Calculate the pH of a buffer that is 0.12.M lactic acid and 0.1OM sodium lactate

Question

Calculate the pH of a buffer that is 0.12.M lactic acid and 0.1OM sodium lactate. The K_a for lactic acid is 1.4 middot 10^-4. Calculate the pH of a buffer that is 0.12M benzoic acid and 0.2M sodium benzoate. The K_a for benzoic acid is 6.3 middot 10^-5. What is the pH of a 0.1M NaCIO solution if the K_a for HCIO is 3.0 middot 10^-8? A 0.2M solution of benzoic acid has a pH of 4. What concentration of sodium benzoate must be present in the solution? How many moles of NH_4 CI must be added to a 2.0L solution of 0.1M NH_3 to form a buffer with a pH of 9.0? Look back al Part B: Part 1. Compare your calculated theoretical pH to the actual pH you recorded in lab and calculate the percent error for each. Look back at Part B: Part 2. Compare your calculated theoretical pH to the actual pH you recorded in lab and calculate the percent error for each.

Explanation / Answer

Q1.

Calculate the pH for:

Lactic acid = 0.12 M

Sodium Acetate = 0.10 M

pKa = -log(Ka) = -log(1.4*10^-4) =3.8538

apply pH equation:

Use Henderson Hasselbach equations

pH = pKa + log(Lactate / Lactic acid)

substitute known data

pH = 3.8538 + log(0.10 / 0.12)

pH = 3.7746

which is acidic, as expected, since it is a weak acid

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