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Sophia Dinh 1D
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Joined: Thu Jul 25, 2019 12:15 am


Postby Sophia Dinh 1D » Wed Jan 29, 2020 10:27 am

when can you approximate that x is 0?

Charisse Vu 1H
Posts: 101
Joined: Thu Jul 25, 2019 12:17 am

Re: approximation

Postby Charisse Vu 1H » Wed Jan 29, 2020 10:30 am

You can approximate x to be 0 when the Ka/Kb value is less than 10^-3. However, you also need to check that the x value you calculate is less than 5% of the initial amount.

andrewcj 2C
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

Re: approximation

Postby andrewcj 2C » Wed Jan 29, 2020 10:32 am

I assume you're referring to calculations using equilibrium constants. If the equilibrium constant you are using is less than 10-3, you can usually assume that subtracting x does not change a constant very much. However, this does not mean that x is zero. For example, if given 10-5 = x2/(0.15-x), you can assume the denominator is 0.15, but the numerator is still x2.

Nathan Nakaguchi 1G
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Re: approximation

Postby Nathan Nakaguchi 1G » Wed Jan 29, 2020 10:39 am

When the K is less than 10^-3 you can assume that something like (.15-x) in the denominator will become just .15 since the x is so small it does practically nothing to that amount. But in the numerator you will still have an x present like x^2.

Philomena 4F
Posts: 27
Joined: Wed Feb 27, 2019 12:16 am

Re: approximation

Postby Philomena 4F » Wed Feb 05, 2020 6:12 pm

Approximation of x is done if K < 10^-3. That means you can take out the x in the denominator (reactants) because it won't have a significant effect on the value you'll obtain at the end. If unsure, you can confirm the approximation when x < 5% of the initial concentration of the molecule asked to be calculated.

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