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# Lecture 15 - Consider a 1.0 M solution of NaOCl(sodium...

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2/10/10 1 74 Consider a 1.0 M solution of NaOCl (sodium hypochlorite). Is the solution? A) Acidic B) Basic C) Neutral NaOCl OCl - Weak base Conjugate of a strong base, NaOH basic, pH > 7.0, [H 3 O + ] < [OH - ] Na + No acid/base effects Recall how to deal with pH, pOH, and K W (Section 18.2) Step 1. List all relevant reactions and their dissociation constants (K a , K b , K w ) ClCH 2 COOH (aq) + H 2 O (l) ! ClCH 2 COO - (aq) + H 3 O + (aq) (1) 3 2.85 a 10 1.4 10 K ! ! " = = 2 H 2 O (l) ! H 3 O + (aq) + OH - (aq) (2) K w = 10 -14 K a >> K w , i.e., stronger acid that H 2 O 7.1. For a given K a (or K b ), find equilibrium concentrations (and pH) 7. Weak Acids and Bases (Section 18.4 and18.5) 75 Calculate the pH, pOH, and the percent dissociation of a 1.0 M ClCH 2 COOH solution (pK a = -log K a = 2.85) (1) is dominant source of H 3 O + Neglect protons from reaction (2) (same as 4.B. Handout page 11) Step 3. Substitute into expression for K a and solve for x. x = 0.037M = [H 3 O + ] 76 Step 2. Make up I.C.E. table for dominant reaction. I C E 1.0 M 0.0 M +x - x 1.0 - x +x 0.0 M + x + x ClCH 2 COOH(aq) + H 2 O(l) ! ClCH 2 COO - (aq) + H 3 O + (aq) K a = 1.4 ! 10 " 3 = ClCH 2 COO " [ ] H 3 O + [ ] ClCH 2 COOH [ ] = x 2 (1.0 - x)

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Lecture 15 - Consider a 1.0 M solution of NaOCl(sodium...

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