ICE BOX
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Re: ICE BOX
If X is smaller than 10^-3, then the affect of subtracting this value from the denominator is negligible.
Re: ICE BOX
when your K value is less than 10^-3 you can assume that it is too small to affect your concentration.
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Re: ICE BOX
If the Kc, Ka, or Kb is smaller than 10^-3, then you can assume to remove the -x because it is small relative to the other number.
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Re: ICE BOX
You can use the approximation if the K value is less than 1X10^-3. After you obtain your final H30+ concentration, you should also make sure the final H30+ concentration is less than 5% of the initial concentration of acid. If it is less than 5%, your approximation is probably fine. If your final concentration is greater than 5% of the initial acid, then your answer could be potentially off, depending on how many significant figures the problem has.
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Re: ICE BOX
yes, the cutoff is 10^-3.
However, I would advise only to use the short cut when the value is 10^-5 since you don't want to take a chance and have your answer be off by a few digits. On the test I would always check your answer using the quadratic formula if you used the short cut.
However, I would advise only to use the short cut when the value is 10^-5 since you don't want to take a chance and have your answer be off by a few digits. On the test I would always check your answer using the quadratic formula if you used the short cut.
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Re: ICE BOX
The cutoff is 10^-3. Yet in cases of weak acids and bases, one may want to check the % ionization to ensure the approximation is valid (i.e, the quadratic formula is still necessary if the final percentage is >5%).
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Re: ICE BOX
When the K value is less than 10^-3 then you can assume that the K value it is too small to affect the concentration.
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Re: ICE BOX
I would agree that 10^-3 would be the cut-off, but that margin is so close. 10^-4 or 10^-5 would be a safer option. If you do decide to neglect x at 10^-3 always check at the end if your answer is withing 5%.
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Re: ICE BOX
if the k is smaller than 10^3, then the x in the ice box can be disregarded in the denominator.
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Re: ICE BOX
If you exclude the x and want to double check afterwards to see if the approximation is accurate, then you can calculate the protonation percentage, or deprotonation percentage depending on the question, and if it is below 5% then the approximation is correct.
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Re: ICE BOX
You also should check again at the end with the 5% dissociation rule. Divide your x by the initial and if it is greater than 5%, then you can't assume it's negligible.
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Re: ICE BOX
When K is less than 10^-3, and you'll notice it is able to be approximated if x/initial concentration is less than 5%
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