5% vs. K < 10^-3

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Jared Khoo 1G
Posts: 107
Joined: Wed Sep 18, 2019 12:16 am

5% vs. K < 10^-3

Postby Jared Khoo 1G » Sun Jan 19, 2020 1:24 pm

What is the difference between the 5% rule and the rule saying that you can disregard x in the denominator if K < 10-3, or are they the same thing. Also, is this mentioned in the textbook and if so, where?

Deepika Reddy 1A
Posts: 125
Joined: Thu Jul 11, 2019 12:15 am

Re: 5% vs. K < 10^-3

Postby Deepika Reddy 1A » Sun Jan 19, 2020 1:41 pm

They are the same rule. If you disregard the x because K is less than 10^-3, at the end you can also check if it corresponds to the 5% rule. If it does follow the 5% rule, this means that the substance barely dissociates so K is small so it was correct to disregard x.

Emily Lo 1J
Posts: 50
Joined: Thu Sep 19, 2019 12:16 am

Re: 5% vs. K < 10^-3

Postby Emily Lo 1J » Sun Jan 19, 2020 4:02 pm

They're the same. You can disregard the X in the denominator when K < 10^-3 which essentially allows you to solve for X without the quadratic formula. It also means that X is small enough to be excluded in the equation.

Posts: 95
Joined: Sat Aug 17, 2019 12:17 am

Re: 5% vs. K < 10^-3

Postby AniP_2D » Sun Jan 19, 2020 9:17 pm

When K<10^-3, you are allowed to approximate and the 5% rule is just a means of confirming that your approximation is valid.

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