Question

1) Calculate the pH of the 1L buffer composed of 500 mL of 0.60 M acetic acid plus 500 mL of 0.60 M sodium acetate, after 0.010 mol of HCl is added (K_a HC₂H₃O₂ = 1.75 x 10^-5). Report your answer to the hundredths place.

2) Calculate the pH of the 1L buffer composed of 500 mL 0.60 M acetic acid plus 500 mL of 0.60 M sodium acetate, after 0.010 mol of NaOH is added (K_a HC₂H₃O₂ = 1.75 x 10^-5). Report your answer to the hundredths place.

3) Lactate is an important component in some intravenous solutions. Given pK_a = 3.86 for lactic acid, calculate the pH of a 2.0 M lactate buffer composed of 1.0 M lactic acid and 1.0 M lactate. Report your answer to the hundredths place.

(Side note on buffer terminology, example "2.0 M lactate buffer": In real life use, buffers are usually called by their conjugate base form, and are specified by their total concentration- the sum of the acid and base forms together in the final solution.)

4) In a lab, you titrate 25.0 mL of 0.100 M acetic acid (CH₃COOH, a weak acid, pKa 4.756, K_a 1.75 x 10^-5), with 0.100 M NaOH. Identify the weak acid-base equilibrium that corresponds to this K_a. which of these choices is correct?

a. CH₃COOH + H₂O ⇌ CH₃COO^- + H₃O⁺

b. CH₃COO^- + H₂O ⇌ CH₃COOH + OH^-

c. CH₃COO^- + H₂O ⇌ CH₃COOH + H₃O⁺

d. CH₃COOH + H₂O ⇌ CH₃COO^- + OH^-

Answer 1

1) mole of CH3COOH = 500 X •60 = 300 mmol mole of CH₂600 = 500x .60= 300 mmole CH₂ cool 300 CH₂coo- inital: 300 added ht: - finally: ago + H+ - 10 o 310 bl = 5-10g 1.75 tloq 290 4.72 310 mole mole of Chacook = 500 x 960 = 300 nmole of CH₂ coo= 500x .60= 300 mmole CH₂ cool + H₂O 300 - CH₃Cook + initial; 300 added On - finally: 290 oH - To o - - - 310 bH = 5-log 1.75 + log 310 = 4.78 290 3 bh = bka + clog [lactate J [lactic acid . pH=3.86+dog =-3-86- @ on titrating Cuzcool with NaOH, Mil get @ CH₃COOH + Ho & CH₂ C00- + H₂O