ICE calculation sig figs

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Shirley Liu 2I
Posts: 64
Joined: Fri Sep 28, 2018 12:16 am

ICE calculation sig figs

Postby Shirley Liu 2I » Sun Jan 20, 2019 5:27 pm

Several questions in the homework ask for the pH of a weak acid given its initial concentration, so we would have to find the "x" value, which equals [H3O] and then find the negative log of that to find pH. However, I noticed that in the solutions and Dr.Lavelle's examples we round/do sig figs for the value of x before we even find the negative log of it to get pH. Why do we do that and why don't we wait until after solving for pH to do sig figs since the pH value would be the final answer?

Rebecca Altshuler 1D
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

Re: ICE calculation sig figs

Postby Rebecca Altshuler 1D » Sun Jan 20, 2019 7:05 pm

I'm not sure, but I've heard from several TA's that it is important not to round any answers until the end because this is how they calculate the test answers. I'm not sure why they would round before getting the final answer, but to be safe I would complete the entire problem and only take sig figs at the end.

Diviya Khullar 1G
Posts: 59
Joined: Fri Sep 28, 2018 12:19 am

Re: ICE calculation sig figs

Postby Diviya Khullar 1G » Sun Jan 20, 2019 7:22 pm

You should not round off until the end. Only account for significant figures when you are at your final answer.

Toru Fiberesima 1L
Posts: 63
Joined: Fri Apr 06, 2018 11:02 am

Re: ICE calculation sig figs

Postby Toru Fiberesima 1L » Sun Jan 20, 2019 7:31 pm

You should always refer to the question, and go by the number of sig figs used there.

Riley Dean 2D
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

Re: ICE calculation sig figs

Postby Riley Dean 2D » Sun Jan 20, 2019 9:41 pm

Don't round any answers until you've reached the end of your work, then round off to as many sig figs as the equation used

NatBrown1I
Posts: 62
Joined: Fri Sep 28, 2018 12:17 am

Re: ICE calculation sig figs

Postby NatBrown1I » Sun Jan 20, 2019 11:08 pm

You shouldn't round your answer until you are finished calculating everything


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