Chap17-part2

Chap17-part2 - Indicate whether the pH increases, decreases...

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Unformatted text preview: Indicate whether the pH increases, decreases or remains the same when (a) Ca(C 6 H 5 COO) 2 is added to a solution of C 6 H 5 COOH (c) (C 5 H 5 NH)(NO 3 ) is added to a solution of C 5 H 5 N (e) ammonia (NH 3 ) is added to a solution of hydrochloric acid (HCl) (d) sodium hydrogen carbonate (NaHCO 3 ) is added to a solution of H 2 CO 3 (e) NaClO 4 is added to a solution of NaOH (a) Ca(C 7 H 5 O 2 ) 2 is added to a solution of HC 7 H 5 O 2 C 6 H 5 COOH ↔ H + + C 6 H 5 COO- Ca(C 6 H 5 COO) 2 ↔ Ca 2+ + 2 C 6 H 5 COO- Addition of the second compound will increase the concentration of C 7 H 5 O 2- , shifting the first equilibrium to the left, decreasing H + , and increasing the pH. (b) (C 5 H 5 NH)(NO 3 ) is added to a solution of C 5 H 5 N C 5 H 5 N ↔ C 5 H 5 NH + + OH- (C 5 H 5 NH)(NO 3 ) ↔ C 5 H 5 NH + + NO 3- Addition of the second compound will increase the concentration of C 5 H 5 NH + , shifting the first equilibrium to the left, decreasing OH- , and decreasing the pH. (c) ammonia (NH 3 ) is added to a solution of hydrochloric acid (HCl) HCl → H + + Cl- NH 3 ↔ NH 4 + + OH- NH 4 + + Cl- → NH 4 Cl OH- + H + ↔ H 2 O Ammonia will increase the concentration of NH 4 + and OH- . The increase in OH- will shift the fourth equilibrium to the right, decreasing H + , and increasing the pH. (d) sodium hydrogen carbonate NaHCO 3 is added to a solution of H 2 CO 3 H 2 CO 3 ↔ HCO 3- + H + NaHCO 3 ↔ Na + + HCO 3- Addition of the second compound will increase the concentration of HCO 3- , shifting the first equilibrium to the left, decreasing H + , and increasing the pH. (e) NaClO 4 is added to a solution of NaOH NaOH → Na + + OH- NaClO 4 → Na + + ClO 4- ClO 4- + H + ← HClO 4 Addition of the second compound will add ClO 4- . But HClO 4 is a strong acid, so the third reaction will lie completely to the left. There will be no change in the pH. Some types of solutions have a very stable pH within a given range. These solutions are called buffers . The primary property of a buffered solution is that the pH changes very little with the addition of a strong acid or base. Buffers are widely used in biomedical research and in medicine. Buffers Buffered Solutions Buffers work because they contain at least one acid species to neutralize OH- ions and at least one base species to neutralize H + ions. However, the acid and base species cannot neutralize each other. One way to make a buffer is to mix NaC 2 H 3 O 2 and HC 2 H 3 O 2 , generating the acid-base pair HC 2 H 3 O 2 /C 2 H 3 O 2- . Another way is to mix NH 4 Cl and NH 3 , generating the acid-base pair NH 4 + /NH 3 . The Henderson-Hasselbach Equation 1) If the concentrations of the buffer components are high enough (see above), then [H + ] = K a , [A- ] = [HA], and pH = pK a ....
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This note was uploaded on 09/13/2011 for the course CHEM 102 taught by Professor Todd during the Spring '08 term at UNC.

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Chap17-part2 - Indicate whether the pH increases, decreases...

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