Sapling HW #5

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SLai_1I
Posts: 101
Joined: Wed Sep 30, 2020 9:52 pm

Sapling HW #5

Postby SLai_1I » Sun Jan 17, 2021 5:10 pm

I've been stuck on this question from sapling for about half an hour now. I keep getting 63.8% but it's wrong. Can anyone help?

The Kb for an amine is 5.542×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.557? Assume that all OH− came from the reaction of B with H2O.

Stuti Pradhan 2J
Posts: 159
Joined: Wed Sep 30, 2020 9:32 pm
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Re: Sapling HW #5

Postby Stuti Pradhan 2J » Sun Jan 17, 2021 5:15 pm

For this problem, I recommend converting the pH to a pOH since you are working with a base. Once you have a pOH, you can use it to figure out the OH- concentration. Since for every one mole of OH- there is also one mole of BH+, you now know the concentration of OH- and BH+. Set up the equation for Kb and plug in the known values to find [B]. To find percent protonation, divide the concentration of BH+ by the formal concentration of B (which is the sum of the concentrations of BH+ and B since the original concentration of B included what has now been protonated), and multiply by 100.

Hope this helps!

SLai_1I
Posts: 101
Joined: Wed Sep 30, 2020 9:52 pm

Re: Sapling HW #5

Postby SLai_1I » Sun Jan 17, 2021 5:27 pm

That's how I've been trying it but I keep getting the same wrong result :(


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