Approximation

[ashwathinair]

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]

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]

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]

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]

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

[ng1D]

You would add for the reactants and subtract for products

[Sara Richmond 2K]

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]

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]

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).