Tricks to Solve Solubility Questions in Seconds | Ksp Comparison Tricks for NEET & JEE

[00:00:00]Hi students. Stop memorizing solubility orders from today. Coming 10 minutes, you are going to learn excellent tricks very much useful to solve the solubility Ksp. You no need to buy heart at all.

[00:00:17]And these questions came in a re-NEET also. Many times it's asked in a NEET and JEE Mains also. Many times the questions came. But students always even a toppers also always take a time to solve this question. In this video, you will rocket. You will solve very easily. Let's see for example, uh solubility order for this is first uh AgCl, next AgBr, AgI. That is the order. Next one is for this is PbCl2, PbBr2, PbI2 is the order.

[00:00:56]Uh next for this is uh BaF2, then SrF2, then CaF2 is the order. For this it is uh SrSO4, next PbSO4, next BaSO4. And for this we can't say like that. How we should apply the trick and we have to solve. Do you want to know how I'm telling so fast? I will teach you step by step, my dear students. Just to follow that.

[00:01:24]Coming to the if the salt is excellent trick. Excellent. If you find this video helpful, please hit on like and subscribe to Komali mam channel to get more tricks and tips from chemistry.

[00:01:38]Let's see if the salt is 1:1 salt like NaCl. One cation, one anion. If NaCl breaks, how you will get Na+ Cl- right?

[00:01:48]Like that. Simple example I'm telling you.

[00:01:51]If suppose any salt is 1:1 type of salt, okay? I'll give you examples, don't worry. Like A B, then the formula to find the solubility is square root of Ksp.

[00:02:06]How we got it, what is the that and all regular class we'll see. If suppose a salt is 1:2 or 2:1.

[00:02:16]Let's say for example, two cations, one anion, A2B salt or A2B salt, two cations, one anion or one cation, two anions, AB2. These type of salts, then solubility formula is S is equal to cube root of Ksp by four. This is the formula. Repeat the formula 1:1. I'll give you examples, don't worry. 1:1, S is equal to square root of Ksp. 1:2 or 2:1, S is equal to cube root of Ksp by four. Okay? Now, let's see for example, if the salt is all the uh they will ask you solubility order.

[00:02:58]Uh so, if all are of same 1:1 type of means, use the same formula. Correct? If all are of same thing means, we'll use this formula, right? You no need to use any formula. Let's see for example, all are AgCl, how it will break, students? Tell me. AgCl breaks into Ag+ + Cl-. So, one cation, one anion, 1:1. Same AgBr also breaks into Ag+ Br-, 1:1. AgI also breaks into 1: Ag+ I-, 1:1. In such cases, just you you how you tell that Ksp value is high means, solubility is high. That's it. How to tell, ma'am, Ksp value? For example, see here. Uh this is zero. 1 2 3 4 5. This is increasing order.

[00:03:55]-1 -2 -3 -4 -5. This is decreasing. Correct, no? So, if I ask you -1 -5, which is the bigger number? -1 is a bigger number. When going what?

[00:04:12]Number decreasing. Correct. So, small variation I'm doing, you see. This is 10 ^ 1, 10 ^ 2, 10 ^ 3, 10 ^ 4, 10 ^ 5. So, 10 ^ 1, 10 ^ 5, which is the bigger number? 10 ^ 5 you will say.

[00:04:28]If I ask you 10 ^ -1 -2, they just simply I'm keeping like this. Suppose if I ask you 10 ^ -1, 10 ^ -5, which is the bigger number? 10 ^ -1 is the bigger number. So, the power negative is there means less number, higher value. So, less number in this all, which is less number? 10 ^ -10 is a less number. So, this is more solubility. Ksp more, solubility is more. You no need to do anything. Just directly AgCl greater than next number 10 ^ -10. You see, 10 -6, -7, -8, -9, -10 will come later 13 will come. So, after that AgBr is more solubility. Then next one is AgI because 10 ^ -17 comes later. Okay, this is the solubility order. Easy. See the next question. PbCl2, PbBr2, PbI2. What is the solubility order? Can you tell me?

[00:05:26]You no need to do anything. See, all are of same type of salts. It breaks into PbCl2 breaks into Tell me how it breaks, you know? Pb2+ + 2Cl-.

[00:05:40]Then all are like what type of 1:2. One cation and two anions it is giving so what are they all of same that means what simply have to do?

[00:05:52]Higher is the Ksp value, more is the solubility. Higher Ksp value means power should be less number. So, -5, -6, -9.

[00:06:04]Which is a less number? I mean power less number greater value I told you right? So, PbCl2 more solubility than PbBr2 than PbI2. Easy. See the next question.

[00:06:19]You will only try this question and put your answer in the comment box. Question number three, what is the order? This question is for you. Okay, first pause this video, put your answer in comment section then only watch the next one.

[00:06:34]Okay, now? Let us see the next question.

[00:06:37]This also uh same easily we'll do it. Ba2+ it breaks into Ba2+ SO42-. Same way all are of same type of salts. Then what is the order?

[00:06:48]-7 less number then greater value, right? So, SrSO4.

[00:06:55]Next number greater number is PbSO4.

[00:06:59]Next greater number is BaSO4. So, third question I gave you homework. Now coming to this question. The correct order of increasing solubility. You see here.

[00:07:11]AgCl is breaks into Ag+ Cl-. 1:1 type of salt. Here AgCl breaks into how? Ag+ + Cl-. So, in this case what is the formula? Solubility is equal to square root of Ksp.

[00:07:29]This is the first example. Next, see the second example. Ag2CrO4.

[00:07:36]It breaks into tell me how it breaks. Ag 2 Ag+ + cro4 2 minus this breaking switch should know then only it is 2 is to 1 2 is to 1 means solubility is equal to cube root of Ksp by 4 and next one third one I will write here caf2 it breaks into how ca2 plus plus 2 into f minus so 1 is to 2 again use the same formula cube root of Ksp by 4 okay students now this case you cannot do like that you have to put the Ksp values so put the Ksp values 2 into 10 to the power of minus 10 then what do you have to do you have to root 2 value is 1.414 into 10 to the power of minus 10 whole the square root means 1 by 2 correct no 2 1's are 2 5's are 10 power of minus 5 this you got it but square roots you got it how you will do cube root this is like let's say Ksp for example I'll put Ksp what is the Ksp value 1 into 10 power of minus 12 divided by 4 is there cube root now how how to solve this that is the logic if you learn this now I'm going to tell you a trick if you follow this trick super in an excellent way one one is to one solid one is to two two is to two two is to one solid very easily you will do it see that how to do here I will I will do it okay here I will do it later I'll erase wait students see here one one cube here I'll do one cube cube cubes mandatorily you you to learn one to 10 if you learn, easily you'll do. 1 cube 1. 2 cube 8. 3 cube how much? 27.

[00:09:45]4 cube 64. 5 cube 125.

[00:09:50]6 cube 216.

[00:09:54]7 cube 512.

[00:09:57]8 cube how much? 8 cube is 6 and 512.

[00:10:03]Sorry, 350 343. Sorry, this is 512. 9 cube is 729.

[00:10:11]10 cube is 1000.

[00:10:14]Now, same way squares also. 1 square 1.

[00:10:17]2 square 2. 3 Oh, sorry. 2 square how much? 4. 3 3 square 9. 4 Ma'am, why, ma'am? This squares is if you learn it, see, students, it's a changer of your solving only. Very, very helpful. If you know this, easily you will do it. 8 square 64. 9 square 81. 10 square is 100. Okay, now? Now, once you know this you know squares, how you will do this question is, let's say for example, I got 1 by 4. 1 by 4 is how much?

[00:11:00]Uh 1 by 4 is 0.25.

[00:11:03]Into 10 to the power of minus 12 cube root. Here, one super logic I'm going to tell you, see.

[00:11:11]10 to the power of minus 12 is there, no? With three table, 12 it will go. 12 by 3. That is the meaning is 10 power of minus 12 cube root means 1 by 3.

[00:11:22]So, 3 1s are 3 4s are. Always, this number you should keep it in a divisible by three table. For example, 10 power of minus 12 divisible. Next number, 10 power of minus 15 is divisible. 10 power of minus 18 is divisible. The three table it should be divisible always. So, this 25 is in 0.25. I'll multiply this with a thousand. Okay? 0.25 I will multiply with a thousand. I will divide with a thousand. Why I'm doing so? I will tell you. I want to uh remove this fractional number. Then I'll get a 250 into 10 power of three goes up minus three, then it will become minus 15. This is cube root. Now, cube root of 250, how to do it? 250 comes after this number, between these two. So, cube root of the between these two means the answer is between six to seven. Okay?

[00:12:27]So, answer is 6. some value into 10 to the power of minus 15 whole to the power of one by one by three. Then three ones are three fives are, right? Minus five.

[00:12:39]So, see here, cube root of 250, how I did? Cube root of 250, how I did? This number is between these two, around 6.3, 6.4. That value will get. Let's say 6.3, 6.4. Six is mandatory. For that three, no need to worry about that. Okay? Next one is if you're able to identify, you can uh roughly you can do that. Next, this you try. Four into uh 10 power of minus 11 divided by four cube root. Okay? Cube root. Now, four four cancel, then it will be 10 power of minus 11 cube root. Oh, 10 power of minus 11 with a three table it will go?

[00:13:19]No, it don't go. So, you have to convert into 12. How to convert? Into 10 divided by 10. Most important thing this is. I will do. Why I do? If this 10 goes top, it will become 10 power of minus 12.

[00:13:34]Still 10 I forgot to write 10 is there, correct? Cube root. So, cube root of 10 power of minus 12 is how much? 10 power of minus four. 12 12 ones are three ones are three fours are into cube root of Still this is left. 10. How to find cube root of 10 means this is off between eight to 27. So, which means that answer is around 2. 2. some value into 10 power of minus four. Easy. In all this, if you see which is a lower number, which is a lower number? Calcium fluoride is the lowest 10 power of minus four. So, higher solubility for CaF2. After that, if you check this is also 10 power of minus five, this is also 10 power of minus five. Students, listen carefully.

[00:14:24]These two are the same numbers. When these powers are of same numbers, in these two which is a bigger number, that is a higher value. For example, 10 power of minus two Uh here one number, 10 power of minus two. Here I'm having a three, here I'm having a two. So, in these two which is a bigger number if I ask, this is a bigger number. Why? It is 0.03, it is 0.02. So, I want to say if these two numbers are same, powers are same here, everything.

[00:14:58]And then which is a bigger number, that is a highest number. So, 1.414 and this is 6.4. Which is a bigger number? 6.4 is a bigger number. That is the value for Ag2CrO4.

[00:15:13]After that, the next the next one is least solubility AgCl. So, which option is the correct answer? CaF2 uh CaF2 Ag2CrO4 AgCl is the correct answer. Is it clear?

[00:15:28]Now, see this one. AgBr breaks into How it breaks into Ag+ + Cl-? So, solubility is Ksp.

[00:15:41]That is how much, students? 5 * 10 ^ of -13. Then it will be how much? Into 10 / 10. Into 10 gives 50 / 10 if it comes up -14. Square root of 50 is here. 49 to 64. So, it will be around 7.something value into 10 ^ of -14 / 2, right? So, square root is there, now? So, -7 it will be. Next, same way do for zinc hydroxide. It breaks into Zn2+ + 2OH-.

[00:16:18]This is 1:2 salt. So, what is the formula? Cube root of Ksp / 4. Then cube root of What is the Ksp value given is 1 * 10 ^ of -15 / 4. So, it is 0.25 * 10 ^ of -15 cube root. How much it will be? Into 1,000 / 1,000 if you do. Into 1,000 if you do, you'll get 250 / 1,000 if it comes up 10 ^ of -3 -15 it will become 18, right? Now, cube root of 250 250 is between these two. So, again, around let's say 6.4 or 3 * 10 ^ of -18 cube root means what is the meaning? Whole to the power of 1/3. -6. This is 10 ^ of -6. Clear? Now, same way Hg2Cl2.

[00:17:09]This logic here is it breaks into Hg22+ + 2Cl-. 1:2 salt. So again solubility is equal to cube root of ksp by 4. Now can you tell me what is the ksp value? 1.3 into 10 power of minus 18 divided by 4.

[00:17:30]This upon solving I'm getting 0.325 into 10 power of minus 18. Normal division I have done I got this. Now here what I want to tell you now, this number 18 is divisible with cube root. Correct? But this is fractions it is there. What is the next number after 18? 21 only. So I will multiply with 1000 divided by 1000 I'll do.

[00:17:55]Multiply with 1000 gives 325 divided by 1000 goes stop. It will be minus 21.

[00:18:01]Then cube root. Cube root of 325. 325 is near to 7. Let's say some 6.9 something because this is 343 right? 343 which means like 6.8 6.9. And 10 power of minus 7. So this is 10 power of minus 6.

[00:18:19]This is minus 7. This is also minus 7.

[00:18:21]So which is the higher solubility? Zinc hydroxide is a higher solubility. This is number one. After that this is also 10 power of minus 7. This is also 10 power of minus 7. But what I told you bigger number between that is the higher value. So what is the bigger number here? That is bigger number is 7 into 10 power of minus 7. That is AgBr is the second portion. Last is 6.9 into 10 power of minus 7. That is the third value. Value. Okay? Now will you try this question also and find and tell me what is the x value? Two questions I gave homework. This is the today's session. See you again in next video with a lots of tricks and tips in chemistry. Let's make your chemistry very very easy. Take care. Have a great day.