Taking x away in a Ka calculation
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Taking x away in a Ka calculation
Why are we able to disregard the -x when calculating the Ka from an ICE chart?
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Re: Taking x away in a Ka calculation
This only applies if the change in composition (x) is less than 5% of the initial value. Usually if Ka is less than 10^-3, I would disregard the x.
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Re: Taking x away in a Ka calculation
If you are calculating ka from given concentrations, so the ka is unknown, you employ the 5% rule. You would first calculate the percent ionization by dividing the equilibrium concentration by the initial concentration of one of the products times 100 in order to determine the change in x. If this answer is less than 5%, then the approximation is ok.
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Re: Taking x away in a Ka calculation
If the x in Ka is so small it's insignificant, (less than 5%) then you can disregard it.
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Re: Taking x away in a Ka calculation
In the example Dr. Lavelle did in class today with kA to find the pH, can someone help explain to me how he was able to approximate it to ?
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Re: Taking x away in a Ka calculation
Sometimes, the x is so small that it doesn't have an effect on the overall concentration. For instance, let's say the initial concentration is 1 x 10^-1 and the K value is extremely small, we would know that the numerator/reactants would also have to be extremely small so that the ratio will equal the K value. Thus, the x will not have an effect on the initial concentration (comparatively).
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