'll be no calculator. So if there's no calculator how do you calculate? I'm going to show you all those things. So relax. Now pH is minus log to base 10 of hydrogen ion concentration. One thing you should note is this H+ that's hydrogen ion. Now I'm using this see the type of bracket I'm using this box this box bracket this box bracket now actually that's bracket means concentration if I write it like this this is not correct this is not hydrogen concentration this is hydrogen in bracket in parenthesis so always use this box bracket here this bracket Here this is hydrogen concentration.

[00:06:06]So pH is minus log of hydrogen concentration to base 10. Minus log of hydrogen concentration to base 10 that is pH. This is the formula we're going to be using to calculate pH. Right? Now there are other relations we are going to use. There are other things we are going to uh use the other variations of this formula. But let's start with this one. Let's look at some examples. Right?

[00:06:33]So, write this example down.

[00:06:36]Example one.

[00:06:39]Example one.

[00:06:43]Calculate.

[00:06:46]Calculate. Let's start from a simple one.

[00:06:49]The pH of 0.01 mole per liter HCl.

[00:07:00]Well, let me start with HCl.

[00:07:03]First of all, please anytime you see something like this to solve, don't just rush and solve. Check the acid given. If it is monoproic or polyrotic what I mean is how many hydrogen, how many ionizable hydrogen do we have in that acid? Because the number of ionizable hydrogen we have will affect your calculation. So the first thing you are to do is check the acid you're g in this case it is HCl you start with your HCl.

[00:07:37]If you ionize your HCl what are we going to have? Hydrogen ion will be given off plus chloride ion will also be given off. Right now at this point we said we asked to calculate the pH of 0.01 mole per liter. Mole per liter is also mole per dm cq is also molar capital letter m. So anyone they use. So pH of 0.01 molar hcl. Meaning what we're given is the concentration of HCl not the concentration of hydrogen. But we need the concentration of hydrogen to solve.

[00:08:19]So now we're given the concent what's the mole ratio? This is one is to one right because just one of this is given one of this. So the concentration here we're given 0.01 molar. This m I told you the same thing as mole per liter is to since this is 1 mole. This is 1 mole. Then this also will be 0.01 m. This simply means that the concentration of hydrogen.

[00:08:47]So from there we can see that the concentration of hydrogen ion is equal to 0.01 molar because it's same thing as that of the hydrogen hydrochloric acid.

[00:09:01]Now we can now apply our formula. They say we should calculate pH. pH is equal to minus log in hydrogen ion concentration. Right? Now take take notes here because sometimes you may not be you may not have a calculator available. So how do you solve that? So we'll be having pH to be equal to minus log of hydrogen ion concentration we're given as 0.01 01 right I can use my normal bracket now now at this point let's do the magic pH let me bring it here please this hope you're writing at this point to have it that pH is equal to minus log in base 10 now check this 0.01 you agree with me that 0.01 1 is same thing as saying 10^ -2 right 0.01 01 is same thing as 10^ -2. I just converted 0.01 to 10 -2 to index 1.

[00:10:10]Now rule of log reading rule of log reading one of the rules of log reading let's revise that rule says that if we have log 10 in base 10 to something else all you have to do since they this number is same as the base just bring this one here I just simplified that but I made a video on logarithm just bring the number to the side here this and this will give you one out right. So in this case what you are doing is this and this this log 10 will cancel this thing that's simple put now this power will come here so we'll be having minus this minus is here then here was -2 so - -2 this one we already cancel this one - 2 is 2 so the pH is 2 if you press your calculator minus log 10^ 2 is actually 2 do you Understand that? So this is one simple one. Let's look at another example that may not be this simple. Example two. Example two says, calculate the pH of 0.02 molar H2SO4.

[00:11:26]Please like I always say the first thing you are to do is look at the acid you are given. Here we given H2SO4. So you ionize it. H2SO4 which is a strong acid. We completely ionize. How many ionizable hydrogen are you seeing here? Two, right? So it means you are going to be having two hydrogen ion right plus SO4. We ionize SO4 2 minus 2 minus because we had two hydrogen ion leaving.

[00:11:58]So you can see now that one mole of this is giving two moles of one mole of H2SO4 sulfuric acid. One mole that's the if you've not watched my video on stochometry go and watch it please will give you two moles of hydrogen ion. One mole of this is giving us two moles of this. Now from the question calculate the pH of 0.02 m H2SO4.

[00:12:26]If one mole of this is giving us two moles of hydrogen ion then 0.020 molar of this will give us what? How many of hydrogen? It means it will give us if one of this is giving two of this then it means this will give us two times of what hydrogen will give us.

[00:12:47]Right? So this will give us 2 * 0.02 for hydrogen ion. Right?

[00:12:56]That's it. Right?

[00:13:00]One of this is giving us two moles. So this will give us what? You can call it X. Then you cross multiply. But you still get the same thing. So at this point we'll be having the concentration of hydrogen ion to be 0 2 * 0.02 will give us what?

[00:13:22]will give us 0.04 right molar.

[00:13:29]At this point, we can now solve. We've gotten the concentration of hydrogen ion. So, we can now solve. To solve now, pH is equal to minus log hydrogen ion concentration. Right? So, minus log hydrogen ion concentration. We now insert it. PH is equal to minus log what is our hydrogen concentration 0.04.

[00:14:00]You see now if you've used 0.02 to solve directly you would have been wrong. Do you understand? That would have been wrong. So now how do we go about it now?

[00:14:14]All right. Now the pH here we're almost done with this particular one is equal to minus log is you know this will be same thing as saying minus log in bracket 0.04 04 converting it to standard form is same thing as saying 4 * 10^ -2 right good now please I recommend you go to the video I made on log reading on log reading I'll leave the the link to the description of this video log reading so you can know how to work with it in a case where you don't have calculator but so I can keep this video simple minus log of this will give plus 1.4.

[00:15:00]So the pH of this is 1.4. I'll leave a I'll leave the link to the video of log reading to the description of this video so that you can uh you can always check that out. Right? So basically always take note of the acid in question. Next off next off hope you are following.

[00:15:21]Let's look at another thing. Let's look at another thing.

[00:15:29]Let's look at another aspect now.

[00:15:32]Another aspect.

[00:15:34]Now let's look at example three. Example three.

[00:15:41]Find the hydrogen ion concentration.

[00:15:46]Find the hydrogen ion concentration of a solution of a solution with pH5.

[00:16:00]Find the hydrogen ion concentration of a solution with pH5.

[00:16:06]Good. Now, if you look at this one, now we're given the pH and asked to find the hydrogen ion concentration.

[00:16:14]But you and I knows that pH is equal to minus log hydrogen ion concentration. Right?

[00:16:24]If that is the case, if you want to make hydrogen ion concentration the subject of the formula, I think if it is the normal way, I think it means divide both side by minus log. Right?

[00:16:39]If we divide both side by minus log this one cancel this one and we're left with this is it not in mathematics that's how to make subject of formula but this is same thing as saying this pH all over minus log this is simply antilog so we can just say 10^ minus pH that's log of pH log of so basically anytime you are asked to find something like that you are given hydrogen ion and ask to find pH or you're given pH and ask to find hydrogen ion concentration.

[00:17:15]Hydrogen ion concentration is just simply 10 raised to power minus pH. You don't need to stress yourself too much.

[00:17:22]You don't need to stress yourself too much. Just do 10 raised to power minus pH and that will give you your answer.

[00:17:30]You don't need to stress. So in that example here we have hydrogen ion concentration to be equal to 10^ minus what is the pH we're giving we're giving the pH as 5 so - 5 that's all so you can you can in the option you can see something like hydrogen ion concentration to equal to 1 * 10^ -5 10 - 5 is same as saying 1 * 10 - 5 or you see something like 0 0 1 2 3 4 5 any one you see are correct but just know just know this formula so you can use it at all times right all right the next thing we are going to look at let's look at have you written this down ensure you are writing and if you not subscribe to my channel do to click on the subscribe button so you can always see more of our lessons right now the next thing we're going to look at is pH and PH and P.

[00:18:36]We're going to look at the idea of PH and P. So let's look at PH and P and the relationship between them, how you can use them to calculate and stuff.

[00:18:50]So PH and P. See, I'm writing the P O. The P is small. O is capital. Right? Now, what's the relationship between PH and P? First of all, we now know what PH is.

[00:19:07]Let's look at P first. P the O is hydroxide ion concentration.

[00:19:14]And P is used when you're calculating the basicity.

[00:19:19]The basicity of maybe you're working with a base. You know base like something like sodium hydroxide, potassium hydroxide. What you're saying is hydroxide hydroxide. So if is a base you're working what to use is P and P is equal to minus log in base 10 of hydroxide ion concentration.

[00:19:43]Hydroxide ion is negative please. So P is equal to minus log hydroxide ion concentration. Right? Now the relationship between pH and p is that pH talking about acid plus p talking about base is equal to 14.

[00:20:05]That is why the full pH scale is from 0 to 14. Acid and base range acid and base range will give us 14. That's what it means that the acid range and the basic range will give us 14. Take note that the notra is always at the middle seven.

[00:20:22]Right? So you can be given some questions to solve with this idea. So please jot down this because this relationship is very very very very important. Do you understand that? Let's look at an example and then we see what we can do with that. So I'm cleaning this. Have you written it? Let's look at an example.

[00:20:42]Don't forget that pH plus p is equal to what? is equal to 14. I'm going to leave an exercise for you when we are done to see if you actually ex if you actually understand. So example, calculate calculate the pH calculate the pH of 0.001 mole per liter sodium hydroxide.

[00:21:15]Please at this point don't fall pre they said you should calculate the pH of then they not gave you a base sodium hydroxide at this point what you have is hydroxide not hydrogen so you cannot calculate the pH directly so first things first you need to get the p because this is a base for base what you get first is the p so you first of all get the p because this is a base and it has oh so you get the p after getting the H you can now find the pH. So first of all let's ionize sodium hydroxide. We ionize to give sodium ion plus hydroxide ion.

[00:21:57]If you check now one mole of this is given one mole of this right meaning the concentration of hydroxide ion will be same thing as that of sodium hydroxide because it's 1 one. So concentration of ion will be 0.001 m. Please this capital letter M is same thing as mole per liter or mole per dmq.

[00:22:22]Do you understand? Now the next step we are going to take is since we've gotten the O the concentration of hydroxide ion we can find P.

[00:22:34]I know P is minus log O concentration right so now we can find P to be equal to minus log hydroxide ion is 01 and I've taugh you how to do this this will imply that P will be equal to minus log in base 10 please they all in base 10 normally you not write the base we assume it's in base 10 0.001 0 01 is same thing as saying 10 power - 3 right and remember what I told you once you see minus 3 and the bases are the same just cancel out the answer is what three if the bases are the same 10 will cancel this 10 this number this minus will cancel this minus p is equal to three now we've gotten p as three but what we are asked to calculate is p not p but remember the relation ationship between PH and P that PH plus P is equal to what class? 14.

[00:23:45]So at this point, let's make PH subject of the formula. Then we'll be having PH to be equal to 14 minus P.

[00:23:56]That will give us the answer PH = 14 minus we've gotten P here as 3. So 14 - 3 which will give us what? 11. So the pH of that solution is 11. Is it acidic or basic? Of course basic cuz it's a base.

[00:24:17]Basic, right? All right. So that's that.

[00:24:22]I'm going to let's let's do one more and then I'm going to give you I'm going to give you an assignment.

[00:24:32]But let's let's let's let let me see if you can do this. Let me let me see if you can do this. Let me see if you can do this. Now, one thing that will help you is start practicing exercises.

[00:24:44]Practice a lot of exercises.

[00:24:47]Practice a lot of exercises. You'll see some challenges. So, exercises number one, find The pH of 0.10 molar H3 PO4 assuming assuming complete dissociation.

[00:25:26]Assuming complete dissociation of all hydrogen ion.

[00:25:39]That's number one. Number two.

[00:25:43]Number two, a trivalent a trivalent acid given as H3X has concentration this is concentration 0.01 01 molar.

[00:26:06]Calculate calculate a hydrogen ion concentration b pH pH. All right, I want to leave this for you to solve. Solve and drop your answer in the comment section. Those of you on my group chat, solve this and drop your soling on the group chat. If you have any question, leave it in the comment section and then I'm going to see you in our next class. Hope you learned something. If you learned something, like this video and also drop a comment for me. See you in my next class. My name is excellent simplified.