when to assume x is insignificant

[Cristian Cortes 1L]

For some questions on sampling week 2, where we would have a number like .032-x and equal it to Kb for an example, when is it fine or restricted to assume x is so insignifcant we can keep it out?

[John Antowan 1K]

I usually use the given equlibrium constant as a bit of a guess. If it is below 1x10^-4, I usually would estimate x is insignificant just to be safe, but I believe Professor Lavelle has mentioned that 1x10^-3 is okay too, just as long as it doesn't change the value next to it (which in your example of .032, a value of x around 1x10^-3 may actually have some effect).

[Aydin Karatas 1F]

Another test to see if the approximation is acceptable is to check (after approximation) x < 5% of the initial concentration where x = the final concentration (so taking the ionization/protonation %).

[Samir 3I]

Yes I believe we can assume x is insignificant when the concentration is less than 1.0x10^-3. Another way to be sure is that if you use the assumption and calculate for x and the final x is less than 5% of the initial concentration then you assumed correctly.

[Christine Ma 3L]

If the calculated x (when omitted) is less than 5% of the initial concentration, then the approximation (that omits x) is valid. If it's greater than 5% then x is not negligible and can't be ignored, which means you have to go back and use the quadratic formula to solve for x.

[Natalie 3k]

Hi, I was confused about this too, but I remember Dr. Lavelle saying that if the equilibrium constant is under 1x10^-3 then you can assume that the change is insignificant, but I've read that 1x10^-4 is more accurate. It can be assumed to be insignificant if it is less than this and doesn't change the value gotten during calculations, which is how I check if it can be done or not.

[Mariah Disc 2C]

You can assume x is insignificant when the concentration is less than 1.0x10^-3! This can also be done by using the assumption and calculating for x and if the final x is less than 5% of the initial concentration then you assumed correct.

[Hasan Mirza 3F]

In some of the sapling problems, the difference between the Ka and concentration needs to be more than 1000 which is 10^3 but in some cases it is better to use 10^-4.

[Rose_Malki_3G]

When the k value is less than 10^-4 we can assume the x value is insignificant. Also if the percent ionization is less than 5%, we know the x value is insignificant.

[305572629]

Assume that x is irrelevant in an ICE table when the equilibrium constant is less than 10^-4

[Zihan Liu 2K]

I think you would assume x is insignificant is when K is smaller than 10^(-4)
To confirm that x is indeed small, use x divided by the initial concentration of the acid/base. If the results are smaller than 5%, then x is indeed insignificant.

I'm not too sure whether this could be applied to bases as well because in base calculations, we normally would let x represent the concentration of OH-. Since it's a base, x is deemed to be very small. Therefore, either this rule can be applied to all the bases, or you simply cannot use it with bases.

[Izamary Marquez 2H]

In addition is there a certain way we should approach every problem whether it is negligible or not? Should we always solve for it anyway?

[Kushaal Madadi 2F]

I think it would be best to always check using the ionization percentage.

[Madilyn Schindler 3E]

We can assume the x value is insignificant if the equilibrium constant is less than 10^-3 (safer if less than 10^-4 as Dr. Lavelle mentioned in lecture) and if the ionization percentage is below 5%.

[Jordan Tatang 3L]

when the equilibrium constant is less than 1.0 x 10^-4. you can verify if the approximation is valid by finding the percent ionized and if it is less than 5% than the approximation is valid.

[Gicelle Rubin 1E]

Hi, I was confused about this too, but I remember Dr. Lavelle saying that if the equilibrium constant is under 1x10^-3 then you can assume that the change is insignificant, but I've read that 1x10^-4 is more accurate. It can be assumed to be insignificant if it is less than this and doesn't change the value gotten during calculations, which is how I check if it can be done or not.

Thanks for your clarification! :)

[Jaden Kwon 3C]

I remember Dr. Lavelle mentioning that a k value of 10^-4 or less is safe enough to assume that x is insignificant. Also, if the percent ionization of a reaction is less than 5% you can also assume x is insignificant.

[Nicoli Peiris 1B]

I believe he said to use the 5% ionization percentage rule! Where if your % is less than 5%, the approximation is valid.

[Cora Chun 2D]

You can approximate when the constant is less than 10^-4, but make sure to always double check if your x value is less than 5% of the initial concentration (x/initial conc.*100<5). If it is greater than 5%, you need to use the quadratic formula.

[Eileen Quach Dis 2A]

When the equilibrium constant is less than 10^-4 you can assume x is insignificant and not include it in the denominator. If you really want, you can verify if it was okay to use the approximation for a given problem by checking if the percent ionization is less than 5%.

[Coleman Morrow]

I was under the assumption that x is insiginificant when it is greater than 1000x smaller than the molarity. So if x is 1.2E-7, and your molarity is 0.042 it would be insignificant.

[Mary Shih 3J]

I have 10^-4 in my notes so I would go with that value instead of -3

[VincentLe_3A]

According to the lectures, it is safe to approximate when the equilibrium constant K is less than 10^-4. To be sure that approximation is appropriate, always check for the 5% rule afterwards, where if the percent ionization is less than 5%, then approximation is appropriate.

[Daniel Huynh 2J]

X is insignificant in equilibrium calculations when x is extremely small or less than 5% of the value it is changing.

[Lorraine Medina 3E]

Dr. Lavelle said x is assumed insignificant when it is less than 10^-4. Hope this helps!

[jessicasilverstein1F]

I would assume this when x is lower than 10^-4

[Lucy_Balish_3G]

We can assume x is insignificant when the equilibrium constant is less that 10^-4.

[Katie Le 3K]

When Ka value is 10^-5. If you are unsure, always double check using percent ionization. If its above 5% you cant use the shortcut

[ellenulitsky Dis 1I]

Use the 5% rule which is the same way of doing percent ionization! Hope this helps!

[Rylee Mangan 1K]

In lecture it was mentioned we can approximate when Ka < 10^-4 but I like to always use the 5% rule to be safe!

[Chloe Shamtob 2H]

You would make x negligible for equilibrium problems if the Ka or Kb is 10^-4 or smaller. Therefore, the change X would be too small to be significant. Make sure that the shortcut is allowed by finding the % ionization. If the percent ionization is less than 5%, your approximation is valid.

[Alen Huang 2G]

You can assume x is insignificant if the ka or kb value is below 10^-4, but make sure you use the 5% rule to make sure!

[Brenda Silva 1B]

We can assume that x is insignificant when Ka or Kb are below 10^-4, to make sure your answer is correct use the 5% rule.

[reyvalui_3g]

It is always good to use the 5% rule to determine if x is insignificant.

[Ryan Agcaoili 2E]

If the value is smaller than 10^-4, then you can utilize approximation.

[Andy Hon 3E]

You can approximate x, when its Ka or Kb value is less than 10^-4.

[Kylie Joe 2A]

I believe when you approximate x and it is smaller than 1x10^-5, you can keep the approximation and assume that the -x is insignificant

[Sejal Parsi 3K]

I think that if the equilibrium constant is under 1x10^-3, you can assume that the change is insignificant, but I've seen that 1x10^-4 is more accurate. It can be assumed to be insignificant if it doesn't change the value you get after calculations.

[Kathy_Li_1H]

Hi! You can assume x is insignificant when the initial concentration is 1000 times larger than the Ka or Kb. If you aren't sure, the safest bet is to not assume x is insignificant.

[Nina Fukui 2J]

I use 10^-4

[Rahul Sobti 1E]

10^-4 and you can always check if the percent ionization is less than 5 % by H+/HA or OH-/AOH

[Navdha Sharma 3J]

I remember that Dr. Lavelle said in his lectures that whenever K is less than 10^-4. Also, you can always check it. If the value of x is less than 5% of the initial molarity, you are good to go!

[Juwan_Madaki_3K]

When the equilibrium constant is 10^-4 or smaller, it's safe to just approximate. However, you can run into errors when you're calculating percent ionization. If your percent is greater than 5%, then you're going to have to re-do the calculation without the approximation.

[Sophia Wendin 3L]

I think the general rule is 10^-4 but it's good to check and make sure x is less than 5% of the initial value.

[Justin Lin 1B]

I would assume X to be insignificant when the K value is 10^-5. You can double check that your approximating correctly by using the 5% rule.

[Charlotte Adams 1A]

Also, I believe for weak acids/bases x is insignificant because you know that because they are weak, they will have a K value that is considered small.

[Alison Perkins 2B]

When the equilibrium constant is less than 10^-4 in your ICE table, you can assume that x is negligent in K calculations.

[Neel Bonthala 2G]

When working with acid and base equations, use the Ka or Kb value to determine if x is insignificant. If the equilibrium constant is less than 10^-4, it's probably safe to assume that not much of the initial amount of the acid/base was deprotonated/protonated. However, to be even more careful, there's one more step you should take. If the equilibrium constant is small enough and you assume x is insignificant, make sure to divide the final equilibrium concentration of H+/OH- and divide it by the initial concentration of the acid/base used. If the percent is less than 5% you're fine. If the percent is greater, then you probably cannot assume x is insignificant, and you should solve it again.

[Chinmayi Mutyala 3H]

Less than 10^-3 but Lavelle said when k is less than 10^-4 to be safe; also if you divide x by the initial concentration and get less than 5%, you know that your assumption is ok.

[Taylor Newville 1C]

K is considered small when it is less than 10^-3, but Dr. Lavelle said that K should be less than 10^-4 to use successive approximation. Always check that the percent ionization is less than 5% to know that x is insignificant because there are many exceptions to the rule.

[Siwa Hwang 3G]

You can assume that x is insignificant when K is less than 1x10^-4 !!

[Ashley Kim 3H]

If in the expression (x)/(initial concentration) x 100 is less than 5%, you can ignore the x value!

[Keon Amirazodi 3H]

When the concentration is less than 10^-3, x can be assumed to be insignificant.

[Emma Strassner 1J]

If K it is less than 10^-3 you can assume, but to be safe it is better to approximate if K is less than 10^-4.

[Claudia_Danysh_2B]

We can assume that x is insignificant whenever K is less than 10^3!!

[Liam Bertrand 3]

You can only assume x is insignificant if the Ka/Kb value is 1x10^-3 times smaller. Basically when Ka or Kb is really really small you can disregard the x

[Karen Elrayes 1L]

It's usually when k is less than 10^-3 but you have to check the percent ionization by diving x by the initial concentration and see if it is less than 5%. Usually when k is super small, it is very likely you can approximate.

[Shivani Kapur 2J]

Dr. Lavelle said to check and see if the ionization percentages are less than 5% but also if the K is less than 10^-3, then you can approximate.

[manisha_joseph_1H]

We can assume that x is insignificant in the case of 0.32 - x for instance when the Ka, Kb, or K given is less than 1.0 x 10^-4 and the percent ionization or deprotonation is less than 5%.

[Brianna Chen 3F]

The rule of thumb I like to use is if the K value is less than 10<-3 (meaning the values are typically 10^-4), we can assume that the approximation rule will be okay to use. However, for acids and bases, I like to check the percentage ionization/protonation to see if it holds to the 5% rule.

[Simran Bains 2C]

when k is equal to or smaller than 1.0x10^-5

[Caelin Brenninkmeijer 1G]

It's usually safe to use this approximation when K is equal to or greater than 10^-4.

[Sarah Huh 1K]

You can assume x is insignificant if it is below 1.0E-4.

[Faaizah Arshad 1H]

You can assume that x is insignificant if the value that you receive for percent ionization is less than 5%. This would mean that your original substance barely dissociated, so the number that you would be subtracting from the initial is negligible.

[Presley Gao 2C]

It is fine or restricted to assume x is so insignificant we can keep it out when it is less than 5% of the initial concentration.

[305405193]

x is insignificant when you get a percent ionization less than 5% and when k is less than 1.0 x 10^-4

[Tobie Jessup 2E]

you cn say x is insignificant when solving the quadratic if the k value is 10^-4 or less.

[joshtully]

It is insignificant when it is by 10^-4 or less.

[Luveia Pangilinan 1A]

in the lecture, Dr.Lavelle prefers to determines if its insignificant if its lets than 10^-4 rather than 10^-3.

[Queena Chu 3E]

We can assume that x is insignificant when the concentration is less than 1.0x^-3. A more accurate way is to see if you can assume that is to solve for x and the assumption is valid of final x is less than 5%.

[DPatel_2L]

We can assume it is insignificant when x is less than 10^-4.

[Aanya Tanti 3C]

You only use it when the equilibrium constant is less than 1.0x10^-4. To check after making the assumption, make sure that x/equilibrium constant is less than 5%

[RyanKopeikin_2I]

I would say if K<10^-3 then you can assume X is insignificant, and if K<10^-4 then you can DEFINITELY assume X is insignificant.

[Akriti Ratti 1H]

X is insignificant when K<10^-4

[Kimiya Aframian IB]

For some questions on sampling week 2, where we would have a number like .032-x and equal it to Kb for an example, when is it fine or restricted to assume x is so insignifcant we can keep it out?

Hi! A general rule for knowing when assuming x is insignificant is okay is if the k value is less than 10^-4. To be sure, you can also calculate the percent dissociation, and if it 5% or less, it is okay to assume x is insignificant. Hope this helps!

[Hasan Mirza 3F]

The general rule is 10^-4 or smaller is fair game. But sometimes you need to make sure that the percent produced is less than 5%.

[gabbi_r2C]

generally speaking, if the equilibrium constant is below 10^-3 or above 10^3, you can assume x is insignificant. to be safe, you can use 10^-4 and 10^4 instead.

[Jeremy Wei 2C]

I believe that Lavelle said during lecture that if the equilibrium constant is below 10^-4 (to be on the safe side), you can assume x as insignificant.

[Jonathan Malau 1F]

It can be assumed that x is insignificant when concentration is less than 1.0x10^-3. Additionally, if the assumption is used, the final x should be less than 5% of the initial concentration.

[Shreyank Kadadi 3K]

He said different things in different lectures, but I think his latest verdict was 1x10^-4 (smaller the better basically). It'll probably be obvious when he wants to omit it though, so I wouldn't worry too much.

[Carly_Lipschitz_3H]

We can assume X is insignificant if the Ka or Kb value is less than 10^-4. To be sure, you have to do the 5% rule as well.

[Gian Boco 2G]

When K is below 10^-4

[Diana Aguilar 3H]

Hi! I believe we can assume x is insignificant when the k value is less than 10^-4

[Ephrem Gerald 2A]

Whenever the K value is less than 10^-4, professor said it is okay to assume that x is insignificant. He also mentioned a check where you could choose x to be significant and one where it isn't and compare the answers and if there is lower than a 5% error, than it was okay to assume x is insignificant.

[Lindsey Walter 3E]

We can assume that x is insignificant as long as x is less than 5% of the original concentration.

[Anne Hogue 2J]

Hello. We can assume that x is insignificant if the k value is less that 10^-4.

[Amy Jordan 2A]

Hi, you can use the 5% ionization rule, or I'm pretty sure you can use the gauge if it's less than 10^-4 you can approximate. Hope this helps!