berk rev: when to ignore x in solubility and equilibrium

[Rosalindbungs]

hi... im relaly confused when you ignore or don't ignore "x" in ICE tables...

for example: there is a question that asks in passage 10 of berkeley review's gen chem part 1 page 212 in solubility chapter:

66. "what is the molar solubility of zinc carbonate in 0.01 M zncl2?

the answer says that the ICE table is an initial concentration of 0.01 for zn ion. i get the ICE table but what im confused about is the actual calculation of "x"

the calculation for the solubility product (ksp) is [zn2+][co3 2-] which is equal to (0.01+x)(x)

the ksp is 2x10^-10 so they ignore x. is there a rule for when to definitely ignore x or keep it?

---

Members don't see this ad.

 

[ModernAlchemist]

hi... im relaly confused when you ignore or don't ignore "x" in ICE tables...

for example: there is a question that asks in passage 10 of berkeley review's gen chem part 1 page 212 in solubility chapter:

66. "what is the molar solubility of zinc carbonate in 0.01 M zncl2?

the answer says that the ICE table is an initial concentration of 0.01 for zn ion. i get the ICE table but what im confused about is the actual calculation of "x"

the calculation for the solubility product (ksp) is [zn2+][co3 2-] which is equal to (0.01+x)(x)

the ksp is 2x10^-10 so they ignore x. is there a rule for when to definitely ignore x or keep it?

There is a table somewhere within the chapter that says when to ignore x. Look back at the chapter.

 

[TwoPaddles]

hi... im relaly confused when you ignore or don't ignore "x" in ICE tables...

for example: there is a question that asks in passage 10 of berkeley review's gen chem part 1 page 212 in solubility chapter:

66. "what is the molar solubility of zinc carbonate in 0.01 M zncl2?

the answer says that the ICE table is an initial concentration of 0.01 for zn ion. i get the ICE table but what im confused about is the actual calculation of "x"

the calculation for the solubility product (ksp) is [zn2+][co3 2-] which is equal to (0.01+x)(x)

the ksp is 2x10^-10 so they ignore x. is there a rule for when to definitely ignore x or keep it?

Yeah there's a table in that chapter but it's very unlikely that you will get a quadratic formula problem on the MCAT.

 

[Rosalindbungs]

i've read the table but because of all of the "cases" it's hard to distinguish when just given a problem. wasn't there a decimal rule? if it's .005% of ksp or something like that?

 

[ShySpliceosome]

The mods will probably jump all over me for bumping a 2-year-old thread, but I figured it was better than starting a new thread on the same topic 😛

I, too, am confused about when you can and cannot ignore x. Isn't there an easier way to remember this than comparing K and Q or memorizing the table in TBR? For some reason, that table really confuses me. I thought that there was a general rule that if Keq < 0.1, you can ignore x. Has anyone else heard of this?

And also, in MCAT questions in which you are expected to determine whether or not x is significant, will the Keq value always be provided?

 

[Jepstein30]

The mods will probably jump all over me for bumping a 2-year-old thread, but I figured it was better than starting a new thread on the same topic 😛

I, too, am confused about when you can and cannot ignore x. Isn't there an easier way to remember this than comparing K and Q or memorizing the table in TBR? For some reason, that table really confuses me. I thought that there was a general rule that if Keq < 0.1, you can ignore x. Has anyone else heard of this?

And also, in MCAT questions in which you are expected to determine whether or not x is significant, will the Keq value always be provided?

Quite honestly, you're pretty unlikely to get a question that requires you to use an ICE table in the first place.. let alone one where you have to consider x. They don't expect you to spend that much time on a question.

 

[rfvbnmju]

99% of the time you'll ignore the -x part. They don't expect you to do quadratic. (Even in actual gen chem class)

Sent from my SPH-M930 using Tapatalk 2