ICE and quadratic formula

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Zoya Mulji 1K
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Joined: Thu Jul 11, 2019 12:15 am

ICE and quadratic formula

Postby Zoya Mulji 1K » Thu Jan 16, 2020 4:54 pm

How do you do the calculations for the ICE table without using the quadratic formula?

Abby Soriano 1J
Posts: 103
Joined: Sat Aug 24, 2019 12:16 am

Re: ICE and quadratic formula

Postby Abby Soriano 1J » Thu Jan 16, 2020 4:58 pm

You can make your calculations quicker without having to use the quadratic formula when you approximate x. When Ka or Kb is small enough, x can be assumed to be insignificantly small in comparison to the initial concentration of weak acid or base given. As a result, rather than writing out the initial concentration - x in the equation for K, you can just write the initial concentration as is.

Cole Woulbroun 1J
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Joined: Thu Jul 25, 2019 12:16 am

Re: ICE and quadratic formula

Postby Cole Woulbroun 1J » Thu Jan 16, 2020 8:06 pm

The ICE table can be calculated without using the quadratic formula when K is less than 10^-3. When K is less than 10^-3, one can reason that the change in concentration of the reactant, which has it's new concentration represented in the denominator, is insignificant and cross the x representing this change out. Without this x value in the denominator, the quadratic equation no longer has to be used to solve for x.

Fatemah Yacoub 1F
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Re: ICE and quadratic formula

Postby Fatemah Yacoub 1F » Thu Jan 16, 2020 8:31 pm

For some problems you must use the quadratic formula, there is no way around it. Even when you ignore K you must do the 5% approximation check.

Jessica Kwek 4F
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Joined: Mon Jan 06, 2020 7:57 am

Re: ICE and quadratic formula

Postby Jessica Kwek 4F » Thu Jan 16, 2020 8:33 pm

You are able to skip the ICE table when K is less than 10^-3. If K is greater than 10^-3, you have to use the quadratic formula to solve for x.

Betania Hernandez 2E
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Joined: Fri Aug 02, 2019 12:15 am

Re: ICE and quadratic formula

Postby Betania Hernandez 2E » Fri Jan 17, 2020 12:24 am

Using the quadratic formula can be skipped if the equilibrium constant is less than 10^-3. The value of x would be so small that it would be negligible in the final answer when figuring out the equilibrium concentrations.

Nikki Razal 1L
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Re: ICE and quadratic formula

Postby Nikki Razal 1L » Fri Jan 17, 2020 2:05 am

you can only avoid using the quadratic formula when you are given a small k value (<10^-3), otherwise you would have to solve for x normally, which may require you to use the quadratic formula

Madeline Phan 1E
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Joined: Sat Aug 17, 2019 12:18 am

Re: ICE and quadratic formula

Postby Madeline Phan 1E » Fri Jan 17, 2020 8:35 am

When your K value is smaller than 10^-3, you can ignore the minus x in the denominator and use an approximation to determine molar concentration. you can then make sure an approximation is allowed by seeing if your x is less than 5 percent of K.

Emma Joy Schaetz 1E
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Re: ICE and quadratic formula

Postby Emma Joy Schaetz 1E » Sat Jan 18, 2020 11:47 am

Abby Soriano 1J wrote:You can make your calculations quicker without having to use the quadratic formula when you approximate x. When Ka or Kb is small enough, x can be assumed to be insignificantly small in comparison to the initial concentration of weak acid or base given. As a result, rather than writing out the initial concentration - x in the equation for K, you can just write the initial concentration as is.


Can you explain this further?

EllieSchmidtke_4I
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Joined: Wed Feb 20, 2019 12:16 am

Re: ICE and quadratic formula

Postby EllieSchmidtke_4I » Sat Jan 18, 2020 1:44 pm

Emma Joy Schaetz 1E wrote:
Abby Soriano 1J wrote:You can make your calculations quicker without having to use the quadratic formula when you approximate x. When Ka or Kb is small enough, x can be assumed to be insignificantly small in comparison to the initial concentration of weak acid or base given. As a result, rather than writing out the initial concentration - x in the equation for K, you can just write the initial concentration as is.


Can you explain this further?


If you have a $1,000,000 and give away $10, you still have relatively $1,000,000. Similarly, if you have an equilibrium constant smaller than k<10^-3, it is safe to assume that your resulting equilibrium constant will be more or less the same value. Therefore if you had the equation (4x^2/1.00-x), and k<10-3, the equation could be approximated to (4x^2/1.00) since the value of x is not large enough to cause a significant change.

Vivianvelazquez_1J
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Re: ICE and quadratic formula

Postby Vivianvelazquez_1J » Sat Jan 18, 2020 2:48 pm

The only time you don't have to use the quadratic formula with doing calculations for the Ice table is when K is less than 10^-3. Once you plug in your calculations from your Ice table into K the new concentration represented in your denominator, is so insignificant you can cross the x which represents the change out. Without the x value in your denominator, you don't need to use the quadratic equation to solve for x.

Sanjana Borle 2K
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Joined: Fri Aug 09, 2019 12:15 am

Re: ICE and quadratic formula

Postby Sanjana Borle 2K » Sat Jan 18, 2020 3:09 pm

If the initial concentration (such as 0.1-x) is small enough, then you can "take away" the x from the bottom ONLY since it is probably a small number, but this is just to make calculations easier. Technically it's not mathematically correct but the difference if you used the quadratic formula is very small.


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