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

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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
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(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.
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(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.
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(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.
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(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.
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(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.
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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
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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 .
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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 . 2) As long as [A - ]/[HA] doesn’t change too much with the addition of new species, the pH is stable and equals the pK a .
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A buffer is formed by adding 5.00 g ammonia (NH 3 ) and 20.0 g ammonium chloride (NH 4 Cl) to enough water to form 2.50 L of solution. Find the pH by using the Henderson-Hasselbach equation NH 4 Cl NH 4 + + Cl - NH 4 + NH 3 + H + K a = 5.6 x 10 -10 Initial concentrations:
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NH 4 + H + NH 3 initial 0.150 0 0.118 change -x x x final 0.150-x x 0.118+x
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