chem ch 16

chem ch 16 - Ch 16: Acid-base equilibria Whats the pH of...

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Ch 16: Acid-base equilibria • What’s the pH of 0.200M acetic acid? K a for acetic acid = 1.8 x 10 -5 . • pH = • What’s the pH of a solution that is made of 0.200M acetic acid and 0.100M sodium acetate? Remember that salts are 100% dissociated into their ions. • pH= • This effect (decrease in H + by adding A - from an external source) is called a common ion effect. • HA H + + A- • Le Chatelier: in the presence of a common ion(A-), the • What is the pH of 1.50M pyridine, C 5 H 5 N? • K b for pyridine = 1.7 x 10 -9 . • pH= 9.703(basic) • What is the pH of a solution that is 1.50M in pyridine and 1.500M in pyridinium chloride, C 5 H 5 NHCl? • pH=5.23 • C 5 H 5 N + H 2 O C 5 H 5 NH + + OH - • NH 3 + HOH NH 4 + + OH- • In the presence of a common ion the • The pH of a 1.0 x 10 -2 M sol’n of HCl is 2.0 • The pH of a 1.0 x 10 -4 M sol’n of HCl is 4.0 • The pH of a 1.0 x 10 -6 M sol’n of HCl is 6.0 • What is the pH of a 1.0 x 10 -8 M sol’n of HCl?
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Buffer Solutions • Solutions that contain a ________and a salt containing the conj base (___) of the __ or a __________and a salt containing the ______________of the __ are called buffer sol’ns. • Buffers have the ability of withstanding small additions of added acid or base without large fluctuations in pH. • In general the ratio of [A-] or [NH 4 + ] btn 10 and 1 [HA] [NH 3 ] 1 10 for buffering to occur. • How do buffers work? • HA H + + A- • add acid A- + H + HA • Tie up added H + as HA • add base HA + OH- HOH + A- • Added base is neutralized by acid • NH 3 + HOH NH 4 + + OH- • add acid NH 3 + H + NH 4 + • add base NH 4 + + OH- NH 3 + HOH • Have 100mL of 3.6x10 -5 M HCl; pH = 4.44 • Add 1mL of 0.10M HCl to the above soln, the pH changes to 2.99 • Add 1mL of 0.10M NaOH to the above soln, pH changes to 10.98 • What if had a buffer sol’n--what happens when add acid and base to the buffer soln? • Have 100mL of a buffer that is 0.10 M Na acetate and 0.20 M acetic acid, pH = 4.435 • Add 1mL of 0.10M HCl to the buffer, pH changes to 4.43. Add 1mL of 0.10M NaOH to the buffer, pH changes to 4.45. pH change calculations • Read example 16.3 p 703 (add acid to acetic acid/acetate buffer) • Practice exercise: Calc the pH of the 0.30 M NH 3 / 0.36 M NH 4 Cl buffer. What is the pH after the addition of 20.0 mL of 0.050 M NaOH to 80.0 mL of the buffer? • What is the pH after the addition of 20.0 mL of 0.050 M HCl to 80.0 mL of the buffer?
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• 16.18 Calc the pH of 1.00 L of the buffer 1.00 M CH 3 COONa/1.00 m CH 3 COOH. What is the pH after add 0.08 mol NaOH Are these buffers: KOH/KCl NaOH/HCl NH 3 /NH 4 Cl NaF/HF Na 2 HPO4/NaH 2 PO4 NaOH/HF NH 3 /HCl HF/HCN CO 2 / HCO 3 - • What mass of C 6 H 5 COONa (sodium benzoate) do you need to add to 400. mL of 0.500M C
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This note was uploaded on 10/12/2010 for the course CHE 150 taught by Professor Bonner during the Spring '10 term at Kentucky.

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chem ch 16 - Ch 16: Acid-base equilibria Whats the pH of...

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