Approximation

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ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

Approximation

Postby ashwathinair » Thu Jan 16, 2020 1:44 pm

Can someone explain how and when we use approximation for ICE tables? Are there other situations you can use them as well? Is this only for acids and bases?

Caroline Beecher 2H
Posts: 51
Joined: Wed Nov 14, 2018 12:21 am

Re: Approximation

Postby Caroline Beecher 2H » Thu Jan 16, 2020 2:12 pm

You can use approximation for weak acids and bases problems when the K value is less than 10^-3. This means it is small enough to not make a huge difference when calculating concentrations, so you wouldn't need to use the quadratic formula. The 5% rule refers to evaluating whether the approximation was valid: getting a percent ionization of less than 5% means the approximation is good.

Cooper Baddley 1F
Posts: 100
Joined: Wed Sep 18, 2019 12:19 am

Re: Approximation

Postby Cooper Baddley 1F » Thu Jan 16, 2020 2:34 pm

Ice tables seem to be useful only when it comes to calculating the number of products and reactants are present at equilibrium for a reaction.

Uisa_Manumaleuna_3E
Posts: 60
Joined: Wed Sep 21, 2016 2:56 pm

Re: Approximation

Postby Uisa_Manumaleuna_3E » Thu Jan 16, 2020 2:47 pm

In class Dr Lavelle told us to use approximation for sure when K is less than 10^-3. But its a little tricky if we have 10^-4. Definitely use approximation with 10^-5, but its a little uncertain for 10^-4

KBELTRAMI_1E
Posts: 108
Joined: Sat Jul 20, 2019 12:17 am

Re: Approximation

Postby KBELTRAMI_1E » Thu Jan 16, 2020 3:01 pm

also how do you know if you add or subtract x in the C section of the ICE table?

ng1D
Posts: 43
Joined: Wed Sep 18, 2019 12:17 am

Re: Approximation

Postby ng1D » Thu Jan 16, 2020 3:33 pm

You would add for the reactants and subtract for products

Sara Richmond 2K
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

Re: Approximation

Postby Sara Richmond 2K » Thu Jan 16, 2020 3:55 pm

Approximation can be used for weak acids and bases problems when the K value is less than 10^-3. This means it is so small that it is not going to make a difference when calculating concentrations. After you use approximation, you should use the 5% rule to check if your calculation was valid/ if the change of concentration was really small enough to consider negligible. The 5% rule states that if the percent ionization is less than 5%, it is okay to use approximation.

MeeraBhagat
Posts: 95
Joined: Sat Aug 24, 2019 12:15 am

Re: Approximation

Postby MeeraBhagat » Thu Jan 16, 2020 4:48 pm

If the K value is less than 10^-3, then the concentrations of products created are small enough in comparison to the original concentration of the reactant(s) that you can consider it insignificant enough to leave the “-x” term out of the reactants when calculating K.

Nicholas_Gladkov_2J
Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

Re: Approximation

Postby Nicholas_Gladkov_2J » Thu Jan 16, 2020 4:56 pm

ashwathinair wrote:Can someone explain how and when we use approximation for ICE tables? Are there other situations you can use them as well? Is this only for acids and bases?



If the K value is less than 10^-3, then for the creation of the equation that is equivalent to the equilibrium constant, it is acceptable to remove the -X value from the equilibrium constant equation. This is because if the equilibrium constant is small, then the concentration of products is small, thus the concentration of reacts remain relatively large, so any change of X is basically nothing (but IT IS NOT 0).


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