Ka approximation

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Elizabeth Bowen 1J
Posts: 53
Joined: Wed Nov 14, 2018 12:20 am

Ka approximation

Postby Elizabeth Bowen 1J » Sun Feb 02, 2020 6:14 pm

I know how we learned that you can do an approximation when Ka is smaller than 10^-3, but I was wondering if anyone can explain how we can check if that approximation is correct or not? (because it's sometimes a gray area if it's only a little smaller)

claudia_1h
Posts: 111
Joined: Fri Aug 09, 2019 12:16 am

Re: Ka approximation

Postby claudia_1h » Sun Feb 02, 2020 6:17 pm

To check if the approximation is valid or not, you need to check if the percent ionization of the original substance is less than or equal to 5%. If it is greater, then you know that x will impact the original substance's molarity enough such that a quadratic must be used.

005391550
Posts: 103
Joined: Thu Jul 25, 2019 12:15 am

Re: Ka approximation

Postby 005391550 » Sun Feb 02, 2020 6:18 pm

you can check if your approximation was valid by calculating the percent deprotonation and seeing if it is less than 5%

J Medina 2I
Posts: 102
Joined: Wed Sep 25, 2019 12:17 am

Re: Ka approximation

Postby J Medina 2I » Sun Feb 02, 2020 6:19 pm

You could probably check by including the -x and then using the Quadratic Formula and then comparing this value to the value you got when you ignored the -x.

TarynD_1I
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

Re: Ka approximation

Postby TarynD_1I » Sun Feb 02, 2020 6:21 pm

you would divide the x amount (found using ice table) by the original concentration and multiply by 100. If this percentage is less than 5%, then the approximation is valid.

Aarushi Solanki 4F
Posts: 107
Joined: Sat Jul 20, 2019 12:17 am

Re: Ka approximation

Postby Aarushi Solanki 4F » Sun Feb 02, 2020 6:36 pm

The method for checking whether your approximation is valid is by calculating whether the percent ionization/deprotonation is less than 5%.

Owen-Koetters-4I
Posts: 50
Joined: Fri Sep 28, 2018 12:16 am

Re: Ka approximation

Postby Owen-Koetters-4I » Sun Feb 02, 2020 6:52 pm

check the percent ionization. if it is smaller than 5% than the approximation is valid


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