{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Module2_Homework_solutions

Module2_Homework_solutions - ENV 6666 Module 2...

This preview shows pages 1–4. Sign up to view the full content.

ENV 6666 Module 2 Homework (with solutions) Key equations needed: 𝑝𝐾 𝑊 = 14.00 , thus { 𝑂𝐻 } = 10 −𝑝𝐾 𝑊 { 𝐻 + } and assumption that I = 0 means we will approximate: { 𝐻𝐴 } ( 𝑇𝑂𝑇 A)( 𝛼 0 ) = ( 𝑇𝑂𝑇 A) { 𝐻 + } { 𝐻 + } +𝐾 𝑎1 and { 𝐴 } ( 𝑇𝑂𝑇 A)( 𝛼 1 ) = ( 𝑇𝑂𝑇 A) 𝐾 𝑎1 { 𝐻 + } +𝐾 𝑎1 Build spreadsheet like so, then plot: Note: “TOTA” column simply adds {HA}+{A-}. It is a good practice to include this column because it can alert you to a programming error, since you know it should always be 1.00E-05.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Charge balance may be expressed as negative charges = positive charges: 𝐶 . 𝐵 .: [ 𝐻 + ] = [ 𝑂𝐻 ] + [ 𝐴 ] Since we use the ‘dilute solution approximation, we use this instead: { 𝐻 + } { 𝑂𝐻 } + { 𝐴 } Consider the charge balance equation a “left-hand side” = “right-hand side” (i.e., LHS = RHS) expression, and add a column to spreadsheet for “LHS – RHS” (i.e., program the cells of a column for [ 𝐻 + ] [ 𝑂𝐻 ] [ 𝐴 ] although we approximate with the Activities { 𝐻 + } { 𝑂𝐻 } { 𝐴 } ) and look for the “zero-crossing”, i.e., when LHS – RHS = 0. Zero-crossing occurs at pH 5.5 as shown: The pH closest to the equilibrium pH would be the one whose “LHS – RHS” is closest to zero (-4.44E-06 is slightly closer to zero than is +5.00E-06). The approximate equilibrium pH is 5.5, but we could insert more spreadsheet rows between pH = 5.0 and pH = 5.5 to get an answer more precise than the nearest 0.5 on the pH scale. This is easy to do, with the result: The value closest to zero is 1.77E-07, so the equilibrium pH = 5.2 (to the nearest 0.1 on pH scale). The values can be read from the pH = 5.2 row. They are: { 𝐻𝐴 } 3.87 𝐸 -6 { 𝐴 } 6.13 𝐸 -6 { 𝐻 + } 6.31 𝐸 -06 { 𝑂𝐻 } 1.58 𝐸 -09
This is solved by the same method used in problem 1, but with one more column and more complicated “alpha” expressions: 𝛼 0 = { 𝐻 + } 2 { 𝐻 + } 2 + { 𝐻 + } 𝐾 𝑎1 + 𝐾 𝑎1 𝐾 𝑎2 𝛼 1 = { 𝐻 + } 𝐾

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern