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test 03 review

# test 03 review - Dr McCord CH302 OVERVIEW for EXAM 3 Fall...

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Textbook Chapters for Exam 3 You still need to know many of the concepts and calculations from Chapter 7 (type 1 problems). Plus, exam 3, WILL have polyprotic acids on it in some form. Polyprotics were introduced in Chapter 7. Also fraction of species (plus charge and mate- rial balance) was in Chapter 7 as well. All of Chapter 8 (although you can skip section 3) is valid for exam 3. You’re responsible for any material covered in class whether it was on the homework or not. This review sheet covers most everything we have done. Also remember that no equations are given on the exams. Values for equilibrium constants are given where needed. Chapter 7 – Type 1 problems and Poly- protic acids and bases You STILL have to be able to solve type 1 problems (like on exam 2). Type 1 problems are the starting point and the equivalence point on pH curves (titrations). Be able to write the appropriate stepwise reactions for poly- protic acids and bases. Know how to calculate the concen- trations of various deprotonated species for polyprotic acids and bases. Remember the numbering for polyprotic acids and their con- jugates run in opposite directions. The first proton off a diprotic acid ( K a1 ) is always the LAST proton going ON to the corresponding conjugate base ( K b2 ). For a triprotic acid: H 3 A ± H + + H 2 A - matches up with K a1 The conjugate reaction is H 2 A - + H 2 O ± H 3 A + OH - and matches up with K b3 . The relationship between the two is K a1 · K b3 = K w . Know what the dominant species are at various pH’s for any acid or base (mono- or polyprotic). Yes, you do have to know the K a ’s or K b ’s, but those would be given. This task is much easier when you know about fraction of species and the plotting of it versus pH. SECTION 7.9 This section is mainly about very dilute solu- tions. The take home lesson in this section is that water itself contributes about 10 -7 M H + to solutions - if your concentrations you mix are less than that, then the contri- bution from water is the main one. Charge Balance: Know how to write out the charge bal- ance for any solution (see page 262). Material Balance: Know how to write out the material balance for any solution. Note that it is all the species in the material balance that make up a fraction of species diagram. Fraction of Species Know about Fraction of Species and the way the plot looks and how you would use it to answer various questions about what species is the major species at a given pH. See my “Fraction of Species” help sheet. Below is a fraction of

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test 03 review - Dr McCord CH302 OVERVIEW for EXAM 3 Fall...

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