lFall 2011 Lect 17 Chem 162 indicators solubility HOME

lFall 2011 Lect 17 Chem 162 indicators solubility HOME -...

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1 Calculators of this type are not allowed for quizzes and the exams. This type is OK. Exam II Tuesday November 8, 2011 in class (lecture). 7:15 PM – 8:35 PM Copyright G Hall November 2011
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Exam II Tuesday November 8, 2011 In Lecture Chapters 13, 14, 15 13.1 up to 15.11 See pages 527-664 Copyright G Hall November 2011 2
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Copyright G Hall November 2011 3 Lecture 17 Outline of Chapter 15 15.9 Indicators 15.10 Titrations End Point vs Equivalence point 15.11 Lewis Acid-Bases Metal ions in solution give basic or acid solutions
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Copyright G Hall November 2011 4 Lecture 17 Outline of Chapter 16 Slightly Soluble Salts; Common Ion Effect
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Why titrations? In reactions monitoring, need to know how much acid or base are produced. In environmental analysis need to know buffering capacity of soil for acid rain damage. For an acid or base spill, need to know how much acid or base is present and potentially what is the acid or base. For foods, need to know the acid or base content. 5 Copyright G Hall November 2011
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Copyright G Hall November 2011 6 Two methods to monitor titrations. Use of a pH meter is the most accurate. Use indicators that change based on the chemical form of the indicator as a function of the pH. Indicators are weak organic acids noted as HIn. HIn(aq) + H 2 O(l) = H 3 O + (aq) + In - (aq) Color 1 color 2
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Copyright G Hall November 2011 7 The useful pH ranges for several common indicators. Note that most indicators have a useful range of about two pH units, as predicted by the expression pK a +/- 1.
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Titration curves Equivalence point is when the moles of acid or base have been neutralized by the base or acid in the respective titrations. End point is when the indicator shows a change in the pH that is close to the equivalence point. Often the end point is higher or lower than the equivalence point and contributes to a small titration error. 8 Copyright G Hall November 2011
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Five Titration Cases Case 1: strong acid with strong base pH = 7 at equivalence point Case 2: weak acid with strong base pH >7 (basic) at equivalence point. Case 3: weak base with a strong acid pH < 7 (acidic) at equivalence point. Case 4: weak base with a weak acid pH depends on the titrants, not often done. Case 5: weak polyprotic acid with strong base pH depends on the pK a’ s of the polyprotic acid. 9 Copyright G Hall November 2011
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Case 1 SA with SB Case 1: HCl(aq) + NaOH(aq) = H + (aq) + OH - (aq) = H 2 O (l) Suppose we have 40-ml of 0.1 M HCl (SA) and titrate that with 0.1 M NaOH (SB). 40 mL * 0.1M = 4 mili moles of acid = x mL * 0.1M where x=40 ml to neutralize the acid. Can calculate pH at different steps in titration. Titrate base into acid. pH at start = 1.0.
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This note was uploaded on 11/09/2011 for the course GEN CHEM 162 taught by Professor Tavss during the Spring '11 term at Rutgers.

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lFall 2011 Lect 17 Chem 162 indicators solubility HOME -...

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