Acid-Base Equilibrium and Spectrophotometry Practice Problems With Answers

Problem 1
What is the pH of the following solutions?
a) 0.35 M hydrochloric acid
b) 0.35 M acetic acid (pKa = 4.76)
c) 0.035 M acetic acid.

Problem 2
A weak acid, HA, has a total concentration of 0.20M and is ionized (dissociated) to 2%;
a) Calculate the Ka for this acid.
b) Calculate the pH for this acidic solution.

Problem 3
Calculate the pH of the following mixtures:
a) 1M acetic acid and 0.5M sodium acetate
b) 0.3M phosphoric acid and 0.8M KH2PO4 (pKa=2.14)

Problem 4
You need to prepare a buffer solution at pH = 7.00 with KH2PO4 and Na2HPO4 (pKa=7.21). If you use a 0.1M solution of KH2PO4, what would be the concentration of Na2HPO4 needed?

Problem 5
You need to prepare a buffer solution at pH = 7.00 with KH2PO4 and Na2HPO4. What would be the respective concentration of these substances if you wished to obtain a final phosphateconcentration ([HPO4-2] + [H2PO4-1]) of 0.3M?

Problem 6
What is the concentration of the amino acid tyrosine (ε=1 420 L mol-1 cm-1) if you obtain an absorbance of 0.71 with a 1 cm cuvette? With a 0.1 cm cuvette?

Problem 7
What would be the absorbance reading of a 37 mM solution of tyrosine?

Problem 8
You wish to determine the concentration of haemoglobin in a blood sample by
spectrophotometry. You first create a standard curve of the absorbance at 412 nm of several solutions of known haemoglobin concentrations. The data for the standard curve is shown below. What is the concentration (in μg/mL) of haemoglobin in your sample if the absorbance obtained at 412 nm was 0.303?

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